[vsnet-grb-info 370] Second epoch K band imaging of GRB 020819

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

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1520
SUBJECT: Second epoch K band imaging of GRB 020819
DATE:    02/08/23 09:03:18 GMT
FROM:    Jochen Greiner at MPI  <jcg@mpe.mpg.de>

S. Klose (Thueringer Landessternwarte Tautenburg),
A. Henden (USRA/USNO),
J. Greiner (MPE Garching), 
D. H. Hartmann (Clemson University),
N. Cardiel, J. Gallego (Universidad Complutense de Madrid), and
U. Thiele (Calar Alto Observatory)
 
report:

A deep second epoch K' band observation of the 130 arcsec radius error 
circle of the HETE burst GRB 020819 (HETE trigger #2275, Seq_4; 
Vanderspek et al. 2002, GCN #1508) has been performed on August 20/21, 
23:11--00:59 UT (about 33 hrs after the GRB), using the Calar Alto 
3.5-m telescope equipped  with the Omega Prime near-infrared camera. 
The integration time was 77 min. The limiting magnitude is about 
K'=20.5 (+/-0.5), the seeing was 1.2 arcsec.

Lacking a K band photometric calibration, we used the (B-R) colors of all 
USNO stars (Monet et al. 1996; http://asteroid.lowell.edu/cgi-bin/koehn/webnet)
in the field for a rough calibration. Assuming their colors are 
representative for their spectral type and assuming zero interstellar 
extinction, the magnitude of the candidate object reported in GCN #1510 
(Henden et al. 2002) is found to have K'=17.6 (conservative error of 0.2 mag).

Photometry of all objects within the HETE/SXC error circle using PSF fitting
(Sextractor) did not reveal any source brighter than K'=19 which faded by 
more than 0.1 mag between the first epoch (Henden et al. 2002, GCN #1510)
and this second epoch observation. This and the findings of Price et al.
2002 (GCN #1511) and Salamanca et al. 2002 (GCN #1512) imply that the 
candidate object proposed earlier (Henden et al. 2002, GCN #1510) is very
unlikely the GRB afterglow.

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