GCN Circular 43442
Subject
Swift trigger on the HMXB 1A 1118-61
Date
2026-01-18T11:57:09Z (7 days ago)
From
K.L. Page at U Leicester <klp5@leicester.ac.uk>
Via
email
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.