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A perfect power-law spectrum even at highest frequencies: The Toothbrush relic | | K. Rajpurohit
; F. Vazza
; M. Hoeft
; F. Loi
; R. Beck
; V. Vacca
; M. Kierdorf
; R. J. van Weeren
; D. Wittor
; F. Govoni
; M. Murgia
; C. J. Riseley
; N. Locatelli
; A. Drabent
; E. Bonnassieux
; | | Date: |
6 Aug 2020 | | 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 14.25,GHz and 18.6,GHz,
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 $alpha_{
m 120,MHz}^{
m 18.6,GHz}=-1.16pm0.03$.
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 to the shock. From the lack
of spectral steepening, we find that either the Sunyaev-Zeldovich decrement
produced by the pressure jump at the shock along the line of sight is small or
the relic is located far behind in the cluster. For the first time, we detect
linearly polarized emission from the "brush" at 18.6,GHz. Compared to
8.3,GHz, the degree of polarization across the brush increases at 18.6,GHz,
suggesting a strong Faraday depolarization towards lower frequencies. The
observed depolarization is consistent with an intervening magnetized screen
that arise from the dense ICM containing turbulent magnetic fields. The
depolarization, corresponding to a standard deviation of the Rotation Measures
as high as $sigma_{
m RM}= 212pm23
m ,rad,m^{-2}$, suggesting that the
brush is located in or behind the ICM. Our findings indicate that the
Toothbrush can be consistently explained by the standard scenario for relic
formation | | Source: | arXiv, 2008.02694 | | Services: | Forum | Review | PDF | Favorites | |
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