TITLE: GCN CIRCULAR NUMBER: 38775 SUBJECT: GRB 250101A: Swift/UVOT Detection DATE: 25/01/02 07:11:25 GMT FROM: Mike Siegel at PSU/Swift MOC mhs18@psu.edu
M. H. Siegel (PSU) and K. L. Page (U. Leicester) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250101A 133s after the BAT trigger (Page et al., GCN Circ. 38752). A fading source consistent with the XRT position (Goad et al., GCN Circ. 37761) and the previously reported optical source, since confirmed by multiple observations (Li et al., GCN Circ. 38753; Mohan et al., GCN Circ. 38754; Zhu et al., GCN Circ., 38755; Wu et al., GCN Circ 38578; Moskvitin & Spiridonova, GCN Circ. 38762; Odeh et al., GCN Circ 38763; Hu et al., GCN Circ. 38764; D'Avino & L. Izzo, GCN Circ. 38768; Escudero-Coca, GCN Circ. 38769; Leonini et al., GCN Circ. 38771) is detected in the initial UVOT exposures.
The preliminary UVOT position is: RA (J2000) = 02:28:16.47 = 37.06864 (deg.) Dec (J2000) = +19:11:39.6 = 19.19433 (deg.) with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence).
Preliminary detections and 3-sigma upper limits 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 133 283 147 18.03 +/- 0.05 v 620 813 39 18.10 +/- 0.28 b 546 738 39 18.66 +/- 0.21 u 291 540 246 17.93 +/- 0.08 w1 670 5019 235 >19.8 m2 4614 4814 197 >19.1 w2 596 4404 216 >18.9
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.164 in the direction of the burst (Schlegel et al. 1998).
We note that the lack of detection in the NUV bands for this bright burst would be consistent with the redshift of z=2.49 reported by Zhu et al. (GCN Circ. 38759).
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