Discovery of a shock front in the merging cluster of galaxies A2163

• Main Authors: Mhlahlo, Nceba, Guennou, Loic, Feretti, Luigina
• Format: Journal Article
• Language: English
• Published: 28-01-2021
• Subjects: Physics - High Energy Astrophysical Phenomena
• DOI: 10.48550/arxiv.2101.12163

=4th Annual Conference on High Energy Astrophysics in Southern
Africa (HEASA2016), `Shock Acceleration in the galaxy cluster ACO2163', 2017,
Publication of Science (PoS) ACO2163 is one of the hottest (mean $kT=12-15.5$ keV) and extremely X-ray
overluminous merging galaxy clusters which is located at $z=0.203$. The cluster
hosts one of the largest giant radio halos which are observed in most of the
merging clusters, and a candidate radio relic. Recently, three merger shock
fronts were detected in this cluster, explaining its extreme temperature and
complex structure. Furthermore, previous XMM-Newton and Chandra observations
hinted at the presence of a shock front that is associated with the gas
`bullet' crossing the main cluster in the west-ward direction, and which heated
the intra-cluster medium, leading to adiabatic compression of the gas behind
the 'bullet'. The goal of this paper is to report on the detection of this
shock front as revealed by the temperature discontinuity in the X-ray
XMM-Newton image, and the edge in the Very Large Array (VLA) radio image. We
also report on the detection of a relic source in the north-eastern region of
the radio halo in the KAT-7 data, confirming the presence of an extended relic
in this cluster. The brightness edge in the X-rays corresponds to a shock front
with a Mach number $M= 2.2\pm0.3$, at a distance of 0.2 Mpc from the cluster
centre. An estimate from the luminosity jump gives $M=1.9\pm0.4$. We consider a
simple explanation for the electrons at the shock front, and for the observed
discrepancy between the average spectral index of the radio halo emission and
that predicted by the $M=2.2$ shock which precedes the 'bullet'.