Ultrahigh-Energy Gamma-ray Emission Associated with Black Hole-Jet Systems

Abstract: Black holes (BH), one of the most intriguing objects in the universe, can manifest themselves through electromagnetic radiations initiated by the accretion flow. Some stellar-mass BHs drive relativistic jets when accreting matter from their companion stars, called microquasars. Non-thermal emission from the radio to tera-electronvolt (TeV) gamma-ray band has been observed from microquasars, indicating acceleration of relativistic particles by the system. Here we report detection of ultrahigh-energy (UHE, photon energy $E>100$TeV) gamma-ray associated with 5 out of 12 microquasars harboring BHs visible by the Large High Altitude Air Shower Observatory, namely, SS 433, V4641 Sgr, GRS 1915+105, MAXI J1820+070, and Cygnus X-1. In the central region of SS 433, extended UHE emission is detected in spatial coincidence with a giant gas cloud, suggesting the hadronic origin of the emission. An elongated source is discovered from V4641 Sgr with the spectrum continuing up to 800 TeV. GRS 1915+105, MAXI J1820+070 and Cygnus X-1 are detected with quasi-stable radiations up to $\sim$100 TeV. The detection of UHE gamma-rays demonstrates that accreting BHs and their environments can operate as extremely efficient accelerators of particles out of 1 peta-electronvolt (PeV), thus contributing to Galactic cosmic rays especially around the `knee' region.