GRB 190823A

V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), A.
Tohuvavohu (U Toronto), J.A. Kennea (PSU), B. Sbarufatti (PSU), A.P.
Beardmore (U. Leicester), J.P. Osborne (U. Leicester) and P.A. Evans
(U. Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has performed further observations of the MAXI-detected burst
GRB 190823A (Iwakiri et al. GCN Circ. 25456
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 ).
The observations now extend from T0+12.3 ks and T0+1148.9 ks with a 
total exposure time of 4.1 ks in Photon Counting (PC) mode.

The source previously reported by Ambrosi et al. (GCN Circ. 25476
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 ) is
fading with 3-sigma significance, and is therefore likely the GRB
afterglow.
Using 147 s of PC mode data and 1 UVOT image, we find an enhanced XRT
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 279.68735, -43.52789 which is
equivalent to:

RA (J2000): 18h 38m 44.97s
Dec(J2000): -43d 31' 40.4"

with an uncertainty of 8.7 arcsec (radius, 90% confidence). This
position is 18.6 arcmin from the MAXI position.  The source is fading
with alpha >0.7.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020932.
The results of the full analysis of the tiled XRT observations are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00085.

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

R. Gaikwad, M. Chavan, V. Sharma and D. Bhattacharya and A. Vibhute (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data showed the detection of a GRB 190823A, which was also detected by Swift-XRT (E. Ambrosi et al., GCN #25476
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 ) and Tiled Swift observations (Evans P. A. et al., GCN #25459
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 ).

The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple pulses of emission with the strongest peak at 2019-08-23 13:30:05.0 UT. The measured peak count rate associated with the burst is 287 cts/s above the background in the combined data of four quadrants, with a total of 1445 cts. The local mean background count rate was 460 cts/s. Using cumulative rates, we measure a T90 of 7.3 s.

It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.

CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.

E. Ambrosi (INAF-IASFPA), A. DAi (INAF-IASFPA) and V. D Elia (ASDC)

report on behalf of the Swift-XRT team:


Swift-XRT has performed follow-up observations of the MAXI-detected

burst GRB 190823A (Iwakiri et al. GCN circ. 25456
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 ) in a series of

observations tiled on the sky.

Total exposure time is 1.8 ks, distributed over 7 tiles. The data were
collected

between T0+12.1 ks and T0+18 ks.


One uncatalogued X-ray source has been detected, with the following details:


RA (J2000.0):      279.68736d = 18:38:44.97

Dec (J2000.0):    -43.52789d = -43:31:40.4

Error: 8.6 arcsec (radius, 90% conf.)

Count-rate:   4.1 (+1.7, -1.3) ��10^-2 ct s^ -1

Distance: 18.6 arcmin from MAXI position


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_GRB00085/ .


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

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 190823A. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00085

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.

W. Iwakiri(Chuo U.), M. Serino(AGU), 
H. Negoro, M. Nakajima, W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.), 
T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN), 
T. Sakamoto,  S. Sugita, H. Nishida, A. Yoshida (AGU), 
Y. Tsuboi,  R. Sasaki, H. Kawai, T. Sato (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 a bright uncatalogued X-ray transient source 
at 13:30:22 UT on 2019 August 23.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (279.278 deg, -43.439 deg) = (18 37 06, -43 26 19) (J2000)
with a 90% C.L. statistical error of 0.17 deg and an additional systematic uncertainty 
of 0.1 deg (90% containment radius).

Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(R.A., Dec) = (280.193, -43.737) deg = (18 40 46, -43 44 13) (J2000)
(R.A., Dec) = (280.285, -43.434) deg = (18 41 08, -43 26 02) (J2000)
(R.A., Dec) = (278.903, -43.205) deg = (18 35 36, -43 12 17) (J2000)
(R.A., Dec) = (278.804, -43.508) deg = (18 35 12, -43 30 28) (J2000) 

The X-ray flux averaged over the scan was 322 +- 29 mCrab
(4.0-10.0keV, 1 sigma error).

There was no significant excess flux in the previous transit at UT 11:57
with an upper limit of 20 mCrab.