[vsnet-grb-info 8636] GRB 091109: Swift/UVOT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10143
SUBJECT: GRB 091109: Swift/UVOT observations
DATE:    09/11/09 12:24:27 GMT
FROM:    Samantha Oates at MSSL  <sro at mssl.ucl.ac.uk>

S. R. Oates (MSSL-UCL) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began observerving the field of GRB 091109 156s
after the BAT trigger (Oates et al., GCN Circ. 10138). We detect the
optical afterglow in the white filter only, which faded rapidly.
The refined UVOT position is:

     RA (J2000)  20:37:01.80
    Dec (J2000) -44: 9:29.6

with an estimated uncertainty of 0.7 arcsec (radius, 90% confidence).
This position is consistent with the XRT refined position (Beardmore
et al., GCN Circ 10140).

Preliminary magnitudes and the 3 sigma upper limits are reported below.

Filter    T_start(s)  T_stop(s)  Exposure      Mag  Err
###########################################################
white        156        306         147     19.88 +\- 0.14
white	     5371       5571        197        > 21.26
v	     4345       5981        393        > 19.94
b	     5166       5365        197        > 20.49
u	     314        6572        615        > 20.97
uvw1	     4755       6392        393        > 20.59
uvm2	     4550       6186        393        > 20.46
uvw2	     4140       5777        393        > 20.68
###########################################################

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.03 mag (Schlegel et al.,
1998, ApJS, 500, 525).  The photometry is on the UVOT photometric system
described in Poole et al. (2008, MNRAS, 383,627).