TITLE: GCN CIRCULAR NUMBER: 37370 SUBJECT: GRB 240828A: SAO RAS AS-500(2) optical observations DATE: 24/09/01 21:05:37 GMT FROM: Moskvitin Alexander at SAO RAS mosk@sao.ru

A. S. Moskvitin and V. V. Vlasyuk (SAO RAS), report on behalf of the GRB follow-up team.

We observed the field of GRB 240828A (Fermi GBM team, GCN 37317; Srijan et al., GCN 37328; Gupta and Di Lalla, GCN 37331; Beardmore et al., GCN 37337; Dalessi and Meegan GCN 37341) with the AS-500(2) 0.5-m Ritchey-Chretien telescope of SAO RAS equipped with CCD-photometer and Andor iXon Ultra EM-CCD DU-897 camera with 512x512 pixels E2V chip. We obtained 40 x 90 sec. images in Rc band on August 31 (2024-08-31T18:44:29 -- 2024-08-31T19:59:08), t_mid - T0 = 3.1852 days.

The OT (Zheng and Filippenko, GCNs 37339, 37349; Moskvitin and Spiridonova, GCN 37344) is marginally detected in our stacked frame with the brightness of R = 21.8 +/- 0.3 calibrated against nearby SDSS stars (magnitudes converted with Lupton 2005 equations) and not corrected for the MW extinction.

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