[vsnet-grb-info 5375] Swift/UVOT initial analysis of GRB071109

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7054
SUBJECT: Swift/UVOT initial analysis of GRB071109
DATE:    07/11/11 01:41:58 GMT
FROM:    Paul Kuin at MSSL  <npkuin at googlemail.com>

N.P.M. Kuin (MSSL/UCL) and M. Perri (ASDC) report on behalf of the
Swift-UVOT team:

The Swift/UVOT observed the INTEGRAL burst GRB 071109 (Mereghetti
et al. GCN Circ. 7046) starting at 22:21 UT, 105 minutes after the
trigger, cycling through exposures in the the uvw1, u, b, uvw2, v
and uvm2 filters. No afterglow is detected at the position of the VLA
measurement (Chandra et al. GCN Circ. 7049). A possible source at
position RA=19:19:42.303,DEC=+02:01:21.14(J2000) was investigated,
since it was detected at the 3-sigma level (u=20.9+/-0.6 mag) in
the coadded U-filter images. This source is considered spurious
since it was not found in any of the other filters, taken before
or after the U-filter exposures.

No other fading source is found within the INTEGRAL error circle
in this is a crowded field.

The following 3-sigma upper limits were determined at the position
of the VLA detection (RA=19:19:51.67,DEC=+02:01:49.88):

Filter  Tstart(s)  Tstop(s)  Exp(s)  Mag (3-sigma Upper Limits)

uvw1    6350       24158     1678     > 21.47
 u      6782       24373      835     > 21.17
 b      7000       24588      835     > 21.56
uvw2    7220       25435     3346     > 22.25
 v      8078       25651      835     > 20.58
uvm2    8300       26033     2189     > 21.73

The values quoted above are not corrected for the expected Galactic
extinction corresponding to a reddening of E_{B-V} = 0.61 mag in the
direction of the burst (Schlegel et al. 1998).