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GCN Circular 23882

Subject
Trigger 888312: Swift detection of 4U 1901+03
Date
2019-02-09T14:51:45Z (5 years ago)
From
Kim Page at U.of Leicester <klp5@leicester.ac.uk>
J. A. Kennea (PSU), H. A. Krimm (NSF/USRA), K. L. Page (U Leicester)
and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 14:28:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located 4U 1901+03 (trigger=888312). The BAT on-board calculated 
location is RA, Dec 285.972, +3.242 which is 
   RA(J2000) = 19h 03m 53s
   Dec(J2000) = +03d 14' 30"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  

This source, 4U 1901+03 is a HMXB X-ray pulsar, which appears to be 
going into another outburst.  The rate has been rising in the 
Swift/BAT transient monitor since 6 February 2019 (MJD 58520) - see
https://swift.gsfc.nasa.gov/results/transients/weak/4U1901p03/ - 
and is currently at 0.016 +/-  0.005 ct s^-1 cm^-2 (15-50 keV; 70 mCrab).  
The rise is also seen in MAXI. 

The last reported outburst of this source was in December 2011 (Sootome et al.,
ATel 3829). 

Due to a Sun observing constraint, Swift cannot slew to the BAT
position until 13:00 UT on 2019 February 17. There will thus be no XRT
or UVOT data for this trigger before this time.
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