LIGO/Virgo/KAGRA S230518h: No transient candidates in CALET observations

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