[vsnet-grb-info 458] GRB 021004 continued IR fading

[GCN Circulars <gcncirc@lheawww.gsfc.nasa.gov>]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1601
SUBJECT: GRB 021004 continued IR fading
DATE:    02/10/07 21:22:19 GMT
FROM:    James Rhoads at STScI  <rhoads@stsci.edu>

James Rhoads, Ingunn Burud, and Andrew Fruchter report
on behalf of a larger collaboration:

H band images of GRB 021004 were obtained at the NASA Infrared
Telescope Facility (IRTF) on October 5, 6, and 7 UT.
Quick look photometry of the October 6 and 7 data show
continued fading of the OT, in contrast to the optical
behavior reported by Stanek et al (GCNC 1598)
over a very similar period.

Date	Time		H	err_H
--------------------------------------
Oct 6	12:26 UT	17.74 	0.05
Oct 7	11:31 UT	18.21	0.05

The errors are the error in 2MASS photometry of our
local photometric calibrator; hence the fading is known
more precisely than the absolute photometry,
and is about 0.47 +- 0.04 mags.

This implies that the transient became bluer from Oct.
6 to Oct 7, with a change in logarithmic spectral slope of
about 0.4.  This could correspond to the arrival of
fresh energy at the blast wave external shock,
carried by slow ejecta.
Interestingly, the color shift corresponds roughly to the
change between a frequency below and above the cooling break.

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