[vsnet-grb-info 6697] GRB 080928: Swift/UVOT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8298
SUBJECT: GRB 080928: Swift/UVOT observations
DATE:    08/09/29 12:54:16 GMT
FROM:    Paul Kuin at MSSL  <npkuin at googlemail.com>

N. P. M. Kuin (MSSL/UCL), T. Sakamoto (NASA/UMBC),and Stephen
Holland (GSFC) report on behalf of the Swift UVOT team

The Swift UltraViolet/Optical Telescope (UVOT) began observations of
GRB080928 (Swift BAT trigger number 326115, Sakamoto et al., GCN Circ.
8292), on September 28, 2008, at 15:04:15 UT, 161 seconds after the
trigger with a setling exposure in the UVOT v filter.

We detect a new source at position :

RA=06:20:16.836 Dec=-55:11:58.95  (95.07015, -55.199708 deg (J2000)),

with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence).

The initial magnitude observed for GRB080928  is given below for the
first observation in the UVOT v filters:

Filter Tstart(s) Tstop(s)  Exp(s)  Magnitude

wh(fc)  179      279       99.8    19.09 +/- 0.14  7.3-sigma
v (fc)  285      479      193.7    19.07 +/- 0.43  2.5-sigma
uvm2   4227     4427      196.6   >19.47 3-sigma upper limit (weak signal)
uvw1   4432     4632      196.6    18.64 +/- 0.19  5.6-sigma
u      4638     4838      199.8    17.96 +/- 0.09 12.1-sigma
b      4843     5043      199.8    18.40 +/- 0.09 11.9-sigma
uvw2   5255     5455      196.6   >19.89 3-sigma upper limit
v      5460     5660      199.8    18.03 +/- 0.15 7.3-sigma

The upper limits in the UV filters uvw2 and uvm2 indicate an
upper limit to the redshift of z < 1.8. An initial rise is seen
up to about 200s in the white filter event data.

The values quoted above are on the UVOT Photometric System
(Poole et al, 2008, MNRAS 383,627). They are not corrected for the
expected galactic reddening of E(B-V) = 0.067 in the direction of
the burst (Schlegel et al. 1998).