{
  "bibcode": "2007GCN..6505....1K",
  "body": "D. A. Kann, A. C. Wilson, S. Schulze, S. Klose, M. Henze, F. Ludwig, U. \nLaux (TLS Tautenburg) and J. Greiner (MPE Garching) report:\n\nWe observed the XRT position (Pagani & Kennea, GCN 6490) of Swift GRB \n070610 (Pagani et al. GCN 6489) with the Tautenburg 1.34m Schmidt \nTelescope in Rapid Response Mode (Klose et al., GCN 3609). Observations \nstarted 640 seconds after the trigger, at an initial airmass of 1.945. \nWeather conditions were good and the airmass decreased during \nobservations. We obtained two sequences of images with 120 seconds \nexposure time each, consisting of 6 Ic, 3 Rc and 3 V images per sequence.\n\nThe optical transient first detected by Stefanescu et al. (GCN 6492) and \nconfirmed by de Ugarte Postigo et al. (GCN 6501) is detected in only three \nimages, thus showing a rapid, short-lived flaring behaviour. Stacks of \nimages were created, but we do not detect the transient in these stacks. \nWe report the following upper limits and magnitudes assuming the USNO B1.0 \nstar at RA = 19:55:03.2, Dec. = +26:14:14.5 has R2 = 15.8 and I = 15.32:\n\ntmid (days)\tfilter\tExp.\tLimit\tOT mag\n0.008407\tIc\t1x120\t19.7\t\n0.012122\tIc\t6x120\t20.2\t\n0.022194\tRc\t3x120\t21.2\t\n0.033376\tIc\t2x120\t20.4\t\n0.036369\tIc\t1x120\t20.2\t19.36 +\\- 0.15\n0.040228\tIc\t3x120\t20.5\t\n0.044356\tRc\t1x120\t21.3\t\n0.046336\tRc\t1x120\t21.3\t20.89 +\\- 0.20\n0.048304\tRc\t1x120\t21.3\t21.78 +\\- 0.50\n\nThe final detection is marginal.\n\nWe note that this flaring behaviour is very uncommon for the afterglow of \na GRB. Furthermore, the maps of Schlegel et al. 1998 give E(B-V) = 3.256, \ntranlating to A_R = 8.7 and A_I = 6.3, at the position of the transient. \nThis would imply the flare in the I band reached 13th magnitude, very \nunusual at such a late time. Furthermore, the X-ray afterglow as seen on \nthe Swift XRT repository webpage \n(http://www.swift.ac.uk/xrt_curves/00281993/index.php) shows a more or \nless constant behaviour, with small flares superposed.\n\nThe behaviour of the transient in both the optical and the X-ray regime as \nwell as the location in the Galactic plane strongly suggest that this is a \nnew Galactic transient source and not a GRB and its associated afterglow.\n\nThis message may be cited.\n\n[GCN OPS NOTE(12jun07): Per author's request, \"A_V\" was changed to \"A_I\".]",
  "circularId": 6505,
  "createdOn": 1181594498000,
  "email": "kann@tls-tautenburg.de",
  "subject": "GRB 070610: TLS RRM sees flaring behaviour - Galactic transient?",
  "submitter": "Alexander Kann at TLS Tautenburg  <kann@tls-tautenburg.de>",
  "eventId": "GRB 070610"
}