S. T. Holland (STScI), A. Y. Lien (NASA/GSFC/ORAU),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
T. Sakamoto (AGU) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of
the Swift Team:
At 09:52:30 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a burst from the Soft Gamma Repeater AXP 1E1547.0-5408
(trigger=558399). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 237.714, -54.277 which is
RA(J2000) = 15h 50m 51s
Dec(J2000) = -54d 16' 35"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a single spike
structure with a duration of about 0.2 sec. The peak count rate
was ~8570 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 09:53:41.8 UT, 71.8 seconds after
the BAT trigger. Using promptly downlinked data we find an X-ray source
with an enhanced position: RA, Dec 237.7266, -54.3063 which is
RA(J2000) = 15h 50m 54.39s
Dec(J2000) = -54d 18' 22.6"
with an uncertainty of 2.7 arcseconds (radius, 90% containment). This
location is 108 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 1.8 arcseconds from that
of AXP 1E1547.0-5408.
A power-law fit to a spectrum formed from promptly downlinked event
data does not constrain the column density.
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 75 seconds after the BAT trigger. No credible counterpart has
been found in the initial data products. The 2.7'x2.7' sub-image covers none 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.
This soft gamma repeater had a major period of activity in October, 2008
(ATEL #1756, Rea et al., 2008) and was last seen by Swift BAT on 2011-12-20.