We present results on searches for gamma-ray counterparts of the LIGO/Virgo gravitational-wave events using CALorimetric Electron Telescope ({sl CALET}) observations. The main instrument of {sl CALET}, CALorimeter (CAL), observes gamma-rays from $sim1$ GeV up to 10 TeV with a field of view of nearly 2 sr. In addition, the {sl CALET} gamma-ray burst monitor (CGBM) views $sim$3 sr and $sim2pi$ sr of the sky in the 7 keV -- 1 MeV and the 40 keV -- 20 MeV bands, respectively, by using two different crystal scintillators. The {sl CALET} observations on the International Space Station started in October 2015, and here we report analyses of events associated with the following gravitational wave events: GW151226, GW170104, GW170608, GW170814 and GW170817. Although only upper limits on gamma-ray emission are obtained, they correspond to a luminosity of $10^{49}sim10^{53}$ erg s$^{-1}$ in the GeV energy band depending on the distance and the assumed time duration of each event, which is approximately the order of luminosity of typical short gamma-ray bursts. This implies there will be a favorable opportunity to detect high-energy gamma-ray emission in further observations if additional gravitational wave events with favorable geometry will occur within our field-of-view. We also show the sensitivity of {sl CALET} for gamma-ray transient events which is the order of $10^{-7}$~erg,cm$^{-2}$,s$^{-1}$ for an observation of 100~s duration.
تحميل البحث