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GCN Circular 28187

Subject
Swift Detection of an SGR-like flare from AX J1846.4-0258
Date
2020-08-01T20:42:51Z (4 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester),
D. M. Palmer (LANL) and A. Tohuvavohu (U Toronto) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 20:11:47 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a flare from AX J1846.4-0258 (trigger=985320).  
Swift did not slew immediately due to an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 281.630, -2.990 which is 
   RA(J2000) = 18h 46m 31s
   Dec(J2000) = -02d 59' 24"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of 0.1 sec or less.  The peak count rate
was ~3300 counts/sec (15-350 keV), at ~0 sec after the trigger. 

Due to a Moon observing constraint, Swift cannot slew to the BAT
position until 23:30 UT on 2020 August 01. Follow-up observations
will be made at that time. 

Based on the short pulse length (16 ms trigger duration), the soft
spectrum (no emission detected above above 100 keV) and the
proximity of the source to the Galactic plane (latitude = 0.27 degrees)
and to a known pulsar, suspect that this burst is from a 
Soft Gamma Repeater or similar source. 

The BAT position is consistent with the pulsar PSR J1846-0258
(=Swift J1846.5-0257 =  AX J1846.4-0258) in supernova remnant Kes 75. 

Fermi-GBM also triggered on this event (Trigger #618005512).
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