TITLE:   GCN CIRCULAR
NUMBER:  24021
SUBJECT: Swift Trigger 895479: Detection of GRO J2058+42
DATE:    19/03/27 21:49:05 GMT
FROM:    Kim Page at U.of Leicester  <klp5@leicester.ac.uk>

J. A. Kennea (PSU), N. J. Klingler (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester) and
B. Sbarufatti (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 21:27:45 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRO J2058+42 (trigger=895479).  Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 314.705, +41.745 which is 
   RA(J2000) = 20h 58m 49s
   Dec(J2000) = +41d 44' 41"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual with an image trigger, the available
BAT light curve shows no significant structure. 

The XRT began observing the field at 21:30:58.4 UT, 193.0 seconds after
the BAT trigger. Using promptly downlinked data we find an X-ray source
with an enhanced position: RA, Dec 314.6977, 41.7766 which is
equivalent to:
   RA(J2000)  = 20h 58m 47.44s
   Dec(J2000) = +41d 46' 35.6"
with an uncertainty of 2.5 arcseconds (radius, 90% containment). This
location is 115 arcseconds from the BAT onboard position, within 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 2.3 arcseconds from a
known X-ray source: 1SXPS J205847.2+414637. This source is in the Swift
XRT 1SXPS catalogue with a mean 0.3-10 keV count-rate of 1.350 +/-
0.043 ct/sec; see http://www.swift.ac.uk/1SXPS/1SXPSJ205847.2%2B414637
for details of these previous observations. No spectrum from the
promptly downlinked event data is yet available to determine the column
density. 

UVOT took a finding chart exposure of 250 seconds with the U filter
starting  193 seconds after the BAT trigger. UVOT detects a 16th mag
source consistent with the XRT position. No  correction has been made
for the large, but uncertain, extinction expected. 

Swift-BAT previously triggered on this source on 2019 March 22 (GCN Circ. 23985)
and earlier today on 2019 March 27 (GCN Circ. 24017)

The BAT transient monitor of this source shows the source to be in outburst: 
https://swift.gsfc.nasa.gov/results/transients/weak/GROJ2058p42/