GCN Circular 24742

K. L. Page (U Leicester), S. D. Barthelmy (GSFC), J.D. Gropp (PSU),
N. J. Klingler (PSU), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), M. J. Moss (GWU), D. M. Palmer (LANL),
B. Sbarufatti (PSU), M. H. Siegel (PSU), K. K. Simpson (PSU) and
A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 14:57:15 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190604B (trigger=906654).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 297.587, -32.932 which is 
   RA(J2000) = 19h 50m 21s
   Dec(J2000) = -32d 55' 56"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 250 sec, with two major peaks at 
~T0 and ~T+155 s. The peak count rate was ~4000 counts/sec (15-350 keV), 
at ~155 sec after the trigger. 

The XRT began observing the field at 14:59:12.5 UT, 116.8 seconds after
the BAT trigger. Using promptly downlinked data we find a bright, variable
uncatalogued X-ray source located at RA, Dec 297.53804, -32.97663 which
is equivalent to:
   RA(J2000)  = 19h 50m 09.13s
   Dec(J2000) = -32d 58' 35.9"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 218 arcseconds from the BAT onboard position. This position
may be improved as more data are received; the latest position is
available at http://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 1.36
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 0.1 s image was 1.11e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 126 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
0.14. 

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 
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/)