[vsnet-grb-info 10815] Swift/UVOT observations of GRB110801A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12236
SUBJECT: Swift/UVOT observations of GRB110801A
DATE:    11/08/02 12:52:23 GMT
FROM:    Massimiliano de Pasquale at MSSL-UCL  <mdp at mssl.ucl.ac.uk>

M. De Pasquale (MSSL-UCL) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 110801A
109 s after the BAT trigger (De Pasquale et al., GCN Circ. 12228).
A source consistent with the XRT position (Evans et al., GCN Circ. 12232)
is detected in the initial and summed UVOT exposures, except in um2 
filter and a detection in uw2, at 2 sigma confidence level. Since
the redshift of this event is 1.86 (Cabrera Lavers, GCN Circ. 12234),
we think the weak detection in uw2 is due to flux in the reddest part
of this filter.

The refined UVOT position is:
     RA  (J2000) =  05:57:44.87 =  89.43695 (deg.)
     Dec (J2000) = +80:57:21.1  =  80.95592 (deg.)
with an estimated uncertainty of 0.51 arc sec. (radius, 90% confidence).

The afterglow shows a quick rise from the first exposure up to ~300s.

Preliminary detections and 3-sigma upper limits using the UVOT photometric 
system (Poole et al. 2008, MNRAS, 383, 627) for the early exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white (fc)         109        259          147         18.06 ± 0.07
white              109       6337          727         17.23 ± 0.05
v                  598       6747          451         17.07 ± 0.06
b                  523       6132          432         17.47 ± 0.05
u (fc)             267        517          246         15.89 ± 0.05
u                  267       5927          488         15.68 ± 0.04
w1                 647       5722          255         17.92 ± 0.11
m2                 622       6904          404         >20.2
w2                 573       6543          452         20.48 ± 0.41

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.08 in the direction of the burst
(Schlegel et al. 1998).