[vsnet-grb-info 6919] GRB 081109A: Possible Swift-UVOT detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8509
SUBJECT: GRB 081109A: Possible Swift-UVOT detection
DATE:    08/11/10 01:35:23 GMT
FROM:    Stefan Immler at NASA/GSFC  <stefan.m.immler at nasa.gov>

S. Immler (CRESST/UMD/GSFC), N. P. M. Kuin (MSSL/UCL), and S. T. Holland 
(CRESST/USRA/GSFC) report on behalf of the Swift UVOT team:

Further analysis of Swift Ultraviolet/Optical Telescope (UVOT) data of 
GRB 081109A (Immler et al., GCN Circ. 8500), starting 75 sec after the 
BAT trigger, gives a tentative detection of an optical source at the 
reported REM position (D'Avanzo et al., GCN Circ 8501) in the white 
filter at a 3.3-sigma level of confidence. The source is not detected in 
any of the other UVOT filters at the limiting magnitudes reported below.

Filter Tstart(s) Tstop(s)  Exp(s)  Magnitude

wh      75       6592     745      21.6+/-0.3
u      287       6181     501      >21.5  (3-sigma UL)
b      543       6387     452      >20.9  (3-sigma UL)
uvw2   593       5362     274      >21.6  (3-sigma UL)
v      617       5566     274      >20.9  (3-sigma UL)
uvm2   641       5771     274      >21.5  (3-sigma UL)
uvw1   666       5976     255      >21.5  (3-sigma UL)

The possible detection in the white filter, combined with the lack of a 
detection in the v filter, is consistent with the source having a 
redshift greater than 5.5.

Follow-up observations, especially in the infrared, are encouraged.