S. D. Barthelmy (GSFC), M. M. Chester (PSU), V. D'Elia (ASDC),
D. Malesani (DARK/NBI), B. Sbarufatti (INAF-OAB/PSU) and
B.-B. Zhang (UAH) report on behalf of the Swift Team:
At 23:21:08 UT, the Swift Burst Alert Telescope (BAT) triggered and
located KS_1947+300 (trigger=583105). Swift slewed immediately to the source.
The BAT on-board calculated location is
RA, Dec 297.350, +30.231 which is
RA(J2000) = 19h 49m 24s
Dec(J2000) = +30d 13' 52"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). This is a very low significance image trigger.
The XRT began observing the field at 23:36:42.6 UT, 934.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright X-ray
source located at RA, Dec 297.39826, 30.20855 which is equivalent to:
RA(J2000) = 19h 49m 35.58s
Dec(J2000) = +30d 12' 30.8"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 170 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 1.5 arcseconds from that
of known X-ray source KS 1947+300. No event data are yet available to
determine the column density using X-ray spectroscopy.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 8.90
x 10^21 cm^-2 (Kalberla et al. 2005).
The initial flux in the 2.5 s image was 5.46e-10 erg cm^-2 s^-1 (0.2-10
UVOT took a finding chart exposure of nominal 150 seconds with the
White filter starting 942 seconds after the BAT trigger. The initial
images are consistent with the identification of the source as KS
1947+300. Because of the density of catalogued stars and the large
but uncertain extinction in the direction of the source, further
analysis is required to report photometric measurements.
The GCN notices were the result of a known race condition in the BAT
on-board software causing a misidentification of the source.
The ground processing correctly identified the source as
KS 1947+300, which is currently in outburst (Kawagoe et al.,
ATEL #5438) and is continually seen by BAT (see
for the current light curve).