[vsnet-grb-info 13059] Trigger 553930: Swift detection of a possible flare from HR 5110

[GCN Circulars]

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  <krimm at milkyway.gsfc.nasa.gov>

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.