TITLE:   GCN CIRCULAR
NUMBER:  6229
SUBJECT: GRB 070328: Swift/UVOT Upper Limits
DATE:    07/03/28 20:18:13 GMT
FROM:    Frank Marshall at GSFC  <marshall@milkyway.gsfc.nasa.gov>

F.E. Marshall (NASA/GSFC) and C.B. Markwardt (GSFC/UMD) report 
on behalf of the Swift UVOT team:

      Swift/UVOT began its initial finding chart exposure of the 
field of GRB 070328 (Markwardt et al. 2007, GCN Circ. 6224) 
98 s after the Swift/BAT trigger. No afterglow candidate is seen 
in the refined XRT error region (Evans et al. 2007, GCN Circ. 6227)
in any of the early UVOT exposures. Three-sigma upper limits
for the initial finding chart exposure and for the total exposure
for each of the UVOT filters are provided below. The times
in the table are from the Swift/BAT trigger.

  Filter  t_start(s)  t_stop(s)  Exp(s)  Mag 3-sig UL

   WHITE      98        198       98        19.6
   WHITE      98       6984      567        21.1
     V        79      11988     1721        20.7
     B       682       6823      397        20.8
     U       657       6619      429        20.4
   UVW1      634       6414      432        20.7
   UVM2      609      12770     1197        21.6
   UVW2      711      11076     1101        21.5

These upper limits are not corrected for extinction.
The Galactic reddening in the direction of the burst is 
E_{B-V} = 0.04 mag (Schlegel et al. 1998).