A&A 605, A48 (2017) DOI: 10.1051/0004-6361/201730940 Astronomy
&
 cESO 2017 
Astrophysics <BR>

LOFAR MSSS: The scaling relation between AGN cavity power and radio luminosity at low radio frequencies 
G.Kokotanekov1, M.Wise1, 2, G. H. Heald3, 2, 4,J.P. McKean2, 4, L. Bîrzan5, D. A. Rafferty5, L. E. H. Godfrey2, 
M.de Vries1,H.T. Intema6,J.W. Broderick2,M.J. Hardcastle7,A. Bonafede8, 5,A.O. Clarke9,R.J.vanWeeren10, 
H. J. A. Rtgering6, R. Pizzo2, M. Iacobelli2, E. Orr2, 11,A. Shulevski2,C.J. Riseley3,R.P. Breton9, 
B. Nikiel-Wroczy´, 
nski12, S. S. Sridhar2, 4, A. J. Stewart13, A. Rowlinson2, 1, A. J. van der Horst14, J. J. Harwood2 
G. Gkan3,D. Carbone1,M.Pandey-Pommier15,C.Tasse16, 17, A. M. M. Scaife9, L. Pratley18, 19, C. Ferrari20, 
J.H. Croston21,V.N.Pandey2, 4,W. Jurusik12, andD.D. Mulcahy9 
1 AntonPannekoek Institute for Astronomy, Universityof Amsterdam, Postbus 94249, 1090GE Amsterdam, The Netherlands 
e-mail: g.d.kokotanekov@uva.nl 2 Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands 3 CSIROAstronomy and Space Science,26 Dick PerryAve.,KensingtonWA6151, Australia 4 Kapteyn Astronomical Institute, Rijksuniversiteit Groningen, Landleven 12, 9747 AD Groningen, The Netherlands 5 Universität Hamburg, Hamburger Sternwarte, Gojenbergsweg112, 21029 Hamburg, Germany 6 Leiden Observatory, Leiden University, Niels Bohrweg2, 2333CA Leiden, The Netherlands 7 School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfeld AL10 9AB, UK 8 Radio Astronomy Institute (IRA) – INAF – via Gobetti 101, 40100 Bologna, Italy 9 Jodrell Bank Centre for Astrophysics, University of Manchester, Manchester, M139PL, UK 
10 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 11 Departmentof Astrophysics, Institute for Mathematics, Astrophysics andParticlePhysics (IMAPP), 
Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands 12 Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Krak, Poland 13 Astrophysics, DepartmentofPhysics, Universityof Oxford,Keble Road, OxfordOX1 3RH,UK 14 DepartmentofPhysics, The GeorgeWashington University, 725 21st StreetNW,Washington,DC 20052, USA 15 Centrede Recherche AstrophysiquedeLyon, ObservatoiredeLyon,9Av. Charles André, 69230 Saint-Genis-Laval, France 16 GEPI, ObservatoiredeParis, CNRS, UniversitéParis Diderot,5place Jules Janssen, 92190 Meudon, France 17 DepartmentofPhysics&Electronics, RhodesUniversity,POBox94,6140 Grahamstown,South Africa 18 Mullard Space Science Laboratory (MSSL), University College London (UCL), Holmbury St Mary, SurreyRH5 6NT, UK 19 Schoolof Chemical andPhysical Sciences,Victoria UniversityofWellington,PO Box 600, 6140Wellington,New Zealand 20 Laboratoire Lagrange, Université Ce d’Azur, Observatoire de la Ce d’Azur, CNRS, Bvd de l’Observatoire, CS 34229, 
06304 Nice Cedex 4, France 21 SchoolofPhysical Sciences,TheOpenUniversity,WaltonHall, MiltonKeynes,MK76AA,UK 
Received5April 2017 / Accepted 30 May 2017 

ABSTRACT 
Wepresentanewanalysisofthewidelyused relationbetweencavitypowerandradio luminosityin clustersofgalaxieswithevidence for strong AGN feedback. We studied the correlation at low radio frequencies using two new surveys – the frst alternative data release of the TIFR GMRTSkySurvey(TGSS ADR1) at 148 MHz and LOFAR’s frst all-sky survey, the MultifrequencySnapshot SkySurvey(MSSS) at 140 MHz.We fnda scaling relation Pcav ∝ Lβ , with a logarithmic slope of β = 0.51 ± 0.14, which is in 
148

good agreement with previous results based on data at 327 MHz. The large scatter present in this correlation confrms the conclusion reached at higher frequencies that the total radio luminosity at a single frequencyis a poor predictor of the total jet power. Previous studies have shown that the magnitude of this scatter can be reduced when bolometric radio luminosity corrected for spectral aging is used. We show that including additional measurements at 148 MHz alone is insufficient to improve this correction and further reducethe scatterinthe correlation.Fora subsetoffour well-resolved sources, weexaminedthe detected extended structuresat low frequencies and compare with the morphology known from higher frequencyimages and Chandra X-ray maps. In the case of Perseus we discuss details in the structures of the radio mini-halo, while in the 2A 0335+096 cluster we observe new diffuse emission associated with multiple X-ray cavities and likely originating from past activity.For A2199 and MS 0735.6+7421, we confrm that the observed low-frequencyradio lobes are confned to the extents known from higher frequencies. This new low-frequencyanalysis highlightsthefactthatexistingcavitypowerto radio luminosity relations are basedona relatively narrow rangeofAGNoutburst ages.We discusshow the correlation couldbeextended usinglow frequencydata from the LOFARTwo-metreSkySurvey(LoTSS) in combination with future, complementary deeper X-ray observations. 
Key words. galaxies: clusters: individual: 2A 0335+096 – galaxies: clusters: individual: Perseus – X-rays: galaxies: clusters – galaxies: clusters: individual: A2199–galaxies: clusters: individual:MS 0735.6+7421 – galaxies: clusters: intracluster medium 
Article publishedby EDP Sciences A48, page1of 20 
1. Introduction 
High-resolution X-ray images have revealed many large-scale interactions between the intracluster medium (ICM) and the central active galactic nucleus (AGN) in galaxy cluster cores (e.g., Perseus: Boehringer et al. 1993;Fabian et al. 2006, 2011; Zhuravleva et al. 2015; and Hydra A: McNamara et al. 2000; Nulsen et al. 2002; Wise et al. 2007). In these systems, the ra<BR>dio jets of theAGN have pushed out cavities in the cluster’s at-mosphere, creating surface-brightness depressions. The energy released by the AGN required to create these cavities appears tobe sufficient to balance the cooling observed in the X-rays (Bîrzan et al. 2004; Rafferty et al. 2006; McNamara&Nulsen 2007). Therefore, the X-ray cavities provide a unique way of measuring the amount of energy dissipated into the ICM from AGN activity. This feedback process is believed to moderate the availability of fuel for the accretion process in a homeostatic way that regulates both the growth of the black hole and the formationof starsin the surroundinggalaxy(Silk&Rees 1998; Gebhardt et al. 2000;Ferrarese&Merritt 2000). 
In many cavity systems, the depressions in X-ray surface brightness are found to be flled with radio emitting plasma. This spatial anti-correlation between the X-rays and radio provides strong circumstantial evidence that theAGN activityis responsible for the observed X-ray cavities. Given this common origin, X-rays directly probe the mechanicaleffects of the feedback pro-cess, while radio observations directly reveal the radiative output of the lobes. Combined X-ray and radio observations can pro-vide constraints on the radio radiativeefficiencies, radio lobe and ICM properties. 
Evidence for this common origin is found in the observed correlation between the power required to create the X-ray cavities and the luminosity of the radio plasma associated with them. Using a sample of 24 systems with pronounced cavities, Bîrzanetal. (2008)fndthatthe scaling relationiswellde<BR>
scribedbyapowerlawofthe form Pcav ∝ Lβ withalogarithmic 
rad 
slope of 0.35 ≤ β ≤ 0.70. They further fnd that the correlation is steeper at 327 MHz than at 1.4 GHz(β327 = 0.51 ± 0.07 vs. β1400 = 0.35 ± 0.07), albeit with similarly large scatters of 
0.80 dex and 0.85 dex, respectively. Subsequent investigations of Cavagnolo et al. (2010)andO’Sullivan et al. (2011)expand the sample size and essentially confrm the Pcav − Lrad scaling re-lation foundby Bîrzan et al. (2008).Hardcastle&Krause (2013, 2014)showthatasignifcant scatterisphysicallyexpectedinthis correlation. 
Although now well established, this correlation suffers from several limitations related to both the radio and the X-ray data. In radio, all of the analysis to date has been based on data from higher frequencies, above 300 MHz.Yet, in objects where low-frequencydata has previously beenavailable, the observed emission tends to be more diffuse and extended (e.g., Lane et al. 2004). At the same time, the original analysis in X-rays was basedonasampleofbrightnearby objectsthatshowa clearsingle pair of cavities. In objects with deeper X-ray data, however, we often seeevidenceof multiple surface brightness depressions atlarger radii(Table3in Vantyghemetal. 2014). These more extended structures are also often poorly described by simple spherical geometry and are usually not as well correlated spa-tially with high frequency radio emission as the inner cavity structures. 
Obtaining sufficiently deep X-ray data for a large sample of these systems is problematic. Extending these studies to higher redshift is also difficult, as it becomes increasingly difficult to both detect and resolve the cavity structures. With the advent of new low-frequency all-sky surveys, however, we can obtain maps of the extended diffuse emission for a large sample of sources. If properly calibrated, the Pcav − Lrad scaling relation canbeapowerful toolin statistical studiesoftheAGN activity and its impact on the surrounding medium over time. 
Inthiswork,weemploylow-frequencyobservationsat140– 150MHzin orderto pursuea more complete pictureofAGN feedback signatures. Our goal is two-fold: to extend the Pcav − Lrad scaling relation to low radio frequencies, and to understand and reduce the observed scatter in this correlation.For the statistical study we derive fuxes from the publicly available First Alternative Data Release of the TIFR GMRTSkySurvey(TGSS ADR1; Intema et al. 2017, hereafter TGSS) at 148 MHz. In or<BR>der to resolve individual clusters and examine the structure of theirextendedradio emissioninthecontextoftheX-raycavities, we reprocess data from LOFAR’s frst all-sky imaging survey, the Multifrequency Snapshot Sky Survey (MSSS; Heald et al. 2015).We focus our analysis on the Bîrzanetal. (2008)sample since it consists of very well known nearby sources which already have a deep ensemble of multi-wavelength data and it includes primarily very bright sources, easily detectable in the shallowlow-frequency surveysavailable sofar. 
In Sect. 2we describe the characteristicsof the cluster sample, the radio observations, and the X-ray data used. Section 3 presents a statistical analysis of the cavity power to radio luminosity relation including the newlow frequencydata.Adetailed discussion comparing these results to previous analyses is also presented.In Sect. 4, we present images fora subsetof objects well-resolved in MSSS and discuss their detailed morphology in comparison withexisting X-ray data.We concludein Sect. 5 with a summary of our analysis and a discussion of the implications of these results. 
We adoptH0 = 70 kms−1 Mpc−1, ΩM = 0.3, and ΩΛ = 0.7 for all calculations throughout this paper. 


2. Data sources and sample selection 
We base our study on theBîrzan et al. (2008)sample of 24 feed<BR>back systems (hereafter B-24). The sample consists of relaxed cool-core clusters showingevidenceofAGN activity. Thisis an X-ray selected sample for which the available X-ray observations have shown clear signatures of cavities and at the same time radio data has demonstrated strong lobes. However, in the radio, these clusters have been primarily studied at higher frequencies which tend to reveal emission associated with the most recent epochofAGN activity. 
Throughout this work we use MSSS (Sects. 2.1 and 2.2) and TGSS (Sect. 2.3)data to study the sample of feedback sys<BR>tems. Based on the data from those two surveys we select two subsamples of the B-24 sample that are described in Sect. 2.4. The Pcav literature values we use for the correlation studies are summarized in Sect. 2.5. We do not include the VLA Low-FrequencySkySurveyRedux at 74 MHz (VLSSr; Cohen et al. 2007;Lane et al. 2012, 2014)in our analysis due to its low sen-sitivity combined with low resolution and insufficient sky coverage (see Sect. 2.6). The Galactic and Extragalactic All-sky MurchisonWidefeld Array survey(GLEAM; Wayth et al. 2015; Hurley-Walker et al. 2017)was released shortly before the sub-mission of this work and we do not include it in our study. 

2.1. MSSS 
MSSS is the frst major imaging campaign with the Low FrequencyArray (LOFAR; van Haarlem et al. 2013).The main goal 
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G.Kokotanekovetal.:Thescaling relation betweenAGNcavitypowerandradio luminosityatlowradio frequencies 
of MSSS is to produce a broadband catalog of the brightest sources in the low-frequency northern sky, creating a calibra-tion sky model for future observations with LOFAR. It covers two frequencywindows: one within the low-band antenna range (LBA;30−75 MHz) and the other in the high-band antenna range (HBA; 119−158 MHz). The LBA surveyis a work in progress and will be examined in a separate publication. In this paper we focusexclusivelyontheHBApartofthe survey,whereeachone of the 3616 felds required to survey the entire northern sky is observed in two seven-minute scans separated by four hours to improve the uv-coverage. 
In this work we use a set of preliminary images (hereafter default images) used by the MSSS team to produce the frst internal version of the MSSS catalog. The preliminary MSSS processing strategy includes primary fux calibration based on a bright, compact calibrator observed before the target snapshot. One round of phase-only, direction-independent calibra-tionis performed usinga VLSSr-basedskymodel(Healdetal. 2015) and then imaging is performed with the AWImager (Tasse et al. 2013)witha simple, shallow deconvolution strategy using 2500 CLEAN iterations. The imaging run per feld incorporates projected baselines shorter than2kλ. Baselines shorter than 100 λ were excluded from the imaging for felds at declination δ ≤ 35 degrees in order to exclude contamination from incompletely sampled large-scalegalactic plane structures and thusprovidea smoother background(see Healdetal. 2015).A correction based on VLSSr and the NRAO VLA Sky Survey (NVSS; Condon et al. 1998)was applied to the MSSS images to compensate for errors in the default fux density scale dependent on the position of the source on the sky(Hardcastle et al. 2016). 


2.2. Reprocessing of MSSS data 
Although the characteristic resolution of the default MSSS im-ages is ∼20, the either high or low declination of the majority of the B-24 systems visible in MSSS results in an average res-olution of ∼3.50 due to the limited subset of the data imaged as described in Sect. 2.1. Thus, the default MSSS images do not allow us to resolve the sources and study the radio features corresponding to the observed X-ray structures.For this reason we developed a strategy to reprocess the data and produce custom images with 20–3000 resolution that allow us to study the mor-phology of the most extended systems in the sample. Furthermore, the resolution of the reprocessed MSSS data matches the resolution of the TGSS image products (discussed in more detail below), which allows for easy and reliable comparison between the two surveys. 
In order to reach angular resolution of 20–3000, we re-processed the long baselines which were not used so far in the default MSSS imaging strategy but were included as part of the MSSS observation. The primary step of the reprocessing is an additional round of phase-only, direction-independent self-calibration in order to fne-tune the calibration for higherresolution imaging capability.We accessed the MSSS archive to obtain the fagged, demixed, and fux-calibrated target snapshot observations. Each snapshot consists of eight measurement sets containing the individual2 MHz-wide bands at 120, 125, 129, 135, 143, 147, 151, and 157 MHz. These bands are treated separately throughout the phase-only self-calibration process accomplished with Black Board Selfcal (BBS; Pandeyet al. 2009). 
The frst step of our reprocessing procedure is to image the default pre-calibrated MSSS datatoa higher resolution.We use AWImager including projected baselinesupto10kλ employing Briggs weighting(Briggs 1995)witha robust parameterof−1. From the resulting map, we extract a high-resolution skymodel, which we use to perform phase-only self-calibration. After the self-calibration loop, the two snapshots are combined (for better uv-coverage) and each of the eight bands is imaged separately using the same imaging parameters as in the frst imaging round. Individual band images are later smoothed to match resolution and weighted by rms noise before they are combined to create the fnal full-band images presentedin Sect. 4. 
To make sure that there are no signifcant astrometric shifts between the separately-calibrated bands, we crossmatched catalogs derived from the individual-band images against TGSS, and assessed the typical difference in positions for the sources common to both. Each feld typically contains several tens of sources detected both in MSSS and TGSS. Although the overall astrometry of each individual feld can differ from TGSSbyupto1−200 , the relative astrometric difference between the MSSS bands was seen to be negligible within the uncertainties, which are <100 for all felds.Wedo fnda small systematic astrometric shift with frequencyonlyin the feldof A262,butevenin this case the difference betweenthetwo most distant bandsisatthe100 level,far smaller than the synthesized beam (20.7500). 
We focused our reprocessing efforts on six felds (A2199, MS 0735.6+7421, 2A 0335+096, MKW3s and A2052, A262, and Perseus) since, based on the 330 MHz and 1.4 GHz VLA maps, only they had sizes that could be potentially resolved at a resolution of 20–3000. Unfortunately, we could not obtain a reliable image at this resolution for the feld of MKW3s and A2052. Due to the presence of three very strong sources in that feld (MKW3s, A2052 and 3C 313), the 10kλ image contained many strong artifacts, which distortfaint features and bias the fux measurements. Thus we use the default MSSS images to measure the fux of those two systems. Furthermore, A262 was not well resolved at 2000 resolution, so we used the reprocessed image only to measure the fux of the source. The successfully reprocessed images of A2199, MS 0735.6+7421, 2A 0335+096, and Perseus are shown and discussedin detailin Sect. 4. 
For several objects in the studied sample deep LOFAR ob-servations are already available. As a sanity check we imaged a small frequency chunk(ν = 142 MHz, Δν = 4 MHz) of a full 8-h LOFAR observation on A2199. This image revealed the same morphology as observed in the reprocessed MSSS image (shown in Sect. 4.4). Furthermore, the total fux of A2199 mea-sured in the test LOFAR image coincides with the fux derived from the MSSS map within 2%. This gives us confdence that the quoted fux densities and the features outlined below are not a product of processing artefacts or poor uv-coverage but real physically existing characteristics of the sources. 


2.3. TGSS 
TGSS was carried out at 148 MHz with the Giant Metrewave RadioTelescope (GMRT). Each pointingwas observed for ∼15min,splitoverthreeormore scansspacedoutintimetoimprove uv-coverage. The TGSS data products have gone through a fully automated pipeline(Intema et al. 2009; Intema 2014), which includes direction-dependent calibration, modeling and imaging to suppress mainly ionospheric phase errors. As a re-sult the fux density accuracy is estimated to be ≈10% and the noise level is below5 mJy/beam for the majority of the point-ings. TGSS and MSSS have a comparable bandwidth (16.7 and 16 MHz) and integration time per feld (15 and 14 min, respectively). The current data release of TGSS covers the skybetween −53 and +90degdeclination.ByincludingtheTGSSdatainour 
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A&A 605, A48 (2017) Table 1. Characteristics of the sample sources and the feld images from MSSS at 140 MHz and TGSS at 148 MHz. 
TF-23 Sample  MF-14 Sample  
Source  z  Coordinates (RA Dec)  Exta TGSS Res.b Noisec (arcsec) (mJy/beam)  Extd MSSS Res.e Noise f (arcsec) (mJy/beam)  
A2199  0.030  16 28 38.0 +39 32 55  Y 25.00 10  Y 21.63 40  
MS 0735.6+7421  0.216  07 41 44.8 +74 14 52  Y 25.00 3  Y 27.77 30  
2A 0335+096  0.035  03 38 35.3 +09 57 55  Y 25.31 5  Y 23.58 11  
Perseus  0.018  03 19 47.2 +41 30 47  Y 25.00 10  Y 20.81 20  
A262  0.016  01 52 46.8 +36 09 05  N 25.00 5  N 20.75 15  
MKW3s  0.045  15 21 51.9 +07 42 31  Y 25.42 7  N 223.05 100  
A2052  0.035  15 16 44.0 +07 01 07  N 25.42 7  N 251.05 150  
A478  0.081  04 13 25.6 +10 28 01  N 25.31 5  N 178.05 30  
Zw 3146  0.291  10 23 39.6 +04 11 10  N 25.85 3.5  N 236.05 30  
Zw 2701  0.214  09 52 49.2 +51 53 05  N 25.00 2.5  N 172.05 10  
A1795  0.063  13 48 53.0 +26 35 44  N 25.00 7  N 269.05 40  
RBS 797  0.350  09 47 12.9 +76 23 13  N 25.00 6  N 185.05 15  
MACS J1423.8  0.545  14 23 47.6 +24 04 40  N 25.00 7  N 270.05 35  
A1835  0.253  14 01 02.3 +02 52 48  N 26.03 4  N 246.05 40  
M84  0.0035  12 25 03.7 +12 53 13  Y 25.14 20  
M87  0.0042  12 30 49.4 +12 23 28  Y 25.31 70  
A133  0.060  01 02 42.1 −21 52 25  Y 32.53 6  
Hydra A  0.055  09 18 05.7 −12 05 44  Y 29.09 30  
Centaurus  0.011  12 48 47.9 −41 18 28  Y 49.90 6  
HCG 62  0.014  12 53 05.5 −09 12 01  N 28.27 3  
Sersic 159/03  0.058  23 13 58.6 −42 44 02  N 52.98 3  
A2597  0.085  23 25 20.0 −12 07 38  Y 29.55 7  
A4059  0.048  23 57 02.3 −34 45 38  Y 43.02 6  

Notes. (a) Indicatesifthe sourceisextendedwith respecttoapoint sourceintheTGSSmap. (b) Resolution of TGSS maps. This column shows one axis of the synthesized beam. The other axis of the TGSS beam is 25.0000 .(c) Local rms noise in TGSS maps, measured within one degfrom the center of the source. (d) Indicates if the source is extended with respect to a point source in either the default or reprocessed MSSS map. (e)ResolutionofMSSSmaps.MSSSmapshavea circular synthesizedbeamwiththe stated diameter. (f )Local rms noise in MSSS maps, measured within one degfrom the center of the source. 
analysis, we can look at the full B-24 sample, for which 30% of the sources are in the southern hemisphere. 
Compared to MSSS, TGSS has a number of advantages and disadvantages, which follow from the different uv-coverage be-tween the two surveys and the different processing schemes used to produce the images. While MSSS is more sensitive to extended diffuse emission, TGSS has a higher resolution than the default MSSS(∼2500 and ∼3.50,respectively). This makes TGSS better at resolving the morphology of the more distant sources and correctly isolating their emission from the contaminating emission of neighboring sources (e.g., Zw3146 and A478). On the other hand, being much more sensitive to extended diffuse emission, MSSS allows us to get a more complete picture of the integratedAGN activityover time. 


2.4. Sample selection 
Since radio galaxies of Fanaroff-Riley type I and II (FRI and FRII;Fanaroff <BR>&Riley1974)are likely to have different particle content, we do not expect them to follow the same relationship (Godfrey&Shabala 2013). Thus, weexclude CygnusA (e.g., McKean et al. 2016)as being the only FRII. In total the sample comprises 23 systems: 21galaxy clusters, onegalaxy group (HCG 62), and one ellipticalgalaxy (M84). Theyrange in red-shift from 0.0035 (M84) to 0.545 (MACS J1423.8+2404). Since we will study this sample with TGSS, we will refer to this sample as the TGSS Feedback sample, shortly TF-23. In this work we use the TF-23 sample to study the Pcav − Lν relation. 
We further defne a subsample of B-24 including only the systems observed by MSSS. This subsample again excludes CygnusAfor beingthe only FRII as well as M87 and M84 for not having MSSS observations of reasonable quality. In total the sample comprises14galaxy clusters and rangesin redshift from 
0.016 (A262) to 0.545 (MACS J1423.8+2404).We will call this sample the MSSS Feedback sample, shortly MF-14.Table 1lists the redshift and coordinates of the sources as well as the properties of the corresponding maps in MSSS and TGSS. 


2.5. X-rays 
The X-ray data used in this work are taken from the literature or based on archival Chandra observations.For the correlation analysis discussed in Sect. 3, we have adopted the values cal-culated for Pcav by Rafferty et al. (2006). These estimates were determined from the existing Chandra exposures for the sample at that time and assume a simple geometrical model to calculate the mean cavity power based on the cavity’s size, pressure, and position relative to the cluster center. This technique for estimating cavity powers has been employed routinely in other studies of feedback systems and can yield variations in the derived values for Pcav of ∼2–4 due to uncertainties in the cavity geometry as well as the methods used to estimate the cavity ages. In this work, we take the literature values from Rafferty et al. (2006)as reported and discuss some of the caveats associated with these estimates belowin Sect. 3. 
For the four resolved sources in our MSSS sample, Perseus, 2A0335+096, MS0735.6+7421, and A2199, we have created 
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G.Kokotanekovetal.:Thescaling relation betweenAGNcavitypowerandradio luminosityatlowradio frequencies 
X-ray surface brightness images and residual maps using the current Chandra archival data. In all four cases, the objects were imaged multiple times with the ACIS detector and we have extracted all of the existing exposures from the Chandra Data Archive. The data were reprocessed using CIAO 4.7 and CALDB 4.6.7 to apply the latestgain and other calibration corrections as well as fltered to remove anycontamination due to background fares. Instrument and exposure maps were created for each exposure individually with the spectral weighting de-termined by the ftting a single temperature, MEKAL thermal model(Mewe et al. 1985; Liedahl et al. 1995)plus foreground Galactic absorption to the total integrated spectrum from the central region of each cluster. Individual background event fles were created for each dataset from the standardACIS blank-sky event fles following the procedure described in Vikhlinin et al. (2005). 
Finally, combined X-ray surface brightness maps were constructedby reprojectingthedataforeachexposuretoa common target point on the sky for each object and then com-bining each exposure into a fnal mosaic. Corresponding mosaics of the exposure maps and background counts were also constructed and used to form the fnal background-subtracted, exposure-corrected X-ray surface brightness images. The X-ray imagesshownin Sect. 4havebeen flteredin energytothe range 0.5−7.0keV.For each object, unsharp-masked imageshave been constructed by subtracting images which have been Gaussian smoothed on two length-scales. The resulting residual images are used in Sect. 4 in conjunction with our reprocessed MSSS radio maps at 140 MHz to study the correspondence, or lack thereof, between the observed, diffuse low-frequency emission and the presence of feedback signatures in the X-ray. 


2.6. VLSSr 
In principle, data at low frequencies such as VLSSr at 74 MHz (Cohen et al. 2007;Lane et al. 2012,2014)could be used to pro-vide extra information which helps constrain the turnover frequencies in the radio spectra (as discussed in Sect. 3.5). With this in mind we have obtained the VLSSr maps, with a resolution of 7500 and an average rms noise of ∼0.1 Jy/beam, and at-tempted to compile VLSSr fux density measurements for our sample. Unfortunately, we could not obtain reliable measurements for more thana thirdof our sample.Two sources are out-side of the VLSSr coverage (Centaurus and Sersic 159/03), three systems are below the detection limit (A478, MACS J1423.8, and HCG 62), and two sources are only marginally detected (RBS 797 and A1835). Due to the low resolution of VLSSr, Zw3146is blendedwiththe emissionfrom close-by sources.For the rest of the sources we analyzed the spectra from which was clear that the available VLSSr points do not help constrain the turnover frequency. Given the incomplete coverage of the sample and the lack of improvement in the ftting results we do not include these points in the subsequent analysis. The radio spectra of the sample systems are discussed in detail in Sect. 3.5. 


3. Sample analysis and correlations 
In this section we use the TF-23 sample of bright feedback systems in order to derive the Pcav − Lν scaling relation at 148 MHz. We also study the radio spectra of the sample sources and com-ment on the correlation between cavity power and bolometric radio luminosity corrected for spectral aging. 
3.1. Radio fux measurements 
Since more than 40% of the TF-23 sample sources are not re-solved at 20–3000 scale, and in many of the resolved sources it is difficult to separate the lobes and the core, we only mea-sure the total fux densities from the sources. In principle, this could introduce a systematic offset to higher radio luminosities in the correlation. However,based on the analysis of Bîrzan et al. (2008), the core emission comprises .20% of the total fux den-sity of these sources for frequencies ≥300 MHz. Due to the steep spectrum of the lobe emission, we expect the core contribution to be even smaller at lower frequencies (140–150 MHz). 
To obtain the fux densities from TGSS, we used the publicly available mosaics at 148 MHz.We used the reprocessed MSSS felds to measure the fux density of A2199, MS 0735.6+7421, 2A 0335+096, Perseus, and A262. These reprocessed maps provide higher resolution which allows us to more easily iso-late the region of interest and disentangle contaminating emission from nearby sources. For the remaining nine sources in the MF-14 sample, the fuxes were extracted from the default MSSS mosaics. 
Our general recipe for obtaining the fux densities consists of two steps. First, we visually inspect the maps and select a nearby region devoid of sources which we use to defne the lo-cal rms noise (Table 1). Then we measure the fux density of the sourceinaregion confnedbythe3σ contour.We used this strategy for well-resolved and marginally resolved sources. For point sources, we measured the fux in a region with the size of the FWHM of the synthesized beam. This was done for HCG62 in TGSS and MACS J1423.8 in MSSS. 
In several felds we noted the presence of strong artifacts in the images. For these objects we use a higher cut-off for the background in order to exclude surrounding artifacts from the measurements.We useda5σ threshold for A4059 and HydraA in TGSS; and for MS 0735.6+7421, Zw 3146, A2199, and A1795 in MSSS. 
In some cases we clearly detect more extended diffuse emission at low frequencies that was not observed in the high frequency maps of Bîrzan et al. (2008). In order to be consistent with the analysis at high frequencies, we restrict the fux den-sity measurements to the morphological features considered at 325 MHz. In TGSS we applied this strategy for Perseus and M87; in MSSS, for Perseus and 2A0335+096. 
We reportthe measuredfuxesinTable2.In accordancewith Bîrzan et al. (2008),the listed uncertainties include the statistical error (thermal noise) plus the uncertainty of the absolute fux scale. The fux scale uncertainty is 10% in MSSS, as well as in TGSS(Intema et al. 2017). 


3.2. Cavity power measurements 
Rafferty et al. (2006)have used Chandra X-ray data to calcu-late the amount of work required to create the observed cavities, which gives a measure of the total mechanical energy pro-ducedby theAGN. The total energy, combined withabuoyancy timescale estimateoftheageofthebubble,providesan estimate of the timeaveraged cavitypower.We adopt the cavitypower estimates of Rafferty et al. (2006)for our correlation analysis. 
Those cavity power estimates have two main limitations. For all systems except two (Perseus and Hydra A) the cavity power is estimated for a single or a pair of cavities; thus the measurements are potentially limited to the energy output of a single outburst. Another mechanism that car-ries energy into the ICM is the mild shocks, with Mach 
A48, page5of 20 

A&A 605, A48 (2017) Table 2. Flux density measurements from MSSS, TGSS, and higher frequencies from literature used for the spectral ftting discussed in Sect. 3.5. 
Source  MSSS 140 MHz S ν (Jy)  TGSS 148 MHz S ν (Jy)  ν (MHz)  P-band S ν (Jy)  ν (MHz)  750 MHz S ν (Jy)  ν (MHz)  L-band S ν (Jy)  ν (MHz)  S -band S ν (Jy)  ν (MHz)  C-band S ν (Jy)  
A2199  54.3 ± 6.1  52.9 ± 5.6  324  24.00 ± 0.96  7501  9.1900 ± 0.0049  14002  3.68 ± 0.12  27003  1.21 ± 0.06  4675  0.313 ± 0.012  
MS 0735.6+7421  5.30 ± 0.83  3.95 ± 0.46  330  0.80 ± 0.03  1425  0.021 ± 0.001  
2A 0335+096  1.10 ± 0.21  1.05 ± 0.19  324  0.21 ± 0.01  14902  0.0367 ± 0.0018  4860  0.01 ± 0.001  
Perseus  58.8 ± 6.3  42.4 ± 4.4  4084  29.00 ± 0.04  7501  21.82 ± 0.28  
A262  0.57 ± 0.15  0.540 ± 0.091  324  0.299 ± 0.012  1365  0.0734 ± 0.0030  
MKW3s  17.3 ± 2.2  15.6 ± 1.8  327  4.73 ± 0.18  1440  0.0897 ± 0.0040  4860  0.0025 ± 0.0001  
A2052  58.5 ± 6.7  59.4 ± 6.3  330  30.9 ± 1.2  7501  11.76 ± 0.041  1490  5.7 ± 0.2  27005  2.02 ± 0.04  4860  0.72 ± 0.03  
A478  0.53 ± 0.14∗  0.305 ± 0.050  327  0.11 ± 0.01  1440  0.027 ± 0.001  
Zw 3146  0.259 ± 0.056∗∗  0.0174 ± 0.0056  324  0.016 ± 0.004∗∗∗  4860  0.00139 ± 0.00007  
Zw 2701  1.36 ± 0.18  1.35 ± 0.15  324  0.21 ± 0.01  4860  0.0043 ± 0.0002  
A1795  7.47 ± 0.90  6.08 ± 0.67  327  3.36 ± 0.14  1465  0.88 ± 0.04  27003  0.48 ± 0.03  48506  0.261 ± 0.034  
RBS 797  0.133 ± 0.035  0.174 ± 0.033  324  0.104 ± 0.006  1475  0.021 ± 0.001  4860  0.0042 ± 0.0003  
MACS J1423.8  0.103 ± 0.044  0.054 ± 0.013  327  0.0269 ± 0.002  1425  0.0044 ± 0.0002  
A1835  0.150 ± 0.055  0.107 ± 0.021  327  0.095 ± 0.007  1400  0.031 ± 0.001  4760  0.0099 ± 0.0004  
M84  14.9 ± 1.9  324  11.1 ± 0.5  1425  05.6 ± 0.2  4860  2.28 ± 0.09  
M87  436 ± 45  324  124 ± 5  1400  138 ± 6  4860  59 ± 2  
A133  9.6 ± 1.0  330  3.60 ± 0.10  1425  0.132 ± 0.005  
Hydra A  317 ± 36  333  152 ± 6  7507  79.9 ± 3.2  1423  39.2 ± 1.6  27008  23.50 ± 0.93  4760  15.0 ± 0.6  
Centaurus  19.5 ± 2.0  327  12.3 ± 0.5  6257  7.160 ± 0.040  1565  3.4 ± 0.1  27009  2.458 ± 0.048  4760  1.37 ± 0.06  
HCG 62  0.0090 ± 0.0039  324  0.008 ± 0.002  1440  0.0050 ± 0.0004  
Sersic 159/03  4.23 ± 0.45  324  1.53 ± 0.06  1425  0.22 ± 0.01  4860  0.056 ± 0.002  
A2597  14.7 ± 1.5  328  8.3 ± 0.3  1400  1.86 ± 0.07  4985  0.37 ± 0.02  
A4059  22.8 ± 2.4  328  9.93 ± 0.40  14402  1.285 ± 0.043  270010  0.35 ± 0.07  486011  0.12 ± 0.04  

Notes. ThevaluesforMSSS,andTGSSderivefromour analysis.The unreferencedvaluesathigher frequencies comefrom Bîrzanetal. (2008). The numbers in superscripts reference the high frequencyfux density measurements coming from the literature. (∗) A478 is not resolved in the MSSS map and is blended with neighboring cluster members. Thus, the fux measurement at 140 MHz includes serious contributions from several surrounding sources. (∗∗) Zw3146 is not resolved in the MSSS map and is blended with neighboring sources. Thus, the fux measurement at 140 MHz includes serious contributions from several surrounding sources. (∗∗∗)Value not identical with the one cited inBîrzan et al. (2008).We 
used the P-band map from Bîrzan et al. (2008)to measure the fux ourselves.  
References.  (1) Pauliny-Toth et al. (1966); (2) Condon et al.  (1998); (3) Andernach et al.  (1981); (4) Burbidge &Crowne  (1979);  
(5) Wall &Peacock (1985); (6) Gregory &Condon (1991); (7) Haynes et al. (1975); (8) Wright &Otrupcek (1990); (9) Sadler  (1984);  
(10) Vollmer et al.(2005); (11) Wright et al. (1994).  

number between 1.2 and 1.7, which are observed in manysystems(Fabian et al. 2006; McNamara et al. 2005; Nulsen et al. 2005a,b; Forman et al. 2005, 2007; Sanders&Fabian 2006; Wise et al. 2007; McNamara&Nulsen 2007). Therefore, the cavity estimates are only lower limits on the energy output of the AGN, and as a consequence, the radiative efficiencies are overestimated. 


3.3. Luminosity and cavitypower uncertainties 
The monochromatic radio luminosity was calculated as 
+ z)−(α+1)
Lν = 4πD2 LS ν(1 , (1) 
where DL is luminosity distance, z is redshift, and S ν is the radio continuumfux density,for whichwehave assumedapower-law spectrum of the form S ν ∝ να.Thevaluesofthe spectral index α are presented inTable 4and are derived from our spectral analysis described in Sect. 3.5. 
To estimate the errors in the luminosity values we propagate the uncertainties of the fux density, luminosity distance, and spectral index using 
s 
!2 !2 
2ΔDL ΔS ν 
ΔLν = Lν ++ (ln(1 + z)Δα)2 . (2) 
DL S ν 
To compute the luminosity distance uncertainties we follow the recipe usedby Godfrey&Shabala (2016).The sources lyingat DL > 70 Mpc have redshift-derived distance estimates and for them we assume ΔDL = 7Mpc corresponding to peculiar velocities of σv ≈ 500 kms−1.For sources with DL < 70 Mpc we as-sume ΔDL = 0.1DL, corresponding to the estimated uncertainty in redshift independent distance measurements(Cappellari et al. 2011). The distances of M84 and M87 are accurate within ∼3% since theyhave been measured with the Hubble SpaceTelescope using the surface brightness fuctuation method(Blakeslee et al. 2009). Thus, the uncertainties in luminosity are greater than the onesof Bîrzanetal. (2008). 
The cavity power measurements that we take from Rafferty et al. (2006)have asymmetric errors. In order to sim-plify the ftting, we assume Gaussian uncertainties in the cavity power measurements and calculate their standard deviation as the average of the positive and negative uncertainties given by Rafferty et al. (2006). The distance uncertainties are not propagated with cavity power, since the cavity power uncertainties are strongly dominatedby other sourcesof error such asvolume estimates(O’Sullivan et al. 2011). 
3.4.Pcav vs.L148 
For our correlation analysis we use the fux density values de-rived from TGSS at 148 MHz for the TF-23 sample.For com-parison we performed the same analysis at 327 MHz using the fux densityvalues publishedby Bîrzanetal. (2008). 
We used orthogonal distance regression to ft a model of the form 
log Pcav = log P0 + β log Lν, (3) 
where Lν is in units of 1042 ergs−1 and P is in units of 1024 W Hz−1. The uncertainties of both radio luminosity and cavity power were taken into account as weights in the ft. The resultoftheregression analysisis presentedinTable 3.The Pcav vs. Lν plots are shownin Fig. 1. 
First, we must note that thare is no signifcant difference be-tweentheftof Bîrzanetal. (2008)onthe sampleof24 sources and our results for the TF-23 sample. This suggests that removing Cygnus A from the sample does not signifcantly bias the correlation. The β reportedby Bîrzanetal. (2008)at327MHz 
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G.Kokotanekovetal.:Thescaling relation betweenAGNcavitypowerandradio luminosityatlowradio frequencies 

Fig. <BR>1. <BR>Cavity (jet) power vs. the total radio luminosity for the TF-23 sample at 327 MHz(left)and 148 MHz(right). The dashed line shows the best-ft power law. It is log Pcav = (1.6± 0.2) + (0.50 ± 0.14)log L327 with intrinsic scatter of 0.86 dex at 327 MHz and log Pcav = (1.4± 0.3) + 
(0.51 ± 0.14) log L148 with intrinsic scatter of 0.85 dex at 148 MHz. 
Table 3. Resultsof fttingEq.(3)for the TF-23 sample. 
νab βc σd 
P0 
327 101.6±0.2 0.50 ± 0.14 0.86 148 101.4±0.3 0.51 ± 0.14 0.85 
Notes. (a) Frequency in MHz. (b) Normalization. (c) Luminosity slope. 
(d) Intrinsic scatter in dex. 
is 0.51 ± 0.07 with a scatter (standard deviation) of 0.81 dex, while for the TF-23 sample we get 0.50 ± 0.14 with a scatter of 0.86 dex.We get the same slopebut higher uncertainty and slightly higher scatter. This small difference is a cumulative ef-fect from severalfactors; most importantly, omitting CygnusA and using different spectral indices when computing the Lν. Other contributors are the different luminosity errors we com-pute, which change the weighting of points during the ft, and the lower fux of Zw3146 we measure from the map at 327 MHz of Bîrzan et al. (2008;seeTable 2). 
We show that thePcav – Lν scaling relation holds at lowradio frequencies.As canbe seen fromTable 3, thereisnodifference between the correlation at 327 MHz and 148 MHz. Theyhave virtually identical slope and scatter. The comparison between the results at 148 MHz and 327 MHz shows that merely moving to ∼150 MHz does not provide us with a better understanding of the correlation between cavity power and monochromatic radio luminosity. Thisis not surprising since the shiftbyafactorof ≈2in frequencycorrespondstoonlyafactorof≈1.4 in terms of electron energy. 
In only two of the 12 resolved sources in TGSS (Perseus and M87) we detect signifcantly more extended low-frequency emission than observed at 327 MHz.For the remainder of the sample, the observed low-frequencyemission is well correlated spatially with higher frequency emission seen at 327 MHz. Therefore, we conclude that for ∼90% of the systems in TF-23 sample, TGSS retrieves the fux density at 148 MHz associated with the same episode(s) of AGN activity seen at higher frequency by Bîrzan et al. (2008)and in the X-rays by Rafferty et al. (2006). Only Perseus and HydraA include cavity power measurements for more than one pair of cavities, and thus more than one episode of activity. Therefore, our analysis at 148 MHz, as well as the analysis of Bîrzan et al. (2008)at higher frequencies, is effectively restrictedtoafairly limited rangeof outburst ages. 
In the reprocessed MSSS images of Perseus and 2A0335+096 (presented in Sect. 4) we clearly detect diffuse emissionextendingwellbeyondtheregions associatedwith the X-ray cavities studied by Rafferty et al. (2006). The X-ray morphology of these objects on this large scale is complex and not well correlated spatially with the observed low-frequency emission. Associating these more extended structures in the radio and X-rays with single, well-defned episodes of AGN activity is not trivial. This complication is most evident in the case of Perseus where even in the radio map, it is difficult to separate emission associated with relicAGN outbursts from the surrounding mini-halo. In the absence of well-defned spatial correlation, including the fux from this more extended radio emission without measurements of corresponding X-ray structures would artifcially result in a correlation with fatter slope and large scatter. This situation indicates that in order to study the correlation over multiple episodes of activity, we would need a sample with deeper X-ray data with multiple cavities and the corresponding low-frequencyradio observations. 
Studying the previously published correlations between Pcav and Lν, Godfrey&Shabala (2016)have raised andexplored the question if the observed correlation is caused by the underlying physical mechanisms or is a result of distance effect related to a selection bias. Isolating the luminosity distance effect, theyfnd a much weaker correlation between Pcav and Lν. The selection effects discussedby Godfrey&Shabala (2016)apply equallyto the sample discussed in the present paper, since theyconsidered 
A48, page7of 20 

A&A 605, A48 (2017)  
Table 4. Spectral information.  
Source  Pointsa  αb  σc  χ2 d r  Radio data used in the fte  
(dex)  (MHz)  
A2199  6  −1.65 ± 0.02  0.24  73  148, 324, 750 (1), 1400 (2), 2700 (3), 4675  
MS 0735.6+7421  3  −2.43 ± 0.04  0.14  9.9  148, 330, 1425  
2A 0335+096  4  −1.17 ± 0.03  0.19  6.8  148, 324, 1490 (2), 4860  
A262  3  −0.96 ± 0.04  0.07  1.0  148, 324, 1365  
Perseus  3  −0.46 ± 0.02  0.04  0.9  148, 408 (4), 750 (1)  
MKW3s  4  −2.72 ± 0.02  0.28  43  148, 327,1440, 4860  
A478  3  −1.00 ± 0.05  0.07  1.5  148, 327,1440  
A2052  6  −1.33 ± 0.01  0.14  31  148, 330, 750 (1), 1490, 2700 (5), 4860  
Zw 3146  3  −0.81 ± 0.07  0.17  1.9  148, 324, 4860  
Zw 2701  3  −1.49 ± 0.02  0.24  30  148, 324, 4860  
A1795  5  −0.90 ± 0.03  0.04  0.8  148, 327, 1465, 2700 (3), 4850 (6)  
RBS 797  4  −1.14 ± 0.03  0.14  6.8  148, 324, 1475, 4860  
MACS J1423.8  3  −1.20 ± 0.05  0.10  0.9  148, 327, 1425  
A1835  4  −0.84 ± 0.03  0.18  7.5  148, 327, 1400, 4760  
M84  4  −0.57 ± 0.02  0.07  9.4  148, 324, 1425, 4860  
M87  3  −0.60 ± 0.03  0.08  5.3  148, 1400, 4860  
A133  3  −2.18 ± 0.03  0.31  52  148, 330, 1425  
Hydra A  6  −0.89 ± 0.02  0.02  1.9  148, 333, 750 (7), 1423, 2700 (8), 4760  
Centaurus  6  −0.76 ± 0.01  0.04  4.0  148, 327, 625 (7), 1565, 2700 (9), 4760  
HCG 62  3  −0.29 ± 0.13  0.04  0.1  148, 325, 1440  
Sersic 159/03  4  −1.09 ± 0.02  0.04  10  148, 325, 1425, 4860  
A2597  4  −1.09 ± 0.02  0.11  10  148, 328, 1400, 4985  
A4059  5  −1.37 ± 0.03  0.22  5.0  148, 328, 1440 (2), 2700 (10), 4860 (11)  

Notes. Points at 148 MHz derive from TGSS. If not designated differently, the higher frequencypoints come from Bîrzan et al. (2008).(a) Number of frequencies used for thepower-law ft. (b) Spectral index derived from thepower-law ft. (c) Intrinsic scatter of the points toward the power-law ft.(d) Reduced χ2of thepower-law ft. (e) The frequencies in MHz used for power-law ftting of the radio spectra. The numbers in parentheses are the references for the literaturevalues andhave the same meaning asinTable 2. 
a larger sample, which includes the objects studied here.We re-fer the reader to the work of Godfrey&Shabala (2016)for a deeper analysis of the distance dependence of the two studied parameters. Although, it seems that at least some of the correlation we measure here is due to this effect, regression taking distance into account does not necessarily correctly account for potential measurement bias.Amore completewaytoinvestigate a likely distance dependence would be to perform a population synthesis simulation in which to create a theoretical sample and study its properties over distance. Such analysis is however be-yond the scope of this paper and we leave it for further work. 


3.5. Spectrum andPcav vs.Lbol 
As the bolometric radio luminosity(Lbol)isexpectedtobea bet-tergauge of the total radiative power, Bîrzan et al. (2008)also study the relation between Lbol and cavity power. Theyconclude thatthe total bolometric radiopowerisnotabetter proxyforcavity power than the monochromatic luminosity at 327 MHz due to the similarly large scatter. Theyfurther show that the scatter is reduced from 0.83 to 0.64 dex if only the lobe emission is con-sidered. This selection, however, reduces the number of studied systemsto13(Table3; Bîrzanetal.2008).Tofurtherinvestigate whether the scatter is due to radio aging, theyinclude the spectrum break frequency(νC)in the regression analysis and derive a tight correlation (Eq. (17); Bîrzan et al. 2008). Theyshow that the knowledge of the lobe break frequencyimproves the scatter by ≈50% (to 0.33 dex), which signifcantly increases the accu-racy by which one can estimate the cavity power of the AGN when cavity data are unavailable. 
Although nowwidely used, the Pcav – Lbol,νC scaling relation is based on a number of simplifying assumptions. Bîrzan et al. (2008)report that the continuous injection model (CI;Kardashev 1962) does not provide acceptable fts to many of the spectra. As an alternative theyadopt the single injection KP model (Kardashev 1962; Pacholczyk 1970). It is, however, by now well established that the KP model makes unrealistic physi-cal assumptions especially for studies of extended FRI type sources (e.g., Tribble 1993; Harwood et al. 2013; Hardcastle 2013). From the 13 points used to derive the Pcav – Lbol,νC re-lation, six systems have only lower or upper limits on the break frequency. However, these limits are treated as detections in the regression analysisof Bîrzanetal. (2008).The actual breakfre<BR>quencies could be far from the limit values, and the resulting impact of these limits on the reduction in the correlation scatter has not been assessed. 
From the remaining seven systems used by Bîrzan et al. (2008)to derive the Pcav – Lbol,νC relation, three include break frequencies obtainedby fttingaKP modeltothe data.For one of these sources (MS 0735.6+7421) the KP ft results in a very high injection index of αi = 1.3, while the typical value for αi in the literatureisin the range 0.5–0.8(Komissarov&Gubanov 1994). The other four systems have their break frequency com-puted using the recipeof Myers&Spangler (1985)assuminga fxed injection index of αi = 0.5. This approximation is based on the KP model and allows estimation of the break frequency by assuming an injection index and providing a measurement of the spectral index between 1.4 and 4.9 GHz. While this strategy conveniently provides break frequencies based on two 
A48, page8of 20 

G.Kokotanekovetal.:Thescaling relation betweenAGNcavitypowerandradio luminosityatlowradio frequencies 
data points, the presented values for those four systems do not include uncertainty estimates. Although correcting for the ef-fects of spectral aging can in principle reduce the scatter in the observed correlation, large uncertainties in the derived break frequencies may distort the reduction in the scatter this correction can yield. 
In an attempt to derive reliable break frequencies and bolometric luminosities, we revisit the radio spectra adding our new low frequency measurements. Plotting the total fux values at 330 MHz, 1.4 GHz, 4.5 GHz, and 8.5 GHz from Bîrzan et al. (2008)we fnd that in several cases the fuxes at 8.5 GHz ap-peared signifcantly higher than expected by extrapolating the lower frequency points. This difference is especially evident in the SED’s of MKW3s, MS0735, and Zw2701. Inspecting the VLA contours provided in Fig. 10 of Bîrzan et al. (2008) we determined that no extended structures are observed on the 
8.5 GHz maps of ten systems – 2A0335, A262, A478, A1795, A2052, MKW3, MS0735, Perseus, RBS797, A133. The emission at this frequencyclearly derives from the compact core. The lobes are partially exposed on the 8.5 GHz map of only eight systems – A2199, Hydra A, Centaurus, Sersic 159/03, A2597, A4059,andM84.Four systems(Zw2701andZw3146,A1835, and HCG 62) are basically unresolved at all frequencies and thereisno observationofMACS J1423.8at8.5GHz.Weargue that the total luminosity at 8.5 GHz primarily derives from the core, as opposed to the aged radio lobes which clearly dominate below 1.4 GHz.For this reason, we have neglected the8 GHz datapointsinour analysisand consideredonlydatabelow5GHz in our SED fts. 
Given the agreement in fux scales between MSSS and TGSS, and the more complete sky coverage of the TGSS sample, we have restricted ourselves to the TGSS fuxes in our spec-tral ftting analysis.We note that in four systems, MSSS shows signifcantly higher fux densities relative to TGSS. These systems include Perseus, A478, Zw3146, and MACS J1423.8 with fux densities that arefactors of 1.4, 1.7, 10.0, and 1.8 higher, respectively. These discrepancies may represent new emission components, issues in the fux density calibration, or, in the case of A478 and Zw3146, blending with neighboring objects due to insufficient angular resolution. Although excluded from the ft-ting process, we have included the MSSS points in the SED plots in Figs. A.1 and A.2 for the purposes of comparison. 
As an alternative to the KP model used by Bîrzan et al. (2008), we could consider ftting a continuous injection (CI) model to the SEDs to correct for the effects of spectral curvature. However, we note recent work has shown that ftting inte-grated spectra with the CI model should be treated with caution (Harwood 2017).In addition, the number of frequencypoints for objects in our sample range from three to six, with 40% of the samplehavingjustthreedatapointsforftting.Withthese limita-tions, we fnd we cannot ft a single, well-constrained and physically justifed electron aging model consistently for all sources. As a result, we are unable to derive a reliable and uniform set of break frequencies and bolometric luminosities for the sample. Given the available data, we therefore fnd that the addition of a single low-frequencyconstraint at 148 MHz is insufficient to im-proveuponthe spectralaging correctionof Bîrzanetal. (2008). 
For this reason, and in order to treat all sources consistently, we have ft a simple power law model to all spectral points. Reconstructing the SEDs, we include the TGSS 148 MHz fux densities, the 330 MHz, 1.4 GHz, and 4.5 GHz VLA measurements, as well as the high frequency literature values used by Bîrzan et al. (2008).We perform the spectral analysis using total fux measurements since the majority of the TF-23 sources have only total fux density measurements at both low and high frequencies.Table 4presents the derived spectral index, the intrin-sic scatter, the reduced chi-squared, the number of ft points, and their origin. Plots of the fts themselves can be seen in Figs. A.1 and A.2. We note that, based on the reduced chi-squared values, the SED’s for many of the sources in the sample are not well ft by a simple power-law. However, as already discussed above, the available data is currently insufficient to consistently ft a more complicated spectral model. The derived spectral in-dices are used for computing the monochromatic luminosities employing Eq.(1). 



4. Resolved systems 
This section describes the morphology of the resolved sources from our reprocessed MSSS felds. We review 2A0335+096, MS 0735.6+7421, A2199, and the Perseus cluster and discuss the new features revealed at 140 MHz. We present both the MSSS and TGSS images and discuss the differences between the two surveys.We compare the low frequencyradio images with Chandra X-ray maps and study the correspondence between the observed radio and X-ray structures. 
4.1.Perseus 
The Perseus cluster, A426, is the brightest cluster in the X-ray sky and has therefore been well studied by all X-ray telescopes. The X-ray emission is sharply peaked on the cluster core, centered on the cDgalaxy NGC 1275 (Perseus A).Apair of X-ray cavities in north (N) and south (S) from the center are coincident with the FRI radio source, 3C84(Pedlar et al. 1990;Boehringer et al. 1993;Fabian et al. 2000;Churazov et al. 2000).More distantbubbles, presumablya productof past activ<BR>ity, are seen to the NW and S. Further to the north, X-rays have revealed a region of fux drop, named the northern trough by Fabianetal.(2011).At 50–80kpcfromthe center, Fabianetal. (2006, 2011)identifya south “bay”of hotgas whichisin ap-proximate pressure equilibrium. They argue that risingbubbles from energetic past outburst have accumulated in the northern trough and the south bay. 
A semi-circular cold front(Markevitch&Vikhlinin 2007), accompanied by a sharp drop of metallicity, is distinguished at ∼100 kpc to the west and south-west of the nucleus of NGC 1275 (Fabian et al. 2011). The northern trough and the southern bay lie along a continuation of the west cold front. In a recent work Walkeretal.(2017)studythe possibility thatthebayisa result ofKelvin-Helmholtz instabilityinthe sloshing cold front. While the morphology inside the cold frontis dominatedby theAGN activity and turbulencein thegas(Hitomi Collaborationetal. 2016), the structures at larger radii are most probably associated with a subcluster merger(Churazov et al. 2003), which also accounts for the east-west asymmetry in the X-ray surface brightness. 
It is known from higher frequencyobservations that the cen-terof Perseus hostsa rare(Ferettietal. 2012)radio mini-halo, whichmaybe generatedby turbulence(Gittietal. 2004)orgas sloshing(ZuHoneetal. 2011; Mazzotta&Giacintucci 2008), presumably induced by an off-axis merger. In our MSSS map at 148 MHz we successfully recover the known general mor-phology of the inner part of the mini-halo and distinguish new structures in this region. 
While the TGSS image only shows the radio emission around the inner cavities (Fig. 2), the reprocessed MSSS map 
A48, page9of 20 Fig. <BR>2. <BR>Perseus cluster. Top left:reprocessed MSSS map with resolution 20.800 × 20.800 and rms noise 20 mJy/beam. The contours start at5σ level and are drawn at 100 mJy/beam × [1, 1.4, 2, 2.8, 4, 5.7, 8, 11, 16, 22, 32, 45, 64, 91, 128]. Top right:Chandra X-ray surface brightness residual map. The imageis producedby unsharp masking using archival datain the 0.5–7keV band with totalexposureof 1.4Ms after standard fltering. Contours correspond to the MSSS image. Bottom:TGSS map with resolution 25.000 × 25.000 and rms noise 10 mJy/beam. The contours start at5σ level and are drawn at 50 mJy/beam × [1, 1.4, 2, 2.8, 4, 5.7, 8, 11, 16, 22, 32, 45, 64, 91, 128, 182, 256]. 


revealstheinnerpartofthe mini-halo(Fig. 2).Beingashortinte<BR>gration survey, MSSS is not deep enough to detect the full scale of the mini-halo, as observed at 330 MHz(Burns et al. 1992; de Bruyn&Brentjens 2005), 610 MHz(Sijbring 1993), and 230−470 MHz(Gendron-Marsolais et al. 2017),but it does re-veal interesting new features within 100 kpc around NGC 1275. 
The inner part of the radio emission follows the general NS orientation of the jets (Fig. 2). The outer part of the diffuse emission continues up to 60 kpc north from center of Perseus A, reachinguptoan arch-likedropinX-ray brightness(Fig. 2). South from the core the mini-halo bends toward the west and stretches up to 100 kpc toward SW, reaching asfar as the cold front. 
The northern part of the diffuse emission shows two pro-nounced features elongated towardNand NW. The NW feature corresponds to the outer NW X-ray cavity. The structure stretching north lies along the main jet axis and is cospatial with a known optical flament (Conselice et al. 2001; Fabian et al. 2011). It extends along the X-ray spur, which con-tinues further than the optical flament. What we see in our MSSS map is presumably the base of the radio structure ob-served at higher frequencies(Burns et al. 1992; Sijbring 1993; de Bruyn&Brentjens 2005), which reaches the X-ray northern trough. 
We further identify two radio “streamers” within the mini-halo.We distinguish an elongated structure which starts at the 
A48, page 10 of 20 

G.Kokotanekovetal.:Thescaling relation betweenAGNcavitypowerandradio luminosityatlowradio frequencies 
eastern edge of the inner north cavity and stretches NE reaching the arch-like drop in X-ray brightness ∼80 kpc from the center. Our MSSS map also shows an enhancement of the radio fux to the south of the core which corresponds to the southern old cavity. 
The outlined radio features once again exemplify the com-plicated morphology at the center of the Perseus cluster. Our shallow MSSS map demonstrates the potential of low-frequency observations on Perseus and promises that the deep LOFAR data will reveal more details of the complex morphology of the mini-halo.We will presenta full track LOFAR observationina fol-lowup paper. The deep LOFAR map is expected to help us con-strain the integrated energy outputof theAGNover the lastfew Myr and verify if the low-frequency radio mini-halo is energetically consistent with the turbulence recently measured with Hitomi (Hitomi Collaboration et al. 2016). 

4.2. 2A 0335+096 
2A 0335+096 is a compact, radio-bright, nearby(z = 0.035) galaxy clusterwitha luminousX-ray core(Sandersetal.2009). The centralgalaxy hasacD morphology that hostsa weak radio source(Farageetal.2012).Ithasanearbycompanion elliptical galaxy situated ∼700 (∼5 kpc) to the north-west(Sanders et al. 2009). Thevelocitiesof the centralgalaxy and the companion derived from optical spectroscopystudies suggest theyare merg-ing(Gelderman 1996;Donahue et al. 2007;Hatch et al. 2007). 
2A0335+096 shows a very complicated morphology in both radio and X-rays. XMM-Newton and Chandra have revealed evidence for an active historyof interaction between theAGN and ICM in the core of 2A 0335+096. X-ray observations show a complex system of X-ray-emitting structures in the core, including flaments, cool clumps, a metal-rich spiral, and at least fve distinct cavities at varying distances and position angles relativetothe centralgalaxy(Mazzottaetal. 2003; Bîrzanetal. 2004;Kaastra et al. 2004;Sanders&Fabian 2006;Sanders et al. 2009).The total4pV enthalpyassociated with the fve cavities is estimated to be5×1059erg(Sandersetal.2009).Thereisasharp drop in X-ray surface brightness at 10 radius to the south-east ofthe core, identifedasacold frontby Mazzottaetal. (2003). Since the feature shows an abrupt density declinebut no signif-cant temperature changeover the edge, Sanders&Fabian (2006) classify it as an isothermal shock, as found in the Perseus cluster. 
The radio source shows a very different morphology at different frequencies. At ∼5 GHz twin lobes associated with op-positely directed radio jets are observed in NE – SW direction extending ∼1200 in length(Sanders et al. 2009). Using the Myers&Spangler (1985)relation,Donahue et al. (2007)esti-mate an age for the radiating electrons of 25 Myr assuming equipartition or50Myrif the magnetic feldisafactorof four less than the equipartitionvalue. Theypropose that an interaction between the central and the nearby companion ellipticalgalaxy may have triggered the current episode of radio activity. 
At 1.5 GHz (Fig. 3) the main observable feature is a clear single peak at the center of the galaxy surrounded by a steep-spectrum emission roughly symmetric around the center (Sarazin et al. 1995;Bîrzan et al. 2008;Sanders et al. 2009).The observed shape and spectral index has led the observed emission to be classifed as a mini-halo. At 330 MHz the mini-halo is not well observed, but a second peak of emission is distinguished 3000 (∼20 kpc) NW from the center(Bîrzan et al. 2008)and the morphology appears clearly elongated in NW-SE direction. 
The cluster hosts an unusual nearby Narrow Angle Tail (NAT) radio source which has been observed at 327 MHz (Patnaik&Singh 1988) and 1.5 GHz(O’Dea&Owen 1985; Sarazin et al. 1995). Its center is situated at ∼380 kpc in the N-W direction from the center of the cluster, but its long tail propagates south getting as close as ∼150 kpc(∼3.50)from the centralgalaxy. No interaction between theNAT source and the core of 2A0335+096 has been observed on previously published images. At low signifcance level the reprocessed MSSS map (Fig.3)shows someevidencethatthediffuse emission surround-ing the core of 2A0335+096 is connected to the emission from theNAT source. This suggest that the two sources might be in-teracting, however, the quality of the data does not allow us to be conclusive about this scenario. 
The diffuse radio emissionat140MHz (Fig. 3)extendsin all directions further than observed at 1.5 GHz (Fig. 3). Similar to the Perseus cluster, the reprocessed MSSS map (Fig. 3)reveals much more diffuse structure than the TGSS image (Fig. 3). Although the reprocessed MSSS map includes signifcant artifacts around point sources, our visual inspection confrmed that the observed extended emission of 2A0335 is authentic since no other source in the maps shows emission with similar ex-tent or morphology. The 140 MHz map (Fig. 3) shows pro-nounced elongated shape along the NW -SE direction. The diffuse emission at 140 MHz spans ∼130 kpc in NW–SE direction and ∼60 kpc in NE–SW direction. The boundaries of the ob-served emission at 140 MHz toward south reach as far as the isothermal shock at ∼10 from the center. 
Figure 3 shows that, besides the central peak of emission, thereis clearlya secondpeakof emission situated3000 (∼20 kpc) in the NW direction from the center. In the MSSS map these two peaks appear equally bright. The central maximum (i) correspondstothevery centerofthe cluster.The secondpeak(ii)is clearly associated with the most pronounced cavity in the system (cavityA, Fig. 3). 
We observe a signifcant extension of the emission toward north-west which includes the distant radio peak (iii). The observationsat140MHz(Fig.3)and148MHzforthe frsttimereveal the bridge between the radio emission associated with the central mini-halo and the radio maximum iii, which appeared disconnected from the core at higher frequencies. Despite thefact that emission at peak iii was observed in deep high-frequencymaps, itis nonetheless foundtobea steep spectrum source.We mea-suredthe spectral indexina circular aperture centeredatpeakiii and foundavalueof ∼−1.8between 147 MHz and 1.5 GHz. This spectral index seems consistent with the idea that this plasma originatedinan older outburstofAGN activity.The distantpeak iii is situated ∼110 kpc from the centralAGN and for it we cal-culate an age of 150 Myr based on the sound speed estimate for the systemby Bîrzanetal. (2004). 
The residual map we calculate based on archival X-ray data (Fig. 3)agrees reasonably well with the image published by Sanders et al. (2009). The only major difference is that cavity Eappears much less pronounced in our residual map. Based on our MSSS image, all of the fve cavity structures identifed by Sanders et al. (2009)contain low frequency emission. There is a clear extension of the radio emission along cavity D, which continues beyond the cavity.Aspur of emission starts at cavity B and continues south through the isothermal shock. Although cavitiesC andE are also fully coveredby the radio emission, theyarenotclearly associatedwithaparticular featuresoftheradio morphology. The association between the radio emission and the X-ray cavities implies that the former is mostly formed from multipleprevious generationsofAGN radiooutbursts.However, the morphology of the cavities is complex and is unclear what the orderof generationof thebubbleswas. 
A48, page 11 of 20 Fig. <BR>3. <BR>2A0335+096. Top left:reprocessed MSSS map with resolution 23.600 × 23.600 and rms noise 11 mJy/beam. Contours start at5σ level and correspond to 55 mJy/beam × [1, 1.2, 1.4, 1.6, 1.8, 2, 2.4, 2.8, 3.2, 3.6]. Individual features are labeled i, ii, and iii. These are discussed in the text. Top right:Chandra X-ray surface brightness residual map. The imageis producedby unsharp masking using archival datain the 0.5–7keV band with total exposure of 101 ks after standard fltering. Green contours correspond to the MSSS image. The fve cavities identifed by Sanders et al. (2009)are marked. The correspondence between these features and our radio map is discussed in the text. Bottom left:TGSS map with resolution 


25.300 × 25.000 and rms noise5mJy/beam. Contours start at3σ level and correspond to 15 mJy/beam × [1, 1.4, 2, 2.8, 4, 5.7, 8, 11]. Bottom right: radio map at 1.5 GHz from Bîrzan et al. (2008). Contours correspond to 0.25 mJy/beam × [1, 1.4, 2, 2.8, 4, 5.7, 8, 11, 16, 22, 32, 45]. 
In general, what we observe with LOFAR appears much more extended and complicated than the picture at higher frequencies. The overall shape of the source does not resemble the traditional symmetric round morphology associated witha mini-halo. The structure is elongated to the NW, following the di-rection defned by the two main radio enhancements (i and ii), that is the direction between the center and cavity A. This di-rection is consistent with the elongation observed at 330 MHz and matches the axis between the centralgalaxy and the nearby companion, as well as the direction of the flament observed in Hα (Sanders et al. 2009). 
If the source is not a mini-halo the other most likely candi-dateis structure formedby activityover time fromtheAGN.We see evidence for this in the correlation between this extended low-frequency radio structure and the X-rays. There is a clear correspondence betweenpeakiandiiandtheX-raycavitiesThe correspondence between radio peak iii and the X-ray morphology is of lower signifcance, which might be due to the quality of the X-ray data. The observed structures seem consistent with relics of past AGN outbursts. Although we cannot defnitively say with the currentlyavailable data, theevidence seems tofavor theAGN interpretationovera simple mini-halo. 
The observed X-ray cavities do not follow the usual simple linear progression,but resemblea networkof structures that are presumably related to multiple outbursts(Sanders et al. 2009). It might be that density inhomogeneity of the surrounding environmenthas defectedthe straightbuoyancyrisepathofthebubbles. Basedonthefact thatthe orientationofthelow frequency 
A48, page 12 of 20 

G.Kokotanekovetal.:Thescaling relation betweenAGNcavitypowerandradio luminosityatlowradio frequencies 
radio peaks i and ii is perpendicular to the small scale radio lobes observed by Donahue et al. (2007), the idea that the ra<BR>dio source has changed orientation over time also seems quite plausible. This interpretation would imply that the source has been defected in the recent past. Based on its circular shape and proximitytothe center, X-raycavityA(coincident withlow frequencyradio peak ii) seems to be the newest one. Considering the buoyancy age of cavity A from Rafferty et al. (2006), the change in direction of the radio source must have happened in the last ∼60 Myr. This value is consistent with the age estimate for the NE-SW radio lobes of Donahue et al. (2007)presented earlier. 
Unfortunately,withthe currentlyavailabledatawe cannotbe conclusive about the origin of the newly observed diffuse radio emission.The proximityoftheNATsource additionally complicates the interpretationof thefaintest and mostextended struc-turetothewestandNW.Weexpectthatthe futuremapfromthe LOFARTwo-metre SkySurvey(LoTSS; Shimwell et al. 2017) will be able to shed light onto the outburst history of thisAGN by showing in greater detail the radio structures corresponding to the numerous X-ray cavities and by revealing the region of interaction between theNAT source and theAGN. 


4.3. MS 0735.6+7421 
The cool-core cluster MS 0735.6+7421 (hereafter MS0735) hosts oneof the most energetic radioAGN known.Itis the most distant(z = 0.22) among the sub-sample of clusters that we re-solvewith MSSS. MS0735 hosts large X-ray cavities in an otherwise relaxed system(Gitti et al. 2007). Each cavity has a diameter of ∼200 kpc and is flled with synchrotron emission from the radio lobes.Aweakbutpowerful shock front encloses the cavitiesandtheradiolobesina cocoon(McNamaraetal.2005).The total energy required to infate the cavities and drive the shock frontisabove1062erg(McNamaraetal. 2009;Vantyghemetal. 2014). 
Both the MSSS map and the TGSS image (Fig. 4)retrievethe main morphology of the source known from higher frequencies. In this system, two symmetric lobes are propagating in northsouth direction.We observeachangeof directionofthe lobesat 140 MHz consistent with the bending visible at 324 MHz. As op-posed to higher frequencies, at 140 MHz the compact core is not distinguished between the bright steep-spectrum lobes, which clearly dominate radio structure. The 140 MHz map does not show more extended diffuse radio emission associated with this object. 
The data from TGSS and MSSS is consistent with the picture from higher frequencies showing the radio emission still trapped inthe surrounding cocoon(Fig. 4).This phenomenonmaybere<BR>lated to thefact that MS0735.6+7421 is the most energetic out-burst observed sofar. The energyof the outburst has clearly dis-placed and compressed material in the cluster atmosphere which mayhave piledupfasterand createda moreeffective confning shelltostoptheadvanceofany radio plasma.Wefndnoevidence in this data for more extended emission corresponding to older outbursts. If present, that emission will presumably peak at even lower frequencies detectable with LOFAR LBA. 


4.4. A2199 
A2199 is a nearby cool-core cluster at z = 0.030. The central dominantgalaxy NGC 6166 hosts the unusual restarted radio source 3C 338. The large-scale structure of 3C 338 can be separated into two regions. The active region includes the core and two symmetric jets terminating in twofaint hot spots. The older region is displaced to the south and consists of two extended steep-spectrum radio lobes connected by a bright fl-amentary structure (Burns et al. 1983; Giovannini et al. 1998). Burns et al. (1983)propose that the shift between the large-scale structure and the restarted jets could indicate a motion of the centralAGN inside thegalaxy. Vacca et al.(2012), on the other hand, suggest that the displacement could also be due to an in-teraction between the old radio lobes withbulk motions in the surrounding medium caused by the sloshing of the cluster core (Markevitch&Vikhlinin 2007). 
The diffuse radio lobes clearly coincide with two large X-ray cavities 25 kpc either side of the nucleus (e.g., Johnstone et al. 2002; Gentile et al. 2007; Nulsen et al. 2013). The low-frequency data at 330 MHz shows the presence of an extension to the south that corresponds to a third X-ray cavity(Gentile et al. 2007). Similar to 2A0335+096 and the Perseus cluster, A2199 hosts an isothermal shock – a sharp drop in X-ray brightness with a pressure jump but no temperature change across it(Sanders&Fabian 2006). It is seen in X-rays as a surface brightness edge 10000 SE from the cluster center and Nulsenetal. (2013)argue thatitis most probablya result of a shock produced by an older, signifcantly more powerful AGN outburst than the one that produced the current outer radio lobes and cavities. 
Our 140 MHz MSSS map is shown in Fig. 5. The new low-frequencydata are consistent with previously published results. In general, the emission at this frequencyappears slightly more extended than it shows on the maps at 327 MHz presented by Gentile et al. (2007)and Bîrzan et al. (2008), even though the comparison is difficult due to the lower angular resolution of our map. Interestingly, at a comparable resolution, the emission on the MSSS map also extends further from the center than on the 74MHzimageof Gentileetal. (2007).Thisismost probablya result of the low sensitivity of VLA at 74 MHz at the time of their observation. 
The radio emission at 140 MHz fully covers the southern X-ray cavity (Fig. 5). Similar to the observed morphology at higher frequencymaps(Bîrzan et al. 2008;Gentile et al. 2007), the eastern lobe appears well confned.We do not detect radio signatures of the powerful outburst which presumably created the isothermal shock. On the other hand, since the SE X-ray edge and the outer radio lobes have comparable scales, it seems con-sistent that the shock front restricts the expansion of the eastern lobe further east. 
Theplumeextending north-wardfromthe northerntipofthe westernlobe, seenatthe330MHzby Gentileetal. (2007)and Bîrzan et al. (2008), is also present at 140 MHz. It appears di-luted in our map due to the lower resolution, which is also the caseat74MHz(Gentileetal.2007). Nulsenetal. (2013)argue that the indistinct appearance of the 10000 front to the northwest would then imply that the turbulence is greater there than on the southeastern side of the cluster center.A more disturbed environmentcouldwellexplainwhythe westernlobehasamoreuntypical shape than the eastern one. Nulsen et al. (2013)showthat ashellof densergasis situatedtothewestofthe westernlobeat 
4.9 GHz. This denser structure seems to inhibit the growth of the lobe toward the west. However, since the shell is discontinued to the north, it leaves room for the lobe to expand in this direction. 
In Fig. 5 we show the TGSS image only for completeness. On this image, the shape of the system looks very different. The lobes do not have their expected morphology and orientation, and only one central peak of emission is observed. Based on 
A48, page 13 of 20 Fig. <BR>4. <BR>MS0735+7421. Top left:reprocessed MSSS map with resolution 27.800 × 27.800 and rms noise 30 mJy/beam. The contours start at5σ level and are drawn at 0.150 mJy/beam × [1, 1.4, 2, 2.8, 4, 5.7]. Top right:Chandra X-ray surface brightness residual map. The image is produced by unsharp maskingusing archivaldatainthe 0.5–7keVbandwith totalexposureof520ks after standard fltering. Green contours correspondto the MSSS image. Bottom: TGSS map with resolution 25.000 × 25.000 and rms noise3mJy/beam. The contours start at5σ level and are drawn at 


15 mJy/beam × [1, 1.4, 2, 2.8, 4, 5.7, 8, 11, 16, 22, 32]. 
our experience calibrating the MSSS data of A2199, where we were getting similar deformations, we believe that the TGSS image suffers from signifcant distortions due to phase calibration problems. As noted earlier in Sect. 2.2, a deeper full-track LO<BR>FAR pointingfor A2199is alreadyavailable. This observationis currently being analyzed and will be published separately. 



5. Discussion and conclusions 
With facilities such as LOFAR, GMRT, and the Murchison Widefeld Array (MWA) online, uniform surveys at low radio frequencies are now becoming available for a large fraction of the sky. The angular resolution and sensitivity of these frst all-sky, low-frequency surveys are well-matched to studies of extended, steep spectrum diffuse emission in cluster feedback systems and will ultimately provide the larger samples necessary for statistical population studies. In this pilot work, we have em-ployed data from the frst all-skyimaging surveys with LOFAR (MSSS at 140 MHz) and the GMRT(TGSS ADR1 at 150 MHz) to study a sample of known, strong AGN feedback sources drawn from Bîrzan et al. (2008). Combining data from both sur-veys, we have searched for the presence of extended, diffuse emission not seen previously at higher radio frequencies and possibly associated with relic emission from previousAGN ac-tivity.Wehave also computed totallow-frequencyfuxes for the sources in the sample in order to test the well-known correlation between high frequencyradio fux and the power required to create the cavity structures seen in the X-ray(Bîrzan et al. 2008; Rafferty et al. 2006). 
For both MSSS and TGSS surveys, images were created and examined for each of the objects in the sample. In the case of the TGSS data, images were extracted from the default mosaics 
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Fig. <BR>5. <BR>A2199. Top left: reprocessed MSSS map with resolution 21.600 × 21.600 and rms noise 40 mJy/beam. The contours start at5σ level and are drawn at 200 mJy/beam × [1, 1.4, 2, 2.8, 4, 5.7, 8, 11, 16, 22, 32, 45]. Top right: Chandra X-ray surface brightness residual map. The image isproducedbyunsharpmaskingusingarchivaldatainthe0.5–7keVbandwithtotalexposureof154ksafter standard fltering.Theeast,west, and south cavities are denoted by “E”, “W”, and “S”, respectively. The SE surface brightness edge is denoted by arrows. Contours correspond to the MSSS image. Bottom:TGSS map with resolution 25.000 × 25.000 and rms noise 10 mJy/beam. The contours start at3σ level and are drawn at 30 mJy/beam × [1, 1.4, 2, 2.8, 4, 5.7, 8, 11, 16, 22, 32, 45, 64, 91, 128, 182]. 
provided as part of the standard TGSS ADR1 data products (Intema et al. 2017)and no additional processing was required. The LOFAR images used in this work were based on a prelimi-nary data release of the MSSS all-skysurvey(Heald et al. 2015). Although the MSSS surveydata included baseline lengths out to 100 km, the initial imaging products produced during the development of the surveyprocessing used a cutoff in baseline length to obtain a nominal angular resolution of ∼20. In this work, we have described a simple reprocessing strategy that takes advantage of data from these longer baselines to both improve the noiseand angular resolutionofthe resulting maps.Wehaveapplied this procedure to all objects in the sample which showed evidence of extended emission in the default, low-resolution maps resulting in improved images with angular resolutions of ∼2500.For the subset of resolved objects, these improved MSSS maps were used to characterize the presence of anydiffuse, extended emission and in all subsequent comparisons to TGSS, high-frequencyradio, and X-ray images. 
Based on the resulting TGSS and MSSS maps, we have mea-sured the total radio fuxes for all sources; however, due to differing sky coverages, not all sources were visible in both sur-veys.Forthe subsetofoverlapping sources,wehave compared the derived fuxes between the two surveys and fnd good agreement. The exceptions are Perseus, where the radio mini-halo shows complicated spatial structure over a large area, and A478 and ZW3146, which are not well resolved in the MSSS maps and blended with nearby sources. Given the agreement in fux scales and the more complete sky coverage of the TGSS sample, we have used the TGSS fuxes in all subsequent analysis of the Pcav − Lν correlation known from higher frequencydata. 
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Estimates for the values of Pcav based on Chandra X-ray data were taken from the literature(Rafferty et al. 2006)and com-pared to the radio luminosity at 148 MHz as inferred from the measured TGSS fux values. At this frequency, we fnd a corre-
∝ L0.51±0.14 
lation of the form Pcav 148 , which is in good agreement with the result foundby Bîrzan et al. (2008)at 327 MHz. 
We fnd a relatively large scatter in the 148 MHz correlation of ∼0.85 dex which again is consistent with the value obtained at327MHzby Bîrzanetal. (2008).Thislarge scattermakesthe derived correlation difficult to use as a reliable proxy for jet power in sources where only radio data is available. In the previous high frequency study, Bîrzan et al. (2008)found that the scatter in the correlation could be signifcantly reduced by in-cluding the effects of spectral aging, although in that analysis the lack of low-frequencydata required a number of simplifying assumptions in order to constrain the break frequency. Including our new data points at 148 MHz with the data at higher frequenciestakenfrom Bîrzanetal. (2008),wehaveexaminedthe spectral energy distributions for our sample in an attempt to pro-vide better constraints on the break frequencies andbyextension an improved correction for the scatter in the observed correlation due to spectral aging. Unfortunately, our results show that including additional measurements at 148 MHz alone is insufficienttofta consistent,physically justifed spectralaging model. We therefore conclude that to improve on the aging correction of Bîrzan et al. (2008)will likely require additional data below 148 MHz, such as with the LOFAR LBA at 30–90 MHz, and data with sufficient angular resolution to clearly resolve emission from the core and lobe regions. 
In four of the sources, Perseus, 2A0335+096, MS0735.6+7421, and A2199, the reprocessed MSSS im-ages show clear evidence for extended, diffuse emission at 140 MHz.We have compared the observed morphology of the extended, diffuse emission in the MSSS maps with corresponding radio images from TGSS and the VLA, as well as X-ray surface brightness and residual maps based on archival Chandra data. In Perseus, we easily resolve the well-known, radio lobes observed at higher frequencies(Pedlar et al. 1990)and associated with the inner cavities seen in X-ray images(Fabian et al. 2000, 2006). The MSSS image also clearly recovers the more extended halo structure seen in previous deep radio maps of Perseus out to radii of ∼100kpc(Burnsetal. 1992; Sijbring 1993;de Bruyn&Brentjens 2005). Theoverall morphologyof the low-frequency radio halo is well-correlated with a number of arc-like edges and ripples visible in the unsharp-masked X-ray image(Fabian et al. 2006)reinforcing the current picture whereby the X-ray and radio structures share a common origin in the recurrentAGN activityof PerseusA. 
We fnd a similar situation in the well-known feedback system 2A0335+096. Although the overall morphology of the low-frequencyemission present in the reprocessed MSSS image con-frms the structure visible in the TGSS maps and hinted at in higher frequency VLA maps(Bîrzan et al. 2008), the diffuse emission detected in the MSSS map is more extended and ex-hibitsarough correspondencetothelarge-scale depressionsseen in the X-ray map outside the inner ∼20 kpc(Sanders et al. 2009). Abridge of low-frequencyemission is also observed connecting the core of 2A0335+096 with a bright peak of low-frequency emission ∼110 kpc to the NW, parallel to the axis of the in-ner cavity system. This peak does not appear to be associated with a known radio source and exhibits a steep spectral index of α ∼−1.8 consistent with remnant plasma from previous AGN activity. Assuming this emission originated in the core of 2A0335+096, we estimate an age of ∼150 Myr for the original outburst based on estimates of the sound speed in the cluster core (Bîrzan et al. 2004).This emission peak, however,does not seem to correlate with an obvious depression in the X-ray map. 
For the remaining two resolved sources in our sample, MS0735.6+7421 and A2199, we fnd the low-frequency emission observed in the MSSS maps corresponds closely with what has been seen at 327 MHz. In both the TGSS and MSSS images for MS0735.6+7421, the low-frequencyemission clearly traces the large-scale, X-ray cavities seen in the X-ray and at higher radio frequencies(McNamara et al. 2005). The low-frequency emissionshowsnoevidenceforastrong central coreandis com-pletely dominated by emission in the lobes corresponding to the X-ray cavities.We fnd noevidence for moreextended,diffuse low-frequency emission outside the well-known cocoon shock in this system(McNamara et al. 2009;Vantyghem et al. 2014), implying that the radio plasmais fully enclosedby the shock.In the case of A2199, the overall morphology of the diffuse emission in both TGSS and MSSS maps agree and is consistent with the structures seeninthe330MHzmapof Bîrzanetal. (2008). Compared to the TGSS image, the fnal, reprocessed MSSS map has higher quality and angular resolution, which allows us to clearly resolve two peaks of low-frequencyemission coincident with the two main X-ray cavities observed in the core along the jet axis(Nulsen et al. 2013), as well as extensions to the S and NW corresponding to an additional cavity and surface brightness jump seen in the X-rays, respectively(Gentile et al. 2007; Nulsen et al. 2013). Taken all together, the morphology of the low-frequency emission in A2199 is consistent with the picture of a system having undergone at least two episodes of AGN activity. 
While the images presented in this work demonstrate the potential of LOFAR to recover extended, diffuse emission, our analysis highlights some important caveats for future low-frequency radio studies of feedback. First, the original sample of Bîrzan et al. (2008)were selected on the basis of containing well-defnedcavity systemsintheX-ray.Withafewexceptions, these cavities and the higher frequencyradio emission they en-close can be linked to a single epoch of AGN activity occurringoverafairly narrow rangeof outburst ages. The same can be said for the “ghost” cavities seen in systems such as Perseus (Fabian et al. 2006)and A2597(Clarke et al. 2005)and found to contain lower frequency radio emission at 330 MHz. At the lower frequencyand moderate angular resolutions provided by TGSS and MSSS, however, the distribution and morphology of the observed low-frequencyradio emission is quite complicated and not easily resolved into individual components that may be associated with well-defned episodesofAGN activity.Asa re-sult, radio fux measurements at these frequencies are difficult to place in the context of the Pcav − Lν correlation found for single episodesofAGN activityat higher frequency. 
The situation is similarly complicated in the X-ray. As even the small sample of objects in this work illustrates, the welldefned surface brightness depressions or “cavities” associated with the radio emission at higher frequencies is harder to identify for older outbursts(≥100 Myr). Even for objects with deeper X-ray exposures such as Perseus and 2A0035+096, the mor-phologies of these outbursts are more complicated, difficult to disentangle from other features possibly related to shocks or core sloshing, and not always well-correlated with the low-frequency radio emission. This complexity is further exacerbated by the lack of sufficientlydeepexposuresfor manyofthenearby,strong feedback systems where we might expect to resolve the X-ray signatures of olderAGN outbursts at larger radii (e.g., Perseus Fabian et al. 2006). Taken altogether, these factors introduce 
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G.Kokotanekovetal.:Thescaling relation betweenAGNcavitypowerandradio luminosityatlowradio frequencies 
considerable uncertainty in estimates for the value of Pcav as-sociated with older or multipleAGN outbursts. 
The LoTSS currently underway will produce images of the full accessible northernskyat angular resolutionsof500 and sen-sitivities of ∼100 µJy. When combined with new high frequency data from surveys such as the VLA SkySurvey(VLASS; Hales 2013), we will have the radio data necessary to both spatially re-solve and spectrally discriminate between different episodes of AGN activity for virtually all nearby feedback systems. In the near-term, these new radio data can be matched to deeper X-ray exposures with Chandra and XMM to better attempt to separate outburst related signatures from otherphysical processes operat-ing in the cluster cores. On the longer term, upcoming missions such as eRosita (Merloni et al. 2012)andAthena (Nandra et al. 2013)will yield larger samples of potential feedback systems as well as information aboutvelocity motionsin thegas from high spectral resolution emission line studies. The combination of these new radio surveys, in particular the low-frequencydata from LoTSS,andimprovedX-raydatawillallowustobuildupa picture of the integrated effectsofAGN output on the surround-ing environment for a large sample of systems over timescales of several 100 Myr. 
Acknowledgements. G.D.K. acknowledges support from NOVA (Nederlandse Onderzoekschool voor Astronomie). B.N.W. acknowledges support from the NCN OPUS UMO-2012/07/B/ST9/04404 funding grant. D.D.M. acknowledges support from ERCStG 307215 (LODESTONE). LOFAR, the Low Frequency Array designed and constructedby ASTRON, hasfacilitiesin several countries, that are owned by various parties (each with their own funding sources), and thatare collectively operatedbythe InternationalLOFARTelescope(ILT)foundation under a joint scientifc policy. GMRT is run by the National Centre for Radio AstrophysicsoftheTata Instituteof Fundamental Research. This research has made use of theNASA/IPACExtragalactic Database (NED) which is oper-atedbytheJet Propulsion Laboratory, California InstituteofTechnology, under contract with the National Aeronautics and Space Administration.We have also usedSAOImage DS9,developedby Smithsonian Astrophysical Observatory. 


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