Mass estimation of the very massive galaxy cluster SRGe CL2305.2$-$2248
  from strong lensing
  The galaxy cluster SRGe CL2305.2$-$2248 (SPT-CL J2305$-$2248, ACT-CL
J2305.1$-$2248) is one of the most massive clusters at high redshifts ($z
\simeq 0.76$) and is of great interest for cosmology. For an optical
identification of this cluster, deep images were obtained with the 1.5-m
Russian-Turkish telescope RTT-150. Together with the open archival data of the
Hubble Space Telescope, it became possible to identify candidates for
gravitationally lensed images of distant blue galaxies in the form of arcs and
arclets. The observed giant arc near the brightest cluster galaxies allowed us
to estimate the radius of the Einstein ring, which is $ 9.8 \pm 1.3 $
arcseconds. The photometric redshift of the lensed source was obtained ($ z_s =
2.44 \pm 0.07 $). Its use in combination with the Einstein radius estimate made
it possible to independently estimate the \cl2305 mass. It was done by
extrapolating the strong lensing results to large radii and using the model
density distribution profiles in relaxed clusters. This extrapolation leads to
mass estimates $ \sim 1.5-3 $ times smaller than those obtained from X-ray and
microwave observations. A probable cause for this discrepancy may be the
process of cluster merging, which is also confirmed by SRGe CL2305.2-2248
morphology in the optical range.
