[vsnet-grb-info 21918] Swift Trigger 895257: Detection of GRO J2058+42 in outburst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24017
SUBJECT: Swift Trigger 895257: Detection of GRO J2058+42 in outburst
DATE:    19/03/27 09:19:51 GMT
FROM:    Kim Page at U.of Leicester  <klp5 at leicester.ac.uk>

A. Y. Lien (GSFC/UMBC) and K. L. Page (U Leicester) report on behalf
of the Neil Gehrels Swift Observatory Team:

At 09:00:17 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRO J2058+42 (trigger=895257).  Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 314.698, +41.822 which is 
   RA(J2000) = 20h 58m 47s
   Dec(J2000) = +41d 49' 20"
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 09:02:24.7 UT, 127.3 seconds after
the BAT trigger. XRT found a bright X-ray source located at RA, Dec
314.6953, 41.7772 which is equivalent to:
   RA(J2000)  = 20h 58m 46.87s
   Dec(J2000) = +41d 46' 37.9"
with an uncertainty of 5.9 arcseconds (radius, 90% containment). This
location is 161 arcseconds from the BAT onboard position, within the
BAT error circle. This position is 4.8 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 event data are yet available to
determine the column density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 7.09e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
131 seconds after the BAT trigger. No credible afterglow candidate has been
found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the
XRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. The
8'x8' region for the list of sources generated on-board covers 100% of the XRT
error circle. The list of sources is typically complete to about 18.0 mag. 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). 
The BAT transient monitor of this source shows it to be in outburst:
https://swift.gsfc.nasa.gov/results/transients/weak/GROJ2058p42/