[vsnet-grb-info 16134] Trigger 630047: Swift detection of 1RXS J180408.9-342058

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17416
SUBJECT: Trigger 630047: Swift detection of 1RXS J180408.9-342058
DATE:    15/02/06 21:26:24 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

S. D. Barthelmy (GSFC), D. N. Burrows (PSU), C. Gronwall (PSU),
M.E. Gropp (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
D. Malesani (DARK/NBI), F. E. Marshall (NASA/GSFC),
B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf
of the Swift Team:

At 20:45:14 UT, the Swift Burst Alert Telescope (BAT) triggered and
located 1RXS J180408.9-342058 (trigger=630047).  Swift slewed to the source. 
The BAT on-board calculated location is 
RA, Dec 271.019, -34.318, which is 
   RA(J2000)  =  18h 04m 05s
   Dec(J2000) = -34d 19' 03"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is typical for image triggers (15 min integration),
there is nothing discernible from the real-time data. 

The XRT began observing the field at 21:04:28.5 UT, 1153.7 seconds
after the BAT trigger. XRT found a bright X-ray source located at RA,
Dec 271.0338, -34.3481 which is equivalent to:
   RA(J2000)  = +18h 04m 8.11s
   Dec(J2000) = -34d 20' 53.2"
with an uncertainty of 5.3 arcseconds (radius, 90% containment). This
location is 116 arcseconds from the BAT onboard position, within the
BAT error circle. This position is 4.8 arcseconds from a known X-ray
source: 1SXPS J180408.1-342048. This source is in the Swift XRT 1SXPS
catalogue with a mean 0.3-10 keV count-rate of 0.0256 +/- 0.0020
ct/sec; see http://www.swift.ac.uk/1SXPS/1SXPSJ180408.1-342048 for
details of these previous observations. 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 1.37e-09 erg cm^-2 s^-1 (0.2-10
keV), corresponding to ~30 counts per second. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 1163 seconds after the BAT trigger. There is an optical counterpart in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	18:04:08.40 = 271.03499
  DEC(J2000) = -34:20:51.2  = -34.34755
with a 90%-confidence error radius of about 0.62 arc sec. This position is 4.0
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.29 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.48. 

This is the second BAT trigger on 1RXS J180408.9-342058. The first
was on January 31st, 2015 at 21:14UT (GCN #17367). The recent rise in
brightness of this object has been reported by the BAT Transient 
Monitor (ATEL #6997) and MAXI (ATEL #7008).