GRB 190718A

V. D'Elia (SSDC), E. Ambrosi (INAF-IASFPA), A. D'Ai (INAF-IASFPA),
N. J. Klingler (PSU), D. M. Palmer (LANL) and A. Tohuvavohu (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 04:41:15 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190718A (trigger=915091).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 336.531, -41.221 which is 
   RA(J2000) = 22h 26m 07s
   Dec(J2000) = -41d 13' 13"
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 ~1700 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 04:42:21.5 UT, 66.4 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 336.57614, -41.20264 which is
equivalent to:
   RA(J2000)  = 22h 26m 18.27s
   Dec(J2000) = -41d 12' 09.5"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 138 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.24 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.3
(+2.81/-2.43) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 69 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 expected
extinction corresponding to E(B-V) of 0.01. 

Burst Advocate for this burst is V. D'Elia (delia AT ssdc.asi.it). 
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/)

P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 1160 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 190718A, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 336.57610, -41.20446 which is equivalent
to:

RA (J2000): 22h 26m 18.26s
Dec (J2000): -41d 12' 16.1"

with an uncertainty of 1.7 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

Martin Jelinek, Jan Strobl (ASU CAS Ondrejov, CZ),
Martin Masek, Petr Janecek, Sergey Karpov, Jakub Jurysek,
Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza
(Institute of Physics, Prague, CZ)

report:

The 30cm robotic telescope FRAM-Auger in Malargue
(Argentina) reacted robotically to the Swift/BAT alert
of GRB190718A (D'Elia et al., GCNC 25082), starting
with a series of 20s unfiltered images at 04:45:11 UT,
i.e. 236s post trigger.

We do not detect any new source at or around the
reported X-ray errorbox reported by Evans et al. (GCN
25084
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 ) at single frames or a combined 20 x 20s image
taken between 236s and 1123s after the initial trigger.
The combined exposure  has a limiting magnitude r'(AB)
= 18.0, as calibrated against the APASS Catalogue.

S. R. Oates (U.Warwick) and V. D'Elia (SSDC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 190718A
70 s after the BAT trigger (D'Elia et al., GCN Circ. 25082
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 ).
No optical afterglow consistent with the XRT position
(Evans et al., GCN Circ. 25084
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 ) is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC            70          219          147         >20.9
u_FC               282          532          246         >20.0
white               70         1184          353         >21.0
v                  612         1061           78         >18.3
b                  538         1159           58         >19.1
u                  282         4874          307         >20.0
w1                 661         4847          235         >19.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.01 in the direction of the burst
(Schlegel et al. 1998).

B. Sbarufatti (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), P.A. Evans (U. Leicester), P. D'Avanzo (INAF-OAB), M.G.
Bernardini (INAF-OAB), E. Ambrosi  (INAF-IASFPA) , D.N. Burrows (PSU),
J. D. Gropp (PSU) and V. D'Elia report on behalf of the Swift-XRT team:

We have analysed 6.4 ks of XRT data for GRB 190718A (D'Elia et al. GCN
Circ. 25082
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 ), from 70 s to 41.2 ks after the  BAT trigger. The data
comprise 349 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN Circ. 25084
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 ).

The late-time light curve (from T0+4.6 ks) can be modelled with a
power-law decay with a decay index of alpha=1.03 (+0.18, -0.17).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.64 (+0.15, -0.14). The
best-fitting absorption column is  7.0 (+4.2, -3.8) x 10^20 cm^-2, in
excess of the Galactic value of 1.2 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.0 x 10^-11 (4.4 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.0 (+4.2, -3.8) x 10^20 cm^-2
Galactic foreground: 1.2 x 10^20 cm^-2
Excess significance: 2.5 sigma
Photon index:	     1.64 (+0.15, -0.14)

If the light curve continues to decay with a power-law decay index of
1.03, the count rate at T+24 hours will be 0.011 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x
10^-13 (5.0 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00915091.

This circular is an official product of the Swift-XRT team.

D. M. Palmer (LANL), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), V. D'Elia (SSDC),
H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-239 to T+963 sec from the recent telemetry
downlink,
we report further analysis of BAT GRB 190718A (trigger #915091)
(D'Elia et al., GCN Circ. 25082
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 ).  The BAT ground-calculated position is
RA, Dec = 336.605, -41.184 deg which is
   RA(J2000)  =  22h 26m 25.2s
   Dec(J2000) = -41d 11' 02.7"
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The mask-weighted light curve shows a main multi-peaked structure
that starts at ~ T0 and ends at ~T+17 s. In addition, there is a weak
pulse at ~T+700 s, which is at the same time as the large flare seen
by the XRT. T90 (15-350 keV) is 720.0 +- 35.8 sec (estimated error
including systematics).

The time-averaged spectrum from T+0.1 to T+17.1 sec (i.e., the duration
of the main emission) is best fit by a simple power-law model.  The power
law
index of the time-averaged spectrum is 1.38 +- 0.26.  The fluence in the
15-150 keV band is 3.6 +- 0.6 x 10^-7 erg/cm2. The spectral analysis for
the total burst duration from ~T0 to ~T+720 s does not produce reasonable
fits due to the large quiescent period from ~T+17 s to ~T+700 s.
The 1-sec peak photon flux measured from T+0.08 sec in the 15-150 keV band
is 1.0 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/915091/BA/