Abstract
Abstract We report on the observations of four well-localized binary black hole (BBH) mergers by the High Energy Stereoscopic System (H.E.S.S.) during the second and third observing runs of Advanced LIGO and Advanced Virgo, O2 and O3. H.E.S.S. can observe 20 deg2 of the sky at a time and follows up gravitational-wave (GW) events by “tiling” localization regions to maximize the covered localization probability. During O2 and O3, H.E.S.S. observed large portions of the localization regions, between 35% and 75%, for four BBH mergers (GW170814, GW190512_180714, GW190728_064510, and S200224ca). For these four GW events, we find no significant signal from a pointlike source in any of the observations, and we set upper limits on the very high energy (>100 GeV) γ-ray emission. The 1–10 TeV isotropic luminosity of these GW events is below 1045 erg s−1 at the times of the H.E.S.S. observations, around the level of the low-luminosity GRB 190829A. Assuming no changes are made to how follow-up observations are conducted, H.E.S.S. can expect to observe over 60 GW events per year in the fourth GW observing run, O4, of which eight would be observable with minimal latency.
Highlights
In 2017, the detection of both gravitational waves (GWs) and electromagnetic radiation from the merger of two neutron stars (NSs), GW170817, revolutionized multimessenger astronomy (Abbott et al 2017)
During O2 and O3, H.E.S.S. observed four binary black hole (BBH) mergers: GW170814, GW190512 180714, GW190728 064510, and S200224ca. For these GW events, the delay between merger and H.E.S.S. observation is at least a few hours, due to the necessity of waiting for the part of the sky containing the merger to be at favorable zenith angles above the telescopes
The low rate of sufficiently well-localized GW events in the previous Advanced LIGO and Advanced Virgo runs meant we were unlikely to have observed an event with a favorable time and position
Summary
In 2017, the detection of both gravitational waves (GWs) and electromagnetic radiation from the merger of two neutron stars (NSs), GW170817, revolutionized multimessenger astronomy (Abbott et al 2017). The electromagnetic radiation was observed as a short set of flashes of low-energy γ-rays, which is commonly referred to as a short gamma-ray burst (GRB). This single event solved a decades-old mystery of high-energy astrophysics by confirming that some short GRBs are produced by the merger of two compact objects, with at least one being an NS. In either GRB progenitor scenario, the catastrophic event launches an ultrarelativistic jet. Interactions within the jet produce the highly variable prompt emission, while the jet’s later
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