{
  "bibcode": "2006GCN..5941....1K",
  "body": "S. Karpov, G. Beskin, S. Bondar, C. Bartolini, G. Greco, A. Guarnieri,\nD. Nanni, A. Piccioni, F. Terra, E. Molinari, G. Chincarini, F.M. Zerbi,\nS. Covino, V. Testa, G. Tosti, F. Vitali, L.A. Antonelli, P. Conconi, G.\nCutispoto, G. Malaspina, L. Nicastro, E. Palazzi, E. Meurs, P.  Goldoni\n\nreport on behalf of the TORTOREM team:\n\nThe field of GRB 061218 (Zane et al. GCN 5936) has been observed by the\nTORTORA (Telescopio Ottimizzato per la Ricerca di Transienti Ottici\nRApidi) wide-field fast camera (12 cm diameter, 20x25 deg FOV) mounted\non REM robotic 60-cm telescope located at La Silla (Chile). The burst\nwas initially outside the camera field of view. The system was repointed\nand the TORTORA began to acquire frames at 04:07:03 UT (118 sec after\ntrigger) with 7.5 Hz frame frequency (0.128 s exposure).\n\nThe summation of 100 frames with 12.8 s. effective exposure (middle time\n04:07:16 UT) did not reveal any source down to the B = 11.3 mag (3-sigma).\n\nWe performed the Fourier analysis of 23 min data set (10000 successive\nframes) to search for the periodic signal at the GRB position. The upper\nlimit for the amplitude of sinusoidal variability is B=16.4 (3-sigma)\nover the 0.01 - 3.5 Hz range.\n\nThe message may be cited.",
  "circularId": 5941,
  "createdOn": 1166544322000,
  "email": "giuseppe.greco2@studio.unibo.it",
  "subject": "GRB 061218: TORTOREM optical upper limits",
  "submitter": "Giuseppe Greco at U Bologna  <giuseppe.greco2@studio.unibo.it>",
  "eventId": "GRB 061218"
}