GCN Circular 6930
Subject
GRB 071013: 3rd TLS Epoch - constraints on variability
Date
2007-10-17T22:22:37Z (17 years ago)
From
Alexander Kann at TLS Tautenburg <kann@tls-tautenburg.de>
D. A. Kann, U. Laux & R. Filgas (TLS Tautenburg) report:
During a serendipitous opening in the cloud cover, we observed the field
of GRB 071013 (Marshall et al., GCN 6907) with the Tautenburg 1.34m
Schmidt telescope under very good conditions, obtaining 4 300 second
images in the Rc band at 4.2 days after the GRB, before clouds returned
and shut us down. We use the same comparison star as given in Kann,
Hoegner & Filgas (GCN 6917), and find the following magnitude of the
possible variable source discovered by Kornienko et al. (GCN 6925) in a
stacked image:
Date Mid-Time Rc dRc
17.78693 4.28046 19.584 0.023
Thus, the magnitude remains unchanged in comparison to the second epoch
(Kann et al., GCN 6926). Between 3.2 and 4.2 days, we rule out, at 3 sigma
confidence level, any additional source (e.g., a rising SN component)
brighter than R = 22.5.
We also analyse the Kornienko Candidate in the stacked image of our first
epoch (Kann, Hoegner & Filgas, GCN 6917). To summarize, from the three
stacked images, we derive the following magnitudes of the possible host
galaxy:
Date Mid-Time Exposure Rc dRc
13.79254 0.28608 13 x 600 19.565 0.009
16.75845 3.25198 6 x 300 19.583 0.015
17.78693 4.28046 4 x 300 19.584 0.023
If the slight magnitude difference between epoch 1 and epoch 2 would be
due to an additional source, it would have had R ~ 24 at 0.29 days.
Assuming the detection by Kornienko et al. is real, and the "host" has R =
19.583, the "host-corrected" magnitude of the Kornienko Candidate is R =
18.56. The decay slope is then found to be alpha ~ 2 between 0.024 and
0.286 days. This is steep but not completely unrealistic. We are thus
unable to rule out that the object found by Kornienko et al. may be a
superposed faint afterglow, although contemporary measurements (Xin et
al., GCN 6929) do not detect it. Since Swift seems to have not slewed at
all and no position more precise than the refined BAT error circle is
known (Palmer et al., GCN 6911), X-ray confirmation will probably not be
forthcoming.
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