TITLE:   GCN CIRCULAR
NUMBER:  33872
SUBJECT: LIGO/Virgo/KAGRA S230518h: No transient candidates in CALET observations
DATE:    23/05/25 06:39:10 GMT
FROM:    Yuta Kawakubo at Louisiana State University <kawakubo1@lsu.edu>

A. Yoshida, T. Sakamoto, S. Sugita (AGU), Y. Kawakubo (LSU),
K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR),
S. Torii, Y. Akaike, K. Kobayashi (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 S230518h T0 = 2023-05-18T12:59:08 UT (GCN33813,33816).

No CGBM onboard trigger occurred around the event time. Based on the
update sky map, the summed probabilities inside the CGBM HXM (7 - 3000 keV)
and SGM (40 keV - 28 MeV) fields of view
are 0 % and 65 %, respectively (and 76 % credible regions of the
update sky map was above the horizon).  The HXM and SGM fields of
view were centered at RA = 152 deg, Dec = +50 deg and RA = 161 
deg, Dec = +42 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 (> 7 sigmas) around the trigger time in either the HXM or the SGM data.

The preliminary CGBM analysis is available at

http://cgbm.calet.jp/cgbm_trigger/O4/S230518h

The CALET Calorimeter (CAL) was operating in the high energy trigger
mode at the trigger time of S230518h. Using the CAL data, we 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. There
was no significant overlap with the LVK high probability localization 
region at T0+-60 sec.  The CAL FOV was centered at RA = 161 deg, 
Dec= +42 deg at T0.

The preliminary CGBM analysis for O4 events can be found here:
http://cgbm.calet.jp/cgbm_trigger/O4