TITLE: GCN CIRCULAR NUMBER: 20480 SUBJECT: Swift Trigger #733426: possible detection of a burst or transient DATE: 17/01/17 23:14:38 GMT FROM: David Palmer at LANL Swift Trigger #733426: possible detection of a burst or transient D. M. Palmer (LANL) reports on behalf of the Swift team: At 2017-01-17 03:37:48 UT, the Swift Burst Alert Telescope (BAT) took a series of waiting mode images that showed peaks of marginal significance, recognized in further ground analysis as a possible unknown source or GRB (Triggers #733426-#733430, GRB 170117A). The most significant image showed a peak at a BAT on-board calculated location RA, Dec 61.589, +21.743 which is RA(J2000) = 04h 06m 21s Dec(J2000) = +21d 44' 35" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The onboard images show a maximum flux level over the T+240 s to T+304 s time interval, while the maximum significance is found over the T+0 s to T+672 s image covering the entire pointing interval. Due to the marginal significance (maximum 6.5 sigma) of the image peak detection, the reality of this detection is uncertain. Its several-minute or longer duration is longer than usual for a GRB, but its distance from the Galactic plane (l,b ~ 172,-22) would be unusual for a Galactic transient. Therefore, both the reality and category of this source are uncertain. A Swift Target of Opportunity follow-up has been requested.