Is A2261 a Fossil Galaxy Cluster in a Transitional Dynamical State?

Abell 2261 (A2661) is a well-studied fossil cluster, but previous studies give contradictory results on its dynamical states, such as X-ray central entropy and magnitude gap. To improve our understanding of state, we conduct multi-object spectroscopic observations with Hectospec the MMT, covering an area out to 5 virial radii from cluster center, get improved completeness membership. Using this new data, calculate multiple indicators including gaussianity, distance offset, velocity offset. These suggest that A2261 moderately relaxed. However, Dressler-Shectman test reveals group candidate south, at projected near radius, overlaps tail-like feature. One galaxies associated would be sufficiently bright reduce This raises possibility could have recently transit in status, if had previously crossed only now found outside. In outskirts, see extended feature located opposite side candidate. On even larger scales, find connects, both sky space, long (~4.4Mpc) filamentary structure Sloan Digital Sky Survey data. support idea was fed into through filament, temporarily breaking resulting minor merger weakly disturbed intracluster medium cluster.