TITLE: GCN CIRCULAR NUMBER: 23797 SUBJECT: Swift Trigger 885960: A third Swift trigger on MAXI J1348-630 DATE: 19/01/27 01:16:05 GMT FROM: Aaron Tohuvavohu at PSU/Swift S. D. Barthelmy (GSFC), J. A. Kennea (PSU), N. J. Klingler (PSU), A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester), B. Sbarufatti (PSU) and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 00:56:09 UT, the Swift Burst Alert Telescope (BAT) triggered and located MAXI J1348-630 (trigger=885960). Swift slewed immediately to the source. The BAT on-board calculated location is RA, Dec 207.035, -63.268 which is RA(J2000) = 13h 48m 08s Dec(J2000) = -63d 16' 02" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is normal for an image trigger, the light-curve showed no significant structure. The XRT began observing the field at 00:59:18.9 UT, 189.3 seconds after the BAT trigger. XRT found a bright X-ray source located at RA, Dec 207.0558, -63.2733 which is equivalent to: RA(J2000) = 13h 48m 13.39s Dec(J2000) = -63d 16' 23.9" with an uncertainty of 4.7 arcseconds (radius, 90% containment). No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 1.09e-08 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 197 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 13:48:12.84 = 207.05348 DEC(J2000) = -63:16:28.5 = -63.27458 with a 90%-confidence error radius of about 0.61 arc sec. This position is 5.9 arc sec. from the center of the XRT error circle. The estimated magnitude is 16.99 with a 1-sigma error of about 0.14. No correction has been made for the large, but uncertain, extinction expected. This source is consistent with the location of the previously reported optical transient associated with MAXI J1348-630 (ATEL #12430).