TITLE:   GCN CIRCULAR
NUMBER:  25830
SUBJECT: LIGO/Virgo S190923y: Upper limits from CALET observations.
DATE:    19/09/24 03:19:03 GMT
FROM:    Yuta Kawakubo at Louisiana State U./CALET  <kawakubo1@lsu.edu>

A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU), 
Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN),
Y. Asaoka, S. Torii (Waseda U), Y. Shimizu, 
T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), 
M. L. Cherry (LSU), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:


The CALET Gamma-ray Burst Monitor (CGBM) was operating at the
trigger time of S190923y T0 = 2019-09-23 12:55:59.646 UT (The
LIGO Scientific Collaboration and Virgo Collaboration, GCN Circ.
25814).

No CGBM on-board trigger occurred around the event time.  Based
on the LIGO-Virgo localization sky map, the summed LIGO probabilities 
inside the CGBM HXM (7 - 3000 keV) and SGM (40 keV - 28 MeV) fields 
of view are 40 % and 55 %, respectively (and 68 % credible region 
of the initial sky map was above the horizon).  The HXM and  SGM 
fields of view were centered at RA = 62.7 deg, Dec = 4.2 deg and 
RA = 55.3 deg, Dec = -2.5 deg at T0, respectively.

Based on the analysis of the light curve data with 0.125 sec time 
resolution from T0-60 sec to T0+60 sec, we found no significant 
excess around the trigger time in either the HXM or the SGM data.

The CALET Calorimeter (CAL) was operating in the high energy trigger
mode at the trigger time of S190923y. Using the CAL data, we have 
searched for gamma-ray events in the 10-100 GeV band from -60 sec 
to +60 sec from the GW trigger time and found no candidates in the 
overwrap region with the LIGO-Virgo high probability localization
region.  The 90% upper limit of CAL is 1.2x10^-5 erg/cm^2/s 
(10-100 GeV) when the summed LIGO-Virgo probability reaches 10%.
The CAL FOV was centered at RA= 55.3 deg, DEC= -2.5 deg at T0.