TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2984 SUBJECT: GRB 050126: Prompt XRT detection and localization DATE: 05/01/26 14:16:46 GMT FROM: David Burrows at PSU/Swift J. A. Kennea, D. N. Burrows, J. E. Hill, D. Morris, J. A. Nousek (PSU), G. Tagliaferri, C. Pagani, S. Campana, A. Moretti, P. Romano, G. Chincarini (OAB), J. Osborne, K. Page, M. Goad, A. Beardmore, A. Wells (U. Leicester), N. Gehrels, N. White, L. Angelini, F. Marshall (NASA/GSFC), P. Giommi (ASI), K. McGowan, K. Mason (MSSL) report on behalf of the Swift XRT team: The Swift XRT instrument reports a preliminary position for GRB 050126. The BAT detected this burst at 12:00:53 UT on January 26, 2005. The S/C slewed to the burst immediately. The XRT was in Manual State taking calibration observations of Mkn 876 in PC mode at the time of the slew. We settled on the BAT position at 12:03:04 and immediately began taking data in PC mode until 12:07:42, when we entered the South Atlantic Anomaly. During this four minute period the XRT detected a very bright and rapidly fading X-ray source. The initial position, based on the raw image data with no correction for stellar aberration, is: RA(J2000) = 18:32:25.8 Dec(J2000) = +42:22:0.4. The estimated uncertainty in this early position is 30 arcseconds. A more accurate position will be sent out when we are able to process these data through the pipeline software.