TITLE: GCN CIRCULAR NUMBER: 40823 SUBJECT: GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24 DATE: 25/06/25 15:10:36 GMT FROM: Alexander Moskvitin at SAO RAS mosk@sao.ru
A. Moskvitin, O. Spiridonova (SAO RAS), N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of GRB follow-up and IKI-GRB-FuN collaborations.
We observed the field of the GRB 250617B (Page et al., GCN 40760; Fermi GBM team, GCN 40763; Bala and Meegan, GCN 40766; Osborne et al., GCN 40767; Williams et al., GCN 40773; Laha et al., GCN 40812) at the redshift of z = 1.396 (Corcoran et al., GCN 40776) with the 1.5-meter AZT-33IK telescope of Mondy observatory on 2025-06-23 and with the 1-m telescope Zeiss-1000 of the SAO RAS on 2025-06-24.
The OT (Page et al., GCN 40760; Moskvitin et al., GCN 40761; Jelinek et al., GCN 40762; Grossan et al., GCN 40771; Ma et al., GCN 40772; Antier et al., GCN 40775; Corcoran et al., GCN 40776; Turpin et al., GCN 40777; Siegel and Page, GCN 40778; Pankov et al., GCN 40783; Gendreau-Distler et al., GCN 40789; Calapai, GCN 40804; also detected in NIR by Schneider et al., GCN 40774) is marginally detected in AZT-33IK stacked image and clearly detected in Zeiss-1000 stacked image. Preliminary results are as following.
Date UT start t-T0 Exp. Filter OT Err. UL telescope (mid, days) (s) (3 sigma) 2025-06-23 16:37:49 5.84791 45*120 R 22.9 0.4 22.7 AZT-33IK 2025-06-24 22:44:03 7.09417 12*300 Rc 23.4 0.2 23.9 Zeiss-1000
This photometry is based on the USNO-B1.0 stars given in Moskvitin et. al, (GCN 40761) and has not corrected for the Galactic extinction.
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