TITLE:   GCN CIRCULAR
NUMBER:  29828
SUBJECT: GRB 210419A: Swift detection of a burst
DATE:    21/04/19 07:11:30 GMT
FROM:    Kim Page at U.of Leicester  <klp5@leicester.ac.uk>

S. Laha (GSFC/UMBC/CRESST), E. Ambrosi (INAF-IASFPA),
A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR),
J. A. Kennea (PSU), K. L. Page (U Leicester) and D. M. Palmer (LANL)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 06:53:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210419A (trigger=1044032).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 86.862, -65.539 which is 
   RA(J2000) = 05h 47m 27s
   Dec(J2000) = -65d 32' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual for an image trigger, no
obvious variation is visible in the immediately-available lightcurve. 

The XRT began observing the field at 06:55:49.0 UT, 127.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 86.85414,
-65.50357 which is equivalent to:
   RA(J2000)  = 05h 47m 24.99s
   Dec(J2000) = -65d 30' 12.9"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 128 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
https://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (7.76 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.3
(+3.15/-2.74) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.57e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 136 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 19.6 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 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.075. 

This source lies within the current (Sector 37) field-of-view of TESS camera 4. 

Burst Advocate for this burst is S. Laha (sib.laha 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/)