GCN Circular 39645
Subject
GRB 250309B / AT2025dws: SAO RAS optical observations
Event
Date
2025-03-10T02:45:01Z (a year ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
Via
Web form
A. S. Moskvitin, O. I. Spiridonova (SAO RAS), A. S. Pozanenko (IKI),
A. Ghosh, S. Razzaque (CAPP, University of Johannesburg),
Yu. V. Sotnikova (SAO RAS) report on behalf of a larger collaboration.
We partially covered the error circle of the GRB 250309B (Preis
and Greiner, GCN 39629; Fermi GBM team, GCN 39635; McDermott et al.,
GCN 39642) with 1-m telescope of SAO RAS, Zeiss-1000,
equipped with the CCD-photometer.
The fields of ZTF25aaitvjt / AT2025dws (Stein et al.,
GCN 39639), XRT sources #1 and #3 (Evans et al., GCN 39633) were
observed in Rc band on March 9/10 night. The AT2025dws source
does not fit into the error circle of ground-based GBM localization
(Fermi GBM group, GCN 39635), but falls into the BALROG localization
field (Preis et al., GCN 39629).
We obtained two epochs of observations for ZTF25aaitvjt / AT2025dws
field. The 1st: on March 9, 21:58:17 -- March 9, 22:29:28 UT,
t_mid - T0 = 14.5893 h = 0.60789 days (5 x 300 sec. exposure);
the 2nd: on March 9, 23:52:03 -- March 10, 00:47:22 UT,
t_mid - T0 = 16.6865 h = 0.69527 days (10 x 300 sec. exposure).
We clearly detected ZTF25aaitvjt / AT2025dws (Stein et al.,
GCN 39639; Pérez-Fournon et al., GCN 39643; Stein and Ahumada,
GCN 39644) in the stacked images. Preliminary photometry is the following.
Date UT start t-T0 Exptime Filter OT Err UL
(mid, days) (s) (3sigma)
2025-03-09 21:58:17 0.60789 5 x 300 Rc 19.52 +/- 0.04 22.0
2025-03-09 23:52:03 0.69527 10 x 300 Rc 19.66 +/- 0.02 22.6
The above photometry includes the OT and a possible host galaxy.
The photometry is based on nearby stars from the USNO-B1.0 catalog
(R2 magnitudes) and has not been corrected for the Galactic extinction.
USNO-B1.0 reference stars
RA Dec R2
14:03:06.24 -08:27:38.9 15.67
14:03:08.07 -08:26:47.1 17.30