GCN Circular 42005
Subject
GRB 250925A: Mondy and AbAO optical observations
Event
Date
2025-09-26T15:27:34Z (6 days ago)
Edited On
2025-09-29T13:35:15Z (3 days ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO) report on behalf of GRB-IKI-FuN:
We observed the field of GRB 250925A detected by Swift (Dichiara et. al, GCN 41985) at z=3.899 (Castro-Tirado et. al, GCN 41997) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) and the AS-32 0.7m telescope of the Abastumani Observatory (AbAO). The observations started at AbAO on 2025-09-25 at 19:24 UT, i.e. ~0.097 days (~2.3 hr) since trigger. In total we obtained 30x120 s exposures with AZT-33IK, and 85x60 s exposures with AS-32. The optical afterglow initially detected by NOT/ORM (Corcoran et. al, GCN 41990) and also observed by (Saikia et. al, GCN 41986; Pavoni & Moretti et. al, GCN 41989; Bochenek & Perley, GCN 41991; Masi et. al, GCN 41992; Mendez et. al, GCN 41995; Castro-Tirado et. al, GCN 41997; Liu et. al, GCN 41998; Ochi et. al, GCN 41999; Xin et. al., GCN 42002; Rakotondrainibe et. al, GCN 42004) is clearly visible in the stacked images from Mondy. Preliminary photometry is as follows:
Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope
(nxs) (mid, days) (3sigma)
2025-09-25 19:24:44 79x60 0.12486 R n/d n/d 21.0 AbAO/AS-32
2025-09-25 20:00:15 6x120 0.12626 R 21.47 0.19 22.3 Mondy/AZT-33IK
2025-09-25 20:12:15 6x120 0.13460 R 21.26 0.15 22.2 Mondy/AZT-33IK
2025-09-25 20:24:16 6x120 0.14294 R 21.32 0.18 22.3 Mondy/AZT-33IK
2025-09-25 20:36:16 6x120 0.15128 R 21.26 0.14 22.3 Mondy/AZT-33IK
2025-09-25 20:48:16 6x120 0.15962 R 21.79 0.24 22.3 Mondy/AZT-33IK
The photometry was calibrated against nearby USNO-B1.0 stars (R2-mags) and not corrected for the Galactic extinction. Using all available r-data we estimate a temporal slope of alpha = -1.17 +/- 0.05.