[vsnet-grb-info 4959] GRB070721A: Swift/UVOT Detection of a Weak Afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6676
SUBJECT: GRB070721A: Swift/UVOT Detection of a Weak Afterglow
DATE:    07/07/27 21:14:26 GMT
FROM:    Frank Marshall at GSFC  <marshall at milkyway.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC), P. Schady (MSSL-UCL) and H. Ziaeepour (MSSL-UCL)
report on behalf of the Swift/UVOT team:

A comparison of the initial Swift/UVOT observations with those taken several days
after the BAT trigger (Ziaeepour et al. GCN Circ. 6639) reveals a weak, fading source
inside the refined XRT error circle (Evans et al. GCN Circ. 6644).
The source is only detected in the initial 100-s exposure with the white
filter starting 88 sec. after the trigger and the initial 400-s exposure with the V
filter starting 194 sec. after the trigger. The 2.4-sigma detection in
white corresponds to 21.4 mag., and the 3.4-sigma detection in V corresponds
to 20.2 mag. The best-fit position is RA, Dec = 3.16343,-28.55020, which is
equivalent to:

RA  (J2000):  00 12 39.22
Dec (J2000): -28 33 00.7

with an uncertainty of 2.0" (radius, 90% confidence).

The source is slightly blended with 18th mag star noted by
Schady and Ziaeepour (GCN Circ. 6648), which is 4.7" away.