S. D. Barthelmy (GSFC), J. A. Kennea (PSU),
F. E. Marshall (NASA/GSFC), A. Maselli (INAF-IASFPA) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:
At 18:12:38 UT, the Swift Burst Alert Telescope (BAT) triggered and
located SGR 1E 1841-045 (trigger=649113). Swift slewed immediately to the source.
The BAT on-board calculated location is
RA, Dec 280.330, -4.930, which is
RA(J2000) = 18h 41m 19s
Dec(J2000) = -04d 55' 47"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows a single spike
with a duration of less than 0.128 sec. The peak count rate
was ~8600 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 18:14:13.2 UT, 95.4 seconds after
the BAT trigger. Using promptly downlinked data we find an X-ray source
located at RA, Dec 280.33029, -4.93495 which is equivalent to:
RA(J2000) = 18h 41m 19.27s
Dec(J2000) = -04d 56' 05.8"
with an uncertainty of 3.8 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 6.3
arcseconds from that of a known X-ray source: 3XMM J184119.3-045612 in
the XMM-NEWTON XMMSSC catalogue.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.71
x 10^22 cm^-2 (Willingale et al. 2013).
UVOT took a finding chart exposure of 150 seconds with the White
filter starting 101 seconds after the BAT trigger. No credible
afterglow candidate has been found in the initial data products. The
2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical
upper limit has been about 19.6 mag, but this is an unusually crowded
field. The 8'x8' region for the list of sources generated on-board
covers 100% of the BAT error circle. The list of sources is typically
complete to about 18 mag. No correction has been made for extinction.