[vsnet-grb-info 16226] Trigger 632888: Swift detection of the magnetar 4U 0142+61

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17507
SUBJECT: Trigger 632888: Swift detection of the magnetar 4U 0142+61
DATE:    15/02/28 05:11:06 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
A. Maselli (INAF-IASFPA), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Swift Team:

At 04:53:25 UT, the Swift Burst Alert Telescope (BAT) triggered and
located 4U 0142+61 (trigger=632888).  Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 26.571, +61.768, which is 
   RA(J2000)  =  01h 46m 17s
   Dec(J2000) = +61d 46' 04"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows 4 short spikes
(<~0.1 s) over a total duration of about 20 sec.  The peak count rate
was ~8000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 04:54:43.2 UT, 78.3 seconds after
the BAT trigger. XRT found a bright X-ray source located at RA, Dec
26.5966, 61.7519 which is equivalent to:
   RA(J2000)  = +01h 46m 23.18s
   Dec(J2000) = +61d 45' 06.8"
with an uncertainty of 5.2 arcseconds (radius, 90% containment). This
location is 72 arcseconds from the BAT onboard position, within the BAT
error circle. This position is 7.3 arcseconds from a known X-ray
source: 1SXPS J014622.3+614502. This source is in the Swift XRT 1SXPS
catalogue with a mean 0.3-10 keV count-rate of 4.610 +/- 0.021 ct/sec;
see http://www.swift.ac.uk/1SXPS/1SXPSJ014622.3%2B614502 for details of
these previous observations. No event data are yet available to
determine the column density using X-ray spectroscopy. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 90 seconds after the BAT trigger. No credible counterpart has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
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 source has been previously detected by BAT on timescales of both
minutes and milliseconds, most recently on February 19 of this year.