TITLE: GCN CIRCULAR NUMBER: 19304 SUBJECT: GRB 160409A found in Swift BAT ground analysis DATE: 16/04/12 19:20:11 GMT FROM: David Palmer at LANL GRB 160409A found in Swift BAT ground analysis P.A. Evans (U. Leicester), J.P. Osborne (U Leicester), K. L. Page (U Leicester), and D.M. Palmer (LANL) report on behalf of the Swift Team At 05:54:14 UT on 2016-04-09 BAT triggered and located GRB 160409A (trigger #682162). Swift did not immediately slew to this source because its location approximately matched a known source (4U 1916-053) in its on-board catalog. The BAT on-board calculated location is RA, dec 289.705,-5.390 which is RA(J2000) = 19h 18m 49s Dec(J2000) = -5d 23' 24" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex peak structure with a duration of about 30 sec. The peak count rate was ~1300 counts/sec (15-350 keV), at ~2 sec after the trigger. The catalogued source, 4U 1916-053, is identified by Simbad as being the LXB V* V1405 Aql. However, this object is 9 arcminutes from the BAT position, and well outside the error circle. BAT has detected a burst from that source (1.1 arcmin offset from the V1405 Aql location) in April 2006. During the 6-minute accumulation that overlaps the trigger, SAX J2103.5+4545 is detected (at lower significance and correspondingly larger position uncertainty) with a 3.3 arcmin offset. Therefore we can confidently state that this trigger did not come from the location of V1405 Aql and is due to a different source. A Swift Target of Opportunity was requested and XRT began observing the field at 00:34:58 UT on 2016-04-12, which is 2.8 days after the BAT trigger. No unknown sources were detected in the 3 kiloseconds of data, although two known sources and possible scattered X-rays from V1405 Aql were seen. No new sources were detected in UVOT down to a limiting magnitude of 21.3 in white. Qualitatively, about half of long GRBs would be visible in a 3 ks XRT observation at that delay after the trigger, so the non-detection of an afterglow does not rule out a GRB.