TITLE:   GCN CIRCULAR
NUMBER:  6442
SUBJECT: GRB 070520B: Swift/UVOT Upper Limits
DATE:    07/05/21 20:04:41 GMT
FROM:    Frank Marshall at GSFC  <marshall@milkyway.gsfc.nasa.gov>

F.E. Marshall (NASA/GSFC) and A. Moretti (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT observed the field of GRB 070520B starting 107 s after
the BAT trigger (Moretti et al., GCN Circ. 6425).  We do not find any source
in any of the UVOT observations inside the refined XRT error circle
(Moretti et al., GCN Circ. 6438). The 3-sigma upper limits for detecting 
a source inside the XRT error circle in the first finding chart (FC)
exposure and co-added frames are:

Filter            T_start(s)   T_stop(s)     Exp(s)     Mag (3-sigma UL)

White (FC)        107          207           98         >20.3
White             107          6197          491        >21.0
V                 213          11338         1356       >20.1
B                 4360         5992          393        >20.3
U                 4155         5788          393        >20.0
UVW1              3950         5583          393        >19.9
UWM2              3745         12043         1094       >20.5
UVW2              4769         10411         1152       >20.9

The values quoted above are not corrected for the expected Galactic
extinction corresponding to a reddening of E(B-V) = 0.04 mag towards
the direction of the burst (Schlegel et al. 1998).

[GCN OPS NOTE(03jun07): Per author's request, the typo in the Subject-line
was changed from "075020B" to "070520B".]