[vsnet-grb-info 28119] Swift-BAT Trigger 1055000: Swift detection of an outburst from 4U 1543-47

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30222
SUBJECT: Swift-BAT Trigger 1055000: Swift detection of an outburst from 4U 1543-47
DATE:    21/06/12 13:58:23 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at star.le.ac.uk>

P. A. Evans (U Leicester), J. A. Kennea (PSU), N. J. Klingler (PSU),
A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester) and
M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 13:01:32 UT, the Swift Burst Alert Telescope (BAT) triggered and
located 4U 1543-47 (trigger=1055000).  This was a 19.1 minute long image
trigger, after which Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 236.772, -47.682 which is 
   RA(J2000) = 15h 47m 05s
   Dec(J2000) = -47d 40' 55"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  No light curve near the trigger time
is available at this moment. We are waiting for ground data for more information. 

The XRT began observing the field at 13:23:51.8 UT, 1339.0 seconds
after the BAT trigger. XRT found a bright X-ray source located at RA,
Dec 236.7907, -47.6693 which is equivalent to:
   RA(J2000)  = 15h 47m 9.77s
   Dec(J2000) = -47d 40' 09.5"
with an uncertainty of 10 arcseconds (radius, 90% containment). This
location is 64 arcseconds from the BAT onboard position, within the BAT
error circle. This position is 11.8" from the position of 4U 1543-47 (ATel #98). 
Assuming a typical GRB power-law spectrum (NH=3e21 cm^-2, gamma=2), the
catalogue entry for this object  is equivalent to a 0.2-10 keV flux of
1.4e-11 erg cm^-2 s^-1; the flux in the 0.1 s XRT image was 1.88e-07
erg cm^-2 s^-1. No event data are yet available to determine the column
density using X-ray spectroscopy. 

UVOT took a finding chart exposure of 150 seconds with the White
filter  starting 1347 seconds after the BAT trigger. The 2.7'x2.7'
sub-image shows the 4U 1543-47 source with a white magnitude of 13.86
and strong coincidence loss.  No correction has been made for
extinction. 

The position of the BAT and XRT sources are consistent with that of
the High-Mass X-ray Binary 4U 1543-47 (Atel #98), thus we believe this
to be an outburst of that source.