[vsnet-grb-info 8306] GRB 090817: Swift/UVOT Observations of a Host Galaxy Candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9831
SUBJECT: GRB 090817: Swift/UVOT Observations of a Host Galaxy Candidate
DATE:    09/08/20 19:17:42 GMT
FROM:    Stephen Holland at USRA/NASA/GSFC/SSC  <Stephen.T.Holland at nasa.gov>

S. T. Holland (CRESST/GSFC/USRA), A. Breeveld (MSSL/UCL), and
W. Baumgartner (GSFC/UMBC) report on behalf of the Swift UVOT team:

      The Swift/UVOT observed the field of GRB 090817 (Beckman et al.,
2009, GCN Circ. 9815) between 11 ks and 284 ks after the INTEGRAL
trigger.  The USNO-B1.0 source 1341-0096763 (Evans et al. 2009, GCN
Circ. 9819, Rumyantsev et al. 2009, GCN Circ. 9828) is detected inside
the XRT error circle (Evans et al., 2009, GCN Circ. 9819). We find no
evidence for variability in this source during our observations.  
Preliminary
magnitudes and 3-sigma upper limits from all of the coadded data are

Filter    Exposure      Mag  Err Sigma
--------------------------------------
v              416    19.86 0.46   2.4
b              787    20.99 0.33   3.4
u             4003    21.49 0.30   3.7
uvw1          4326   >22.0   ...   ...
white          413    21.19 0.37   3.2

The quoted magnitudes and upper limits have not been corrected for the
expected Galactic extinction along the line of sight corresponding to
a reddening of E_{B-V} = 0.66 mag (Schlegel et al., 1998, ApJS, 500,
525). All photometry is on the UVOT photometry system described in
Poole et al. (2008, MNRAS, 383, 627).

       The UVOT coordinates of this source are

  RA (J2000.0)  04:15:51.85  =   63.96604 (deg)
Dec (J2000.0) +44:07:44.5   =  +44.12902 (deg)

with an estimated uncertainty of 1.0 arcsec (radius, 90% confidence,
statistical + systematic). The dereddened colours of the source are
not consistent with a stellar spectrum. However, the colours are
consistent with an Sm or Im galaxy (de Vaucouleurs, 1961, ApJS, 5,
233). This suggests that the source may be the host galaxy of GRB
090817.  If this galaxy has an absolute magnitude similar to that of
the LMC then it is located at a redshift of approximately z = 0.05.
An intrinsically fainter galaxy would be closer. Follow-up
spectroscopy is encouraged to verify this.