GRB 180523A

A. Tezuka, A. Yoshida, T. Sakamoto, V. Pal'shin, Y. Kawakubo,
S. Matsukawa, H. Onozawa (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),
A. V. Penacchioni, P. S. Marrocchesi (U of Siena)
and the CALET collaboration:

The long-duration, bright GRB 180523A (INTEGRAL SPI-ACS trigger #8063)
triggered the CALET Gamma-ray Burst Monitor (CGBM) at 18:20:26.844 UTC
on 23 May 2018. The burst signal was seen by all CGBM detectors.

The burst light curve shows a bright, multi-peaked pulse which
starts at T+1.3 sec, peaks at T+18.5 sec and ends at ~T+37.3 sec,
followed by a very weak pulse seen from ~T+88 sec to ~T+109 sec.
The T90 and the T50 durations measured by the SGM data are
50.0 +- 35.6 sec and 9.9 +- 0.8 sec (40-1000 keV), respectively.

The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1211134810/

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

K. Hurley, on behalf of the IPN,

I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin,
on behalf of the HEND-Odyssey GRB team,

A. Kozlova, S. Golenetskii, R. Aptekar, D. Frederiks, D.Svinkin,
and T. Cline on behalf of the Konus-Wind team,

A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo,
and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,

S. Barthelmy, J. Cummings, H. Krimm, and D. Palmer,
on behalf of the Swift-BAT team, and

W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr,
on behalf of the GRS-Odyssey GRB team, report:

The long-duration GRB 180523A (CGBM detection: Tezuka et al., GCN Circ. 
22738
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was detected by Konus-Wind, INTEGRAL (SPI-ACS), Mars-Odyssey (HEND), 
CALET (CGBM),
and Swift(BAT) at about 66029 s UT (18:20:29).
The burst was outside the coded field of view of the BAT.

We have triangulated it to a preliminary, 3 sigma error box whose 
coordinates are:
---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
    96.875 (06h 27m 30s) +45.896 (+45d 53' 45")
  Corners:
    94.906 (06h 19m 37s) +45.533 (+45d 31' 58")
    97.577 (06h 30m 18s) +47.934 (+47d 56' 02")
    98.890 (06h 35m 34s) +46.191 (+46d 11' 26")
    96.260 (06h 25m 02s) +43.715 (+43d 42' 53")
  ---------------------------------------------
The error box area is 5.54 sq. deg, and its maximum
dimension is 4.3 deg (the minimum one is 1.8 deg).
The Sun distance was 37 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB180523_T66028/IPN/

The Konus-Wind time history and spectrum will be given in a forthcoming
GCN Circular.

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 180523A
(IPN Triangulation: Hurley et al., GCN Circ. 22740
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triggered Konus-Wind at T0=66028.802 s UT (18:20:28.802).

The burst light curve shows a bright main pulse lasting about 35 s,
which is followed by a fainter second episode which
started at ~T0+87.4 s and lasted up to ~T0+87.9 s.
The emission in the main pulse is seen up to ~2 MeV.

As observed by Konus-Wind, the burst
had a fluence of 1.06(-0.08,+0.08)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+12.368 s,
of 1.11(-0.22,+0.22)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the main episode
(measured from T0 to T0+36.608 s)
is best fit in the 20 keV - 2 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.69(-0.06,+0.07),
the high energy photon index beta = -2.68(-0.30,+0.19),
the peak energy Ep = 307(-17,+18) keV
(chi2 = 49/61 dof).

The spectrum near the maximum count rate
(measured from T0+12.288 to T0+14.080 s)
is best fit in the 20 keV - 2 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.51(-0.14,+0.16),
the high energy photon index beta = -2.66(-0.89,+0.29),
the peak energy Ep = 325(-39,+49) keV
(chi2 = 53/55 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180523_T66028/

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.