[AAVSO-HEN] GRB 070616: No Evidence for I Band Afterglow

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TITLE:   GCN CIRCULAR
NUMBER:  6629
SUBJECT: GRB 070616: No Evidence for I Band Afterglow
DATE:    07/07/15 16:06:28 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann at tls-tautenburg.de>

D. A. Kann & A. C. Wilson (TLS Tautenburg) report:

We reobserved the field of GRB 070616 (Starling et al., GCN 6542) with the 
Tautenburg 1.34m Schmidt telescope. We obtained 6 x 300 second images in 
the I band in good observing conditions but with a few passing clouds. 
Using the same USNOB1.0 star as used by Kann et al. (GCN 6545), we 
determine the following limiting magnitude:

date		time (days)	exp. time	Ic limit
070715.00750	28.32031	6 x 300		21.6

Using this star and three other unsaturated, isolated stars, we determine 
differential magnitudes between the star that is blended with the 
afterglow (de Pasquale et al., GCN 6557) and these stars at both epochs.

We find that between the two epochs the star has become fainter by 0.064, 
0.023, 0.041 and 0.001 magnitudes in comparison to the other four stars. 
The typical errors are 0.02 magnitudes.

We therefore conclude that we detect no significant fading between epoch 
one (star + possibly blended afterglow) and epoch two (star only), placing 
a limit of Ic > 20 on the afterglow at the first epoch (Kann et al., GCN 
6545).

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