[vsnet-grb-info 4486] GRB070406: Swift UVOT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6258
SUBJECT: GRB070406: Swift UVOT observations
DATE:    07/04/08 00:33:09 GMT
FROM:    Wayne Landsman at GSFC/SSAI  <landsman at milkyway.gsfc.nasa.gov>

W. Landsman (NASA/GSFC), M. Chester (PSU) and S. McBreen (MPE) report on 
behalf of the Swift UVOT team:

Swift/UVOT observed the field of GRB 070406 starting 20.6 hours after 
the trigger.   Swift did not autonomously slew because the burst was 
below the trigger threshold.

Comparison with pre-burst DSS and SDSS images show no new source within 
the BAT error circle with the following 3 sigma upper limits in the 
co-added frames in all filters:

Filter   T_start  T_Stop   Exp(s)  Mag 3-sig UL
          (s)      (s)
V        84712   132829    1407     21.6
B        74251   139272    3360     23.0
U       102871   138592    2539     22.4
UVW1     98648   137680    3666     24.3
UVM2     90394   133486    2845     23.5
UVW2     80549   131916    2626     23.9
White    75162   115280    1318     22.6

The blue galaxy found in pre-burst SDSS images (Kann, GCN 6256)  within 
the tentative XRT error circle (Troja et al., GCN 6255) is found from 
the UVOT observations to be unusually  bright in the UV filters.

      Mag      Err
V      20.05    0.15
B      20.06    0.05
U      19.11    0.04
UVW1   18.83    0.04
UVM2   18.52    0.05
UVW2   18.67    0.04

However, there is no compelling evidence of variability of this source 
within the individual UVOT frames.