[vsnet-grb-info 2621] GRB060108: P200 Ks Observations

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4458
SUBJECT: GRB060108: P200 Ks Observations
DATE:    06/01/10 00:27:40 GMT
FROM:    S. Bradley Cenko at Caltech  <cenko at srl.caltech.edu>

S. B. Cenko (Caltech), J. Colbert, H. Teplitz (JPL / Spitzer Science
Center), and D. B. Fox (Penn State) report on behalf of the
Caltech-NRAO-Carnegie GRB collaboration:

We have imaged the field of GRB060108 (Oates et al., GCN 4443; Sakamoto et
al., GCN 4445) with the Wide-Field Infrared Camera mounted on the Palomar
200-inch Hale Telescope.  Our observations consisted of 30 x 30 s images
in the Ks band taken in moderate-to-poor external conditions (seeing ~
1.5-2.0").  The mean epoch of our observations is approximately 06:45 UT
January 9 (~ 16.1 hours after the burst).  We note these observations are
roughly contemporaneous with the VLT J-band observations reported by
D'Avanzo et al. (GCN 4452).

Inside the revised XRT error circle (Page et al., GCN 4453) we find no
sources.  Our limiting magnitude, calculated with respect to several 2MASS
objects in the field, is Ks > 18.5.

Performing a similar analysis to Malesani et al. (GCN 4454) and using the
XRT results from Page et al. (GCN 4453), we find we can constrain the
x-ray-to-optical spectral index, beta_OX, to be < 0.7.  While this in
itself is not inconsistent with the standard fireball model (Sari, Piran,
& Narayan, 1998, ApJ, 497, L18), together with the deep early R-band
(Guidorzi et al., GCN 4447) and contemporaneous J-band limits, this
provides further evidence for the exceptional (i.e. either very dark or
very high-z) nature of this event.