GRB 180923A

W. Maruyama, H. Negoro (Nihon U.), M. Serino (AGU),
M. Nakajima, A. Sakamaki (Nihon U.),
T. Mihara, S. Nakahira, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN),
T. Sakamoto, S. Sugita, Y. Kawakubo, T. Hashimoto, A. Yoshida (AGU),
N. Kawai, M. Sugizaki, Y. Tachibana, K. Morita (Tokyo Tech),
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA),
Y. Ueda, A. Tanimoto, T. Morita, S. Yamada (Kyoto U.),
Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.),
H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.),
M. Yamauchi, K. Hidaka, S. Iwahori (Miyazaki U.),
T. Kawamuro (NAOJ),
K. Yamaoka (Nagoya U.),
M. Shidatsu (Ehime U.) 
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source 
at 2018-09-23T04:08:25 UT .
We obtain the source position at
(R.A., Dec) = (38.304 deg, 6.301 deg) = (02 33 12, +06 18 03) (J2000)
with a rectangular error box with the following corners:
(R.A., Dec) = (37.429, 7.302) deg = (02 29 42, +07 18 07) (J2000)
(R.A., Dec) = (37.165, 6.998) deg = (02 28 39, +06 59 52) (J2000)
(R.A., Dec) = (39.010, 5.456) deg = (02 36 02, +05 27 21) (J2000)
(R.A., Dec) = (39.274, 5.760) deg = (02 37 05, +05 45 35) (J2000) .
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 162 +- 26 mCrab
(4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at UT 02:35
and in the next transit at 05:41 UT with an upper limit of 20 mCrab for each.

V. Lipunov, E. Gorbovskoy, D. Vlasenko, N.Tiurina,
V.Kornilov, A.Kuznetsov, V.Chazov, I.  Gorbunov,
D.Zimnukhov, D.Kuvshinov, P.Balanutsa, V.Vladimirov,
Lomonosov Moscow State University,SAI

A. Tlatov, V.Senik, D. Dormidontov
Kislovodsk Solar Station of the Pulkovo Observatory

D. Buckley,
South African Astronomical Observatory (SAAO)

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias (IAC)

R. Podesta, F. Podesta, C. Lopez, C.Francile
Observatorio Astronomico Felix Aguilar (OAFA)

H.Levato,
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

O. Gres, N.M.Budnev , Yu.Ishmuhametova
Irkutsk State University (ISU)

A. Gabovich, V. Yurkov, Yu. Sergienko
Blagoveschensk Educational State University (BSPU)

MASTER-OAFA robotic telescope (MASTER-Net: http://observ.pereplet.ru, 
Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in 
Argentina (OAFA observatory of San Juan National University) was starting 
survey on the MAXI  GRB180923.17 error-box (ra=02 33 12 dec=+06 18 02 r=1) 
2777 sec after notice time and 7954 sec after trigger time at 2018-09-23 
06:21:04 UT. The 5-sigma upper limit on our first (60s exposure)  set is 
about 17.9 mag

No OT detected.

The galacitc latitude b =  0 deg.

The observations made on zenit distance = 39 deg.The moon (97 % bright
part) is 42 deg. above the horizon. The distance between  moon and  object
is 59
The sun  altitude  is -48.6 deg.
The object can be observed till sunrise at 2018-09-23 10:25:33
  .


The cover map is availavle at 
http://observ.pereplet.ru/images/GRB180923A_cover_map.png

Only for MASTER-team:

The OT candidate available here 
https://200.123.254.238:49004//master2/trans.php?wh=transients.coord2000@%27%3C%2838.3d%2C6.30056d%29%2C2d%3E%27%3A%3Ascircle+and+transients.datetime%3E%3D%272018-09-23+04%3A08%3A30%27&class=9&t2=MAXI+GRB180923.17+optical+counterpart+candidate

The full information about this GRB180923.17 available here 
https://200.123.254.238:49004//master2/grb.php?not=2018-09-23+05%3A34%3A46.484065&sat=MAXI&gcrd=%2838.3d%2C6.30056d%29&eb=1&trig=2018-09-23+04%3A08%3A30&n=GRB180923.17


The message may be cited.

A. V. Penacchioni, A. Yoshida, T. Sakamoto, V. Pal'shin,
S. Sugita, Y. Kawakubo, A. Tezuka, S. Matsukawa, H. Onozawa,
T. Ito, H. Morita, Y. Sone (AGU), K. Yamaoka (Nagoya U),
S. Nakahira (RIKEN), I. Takahashi (IPMU), Y. Asaoka,
S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
W. Ishizaki (ICRR), M. L. Cherry (LSU),
S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena)
and the CALET collaboration:

The MAXI GRB 180923A (Maruyama et al., GCN Circ. 23257
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 ) was detected
in ground analysis of the CALET Gamma-ray Burst Monitor (CGBM) data
near the MAXI/GSC trigger time at T0=04:08:25 UT on 23 September 2018.
The burst signal was seen by all CGBM detectors.

The burst light curve shows a multi-peaked structure which starts
at T-18 sec and ends at T+107 sec.
The T90 and the T50 durations measured by the SGM data are
122 +- 15 sec and 95 +- 58 sec (40-1000 keV), respectively.
The significant emission is seen only below ~100 keV.

The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1221710834/

The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at the Waseda University.

A.Kozlova, S. Golenetskii, R.Aptekar, D. Frederiks,
M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko,
and T. Cline on behalf of the Konus-Wind team, report:

The long-duration GRB 180923A localized by MAXI/GSC (Maruyama et al., GCN
23257
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 ) and observed by CALET (GBM: Penacchioni et al., GCN 23259
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 ) was
detected by Konus-Wind (KW) in the waiting mode.

The burst light curve shows two episodes, started at ~T0(MAXI)-19 s
with a total duration of ~ 127 s.

As observed by KW, the burst had a fluence of
5.42(-0.65,+1.26)x10^-6 erg/cm2 and a 2.944-s peak flux,
measured from ~T0(MAXI)+93.3 s, of 3.47(-0.92,+1.15)x10^-7 erg/cm2/s
(both in the 20 - 1000 keV energy range).

Modeling the KW 3-channel time-integrated spectrum
(from ~T0(MAXI)-18.6 s to ~T0(MAXI)+108 s)
by a simple power-law model yields a power law
index of -2.2(-0.2,+0.2), chi2=0.2/1 dof.

The KW light curve of this burst is available at
http://www.ioffe.rssi.ru/LEA/GRBs/GRB180923A

All the quoted errors are estimated at the 1 sigma confidence level.
All the presented results are preliminary.