TITLE: GCN CIRCULAR NUMBER: 16413 SUBJECT: Swift-BAT trigger 601928: Detection of a possible outburst from V490 Cep DATE: 14/06/17 07:34:51 GMT FROM: Phil Evans at U of Leicester P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 06:37:31 UT, the Swift Burst Alert Telescope (BAT) triggered on a possible source (trigger=601928). Swift slewed immediately to the event. The BAT on-board calculated location is RA, Dec 324.790, +56.953 which is RA(J2000) = 21h 39m 10s Dec(J2000) = +56d 57' 12" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This is a very long image trigger with duration of 1088 s. As is usual with an image trigger, the available BAT light curve shows no significant structure. The XRT began observing the field at 06:59:41.9 UT, 1330.1 seconds after the BAT trigger. XRT found a bright X-ray source located at RA, Dec 324.8792, 56.9866 which is equivalent to: RA(J2000) = +21h 39m 31.01s Dec(J2000) = +56d 59' 11.8" with an uncertainty of 6.1 arcseconds (radius, 90% containment). This location is 212 arcseconds from the BAT onboard position. This position is 3.0 arcseconds from V490 Cep, a high mass X-ray binary, however it is more than 2-sigma away from the BAT position, and so possibly unrelated to the trigger. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 6.00e-10 erg cm^-2 s^-1 (0.2-10 keV). Because XRT centroided on the high mass X-ray binary V490 Cep, it is likely that this object is in outburst, and it is this which triggered the BAT. However we cannot rule out the possibility that BAT triggered on a GRB coincidentally close to V490 Cep on the sky. Burst Advocate for this burst is P. A. Evans (pae9 AT star.le.ac.uk). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)