[vsnet-grb-info 21890] Swift detection of LS I +61 303
GCN Circulars
gcncirc at capella2.gsfc.nasa.gov
Sun Mar 24 06:17:33 JST 2019
TITLE: GCN CIRCULAR
NUMBER: 23989
SUBJECT: Swift detection of LS I +61 303
DATE: 19/03/23 21:16:23 GMT
FROM: Boris Sbarufatti at PSU <bxs60 at psu.edu>
S. D. Barthelmy (GSFC), J.D. Gropp (PSU), A. Y. Lien (GSFC/UMBC),
D. M. Palmer (LANL) and B. Sbarufatti (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:
At 20:30:47 UT, the Swift Burst Alert Telescope (BAT) triggered and
located LS I +61 303 (trigger=894557). Swift slewed immediately to
the source.
The BAT on-board calculated location is
RA, Dec 40.153, +61.246 which is
RA(J2000) = 02h 40m 37s
Dec(J2000) = +61d 14' 45"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed multiple short
spikes with a total duration of about 20 sec. The peak count rate
was ~2400 counts/sec (15-350 keV), at ~3 sec after the trigger.
The XRT began observing the field at 20:32:12.5 UT, 85.3 seconds after
the BAT trigger. Using promptly downlinked data we find an X-ray source
with an enhanced position: RA, Dec 40.1330, 61.2290 which is equivalent
to:
RA(J2000) = 02h 40m 31.91s
Dec(J2000) = +61d 13' 44.2"
with an uncertainty of 2.0 arcseconds (radius, 90% containment). This
location is 70 arcseconds from the BAT onboard position, within the BAT
error circle. 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 2.0 arcseconds from LS I +61 303. This source is in the
Swift XRT 1SXPS catalogue with a mean 0.3-10 keV count-rate of
0.19600 +/- 0.00093 ct/sec; see
http://www.swift.ac.uk/1SXPS/1SXPSJ024031.5%2B611344
for details of these previous observations.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 9.01
x 10^21 cm^-2 (Willingale et al. 2013).
UVOT data cannot properly be analyzed at this time. A full analysis
will be possible once the full dataset comes to the ground.
The light curve from the BAT transient monitor is available at
https://swift.gsfc.nasa.gov/results/transients/weak/LSIp61303/
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