Heated Intracluster Gas and Radio Connections: the Singular case of MKW3s

Similarly to other cluster of galaxies previously classified as cooling flow systems, the Chandra observation of MKW3s reveals that this object has a complex X-ray structure hosting both a X-ray cavity and a X-ray filament. Unlike the other clusters, however, the temperature map of the core of MKW3s shows the presence of extended regions of gas heated above the radially averaged gas temperature at any radius. As the cluster does not show evidences for ongoing major mergers Mazzotta et al. suggest a connection between the heated gas and the activity of the central AGN. Nevertheless, due to the lack of high quality radio maps, this interpretation was controversial. In this paper we present the results of two new radio observations of MKW3s at 1.28GHz and 604MHz obtained at the GMRT. Together with the Chandra observation and a separate VLA observation at 327MHz from Young, we show unequivocal evidences for a close connection between the heated gas region and the AGN activity and we briefly summarize possible implications.Comment: To appear in a special issue of the "Journal of the Korean Astronomical Society" (JKAS). Proceedings of the International conference on Cosmic Rays and Magnetic Fields in Large Scale Structure, Busan, Korea, 200

Occurrence of radio minihalos in a mass-limited sample of galaxy clusters

We investigate the occurrence of radio minihalos --- diffuse radio sources of unknown origin observed in the cores of some galaxy clusters --- in a statistical sample of 58 clusters drawn from the Planck Sunyaev-Zel'dovich cluster catalog using a mass cut ($M_{500}>6\times 10^{14} M_{\odot}$). We supplement our statistical sample with a similarly-sized non-statistical sample mostly consisting of clusters in the ACCEPT X-ray catalog with suitable X-ray and radio data, which includes lower-mass clusters. Where necessary (for 9 clusters), we reanalyzed the Very Large Array archival radio data to determine if a mihinalo is present. Our total sample includes all 28 currently known and recently discovered radio minihalos, including 6 candidates. We classify clusters as cool-core or non-cool core according to the value of the specific entropy floor in the cluster center, rederived or newly derived from the Chandra X-ray density and temperature profiles where necessary (for 27 clusters). Contrary to the common wisdom that minihalos are rare, we find that almost all cool cores - at least 12 out of 15 (80%) - in our complete sample of massive clusters exhibit minihalos. The supplementary sample shows that the occurrence of minihalos may be lower in lower-mass cool-core clusters. No minihalos are found in non-cool-cores or "warm cores". These findings will help test theories of the origin of minihalos and provide information on the physical processes and energetics of the cluster cores.Comment: 34 pages, accepted for publication in ApJ. Added a section "Definition of a minihalo" and an appendix "Radio size and average surface brigthtness of minihalos and halos

Low frequency follow up of radio halos and relics in the GMRT Radio Halo Cluster Survey

We performed GMRT low frequency observations of the radio halos, relics and new candidates belonging to the GMRT Radio Halo Cluster Sample first observed at 610 MHz. High sensitivity imaging was performed using the GMRT at 325 MHz and 240 MHz. The properties of the diffuse emission in each cluster were compared to our 610 MHz images and/or literature information available at other frequencies, in order to derive the integrated spectra over a wide frequency range.Beyond the classical radio halos, whose spectral index $\alpha$ is in the range $\sim1.2\div1.3$ (S$\propto\nu^{-\alpha}$), we found sources with $\alpha\sim1.6\div1.9$. This result supports the idea that the spectra of the radiating particles in radio halos is not universal, and that inefficient mechanisms of particle acceleration are responsible for their origin. We also found a variety of brightness distributions, i.e. centrally peaked as well as clumpy halos. Even though the thermal and relativistic plasma tend to occupy the same cluster volume, in some cases a positional shift between the radio and X-ray peaks of emission is evident. Our observations also revealed the existence of diffuse cluster sources which cannot be easily classified either as halos or relics. New candidate relics were found in A1300 and in A1682, and in some clusters "bridges" of radio emission have been detected, connecting the relic and radio halo emission. Combining our new data with literature information, we derived the LogL$_{\rm X}$-LogP$_{\rm 325 MHz}$ correlation for radio halos, and investigated the possible trend of the spectral index of radio halos with the temperature of the intracluster medium.Comment: 19 pages, 10 figures, 5 tables, accepted for publication on A&

Brightest Cluster Galaxies in the Extended GMRT radio halo cluster sample. Radio properties and cluster dynamics

Brightest Cluster Galaxies (BCGs) show exceptional properties over the whole electromagnetic spectrum. Their special location at the centres of galaxy clusters raises the question of the role of the environment on their radio properties. To decouple the effect of the galaxy mass and of the environment in their statistical radio properties, we investigate the possible dependence of the occurrence of radio loudness and of the fractional radio luminosity function on the dynamical state of the hosting cluster. We studied the radio properties of the BCGs in the Extended GMRT Radio Halo Survey (EGRHS). We obtained a statistical sample of 59 BCGs, which was divided into two classes, depending on the dynamical state of the host cluster, i.e. merging (M) and relaxed (R). Among the 59 BCGs, 28 are radio-loud, and 31 are radio--quiet. The radio-loud sources are located favourably located in relaxed clusters (71\%), while the reverse is true for the radio-quiet BCGs, mostly located in merging systems (81\%). The fractional radio luminosity function (RLF) for the BCGs is considerably higher for BCGs in relaxed clusters, where the total fraction of radio loudness reaches almost 90\%, to be compared to the $\sim$30\% in merging clusters. For relaxed clusters, we found a positive correlation between the radio power of the BCGs and the strength of the cool core, consistent with previous studies on local samples. Our study suggests that the radio loudness of the BCGs strongly depends on the cluster dynamics, their fraction being considerably higher in relaxed clusters. We compared our results with similar investigations, and briefly discussed them in the framework of AGN feedback.Comment: 12 pages, 6 figures, 3 tables, A&A accepte

Mapping the particle acceleration in the cool core of the galaxy cluster RX J1720.1+2638

We present new deep, high-resolution radio images of the diffuse minihalo in the cool core of the galaxy cluster RX J1720.1+2638. The images have been obtained with the Giant Metrewave Radio Telescope at 317, 617 and 1280 MHz and with the Very Large Array at 1.5, 4.9 and 8.4 GHz, with angular resolutions ranging from 1" to 10". This represents the best radio spectral and imaging dataset for any minihalo. Most of the radio flux of the minihalo arises from a bright central component with a maximum radius of ~80 kpc. A fainter tail of emission extends out from the central component to form a spiral-shaped structure with a length of ~230 kpc, seen at frequencies 1.5 GHz and below. We find indication of a possible steepening of the total radio spectrum of the minihalo at high frequencies. Furthermore, a spectral index image shows that the spectrum of the diffuse emission steepens with the increasing distance along the tail. A striking spatial correlation is observed between the minihalo emission and two cold fronts visible in the Chandra X-ray image of this cool core. These cold fronts confine the minihalo, as also seen in numerical simulations of minihalo formation by sloshing-induced turbulence. All these observations favor the hypothesis that the radio emitting electrons in cluster cool cores are produced by turbulent reacceleration.Comment: 16 pages, 11 figures, accepted for publication in The Astrophysical Journa

IGR J14488-4008: an X-ray peculiar giant radio galaxy discovered by INTEGRAL

In this paper we report the discovery and detailed radio/X-ray analysis of a peculiar giant radio galaxy (GRG) detected by INTEGRAL, IGR J14488-4008. The source has been recently classified as a Seyfert 1.2 galaxy at redshift 0.123; the radio data denote the source to be a type II Fanaroff-Riley radio galaxy, with a linear projected size exceeding 1.5 Mpc, clearly assigning IGR J14488-4008 to the class of GRG. In the X-rays, the source shows a remarkable spectrum, characterised by absorption by ionised elements, a characteristic so far found in only other four broad line radio galaxies.Comment: 7 pages, 3 tables, 5 figures. Accepted for publication on MNRA

Discovery of a radio relic in the low mass, merging galaxy cluster PLCK G200.9-28.2

Radio relics at the peripheries of galaxy clusters are tracers of the elusive cluster merger shocks. We report the discovery of a single radio relic in the galaxy cluster PLCK G200.9-28.2 ($z=0.22$, $M_{500} = 2.7\pm0.2 \times 10^{14} M_{\odot}$) using the Giant Metrewave Radio Telescope at 235 and 610 MHz and the Karl G. Jansky Very Large Array at 1500 MHz. The relic has a size of $\sim 1 \times 0.28$ Mpc, an arc-like morphology and is located at 0.9 Mpc from the X-ray brightness peak in the cluster. The integrated spectral index of the relic is $1.21\pm0.15$. The spectral index map between 235 and 610 MHz shows steepening from the outer to the inner edge of the relic in line with the expectation from a cluster merger shock. Under the assumption of diffusive shock acceleration, the radio spectral index implies a Mach number of $3.3\pm1.8$ for the shock. The analysis of archival XMM Newton data shows that PLCK G200.9-28.2 consists of a northern brighter sub-cluster, and a southern sub-cluster in a state of merger. This cluster has the lowest mass among the clusters hosting single radio relics. The position of the Planck Sunyaev Ze'ldovich effect in this cluster is offset by 700 kpc from the X-ray peak in the direction of the radio relic, suggests a physical origin for the offset. Such large offsets in low mass clusters can be a useful tool to select disturbed clusters and to study the state of merger.Comment: 10 pages, 7 figures, 4 tables. Accepted for publication in MNRA

New Detections of Radio Minihalos in Cool Cores of Galaxy Clusters

Cool cores of some galaxy clusters exhibit faint radio minihalos. Their origin is unclear, and their study has been limited by their small number. We undertook a systematic search for minihalos in a large sample of X-ray luminous clusters with high-quality radio data. In this article, we report four new minihalos (A 478, ZwCl 3146,RXJ 1532.9+3021, and A 2204) and five candidates found in the reanalyzed archival Very Large Array observations.The radio luminosities of our minihalos and candidates are in the range of 102325 W Hz1 at 1.4 GHz, which is consistent with these types of radio sources. Their sizes (40160 kpc in radius) are somewhat smaller than those of previously known minihalos. We combine our new detections with previously known minihalos, obtaining a total sample of 21 objects, and briefly compare the cluster radio properties to the average X-ray temperature and the total masses estimated from Planck.We find that nearly all clusters hosting minihalos are hot and massive. Beyond that, there is no clear correlation between the minihalo radio power and cluster temperature or mass (in contrast with the giant radio halos found in cluster mergers, whose radio luminosity correlates with the cluster mass). Chandra X-ray images indicate gas sloshing in the cool cores of most of our clusters, with minihalos contained within the sloshing regions in many of them. This supports the hypothesis that radio-emitting electrons are reaccelerated by sloshing. Advection of relativistic electrons by the sloshing gas may also play a role in the formation of the less extended minihalos