TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3374
SUBJECT: GRB 050502a: Swift XRT Upper Limit
DATE:    05/05/06 20:50:21 GMT
FROM:    Cheryl Pauline Hurkett at Leicester U  <cph9@star.le.ac.uk>

C. Hurkett, K.Page, J. P. Osborne (U Leicester), B. Zhang (UNLV), J.
Kennea, D. N. Burrows (PSU) and N. Gehrels (NASA/GSFC) report on behalf of
the Swift XRT team:

  The Swift XRT observed the INTEGRAL burst GRB 050502a for ~2.5ks from
13:17 UT to 18:42 UT on 02 May 2005; for ~2.5 ks from 15:00 UT to 20:01 UT
on 03 May 2005 and for ~43 ks from 00:28 on 04 May 2005 to 23:10 on 05 May
2005.

  In the first observation (02 May 2005) we detect no source in a 20
arcsec radius circle centred at the position of the optical counterpart
identified by Yost et al 2005 (GCN 3322), with a 90% confidence upper
limit of 1.03e-3 counts/s (0.2 - 10.0 keV).

  Combining data from all three observations, we obtain 35.5 ks of good
data after normal data screening.  We still detect no source in a 20 arcsec
radius circle centred at this position, with a 90% confidence upper limit
of 1.8e-4 counts/s (0.2 - 10.0 keV). Assuming a Crab-like spectrum, this
corresponds to 7e-15 ergs/cm2/s (0.5 - 10.0 keV).

  Compared to other Swift XRT afterglows, GRB 050502a is unusually faint
at these times.