TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2853 SUBJECT: GRB041217: The First GRB Located On-Board Swift DATE: 04/12/17 23:59:44 GMT FROM: Ed Fenimore at LANL D. Palmer (LANL), E. Fenimore (LANL), S. Barthelmy (GSFC), G. Chincarini (OAB), J. Cummings (GSFC), N. Gehrels (GSFC), P. Giommi (ASDC), M. Goad (U.Leicester), D. Hullinger (UMD), H. Krimm (USRA), C. Markwardt (UMD), K. Mason (MSSL), K. McLean (LANL), J. Nousek (PSU), J. Osborne (U.Leicester), A. Parsons (GSFC), G. Sato (ISAS), M. Suzuki (Saitama), J. Tueller (GSFC), A. Wells (U.Leicester), N. White (GSFC), on behalf of the Swift BAT team. On Dec 17 2004, 7:28:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located on-board an apparent gamma-ray burst. The spacecraft did not autonomously slew to the burst since automated slewing is not yet enabled. The location is RA/Dec 164.79, -17.95 (J2000). This is about 42 degrees off the bore sight in the partially encoded field of view. The Swift attitude control system is still undergoing calibration, but we estimate that the position is within 12 arcmin (radius). The on-orbit location differed from a location processed on the ground by about 6 arcmin. After calibration we expect on-board locations to be within 4 arcmin. The burst can be characterized as a smooth profile with a rise time of 2 sec and a fall time of 6 sec. The T90 was ~6.7. Although BAT is still undergoing calibration, ground processing gives a power law spectrum with a number index of -1.6 and a fluence of 5E-6 erg/cm^2 in the ~20 to 200 keV range. The peak was about 4.4 cts/cm^2/sec in ~15 to 200 keV. [GCN OPS NOTE (18-19dec04): "UL" was changed to "U.Leicester". And the words "(J2000)" and "(radius)" were added to the position estimate.]