[vsnet-grb-info 20834] GRB 180703B: further analysis of CGBM data

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22932
SUBJECT: GRB 180703B: further analysis of CGBM data
DATE:    18/07/09 14:07:10 GMT
FROM:    Takanori Sakamoto at AGU  <tsakamoto at phys.aoyama.ac.jp>

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

Using the CALET Gamma-ray Burst Monitor (CGBM) event data
we report further analysis of the bright, short-duration, soft spectrum
GRB 180703B (Fermi-LAT detection: Racusin et al. GCN Circ. 22884;
CGBM detection: Takahashi et al. GCN Circ. 22888;
Fermi-GBM detection: Poolakkil and Meegan GCN Circ. 22897;
IPN localization: Hurley et al. GCN Circ. 22908;
Konus-Wind observation: Frederiks et al. GCN Circ. 22914).

Using a 16-ms binned light curve of the sum of HXM1 and HXM2 detectors,
the estimated spectral lag for the 25-50 keV to 100-300 keV bands is
43 ± 30 ms (68% CL).  This value is more consistent with lags of long rather
than short GRBs.

We also obtained more precise estimates of T90 and T50 using the SGM 16-ms lc:
1.44 s +- 0.10 s and 0.34 +- 0.06 sec (40-1000 keV), respectively.

The time-averaged spectrum of the burst (measured by the SGM from T0+0.032 sec
to T0+1.856 sec, where T0=22:46:51.183 UTC) is best fit in the 30-1000 keV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.83(-0.32, +0.36) and Ep = 143(-13, +15) keV (chi2 = 62/59 dof).
The resulting fluence in this energy range is 5.98(-0.43, +0.46)x10^-6 erg/cm2.
The quoted errors are at 90% CL.

All the quoted values are preliminary.