GCN Circular 6220
Subject
GRB070318: Swift UVOT indicates unusual optical/UV afterglow
Date
2007-03-21T21:08:42Z (17 years ago)
From
Mat Page at MSSL/Swift <mjp@mssl.ucl.ac.uk>
M.J. Page (MSSL-UCL), F.E. Marshall (NASA/GSFC) S. Immler (GSFC/USRA) S.
T. Holland (CRESST/GSFC/USRA) and J.R. Cummings (GSFC/UMBC) report on
behalf of the Swift/UVOT team:
The optical/UV afterglow of GRB 070318 (Cummings et al, GCN 6210)
decayed to magnitude of 21.5 in the UVOT white filter in the first 24
hours after the BAT trigger, and has remained at approximately constant
brightness for at least 48 hours since that time. Examination of the
Supercosmos scan of the UK Schmidt sky survey plate at this location
reveals no evidence for a host galaxy (the plate limit is Bj>22 mag).
For the flattening of the lightcurve to be due to the host galaxy, the
host galaxy would have to be very luminous (Mb ~ -22) and have an
unusually blue spectrum (e.g. peaking in the U band, observer frame). It
therefore seems more likely that this is an afterglow with a very
unusual lightcurve.
Swift continues to monitor the afterglow. Further ground-based
observations are encouraged.