GCN Circular 24553

M. J. Moss (George Washington University), C. Gronwall (PSU),
J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU),
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 16:04:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190515B (trigger=903845).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 98.840, +52.295 which is 
   RA(J2000) = 06h 35m 22s
   Dec(J2000) = +52d 17' 41"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 20 sec.  The peak count rate
was ~800 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 16:05:43.7 UT, 82.4 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 98.84892, 52.31725 which
is equivalent to:
   RA(J2000)  = 06h 35m 23.74s
   Dec(J2000) = +52d 19' 02.1"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 82 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 consistent with the Galactic value of 1.27
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 7.78e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 92 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 84% 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
0.09. 

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/)

[GCNOPS NOTE(15may19): Per author's request, the GRB name "190515A" was changed
to "190515B" in the Subject lines in the first paragraph.]