[vsnet-grb-info 4636] GRB070508: Swift/UVOT Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6392
SUBJECT: GRB070508: Swift/UVOT Observations
DATE:    07/05/08 22:24:16 GMT
FROM:    Frank Marshall at GSFC  <marshall at milkyway.gsfc.nasa.gov>

F.E. Marshall (NASA/GSFC) and D. Grupe (PSU) report on behalf of the 
Swift/UVOT team:

UVOT began observing GRB 070508 68s after the BAT trigger 
(Grupe et al., GCN Circ. 6383). A fading afterglow is  
detected in the White and V filters, while no afterglow is seen
in the B, U, or UV  filters. We use the first white exposure 
to obtain an improved position of

RA(J2000) = 20h 51m 11.68s  Dec(J2000) = -78d 23' 05.0"

with a 90% confidence statistical uncertainty in each axis of 0.5".
There is also a 1-sigma systematic uncertainty in the UVOT
aspect solution of about 0.3". This revised position is 0.6" from 
the initial UVOT position reported by Grupe et al. and 2.3" from the 
position for the I-band object reported by Berger and Burgasser 
(GCN Circ. 6386).

Thoene et al. (GCN Circ. 6389) have suggested a redshift of
greater than 3.5 based on their detections in the I and R bands
and lack of detection in V band. The UVOT detection in the V filter 
indicates a redshift of less than 5.

Photometry results with statistical errors are given below
for the 7 UVOT filters. The start and stop times (in seconds)
are referenced to the trigger time, and the total exposure
time (Exp.) is given in seconds.

           T_start  T_stop    Exp.          Mag

White         86      185      98         19.8+/-0.12 (1-sigma)
V            192      571     393         19.7+/-0.22 (1-sigma)
B            669     1946      86        >19.6 (90% confidence)
U            644     1933     117        >18.4 (90% confidence)
UVW1         620     7389     283        >18.2 (90% confidence)
UWM2        1705     7215     236        >17.8 (90% confidence)
UVW2         698     6806     294        >18.6 (90% confidence)

No correction has been made for the expected Galactic reddening of 
E(B-V)=0.14