[vsnet-grb-info 9323] GRB 100526A: Gemini/NIRI infrared afterglow candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10806
SUBJECT: GRB 100526A: Gemini/NIRI infrared afterglow candidate
DATE:    10/05/27 11:41:49 GMT
FROM:    Daniel Perley at U.C. Berkeley  <dperley at astro.berkeley.edu>

D. A. Perley (UC Berkeley) reports on behalf of a larger collaboration:

We imaged the field of GRB 100526A (Vetere et al., GCN 10797) with the 
Near-InfraRed Imager (NIRI) on Gemini-North starting at 08:29 UT on 
2010-05-27.  We obtained 18 exposures of 60 seconds each in K-band and 
H-band.

At the edge of the XRT error circle (Beardmore et al., GCN 10800) we 
clearly detect a source with no SDSS counterpart in the K-band image. 
It is also present, but much fainter, in H-band.  The position (J2000) is:

RA  =  15:23:04.480
Dec = +25:37:55.23
(+/- 0.4")

Preliminary photometry relative to a single 2MASS star in the field 
(2MASS 1523017+2538260) gives:

K = 19.09 +/- 0.13  (t_mid = 16.21 hours)
H = 21.15 +/- 0.17  (t_mid = 16.75 hours)

This is an extremely red color, corresponding to a spectral slope of 
beta~5.5.  If this object is confirmed as the afterglow (rather than a 
host or background galaxy), its flux and color are reminiscent of GRB 
070306 (Jaunsen et al. 2008) at similar times.  That object had a visual 
extinction of A_V~5.5 mag and is among the most heavily extinguished 
afterglows known.  The large inferred XRT absorption column (Vetere et 
al., GCN 10804) of this event is also consistent with a highly 
dust-extinguished event at low to moderate redshift.

We thank Richard McDermid and the Gemini staff for acquiring these 
observations.