TITLE:   GCN CIRCULAR
NUMBER:  6591
SUBJECT: GRB 070628 Swift-UVOT Refined Analysis
DATE:    07/06/30 00:43:01 GMT
FROM:    Wayne Landsman at GSFC/SSAI  <landsman@milkyway.gsfc.nasa.gov>

W. Landsman (GSFC/SSAI),  F.E. Marshall  (NASA/GSFC) and  S.T. Holland  
(CRESST/GSFC/USRA) report on behalf of the Swift/UVOT team.

The Swift/UVOT observed the field of GRB 070628 starting 1099 sec after 
the trigger (Holland et al., GCN Circ. 6584).    We strongly detect the 
afterglow in the white and V filters, and have a weak detection in the B 
filter.    The refined afterglow position is

RA(J2000)  =  07h 41m 06.09s
Dec(J2000) = -20d 16' 45.4"

with an uncertainty of 0.7" (radius, 90% containment, including  
systematic uncertainty).  This is within the refined XRT error circle 
(Perri et al. GCN Circ. 6587).
   
Magnitudes and upper limits are reported below.

Filter   Tstart  Tstop    Exp       Mag
          (s)     (s)     (s)

WHITE    1099    1199      98     19.65 ± 0.11
         1202    1302      98     19.62 ± 0.11
         6628    6827     197     20.59 ± 0.15
        11691   11990     295    >21.2 (3 sigma)


V        1309    1708     393     18.88  ± 0.11
         1850    5804     256     19.55  ± 0.25
        13207   13506     295    >19.6 (3 sigma)

B        1786    6622      78     20.7 ± 0.3
         7856    8055     197    >20.4 (3 sigma)
                        
U        6217    6417     197    >20.0 (3 sigma)

UVW1     6014    6213     197    >19.8 (3 sigma)

UVM2     5809    6008     197    >19.6 (3 sigma)

UVW2     6833    7032     197    >19.9 (3 sigma)


The above magnitudes are not corrected for the large and uncertain 
extinction expected at the low Galactic latitude of GRB 070628.  

A power-law fit  to the white filter observations gives a decay index of 
~0.55 +/- 0.3.

[GCN OPS NOTE(30jun07):  Per author's request, the authors line
was added.]