TITLE:   GCN CIRCULAR
NUMBER:  22020
SUBJECT: Trigger 779351: Swift detection of Swift J0243.6+6124
DATE:    17/10/16 08:25:52 GMT
FROM:    Kim Page at U.of Leicester  <klp5@leicester.ac.uk>

A. P. Beardmore (U Leicester), A. A. Breeveld (UCL-MSSL),
J.D. Gropp (PSU), K. L. Page (U Leicester), T. Sakamoto (AGU) and
B. Sbarufatti (PSU) report on behalf of the Swift Team:

At 07:53:29 UT, the Swift Burst Alert Telescope (BAT) triggered and
located Swift J0243.6+6124 (trigger=779351).  Swift slewed immediately to the 
location. The BAT on-board calculated location is RA, Dec 40.908, +61.433 
which is 
   RA(J2000) = 02h 43m 38s
   Dec(J2000) = +61d 25' 59"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty). The light-curve shows the known 9.86 s periodicity, 
as was noted in GCN 22017. 

The XRT began observing the field at 07:54:27.1 UT, 57.6 seconds after
the BAT trigger. XRT found a bright X-ray source located
at RA, Dec 40.9175, 61.4328 which is equivalent to:
   RA(J2000)  = +02h 43m 40.20s
   Dec(J2000) = +61d 25' 58.1"
with an uncertainty of 5.6 arcseconds (radius, 90% containment), 
consistent with the location of Swift J0243.6+6124. No event data are 
yet available to determine the column density using X-ray spectroscopy. 
The XRT light-curve also shows the 9.86 s periodicity. 

Swift J0243.6+6124 was first detected by Swift/BAT on October 3, 2017
(GCN 21960; ATel 10809). It has since been brightening in the
gamma-rays. The daily light curve from the BAT transient monitor is
available at
https://swift.gsfc.nasa.gov/results/transients/weak/SwiftJ0243.6p6124/