GCN Circular 23763

P. A. Evans (U Leicester), N. J. Klingler (PSU),
N. P. M. Kuin (UCL-MSSL), K. L. Page (U Leicester),
D. M. Palmer (LANL) and B. Sbarufatti (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 10:06:57 UT, the Swift Burst Alert Telescope (BAT) triggered and
located MAXI J1631-479 (trigger=884906).  Swift slewed immediately to the target. 
The BAT on-board calculated location is 
RA, Dec 247.749, -47.773 which is 
   RA(J2000) = 16h 31m 00s
   Dec(J2000) = -47d 46' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is typical for an image trigger, there is nothing
visible in the real-time light curve. 

The XRT began observing the field at 10:09:01.2 UT, 123.6 seconds after
the BAT trigger. XRT found a bright X-ray source located
at RA, Dec 247.8088, -47.8065 which is equivalent to:
   RA(J2000)  = 16h 31m 14.11s
   Dec(J2000) = -47d 48' 23.4"
with an uncertainty of 5.2 arcseconds (radius, 90% containment). No
event data are yet available to determine the column density using
X-ray spectroscopy. 

The initial flux in the 0.1 s image was 4.51e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White
filter  starting 133 seconds after the BAT trigger. No credible
afterglow candidate has  been found in the initial data products. The
2.7'x2.7' sub-image covers 100% of  the XRT error circle. The 8'x8'
region for the list of sources generated on-board covers 100% of the
XRT error circle. Because of the density of catalogued stars,  further
analysis is required to report an upper limit for any counterpart in
the  region. No correction has been made for the large, but uncertain,
extinction  expected. 

This source is currently active, as shown at 
https://swift.gsfc.nasa.gov/results/transients/AXJ1631.9-4752/. BAT 
has previously triggered on this source (trigger 878548 and 882561; 
GCNs 23550
Not found
 
 
 and 23639
Not found
 
 
). The trigger was initially mis-identified as AX 
1631.9-4752, given the close proximity of the two sources. The XRT
position is coincident with the radio localisation given in ATel
12396.