TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4641 SUBJECT: Swift-BAT trigger 180151 is unknown origin at this time DATE: 06/02/04 00:45:13 GMT FROM: Scott Barthelmy at NASA/GSFC A. Retter (PSU), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), N. Gehrels (GSFC), S. Hunsberger (PSU), J. Kennea (PSU), H. Krimm (GSFC/USRA) on behalf of the Swift team: At 23:55:35 UT, Swift-BAT had an 80-sec image trigger. And because of an observing constraint, the spacecraft did not slew to the flight-derived location; and so there are no immediate XRT or UVOT data products to analyze. We note that the star tracker was not in lock at the time of the trigger. Past experience shows that the gyros are able to maintain sufficient tracking to prevent drift and therefore false triggers, but it is still possible that this current trigger is a false positive. We will get the full data set in about 2 hours and may be able to determine the validity of this trigger at that time.