TITLE:   GCN CIRCULAR
NUMBER:  8523
SUBJECT: GRB 081109A: confirmation of possible detection host galaxy
DATE:    08/11/17 00:02:24 GMT
FROM:    Paul Kuin at MSSL  <npkuin@googlemail.com>

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

Continued observations by the Swift UltraViolet/Optical Telescope
(UVOT) of the field of GRB 081109A  (Immler et al., GCN Circ. 8500,
Kuin and Immler, GCN Circ. 8504, Immler et al., GCN Circ. 8509)
confirm that a weak source is present close to the REM position
(D'Avanzo et al, GCN Circ. 8501) and also close to the refined
XRT position (Beardmore et al., GCN Circ. 8506).

We detect a constant source in 166 images totaling 54.4 ks of exposure time
over a period of 544 ks (~1 week) in the UVOT white filter at position:

RA = 22:03:09.579, Dec = -54.42.40.49 (J2000)

with an uncertainty of 0.8 arcsec (90% confidence). The source
magnitude in the summed image is wh = 22.86 +/- 0.09 mag (11.5 sigma detection).

The values quoted above are on the UVOT Photometric System
(Poole et al, 2008, MNRAS 383,627). They are not corrected for the
expected galactic reddening of E(B-V) = 0.019 in the direction of
the burst (Schlegel et al. 1998).

We interpret this image as the possible host galaxy. In that case the
REM position offset suggests that the GRB took place on the edge of the
host galaxy. The source we detect is also just outside the XRT error
circle.