[vsnet-grb-info 2553] GRB 051221A: Detection at 251nm with Swift UVOT

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4390
SUBJECT: GRB 051221A: Detection at 251nm with Swift UVOT
DATE:    05/12/23 19:05:11 GMT
FROM:    Pete Roming at PSU  <roming at astro.psu.edu>

P. Roming (PSU), A. A. Breeveld (UCL-MSSL), F. Marshall, A. Parsons, R. 
Fink (GSFC), & M. Ajello (MPE) on behalf of the Swift/UVOT team:

We have created a summed image from 2.78 ksec of exposure on GRB051221A 
(Parsons et al., GCN 4363) through the "UVW1" filter of the Swift UVOT. 
 From the summed image we detect a source at 4.8-sigma confidence with a 
position coincident with the one reported by Bloom (GCN 4367) and Berger 
(GCN 4369). The magnitude of the source is 20.2+/-0.2 as determined by the 
Swift analysis tool, uvotsource.

Examination of individual frames suggests that the source is not 
distinguishable above background in the individual short (50-s and 100-s) 
exposures and is only visible at the 3-sigma level in one of the early ~600 
second exposures of the sequence.