A New Shock in the Premerging Cluster Pair 1E2215-2216

Abstract The galaxy cluster pair 1E2216.0-0401 and 1E2215.7-0404 represents a major cluster merger in its early stages, a phase that has been scarcely explored in previous studies. Within this system, both axial and equatorial merger shocks have been identified. Recent XMM-Newton observations of the southern region of the cluster pair have increased the total exposure time to approximately 300 ks, enhancing the sensitivity to detect faint shock features in the cluster outskirts. Through a combined analysis of XMM-Newton and Chandra data, including both imaging and spectral techniques, a new shock front has been identified at approximately 2 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">′</mml:mi> </mml:mrow> </mml:mover> </mml:math> 3 south of the X-ray brightness peak of 1E2215. This shock front exhibits a surface brightness ratio of 1.33 ± 0.07 and a temperature ratio of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1.2</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.14</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.13</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> in XMM-Newton, consistent with Chandra results. The Mach number, independently calculated from both the temperature and surface brightness discontinuities, yields consistent values of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi class="MJX-tex-calligraphic" mathvariant="script">M</mml:mi> <mml:mo>≈</mml:mo> <mml:mn>1.2</mml:mn> </mml:math> . The age, velocity, and spatial distribution of this shock suggest that it shares a common physical origin with the previously identified equatorial shock.