[vsnet-grb-info 11515] Swift detection of a burst from LS I +61 303

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12914
SUBJECT: Swift detection of a burst from LS I +61 303
DATE:    12/02/05 12:25:11 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

D. N. Burrows (PSU), M. M. Chester (PSU), V. D'Elia (ASDC),
D. M. Palmer (LANL), P. Romano (INAF-IASFPA), C. J. Saxton (UCL-MSSL),
E. Sonbas (NASA/GSFC/Adiyaman Univ.), M. Stamatikos (OSU/NASA/GSFC)
and G. Stratta (ASDC) report on behalf of the Swift Team:

At 11:47:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a burst consistent with the known High Mass X-Ray binary
LS I +61 303 (trigger=513505).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 40.100, +61.220 which is 
   RA(J2000) = 02h 40m 24s
   Dec(J2000) = +61d 13' 13"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single short spike
with a duration of about 64 ms or less.  The peak count rate
was 1500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 11:48:42.0 UT, 77.5 seconds after
the BAT trigger. Using promptly downlinked data we find an X-ray source
with an enhanced position: RA, Dec 40.1326, 61.2290 which is equivalent
to:
   RA(J2000)  = 02h 40m 31.83s
   Dec(J2000) = +61d 13' 44.4"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
position may be improved as more data are received; the latest position
is available at http://www.swift.ac.uk/sper. This position is 1.2
arcseconds from that of a known X-ray source: LS I +61 303, and
65.1 arcseconds from the on-board BAT position. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 7.57
x 10^21 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White 
filter starting 80 seconds after the BAT trigger, and a finding chart 
exposure of 250 seconds with the U filter starting 293 seconds after 
the BAT trigger.  A source consistent with the position of LS I +61 
303 is detected, with white = 13.8 and u = 12.5 (1-sigma errors of
about 0.1.).  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. The list of sources is
typically complete to about 18 mag. No   correction has been made for
the large, but uncertain extinction  expected. 

The BAT position is within 1.1 arcminutes of the micro-quasar source
LS I +61 303, and the XRT position is consistent in both position and
observational characteristics to our previous observations of this
source.  This location has previously been the source of similar
magnetar-like bursts (Torres et al. Astrophys. J., 744, 106 (2012)).