X-ray study of the double radio relic Abell 3376 with Suzaku

TL;DR

This study uses Suzaku X-ray observations to analyze the shock structures and dynamics of the merging galaxy cluster Abell 3376, revealing details about its shock Mach numbers, age, and merger orientation.

Contribution

First detailed X-ray spectral analysis of Abell 3376's double relics, confirming shock Mach numbers and estimating the merger's dynamical age and geometry.

Findings

Detected a strong western shock with Mach number 2.8

Identified a weaker eastern shock with Mach number 1.5

Estimated the shock age to be approximately 0.6 Gyr

Abstract

We present an X-ray spectral analysis of the nearby double radio relic merging cluster Abell 3376 ($z$ = 0.046), observed with the $Suzaku$ XIS instrument. These deep ($\sim$360 ks) observations cover the entire double relic region in the outskirts of the cluster. These diffuse radio structures are amongst the largest and arc-shaped relics observed in combination with large-scale X-ray shocks in a merging cluster. We confirm the presence of a stronger shock (${\cal M}_{\rm{W}}$ = 2.8 $\pm~0.4$) in the western direction at $r\sim26$', derived from a temperature and surface brightness discontinuity across the radio relic. In the East, we detect a weaker shock (${\cal M}_{\rm{E}}$ = 1.5 $\pm~0.1$) at $r\sim8$', possibly associated to the 'notch' of eastern relic, and a cold front at $r\sim3$'. Based on the shock speed calculated from the Mach numbers, we estimate that the dynamical age of the shock front is $\sim$0.6 Gyr after core passage, indicating that Abell 3376 is still an evolving merging cluster and that the merger is taking place close to the plane of the sky. These results are consistent with simulations and optical and weak lensing studies from the literature.