GRB 190804B

T. Sato (Chuo U.), H. Negoro, M. Nakajima, W. Maruyama, M. Aoki, 
K. Kobayashi (Nihon U.), T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN), 
T. Sakamoto, M. Serino, S. Sugita, H. Nishida, A. Yoshida (AGU), 
Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai (Chuo U.),  M. Shidatsu (Ehime U.),
N. Kawai, M. Sugizaki, M. Oeda, K. Shiraishi (Tokyo Tech), S. Nakahira, Y. Sugawara, 
S. Ueno, H. Tomida, M. Ishikawa, N.Isobe, R. Shimomukai, M. Tominaga (JAXA), 
Y. Ueda, A. Tanimoto, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake (Kyoto U.), 
H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), 
M. Yamauchi, S. Iwahori, Y. Kurihara, K. Kurogi, K. Miike (Miyazaki U.), 
T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU)
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered on an uncatalogued X-ray transient source at 
07:58:15 UT on  2019 August 04.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (239.895 deg, -44.773 deg) = (15 59 34, -44 46 22) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.29 deg and 0.24 deg, respectively. 
The roll angle of the long axis from the north direction is 39.0 deg counterclockwise. 
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 118 +- 21 mCrab
(4.0-10.0keV, 1 sigma error).

Without assumptions on the source constancy,we obtain a rectangular error
box for the transient source with the following corners:
(R.A., Dec) = (240.071, -43.705) deg = (16 00 17, -43 42 17) (J2000)
(R.A., Dec) = (239.431, -43.730) deg = (15 57 43, -43 43 47) (J2000)
(R.A., Dec) = (239.594, -45.994) deg = (15 58 22, -45 59 38) (J2000)
(R.A., Dec) = (240.259, -45.968) deg = (16 01 02, -45 58 04) (J2000)
There was no significant excess flux in the previous transit at 06:25 UT, 
and in the next transit at 09:30 UT with an upper limit of 20 mCrab for each.

P. A. Evans (U. Leicester) reports on behalf of the Swift team:

Swift has initiated a series of observations, tiled on the sky, of the
MAXI GRB 190804B. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00082

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. The probability of finding
serendipitous sources, unrelated to the MAXI event is high: any X-ray source
considered to be a probable afterglow candidate will be reported via a GCN Circular
after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

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

J.P. Osborne (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (ASDC),
V. D'Elia (ASDC), A. Tohuvavohu (PSU), J.A. Kennea (PSU), B. Sbarufatti
(PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A.
Evans (U. Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the MAXI-detected
burst GRB 190804B (Sato et al. GCN Circ. 25262
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 ) in a series of
observations tiled on the sky. The total exposure time is 1.3 ks,
distributed over 7 tiles; the maximum exposure at a single sky location
was 395 s. The data were collected between T0+37.2 ks and T0+38.6 ks,
and are entirely in Photon Counting (PC) mode. 

Two uncatalogued X-ray sources have been detected, however none of them
is above the RASS limit or shows definitive signs of fading. Therefore,
at the present time we cannot identify which, if any, is the afterglow.
Details of these sources are given below:

Source 1:
  RA (J2000.0):  239.7568  =  15:59:1.62
  Dec (J2000.0): -44.6361  =  -44:38:09.8
  Error: 4.1 arcsec (radius, 90% conf. [Enhanced position])
  Count-rate: 0.031 [+0.014, -0.011] ct s^-1   
  Distance: 606 arcsec from MAXI position.
  Flux: (1.38 [+0.60, -0.46])e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 2:
  RA (J2000.0):  240.0251  =  16:00:6.02
  Dec (J2000.0): -44.7816  =  -44:46:53.9
  Error: 3.9 arcsec (radius, 90% conf. [Enhanced position])
  Count-rate: 0.113 [+0.038, -0.031] ct s^-1   
  Distance: 333 arcsec from MAXI position.
  Flux: (5.1 [+1.7, -1.4])e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV)

The results of the XRT-team automatic analysis of the tiled XRT
observations, including a position-specific upper limit calculator, are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00082.

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

J.P. Osborne (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (ASDC),
V. D'Elia (ASDC), A. Tohuvavohu (PSU), J.A. Kennea (PSU), B. Sbarufatti
(PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A.
Evans (U. Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has conducted further observations of the field of the
MAXI-detected burst GRB 190804B (Sato et al. GCN Circ. 25262
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 ). The
observations now extend from T0+37.2 ks to T0+273.4 ks. 

Of the sources reported by Osborne et al. (GCN Circ. 25273
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 ), "Source 2"
has faded from 1.1e-01 count/s to 1.1e-03 count/s between observations
and is	believed to be the afterglow.  The position of this source
(astrometrically enhanced by using the XRT-UVOT alignment and matching
UVOT field sources to the USNO-B1 catalogue) is RA, Dec=240.0251,
-44.7816 which is equivalent to:

RA (J2000): 16:00:6.02
Dec(J2000): -44:46:53.9

with an uncertainty of 3.8 arcsec (radius, 90% confidence). Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and
Evans et al. (2009, MNRAS, 397, 177). This position is 5.6 arcmin from
the MAXI position.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020916.
The results of the full analysis of the tiled XRT observations are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00082.

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