{
  "bibcode": "2007GCN..6930....1K",
  "body": "D. A. Kann, U. Laux & R. Filgas (TLS Tautenburg) report:\n\nDuring a serendipitous opening in the cloud cover, we observed the field \nof GRB 071013 (Marshall et al., GCN 6907) with the Tautenburg 1.34m \nSchmidt telescope under very good conditions, obtaining 4 300 second \nimages in the Rc band at 4.2 days after the GRB, before clouds returned \nand shut us down. We use the same comparison star as given in Kann, \nHoegner & Filgas (GCN 6917), and find the following magnitude of the \npossible variable source discovered by Kornienko et al. (GCN 6925) in a \nstacked image:\n\nDate\t\tMid-Time\tRc\tdRc\n\n17.78693\t4.28046\t\t19.584\t0.023\n\nThus, the magnitude remains unchanged in comparison to the second epoch \n(Kann et al., GCN 6926). Between 3.2 and 4.2 days, we rule out, at 3 sigma \nconfidence level, any additional source (e.g., a rising SN component) \nbrighter than R = 22.5.\n\nWe also analyse the Kornienko Candidate in the stacked image of our first \nepoch (Kann, Hoegner & Filgas, GCN 6917). To summarize, from the three \nstacked images, we derive the following magnitudes of the possible host \ngalaxy:\n\nDate\t\tMid-Time\tExposure\tRc\tdRc\n\n13.79254\t0.28608\t\t13 x 600\t19.565\t0.009\n16.75845\t3.25198\t\t6 x 300\t\t19.583\t0.015\n17.78693\t4.28046\t\t4 x 300\t\t19.584\t0.023\n\nIf the slight magnitude difference between epoch 1 and epoch 2 would be \ndue to an additional source, it would have had R ~ 24 at 0.29 days. \nAssuming the detection by Kornienko et al. is real, and the \"host\" has R = \n19.583, the \"host-corrected\" magnitude of the Kornienko Candidate is R = \n18.56. The decay slope is then found to be alpha ~ 2 between 0.024 and \n0.286 days. This is steep but not completely unrealistic. We are thus \nunable to rule out that the object found by Kornienko et al. may be a \nsuperposed faint afterglow, although contemporary measurements (Xin et \nal., GCN 6929) do not detect it. Since Swift seems to have not slewed at \nall and no position more precise than the refined BAT error circle is \nknown (Palmer et al., GCN 6911), X-ray confirmation will probably not be \nforthcoming.\n\nThis message may be cited.",
  "circularId": 6930,
  "createdOn": 1192659757000,
  "email": "kann@tls-tautenburg.de",
  "subject": "GRB 071013: 3rd TLS Epoch - constraints on variability",
  "submitter": "Alexander Kann at TLS Tautenburg  <kann@tls-tautenburg.de>",
  "eventId": "GRB 071013"
}