GCN Circular 3408
Subject
GRB050416: Afterglow detection at 188 nm with Swift UVOT
Event
Date
2005-05-10T20:46:59Z (21 years ago)
From
Derek Fox at CIT <derekfox@astro.caltech.edu>
Derek B. Fox (Caltech) reports on behalf of a larger collaboration:
"We have created a summed image from the first 10.14 ksec of exposure
on GRB050416 (BAT trigger #114753; Sakamoto et al., GCN 3264) through
the "UVW2" filter of the Swift UVOT. Earlier reports have discussed
the detection of the optical afterglow of this event (Cenko & Fox, GCN
3265) in the U, B, and V filters (Schady et al., GCN 3280). The UVW2
sequence consists of nine ~10-second exposures taken from 4 to 15
minutes after the burst; two ~100-second exposures taken 18 and 29
minutes after the burst, and 11 ~900-second exposures taken from 92
minutes to 2 days after the burst. The final summed frame was
astrometrically registered to the USNO B-1.0 catalog.
At the position of the optical afterglow we detect a source at
>3-sigma confidence with a mean count rate of 6.0 +/- 0.7 cts/ksec
according to the default uvotdetect analysis. Examination of
individual frames suggests that the source is not distinguishable
above background in the individual short (10-s and 100-s) exposures,
being most prominent in the early ~900 second exposures of the
sequence.
The UVW2 filter bandpass is centered at 188 nm with a width of 76 nm.
Since it is unlikely that significant afterglow emission would be
detected blueward of the host galaxy Lyman limit at 91 nm -- with
significant suppression redward to the Lyman-alpha resonance at 122 nm
-- we suggest that this detection implies a redshift constraint for
GRB050416 of z <~ 1.0."