GCN Circular 36180

S. Dichiara (PSU), J.D. Gropp (PSU), R. Gupta (NASA/GSFC),
F. E. Marshall (NASA/GSFC), M. J. Moss (GSFC),
P. T. O'Brien (U Leicester), M. H. Siegel (PSU) and
M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 12:22:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 240419B (trigger=1223072).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 325.877, +4.234 which is 
   RA(J2000) = 21h 43m 30s
   Dec(J2000) = +04d 14' 01"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex structure lasted 
for ~40 seconds and returned to background before showing three bright pulses at 
~100 seconds for a total duration of 160 seconds.  The peak count rate
was ~2049 counts/sec (15-350 keV), at ~119 sec after the trigger. 

The XRT began observing the field at 12:25:20.7 UT, 148.4 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 325.89615, 4.23548 which
is equivalent to:
   RA(J2000)  = 21h 43m 35.08s
   Dec(J2000) = +04d 14' 07.7"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 68 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 consistent with the Galactic value of 6.84
x 10^20 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 7.01e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 158 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
0.077. 

Burst Advocate for this burst is S. Dichiara (sbd5667 AT psu.edu). 
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/)