{
  "bibcode": "2025GCN.40451....1P",
  "body": "N. Pankov (HSE, IKI), A. Novichonok (Petrozavodsk State University, KIAM), I. Nikolenko (INASAN), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:\n\nWe performed optical observations of the field of EP250511a (Lian et. al, GCN 40429; Li et. al, GCN 40434) using the 1-meter Zeiss-1000 telescope of the Simeiz (Koshka) Observatory. The R-band observations began on 2025-05-11 19:37:13 UT, i.e. ~0.51 days since trigger at a low altitude (~40 deg) and in the presence of the full Moon. The optical counterpart (Schneider et. al, GCN 40431; Li et. al, GCN 40433; Sanchez-Sierras et. al, GCN 40449) is not detected in the stacked image of an exposure of 86*60 sec. The preliminary upper limit is given below:\n\nDate       UT start  t-T0         Exp.    Filter   OT   Err.     UL\n                     (mid, days)  (n*s)                       (3sigma)\n2025-05-11 19:37:13  0.51405      86*60     R      n/d  n/d     18.9\n\nThe photometry was calibrated using nearby stars from USNO-B1.0 and has not been corrected for the Galactic extinction. Our result is consistent with non-detections reported by (Lipunov et. al, GCN 40432; Brivio et. al, GCN 40435; Zhong et. al, GCN 40442; Busmann et. al, GCN 40445).\n\nRef. stars\nUSNO-B1.0\nRA Dec R2\n202.1106 -2.6632 15.94\n202.0790 -2.7119 15.27\n202.0868 -2.7163 15.00",
  "submitter": "Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>",
  "subject": "EP250511a: Koshka Zeiss-1000 Optical Upper Limit",
  "createdOn": 1747132024976,
  "submittedHow": "web",
  "format": "text/plain",
  "eventId": "EP250511a",
  "circularId": 40451
}