J/A+A/669/A1 Abell 2256 radio images (Rajpurohit+, 2023)
Deep low-frequency radio observations of Abell 2256.
II: The ultra steep spectrum radio halo.
Rajpurohit K., Osinga E., Brienza M., Botteon A., Brunetti G., Forman W.R.,
Riseley C.J., Vazza F., Bonafede A., van Weeren R.J., Brueggen M.,
Rajpurohit S., Drabent A., Dallacasa D., Rossetti M., Rajpurohit A.S.,
Hoeft M., Bonnassieux E., Cassano R., Miley G.K.
<Astron. Astrophys. 669, A1 (2023)>
=2023A&A...669A...1R 2023A&A...669A...1R (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Radio sources
Keywords: galaxies: clusters: individual: Abell 2256 -
galaxies: clusters: intracluster medium - acceleration of particles -
radiation mechanism: non-thermal -
large-scale structures of Universe - turbulence
Abstract:
We present the first detailed analysis of the radio halo in the
merging galaxy cluster Abell 2256 using the LOw Frequency ARray, the
upgraded Giant Metrewave Radio Telescope, and the Karl G. Jansky Very
Large Array. Radio observations (120MHz-2GHz) combined with archival
Chandra and XMM-Newton X-ray data allowed us to study the central
radio halo emission with unprecedented detail. The integrated radio
emission from the entire halo is characterized by an ultra-steep
spectrum, which can be described by a power law with
alpha144MHz1.5GHz=-1.63±0.03 and radial steepening in the outer
regions. The halo is significantly underluminous according to the
current scaling relations between radio power and mass at 1.4GHz, not
at 150MHz; ultra-steep spectrum halos are predicted to be
statistically underluminous. Despite the complex structure of this
system, the halo morphology is remarkably similar to that of the X-ray
emission. The radio surface brightness distribution across the halo is
strongly correlated with the X-ray brightness of the intracluster
medium (ICM). The derived correlations show sublinear slopes and
distinct structures: the core is IR∝IX1.51, the
outermost region IR∝IX0.41, and we find radio
morphological connections with X-ray discontinuities. We also find a
strong anticorrelation between the radio spectral index and the X-ray
surface brightness, implying radial steepening. We suggest that the
halo core is either related to old plasma from previous active
galactic nuclei activity, being advected, compressed, and
reaccelerated by mechanisms activated by the cold front or less
turbulent with strong magnetic field in the core. The change in the
radio versus X-ray correlation slopes in the outer regions of the halo
could be due to a radial decline of the magnetic field, the increase
in the number density of seed particles, or increasing turbulence. Our
findings suggest that the emitting volume is not homogenous according
to turbulent reacceleration models.
Description:
The new radio observations analyzed are from the upgraded Giant
Metrewave Radio Telescope. The total observing time was 12h covering a
frequency range of 650-950MHz. To understand the interplay between
the thermal and non-thermal plasma in the central region of the
cluster, archival Chandra X-ray data are also analyzed.
Objects:
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RA (2000) DE Designation(s)
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17 03 43.5 +78 43 03 Abell 2256 = ACO 2256
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 103 2 List of fits images
fits/* . 2 Individual fits images
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See also:
J/AJ/123/2261 : Radial velocities in A2256 (Berrington+, 2002)
J/AJ/125/2393 : A2256 galaxies redshifts and 1.4GHz fluxes (Miller+, 2003)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 48 A19 "datime" Obs.date Observation date
50- 54 I5 Kibyte size Size of FITS file
56- 81 A26 --- FileName Name of FITS file, in subdirectory fits
83-103 A21 --- Title Title of the FITS file
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Acknowledgements:
Kamlesh Rajpurohit, kamlesh.rajpurohit(at)unibo.it
(End) Patricia Vannier [CDS] 09-Nov-2022