Nine years of gamma-ray burst observations with the CALET Gamma-ray Burst Monitor

The CALorimetric Electron Telescope (CALET), a scientific payload for cosmic-ray observations on the International Space Station, contributes instantaneous sky coverage in X-rays and gamma-rays for gamma-ray burst (GRB) observations. The CALET Gamma-ray Burst Monitor (CGBM), the secondary scientific instrument of CALET, can observe GRB prompt emissions in the energy range from 7 keV to 20 MeV. CGBM has operated without serious issues for over 9 years since the observation started in October 2015. As of April 2025, CGBM has been triggered 384 times by GRBs out of a total of 1,888 triggers. If we consider a threshold duration of 2 seconds, 51 of the CGBM GRBs were classified as short GRBs. As a result of spectral analysis for nine short GRBs, we found that CGBM detected short GRBs, of which Epeak is comparable to that of GRB 170817A, the only case of a GRB associated with a binary neutron star merger. Although it depends on the spectra of GRBs, the CGBM requires fluxes that are at least a few times higher than that of GRB 170817A for detection and several times higher for spectral analysis in order to ensure sufficient statistics. We also have searched for electromagnetic counterparts of gravitational waves (GWs) reported by LIGO/Virgo/KAGRA. Although 208 GW events have been reported in O4 as of the end of April 2025, there were no significant signals associated with any GW events in O4 in the CGBM data.