Reconstruction of Radio Relics and X-ray Tails in an Off-axis Cluster
  Merger: Hydrodynamical Simulations of A115
  Although a merging galaxy cluster is a useful laboratory to study many
important astrophysical processes and fundamental physics, only limited
interpretations are possible without careful analysis of the merger scenario.
However, the study is demanding because a thorough comparison of
multi-wavelength observations with detailed numerical simulations is required.
In this paper, we present such a study for the off-axis binary merger A115. The
system possesses a number of remarkable observational features, but no
convincing merger scenario, explaining the shape and location of the radio
relic in harmony with the orientation of the cometary X-ray tails, has been
presented. Our hydrodynamical simulation, with adaptive mesh refinement,
suggests that the cometary X-ray tail of A115 might be a slingshot tail and can
arise $\sim0.3$ Gyrs after the impact and before the two subclusters reach
their apocenters. This scenario can predict the location and orientation of the
giant radio relic, which is parallel to the northern X-ray tail. In addition,
our study indicates that diffusive shock acceleration alone cannot generate the
observed radio power unless aided by stronger magnetic fields and/or more
significant presence of fossil electrons.
