GRB 180116A

Y. Shimizu (Kanagawa U), A. Yoshida, T. Sakamoto, V. Pal'shin, Y. Kawakubo,
M. Moriyama, Y. Yamada, A. Tezuka, S. Matsukawa (AGU), K. Yamaoka (Nagoya U),
S. Nakahira (RIKEN), I. Takahashi (IPMU), Y. Asaoka, S. Ozawa, S. Torii (Waseda U),
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, soft and weak GRB 180116A (Kawai et al., GCN circ. 22347
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 ;
Stanbro et al., GCN circ. 22356
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 ) was detected by the CALET Gamma-ray Burst
Monitor (CGBM) in the survey mode.  The burst signal is only seen below 100 keV
in all CGBM instruments, confirming its soft nature.

The light curve of the HXM shows several overlapping pulses.  The emission
starts at T-5 sec, peaks at T+11 sec and ends at T+47 sec, where T0 is the
Fermi-GBM trigger time at 00:36:52.81 UT.  The T90 and the T50 durations
measured by the combined HXM data (HXM1+HXM2) are 46 +- 10 sec and
27 +- 10 sec (10-300 keV), respectively.

The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1200098002/

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

M. Stanbro and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 00:36:52.81 UT on 16 January 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180116A (trigger 537755817 / 180116026)
which was also detected by the MAXI/GSC (H. Kawai et al. 2018, GCN 22347
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 ).
The GBM on-ground location is consistent with the MAXI/GSC position.

The angle from the Fermi LAT boresight at the GBM trigger time is 39
degrees.

The GBM light curve consists of several episodes
with a duration (T90) of about 60 s (50-300 keV).
The time-averaged spectrum from T0-3.07 s to T0+58.37 s is
best fit by a simple power law function with index -1.72 +/- 0.05.

The event fluence (10-1000 keV) in this time interval is
(3.54 +/- 0.28)E-06  erg/cm^2. The 1-sec peak photon flux measured
starting from T0-1.47 s in the 10-1000 keV band
is 1.98 +/- 0.24 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

H. Kawai (Chuo U.), H. Negoro (Nihon U.), M. Serino (AGU), S. Nakahira (RIKEN),
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA),
T. Mihara, M. Sugizaki, W. Iwakiri, M. Shidatsu, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN),
N. Kawai, S. Sugita, T. Yoshii, Y. Tachibana, S. Harita, Y. Muraki, K. Morita (Tokyo Tech),
A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU),
H. Tsunemi, T. Yoneyama (Osaka U.),
M. Nakajima, T. Kawase, A. Sakamaki (Nihon U.),
Y. Ueda, T. Hori, A. Tanimoto, S. Oda, T. Morita, S. Yamada (Kyoto U.),
Y. Tsuboi, Y. Nakamura, R. Sasaki, T. Sato (Chuo U.),
M. Yamauchi, C. Hanyu, K, Hidaka (Miyazaki U.),
T. Kawamuro (NAOJ),
K. Yamaoka (Nagoya U.)

report on behalf of the MAXI team:
The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient 
source at 00:37:30 UT on 16 January 2018.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (215.655 deg, 18.959 deg) = (14 22 37, +18 57 32) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.13 deg and 0.11 deg, respectively.
The roll angle of long axis from the north direction is 158.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 609 +- 65 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) = (214.873, 19.864) deg = (14 19 29, +19 51 48) (J2000)
(R.A., Dec) = (214.781, 19.788) deg = (14 19 07, +19 47 16) (J2000)
(R.A., Dec) = (216.314, 18.226) deg = (14 25 15, +18 13 31) (J2000)
(R.A., Dec) = (216.405, 18.300) deg = (14 25 37, +18 18 01) (J2000)
There was no significant excess flux in the previous transit at UT 23:04
with an upper limit of 20 mCrab.