TITLE: GCN CIRCULAR NUMBER: 40843 SUBJECT: GRB 250625A: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart DATE: 25/06/26 17:11:34 GMT FROM: Nello Ruocco at Osservatorio Nastro Verde - Sorrento (Naples) - Italy - MPC Code C82 osservatorionastroverde@gmail.com

Nello Ruocco at Osservatorio Nastro Verde - Sorrento (Naples) - Italy in a large collaboration with: M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, Department of Physics and Astronomy) report:

Following the Swift trigger no. 1327910 (GCN 40825 M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), J. J. DeLaunay (PSU),R. Gupta (NASA GSFC), J. A. Kennea (PSU), D. M. Palmer (LANL),B. Sbarufatti (INAF-OAB) and M. H. Siegel (PSU) report on behalf ofthe Neil Gehrels Swift Observatory Team) from the Swift Burst Alert Telescope (BAT), we pointed at the coordinates RA(J2000)=17h 26m 02.09s: Dec(J2000)= +22d 16' 03.5" and started our observations with telescope of Nastro Verde Observatory - Sorrento (Naples), Italy. Member of: AAVSO - American Association of Variable Star Observers. GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani.

The observations started at 19:30 UT of 2025/06/25, after about 3.30 hours after the GRB trigger, with clear sky, with principal telescope SC 0.35 f/10 with focal reduced + CCD Sbig ST10 XME I took 13 unfiltered images of 120 sec . Start End 19:30:01 UT 19:56:45 UT

All images, calibrated with masterdark and masterflat have been measured with Thycho Tracker software We have detected a faint source at the enhanced position reported by Swift Burst Alert Telescope (BAT) at following position

RA (J2000.0) 17 26 02.13 Dec (J2000.0) +22 16 07.7

with the following photometry and astrometry:

GRB 250625A 17 26 02.13 +22 16 07.7 20.2 V C82

Magnitudes were estimated with the ATLAS cat. and are not corrected for galactic dust extinction.

The message may be cited.

View this GCN Circular online at https://gcn.nasa.gov/circulars/40843. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...