[vsnet-grb-info 22048] GRB 190422A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24147
SUBJECT: GRB 190422A: Swift detection of a burst
DATE:    19/04/22 23:15:41 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

M. J. Moss (George Washington University), S. D. Barthelmy (GSFC),
J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU),
N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
M. H. Siegel (PSU) and A. Tohuvavohu (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 22:55:29 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190422A (trigger=899979).  Swift did not slew until ~T+8 min 
due to an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 182.124, -60.238 which is 
   RA(J2000) = 12h 08m 30s
   Dec(J2000) = -60d 14' 15"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of at least 220 sec, where data are currently
available. The peak count rate based on the available data
was ~2000 counts/sec (15-350 keV), at ~175 sec after the trigger. 

The XRT began observing the field at 23:04:18.5 UT, 529.3 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 182.03650, -60.22311 which is
equivalent to:
   RA(J2000)  = 12h 08m 08.76s
   Dec(J2000) = -60d 13' 23.2"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 165 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.  We cannot determine whether the source is
fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (8.59 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 1.1
(+1.25/-0.89) x 10^22 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 531 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 none of
the XRT error circle. 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 mag. No correction has been made for the large, but
uncertain, extinction expected. 

This source lies within the current (Sector 11) field-of-view of TESS camera 2. 

Burst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com). 
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/)