TITLE: GCN CIRCULAR NUMBER: 43442 SUBJECT: Swift trigger on the HMXB 1A 1118-61 DATE: 26/01/18 11:57:09 GMT FROM: K.L. Page at U Leicester <klp5@leicester.ac.uk> R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL), K. L. Page (U Leicester) and T. Sakamoto (AGU) report on behalf of the Neil Gehrels Swift Observatory Team: At 11:27:54 UT, the Swift Burst Alert Telescope (BAT) triggered and located the HMXB 1A 1118-61 (trigger 1442056). Swift slewed immediately to the source. The BAT on-board calculated location is RA, Dec 170.230, -61.909 which is RA(J2000) = 11h 20m 55s Dec(J2000) = -61d 54' 32" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is usual for an image trigger, the light-curve does not show significant structure. The XRT began observing the field at 11:29:57.7 UT, 122.8 seconds after the BAT trigger. XRT found a bright X-ray source located at RA, Dec 170.2386, -61.9161 which is equivalent to: RA(J2000) = 11h 20m 57.26s Dec(J2000) = -61d 54' 58.0" with an uncertainty of 5.1 arcseconds (radius, 90% containment). This location is 29 arcseconds from the BAT onboard position, within the BAT error circle. This position is 1.8 arcseconds from a known X-ray source: 1A 1118-61. This source is in the Swift XRT LSXPS catalogue with a mean 0.3-10 keV count-rate of 0.2537 +/- 0.0012 ct/sec; see https://www.swift.ac.uk/LSXPS/LSXPS%20J112057.1-615459 for details of these previous observations. No event data are yet available to determine the column density using X-ray spectroscopy. UVOT took a finding chart exposure of 250 seconds with the U filter starting 188 seconds after the BAT trigger. The source is clearly detected at a U magnitude of 12.7. No correction has been made for the large, but uncertain, extinction expected. This is the second recent trigger by Swift-BAT on this source, following yesterday's event reported in GCN Circ. 43435, showing that the source is increasing in brightness. View this GCN Circular online at https://gcn.nasa.gov/circulars/43442. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...