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GCN Circular 394

GRB990806 UBVRIJHK observations
1999-08-07T17:17:41Z (25 years ago)
Brad Schaefer at Yale U <>
Bradley E. Schaefer (Yale) reports:

"I have obtained UBVRIJHK images of the BeppoSAX 2' radius region 
(Gandolfi et al., BeppoSAX mail n. 99/23 or GCN 393) for GRB990806.  
These observations were made from 1999 August 7 6:57 UT to 10:53 UT (16.48
to 20.39 hours after the burst), with a total exposure time of 5.1 hours
due to the simultaneous integrations in the infrared and optical.  The
total integrations times are:
	U  -  60 min.
	B  -  64 min.
	V  -  30 min.
	R  -  15 min.
	I  -  15 min.
	J  -  60 min.
	H  -  30 min.
	K  -  33 min.
These images were taken with the Yale 1 m telescope on Cerro Tololo with
the recently upgraded AndiCam IR/optical camera; which is well suited to
obtaining UBVRIJHK of GRB optical transients within the first day or so
after the burst.

No variable source was identified in or near the GRB990806 region.
Comparisons were made between my V, R, and I images with the Digital Sky
Survey, the ESO R sky survey, and the ESO J sky survey.  This use of
multiple images and colors for both before and after allowed for the ready
elimination of cosmic rays and color effects which can raise false alarms.
(For example, my R image shows two point sources in the BeppoSAX 2' circle
that do not appear on the Digital Sky Survey despite the indications of
the magnitude; whereas my VRI images show the sources are very red and
both sources do appear near the threshold on the ESO R image.)  The area
examined was a region 10.24'X10.24' centered roughly on the BeppoSAX
position.  The threshold for reasonable completeness in the comparison is
roughly R=20.5 mag.  As always, further analysis can push somewhat deeper,
yet it is clear that any associated optical transient must be close to
this quoted limit if not fainter.  I will try to obtain deeper comparison
images tomorrow morning."
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