Chandra Observations of the Spectacular A3411–12 Merger Event

Abstract

We present deep Chandra observations of A3411-12, a remarkable merging cluster that hosts the most compelling evidence for electron re-acceleration at cluster shocks to date. Using the Y X − M scaling relation, we find r 500 ∼ 1.3 Mpc, M 500 = (7.1 ± 0.7) × 10 14 M , kT = 6.5 ± 0.1 keV, and a gas mass of M g,500 = (9.7 ± 0.1) × 10 13 M . The gas mass fraction within r 500 is f g = 0.14 ± 0.01. We compute the shock strength using density jumps to conclude that the Mach number of the merging subcluster is small (M ≤ 1.15 +0.14 −0.09 ). We also present pseudo-density, projected temperature, pseudopressure, and pseudo-entropy maps. Based on the pseudo-entropy map we conclude that the cluster is undergoing a mild merger, consistent with the small Mach number. On the other hand, radio relics extend over Mpc scale in the A3411-12 system, which strongly suggests that a population of energetic electrons already existed over extended regions of the cluster.

X-ray study of the merging galaxy cluster Abell 3411-3412 with XMM-Newton and Suzaku

“…4. Both Suzaku and XMM-Newton results confirm the southeastern edge is a M ∼ 1.2 shock front, which agrees with the previous result from Chandra surface brightness fit (van Weeren et al 2017;Andrade-Santos et al 2019). Such a low Mach number supports the particle re-acceleration scenario at the shock front.…”

“…Fitting with fixed r edge and C, we obtain C-stat/d.o.f = 76.4/44. If we free the C parameter, the fitted C XMM−Newton = 1.09 ± 0.08, which means the data are consistent with the lack of a density jump, but are consistent with the result of Andrade-Santos et al (2019). The reason that we do not detect an edge in the XMM-Newton profile could be the missing pixels around the edge.…”

“…Later, Golovich et al (2019b) increased the optical sample from 174 to 242 galaxies and confirmed the redshift. From the same dataset, recently, Andrade-Santos et al (2019) use the Y X − M scaling relation to find r 500 ∼ 1.3 Mpc, kT = 6.5 ± 0.1 keV, and M 500 = (7.1 ± 0.7) × 10 14 M , which is much lower than the result from the previous dynamic analysis. Based on the Chandra X-ray flux map, the core of one sub-cluster is moving towards the northeast and shows bullet-like morphology while another sub-cluster core has been entirely stripped during the previous passage.…”

“…3. The southern edge was claimed as a cold front previously (Andrade-Santos et al 2019). With our XMM-Newton analysis, the temperature jump prefers a shock front scenario.…”

“…Golovich et al (2019b) suggest this shock could be produced by an optically poor group. Besides the southwest shock, Andrade-Santos et al (2019) report a south surface brightness discontinuity as a cold front from the core debris of the sub-cluster Abell 3412; a potential surface brightness discontinuity in front of the southeast shock; and a bow shock in front of the "bullet" with M SB = 1.15 +0.14 −0.09 . In this paper, we analyse archival XMM-Newton and Suzaku data in order to constrain the thermodynamical property of the reported shock and to characterise the other X-ray surface brightness discontinuities.…”