Search for GeV Gamma-ray Counterparts of Gravitational Wave Events by CALET

TL;DR

This study used the CALET instrument on the ISS to search for gamma-ray counterparts to several gravitational wave events, setting upper limits on gamma-ray emission and highlighting future detection prospects.

Contribution

First analysis of gamma-ray counterparts to GW events using CALET, providing upper limits and sensitivity estimates for high-energy gamma-ray detection.

Findings

Upper limits on gamma-ray emission from GW events range from 10^{49} to 10^{53} erg s^{-1}.

CALET's sensitivity for transient gamma-ray events is approximately 10^{-7} erg cm^{-2} s^{-1}.

No gamma-ray counterparts were detected in the analyzed GW events.

Abstract

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 $\sim2\pi$ 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.