[vsnet-grb-info 4926] Swift/UVOT Observations of GRB070721A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6648
SUBJECT: Swift/UVOT Observations of GRB070721A
DATE:    07/07/21 18:56:56 GMT
FROM:    Patricia Schady at MSSL/Swift  <ps at mssl.ucl.ac.uk>

P. Schady (MSSL-UCL) and H. Ziaeepour (MSSL-UCL) report on behalf of the 
Swift/UVOT team:

The Swift/UVOT observed the field of GRB 070721A starting 69 s after the 
BAT trigger (Ziaeepour et al. GCN Circ.6639). We do not find any source, 
in any of the UVOT observations inside the refined XRT error circle (Evans 
et al., GCN Circ.6644). However, we note that there is an 18th mag star 4 
arcseconds from the XRT refined position.

The 3-sigma upper limits for detecting a source inside the XRT error 
circle are:

Filter  T_mid(s)  Exp(s)  Mag (3-sig upper limit)
=================================================
White   1088      156     > 21.7
V       1194      453     > 20.9
B       1509      97      > 19.5
U       1359      117     > 20.0
UVW1    1334      117     > 19.6
UVM2    1309	  117     > 19.2
UVW2    1530      97      > 19.4

where T_mid is the weighted mid time of the coadded exposure. The values 
quoted above are not corrected for the expected Galactic extinction 
corresponding to a reddening of E(B-V) = 0.01 mag in the direction of the 
burst (Schlegel et al. 1998).