{
  "circularId": 40086,
  "createdOn": 1743938875515,
  "bibcode": "2025GCN.40086....1P",
  "body": " N. Pankov (HSE), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of\nIKI GRB-FuN:\n\nWe observed GRB 250404A / EP250404a (Fermi GBM team, GCN 40050; Hu et al.,\nGCN 40051). The optical counterpart (Jiang et al., GCN 40052; Perez-Garcia\net al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et\nal., GCN 40063; Odeh et al., GCN 40064; He et al., GCN 40069; Pérez-Fournon\net al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN\n40073; Taguchi et al., GCN 40074; Brivio et al., GCN 40075; Ruocco et al.,\nGCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083; Li\net al., GCN 40084; Yin et al., GCN 40085) is early detected on 2025-04-04\nand was observed between (UT) 14:50:52 and 17:09:01. We obtained an upper\nlimit on 2025-04-05. Preliminary photometry of some stacked images is the\nfollowing\n\nDate UT start t-T0 Filter Exp. OT Err. UL(3sigma)\n(mid, days) (s)\n\n2025-04-04 14:50:52 0.04244 R 40*90 16.53 0.02 22.4\n2025-04-04 16:01:21 0.08999 R 28*120 17.96 0.03 22.2\n2025-04-05 15:08:33 1.05611 R 42*90 n/d n/d 21.5\n\nThe photometry is based on nearby USNO-B1.0 stars.\n",
  "eventId": "GRB 250404A",
  "submitter": "Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>",
  "submittedHow": "email",
  "subject": "GRB 250404A / EP250404a: Mondy optical observations"
}