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Abstract

SRGe CL2305.2–2248 (SPT-CL J2305–2248, ACT-CL J2305.1–2248) is one of the most massive galaxy clusters at high redshifts (z≃0.76) and is of great interest for cosmology. Deep images have been obtained at the Russian–Turkish 1.5-m telescope (RTT-150) for an optical identification of this cluster. In combination with the open Hubble Space Telescope archival data, they have made it possible to select 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 allows the Einstein radius to be estimated, 9.8±1.3 arcsec. The photometric redshift of the lensed source has been found (z_s=2.44±0.07). Its use in combination with the Einstein radius estimate has made it possible to independently estimate the mass of SRGe CL2305.2–2248 by extrapolating the strong-lensing results to large radii and using model density profiles in relaxed clusters. This extrapolation leads to mass estimates smaller than those obtained from X-ray and microwave observations by a factor of ∼1.5−3. A probable cause of this discrepancy may be the galaxy merger process, which is also confirmed by the morphology of SRGe CL2305.2–2248 in the optical range.