TITLE:   GCN CIRCULAR
NUMBER:  11564
SUBJECT: GRB 101225A: HST observations - no host detected
DATE:    11/01/13 12:46:08 GMT
FROM:    Nial Tanvir at U.Leicester  <nrt3@star.le.ac.uk>

N.R. Tanvir (U. Leicester), A.J. Levan (U. Warwick), J.P.U. Fynbo,
D. Malesani, J. Hjorth (DARK/NBI), D. Xu, A. Gal-Yam (Weizmann Inst.)
K. Wiersema, P.A. Evans (U. Leicester) & D.F. Bersier (Liverpool JMU)
report:

We observed the location of GRB 101225A (Racusin et al. GCN 11493; Xu
et al.�� GCN 11495) using HST/ACS on 2011 Jan 13 beginning at 00:25 UT,
approximately 18 days post-burst.�� Images were obtained in the F606W
and F435W filters.�� Contrary to the claim in Xu et al. (GCN 11519), we
find no evidence for extension in either image, and thus no indication
of a host galaxy.�� We do, however, find the colour of the optical
transient is now quite red with an (AB) colour of F435W-F606W=1.6,
confirming the reddening trend from the initially very blue colour
(Chornock et al. GCN 11507).�� The magnitude (F606W(AB)=24.6) is
consistent with a continuing post-break power-law decline in the
R-band with a slope t^-1.

We note that if this event is at a redshift as low as z=0.07, as
suggested by an analysis of the X-ray data (Campana et al.�� GCN
11501), then any host galaxy beneath the transient would have to be
both very faint (less than about M_R=-12) and compact not to be seen
in the HST images.

We thank the STScI staff for rapidly implementing these observations.

[GCN OPS NOTE(13jan11): Per author's request, DX was added to the autor list.]