{
  "eventId": "GRB 260310A",
  "format": "text/plain",
  "subject": "GRB 260310A / AT2026fgk: SAO RAS optical observations",
  "submittedHow": "web",
  "submitter": "Alexander Moskvitin at SAO RAS <mosk@sao.ru>",
  "bibcode": "2026GCN.44006....1M",
  "createdOn": 1773503212733,
  "body": "A. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS),\nA. Pozanenko (IKI), N. Pankov (IKI), A. Volnova (IKI),\nreport on behalf of GRB follow-up team and IKI-GRB-FuN.\n\nWe observed the field of the AT2026fgk, potential counterpart \nof the GRB 260310A (Fermi GBM team, GCN 43951; Hamburg and Meegan, \nGCN 43975; Salunke et al., GCN 43958) with the Zeiss-1000 \n1m telescope of the SAO RAS equipped with the CCD photometer.\nWe obtained series of 300 sec images in B, V, Rc, Ic filters \non March 12/13 and 13/14. The observations carried out \nunder a good weather conditions and typical seeing of 1\".5--2\".5.\n\nThe candidate discovered by GOTO (O'Neill et al. 2026, TNS Discovery \nReport 294132) and observed by numerous observatories (Konno et al., \nGCN 43974; Hinds et al., GCN 43977; Lipunov et al., GCN 43978;\nMartin-Carrillo et al., GCN 43979; Moren Méndez et al., GCN 43980;\nde Ugarte Postigo et al., GCN 43984; Hsu et al., GCN 43986; \nPursiainen et al., GCN 43990; Becerra et al., GCN 43991; Li et al., \nGCN 43993; Jayaraman et al., GCN 43994; Stein et al., GCN 43996;\nMartin-Carrillo et al., GCN 44000; Watson et al., GCN 44001; \nLai et al., GCN 44002; Izzo, GCN 44003; Brivio et al., GCN 44004; \nRhodes et al., GCN 44005) is clearly detected in our images \nwith the following brightness.\n\nDate       UT_start  t_mid - T0, filter  exp,   mag   +/- err  \n                     days                s     \n2026.03.12T23:27:00  2.80565     B       5*300  18.77 +/- 0.01\n2026.03.12T23:09:50  2.79577     Rc      6*300  18.00 +/- 0.01\n2026.03.13T23:56:42  3.82450     B       5*300  18.92 +/- 0.01\n2026.03.13T23:45:30  3.81664     Rc      4*300  18.14 +/- 0.01\n\nThis preliminary photometry is based on the nearby stars from \nPanSTARRS catalogue. Magnitudes of standards converted to B, Rc \nwith the Lupton 2005 equations. The magnitudes of the AT2026fgk \nare not corrected for Galactic and host extinction \nand may be contaminated by the host galaxy.\n\nWe can not trace any colour evolution between the two epochs \n(2.8 and 3.8 days after GRB trigger).",
  "circularId": 44006
}