GCN Circular 22416

S. D. Barthelmy (GSFC), P. D'Avanzo (INAF-OAB), A. Deich (PSU),
C. Gronwall (PSU), A. Melandri (INAF-OAB), K. L. Page (U Leicester)
and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 05:37:23 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a source in the Galactic plane (trigger=810300).  Swift 
could not immediately slew to the location due to an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 254.545, -42.709 which is 
   RA(J2000) = 16h 58m 11s
   Dec(J2000) = -42d 42' 31"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Due to the duration of the image that
led to the alert (27 minutes), no lightcurve is immediately available. 

Due to an observing constraint, Swift will not slew until T0+46.4
minutes. There will be no XRT or UVOT data until this time. 

Based on the duration of the discovery image (27 minutes) and 
the source's location on the Galactic plane (lat = 0.05, lon = 343.24)
we believe that this is a previously-unknown Galactic transient,
which we name Swift J1658.2-4242 .