TITLE:   GCN CIRCULAR
NUMBER:  7823
SUBJECT: GRB 080603B: TLS Afterglow Observation
DATE:    08/06/05 15:24:14 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann@tls-tautenburg.de>

D. A. Kann, U. Laux and S. Ertel (TLS Tautenburg) report:

We observed the field of the Swift GRB 080603B (Mangano et al., GCN 7794) 
with the TLS 1.34m Schmidt telescope in mediocre observing conditions (low 
airmass but high humidity and moderate transparency). We obtained a total 
of 6 x 600 sec images at mid-time June 4.980179. The afterglow 
(Rujopakarn, Guver, & Smith, GCN 7792) is faintly visible in each image. 
We stacked all six images. Assuming the USNOB1.0 star with ID 1580-0163070 
at RA = 11:46:29.297, Dec. +68:03:23.43 (USNOB1.0 catalog value) to have 
R1 = 17.97 mag, we measure for the afterglow:

dt	Rc	dRc

1.16197	21.32	0.04 (statistical only)

In comparison to the magnitude measured by Xin et al. (GCN 7814) 0.8 days 
after the GRB, this implies a steep decay of alpha ~ 2.5. It is unclear if 
this is due to a break or to the use of different comparison stars. The 
comparison star used by Zhuchkov et al. GCN 7803, and Xin et al., GCN 
7814, is saturated in our images. Further observations are warranted.

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