J/A+A/642/L13 The Toothbrush relic 14.25GHz image (Rajpurohit+, 2020)
A perfect power-law spectrum even at highest frequencies: The Toothbrush relic.
Rajpurohit K., Vazza F., Hoeft M., Loi F., Beck R., Vacca V., Kierdorf M.,
van Weeren R.J., Wittor D., Govoni F., Murgia M., Riseley C.J.,
Locatelli N., Drabent A., Bonnassieux E.
<Astron. Astrophys. 642, L13 (2020)>
=2020A&A...642L..13R 2020A&A...642L..13R (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Radio sources
Keywords: globular clusters: individual: 1RXS J0603.3+4213 -
galaxies: clusters: intracluster medium - acceleration of particles -
radiation mechanisms: non-thermal - galaxies: magnetic fields
Abstract:
Radio relics trace shock fronts generated in the intracluster medium
(ICM) during cluster mergers. The particle acceleration mechanism at
the shock fronts is not yet completely understood. We observed the
Toothbrush relic with the Effelsberg and Sardinia Radio Telescope at
14.25GHz and 18.6GHz, respectively. Unlike previously claimed, the
integrated spectrum of the relic closely follows a power law over
almost three orders of magnitude in frequency, with a spectral index
of α58MHz18.6GHz=-1.16±0.03. Our finding is consistent
with a power-law injection spectrum, as predicted by diffusive shock
acceleration theory. The result suggests that there is only little
magnetic field strength evolution downstream of the shock. From the
lack of spectral steepening, we find that either the
Sunyaev-Zeldovich decrement produced by the pressure jump is less
extended than ∼600kpc along the line of sight or, conversely, that the
relic is located far behind in the cluster. For the first time, we
detect linearly polarized emission from the "brush" at 18.6GHz.
Compared to 8.3GHz, the degree of polarization across the brush
increases at 18.6GHz, suggesting a strong Faraday depolarization
toward lower frequencies. The observed depolarization is consistent
with an intervening magnetized screen that arises from the dense ICM
containing turbulent magnetic fields. The depolarization,
corresponding to a standard deviation of the rotation measures as high
as σRM=212±23rad/m2, suggests that the brush is located in
or behind the ICM. Our findings indicate that the Toothbrush relic can
be consistently explained by the standard scenario for relic
formation.
Description:
The radio observations at 14.25GHz were performed with the Effelsberg
100m telescope with the new Ku-band receiver in dual polarization
mode. The total on-source observation time was 20h with a 2500MHz
bandwidth. We obtained 31 coverages of a field of 11x7arcmin2.
Objects:
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RA (2000) DE Designation(s)
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06 03.3 +42 14 Toothbrush relic = RX J0603.3+4214
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 98 1 Information on fits image
fits/* . 1 Fits image
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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- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 30 I3 Kibyte size Size of FITS file
32- 55 A24 --- FileName Name of FITS file, in subdirectory fits
57- 98 A42 --- Title Title of the FITS file
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Acknowledgements:
Kamlesh Rajpurohit, kamlesh.rajpurohit(at)unibo.it
(End) Patricia Vannier [CDS] 28-Sep-2020