TITLE: GCN CIRCULAR NUMBER: 35858 SUBJECT: Swift detection of Swift J151857.0-572147 DATE: 24/03/04 09:14:44 GMT FROM: P.A. Evans at U. Leicester <pae9@leicester.ac.uk> E. Ambrosi (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR), P. A. Evans (U Leicester), J. A. Kennea (PSU), A. Melandri (INAF-OAR), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 08:53:10 UT, the Swift Burst Alert Telescope (BAT) triggered and located Swift J151857.0-572147 (trigger=1218604). Swift slewed immediately to the object. The BAT on-board calculated location is RA, Dec 229.732, -57.354 which is RA(J2000) = 15h 18m 56s Dec(J2000) = -57d 21' 15" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is usual with an image trigger, the BAT light curve does not show any significant structure. The XRT began observing the field at 08:56:20.6 UT, 189.7 seconds after the BAT trigger. XRT found a bright X-ray source located at RA, Dec = 229.7358, -57.3617 which is equivalent to: RA(J2000) = 15h 18m 56.59s Dec(J2000) = -57d 21' 42.1" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 28 arcseconds from the BAT onboard position, within the BAT error circle, and consistent with the localisation of Swift J151857.0-572147 reported in GCN Circs. 35849 & 35853. UVOT took a finding chart exposure of 250 seconds with the U filter starting 195 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. This object is the same as BAT trigger 1218452, which was originally identified as GRB 240303A (Lien et al., GCN Circ. 35849) but later confirmed as a Galactic transient Swift J151857.0-572147 (Kennea et al., GCN Circ. 35853). View this GCN Circular online at https://gcn.nasa.gov/circulars/35858. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...