TITLE:   GCN CIRCULAR
NUMBER:  40653
SUBJECT: GRB 250527C: CrAO Optical Upper Limit
DATE:    25/06/09 10:19:33 GMT
FROM:    Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>

N. Pankov (HSE, IKI), S. Nazarov (CrAO), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:

We observed the field of GRB 250527C detected by Fermi/GBM (Trigger 770047117) and further localized by Swift/BAT-GUANO (Delaunay et. al, GCN 40563). The field has also been observed by Swift/XRT (Evans, GCN 40564), and Swift/UVOT (Klingler, GCN 40574). Our observations were carried out using the Sintez-Newton 0.36-meter telescope installed at the Crimean Astrophysical Observatory (CrAO). The series of images has taken in the R-filter. We do not detect candidate transients in comparison with USNO-B1.0, and PS1 catalogs in the stacked image of 22*120 sec. Particularly, we were searching for candidates inside localization circles of X-Ray sources provided in (Evans, GCN 40564). The preliminary upper limit is given below:

Date       UTstart   T-T0   Exposure Filter OT  Err     UL
                              (n*T)                  (3-sigma)
2025-05-28 23:46:57 1.42390  22*120     R   n/d n/d    19.1

The photometry was calibrated using nearby USNO-B1.0 stars (R2 magnitudes) and has not been corrected for the Galactic extinction.