TITLE: GCN CIRCULAR NUMBER: 39085 SUBJECT: GRB 250129A: Swift/UVOT Detection DATE: 25/01/29 14:51:44 GMT FROM: Mike Siegel at PSU/Swift MOC mhs18@psu.edu
M. H. Siegel (PSU) and A. P. Beardmore (U. Leicester) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250129A 1185 s after the BAT trigger (Beardmore et al., GCN Circ. 39066). A source consistent with the XRT position (Goad et al., GCN Circ. 39082) and the previously reported optical counterpart (Francile et al., GCN Circ. 39065; Belkin et al, GCN Circ. 39072; Ghosh et al., GCN Circ 39077; Schneider et al. GCN Circ. 39078, Brivio et al., GCN Circ. 39079.) is detected in the initial UVOT exposures. The UVOT light curve shows some evidence of fading.
The lack of detection of this bright burst in the NUV filters would be consistent with the redshift of 2.15 reported by Schneider et al. (GCN Circ, 39071) and Izzo et al. (GCN Circ. 39073).
The preliminary UVOT position is: RA (J2000) = 13:14:42.41 = 198.67670 (deg.) Dec (J2000) = +05:01:50.3 = 5.03064 (deg.) with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence).
Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag white (fc) 1185 1335 147 17.43+/-0.04 white 1468 1835 58 17.39+/-0.07 white 5450 5650 196 17.63+/-0.04 v 1343 1885 77 17.24+/-0.17 v 10957 11667 690 17.98+/-0.08 b 1444 1809 58 17.29+/-0.11 b 5245 16960 649 17.63+/-0.04 u 1418 1785 38 16.93+/-0.15 uvw2 5656 5845 186 >19.77
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.037 in the direction of the burst (Schlegel et al. 1998).
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