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GCN Circular 33872

LIGO/Virgo/KAGRA S230518h: No transient candidates in CALET observations
2023-05-25T06:39:10Z (14 days ago)
Yuta Kawakubo at Louisiana State University <>
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 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:
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