TITLE: GCN CIRCULAR NUMBER: 18637 SUBJECT: Subject: GRB 151122A: Swift detection of a burst DATE: 15/11/23 20:25:59 GMT FROM: David Palmer at LANL David Palmer reports on behalf of the Swift team: On November 22, at 17:00:40 UT, BAT rate-triggered and detected a 6.0 sigma peak in an image. Because this was below the nominal 6.5 sigma threshold, BAT did not trigger a burst response. However, ground analysis leads us to believe that this is a real burst, GRB 151122A (trigger #664653) with an onboard-calculated location RA,dec = 299.704, -19.899, which is RA(J2000) = 19h 58m 49s dec(J2000) = -19d 53’ 56” with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The lightcurve shows a slow-rise, fast decay peak from T-5 s to T+12 s, following by a possible second lower peak extending to T+45 s. The peak count rate was ~1500 counts/sec (15-350 keV), at ~6 sec after the trigger. The peak of this burst was after a pre-planned slew had started, thus only the initial rise of this burst was imaged on board. However, the burst was also seen by Fermi GBM (trigger #469904449) which gave a final ground-calculated position of RA,dec = 292.950, -21.350 with an 11.1 degree statistical error radius and a 1-sigma location contour that contains the BAT location. The GBM lightcurve is also consistent with the BAT lightcurve. Therefore we believe that both of these triggers are the same astrophysical GRB at the location found by BAT A Target Of Opportunity Swift observation has been accepted for this GRB.