TITLE: GCN CIRCULAR NUMBER: 14396 SUBJECT: Trigger 553930: Swift detection of a possible flare from HR 5110 DATE: 13/04/19 17:54:44 GMT FROM: Hans Krimm at NASA-GSFC W. H. Baumgartner (GSFC/UMBC), M. M. Chester (PSU), S. T. Holland (STScI), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 17:24:37 UT, the Swift Burst Alert Telescope (BAT) triggered and located a possible trigger from the RS CVn flare star HR 5110 (trigger=553930). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 203.650, +37.239 which is RA(J2000) = 13h 34m 36s Dec(J2000) = +37d 14' 20" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is usual with an image trigger, the BAT light curve does not show any significant features. The XRT began observing the field at 17:26:43.4 UT, 125.9 seconds after the BAT trigger. Using promptly downlinked data we find an X-ray source located at RA, Dec 203.70026, 37.18112 which is equivalent to: RA(J2000) = 13h 34m 48.06s Dec(J2000) = +37d 10' 52.0" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 253 arcseconds from the BAT onboard position, outside the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. This position is 5.5 arcseconds from that of HR 5110. We note that the XRT data are highly affected by optical loading from the star, and therefore we cannot determine at this time if there is any enhanced X-ray emission detected from this source. UVOT took a finding chart exposure of 250 seconds with the UVW2 filter starting 123 seconds after the BAT trigger. No new source is detected in the initial data products. Analysis of the UVOT data is complicated by the presence of the 5th magnitude star HR 5110. Since this was a low-significance (6.0 sigma) image trigger, it is not possible to tell from the rapidly available BAT data whether or not this is a real event. Further information will be available once the full BAT data is available.