93 research outputs found
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
Discovery of a giant radio halo in a new Planck galaxy cluster PLCKG171.9-40.7
We report the discovery of a giant radio halo in a new, hot, X-ray luminous
galaxy cluster recently found by Planck, PLCKG171.9-40.7. The radio halo was
found using Giant Metrewave Radio Telescope observations at 235 MHz and 610
MHz, and in the 1.4 GHz data from a NRAO Very Large Array Sky Survey pointing
that we have reanalyzed. The diffuse radio emission is coincident with the
cluster X-ray emission, has an extent of ~1 Mpc and a radio power of ~5x 10^24
W/Hz at 1.4 GHz. Its integrated radio spectrum has a slope of alpha~1.8 between
235 MHz and 1.4 GHz, steeper than that of a typical giant halo. The analysis of
the archival XMM-Newton X-ray data shows that the cluster is hot (~10 keV) and
disturbed, consistent with X-ray selected clusters hosting radio halos. This is
the first giant radio halo discovered in one of the new clusters found by
Planck.Comment: 9 pages, 8 figures and 4 tables. Corrected Figure 7. Matches ApJ
published versio
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 (). 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 is in the
range (S), we found sources with
. 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-LogP 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 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
Parsec--scale radio jets in gamma--ray loud sources
We will present a multiepoch study of the three blazars 0954+658 (BL--Lac),
PKS1510--089 (HPQ) and 1749+096 (BL--Lac). The first two sources are known to
be --ray loud. Our study is based on milliarcsecond resolution
polarimetric observations carried out with the VLBA at 8.4 GHz. The
observations took place between January 1999 and May 2001. Superluminal motion
is detected along the jet of PKS1510--089 and 1749+096, with for all features. Magnetic field structure is revealed along the jets of
0954+658 and PKS 1510--089. The polarisation properties of the parsec--scale
jets remain stationary in all sources, regardless of their total flux density
variability in the radio band and of the presence of superluminal features.Comment: 4 pages, 3 figures, to appear in the proceedings of the connference
"Relativistic jets in the Chandra and XMM era", Bologna, 23-27/9/02 (New
Astr. Rev.
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
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