TITLE:   GCN CIRCULAR
NUMBER:  9351
SUBJECT: GRB 090510: Swift/UVOT host galaxy candidates
DATE:    09/05/11 23:50:50 GMT
FROM:    Paul Kuin at MSSL  <npkuin@googlemail.com>

N. P. M. Kuin (MSSL/UCL), S. Oates (MSSL/UCL), M. De Pasquale (MSL/UCL),
E.A. Hoversten (PSU), and F. Marshall (GSFC) report on behalf of the
Swift UVOT team.

The Swift UltraViolet/Optical Telescope (UVOT) continued observations of
the short hard burst GRB 090510 (Swift BAT trigger number 351588;
Hoversten et al. GCN Circ. 9331) today. The summed image in the white
filter taken between 92.7ks and 127.6 ks shows that the source has faded
from the initial magnitude of wh = 18.76 mag at T+800 and is now possibly
detected at 3.3 sigma at a magnitude of 22.9+/-0.3.  Observations between
T+2000s and T+100ks show a decay index of about 1.  There are also two
nearby sources at the 6 sigma level detectable, which we consider to be
possible hosts of GRB 090510.

The first, nearest, candidate is at  position RA, DEC = 333.55220, -26.584525
(22h 14m 12.53s, -26d 35m 04.29s (J2000)), with a diameter of 2.3", and the
second, more extended, candidate is found at position  RA, DEC =
333.54963, -26.582294 (22h 14m 11.91s, -26d 34m 56.26s (J2000)), is more
elongated with a diameter of about 3.1". The estimated positional accuracy
is 0.7" for both sources. Both sources have a wh magnitude of 21.61 +/- 0.17.

We encourage follow-up observations.

We would like to make a correction:  The UVOT positional error on GRB 090510
quoted in GCN 9342 was too large. The correct uncertainty in the GRB position
was 0.61" (90% confidence radius).