TITLE: GCN CIRCULAR NUMBER: 6930 SUBJECT: GRB 071013: 3rd TLS Epoch - constraints on variability DATE: 07/10/17 22:22:37 GMT FROM: Alexander Kann at TLS Tautenburg 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. This message may be cited.