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

TL;DR

This paper reports the detection of ultrahigh-energy gamma-ray emission from multiple microquasars, revealing their role as efficient particle accelerators up to PeV energies and their potential contribution to Galactic cosmic rays.

Contribution

It provides the first observational evidence of microquasars emitting gamma rays above 100 TeV, highlighting their significance in high-energy astrophysics.

Findings

Detection of gamma rays >100 TeV from four microquasars.

Evidence of hadronic processes in SS 433's emission.

Microquasars can accelerate particles to PeV energies.

Abstract

Black holes (BH), one of the most intriguing objects in the universe, can manifest themselves through electromagnetic radiation initiated by the accretion flow. Some stellar-mass BHs drive relativistic jets when accreting matter from their companion stars, forming microquasars. Non-thermal emission from the radio to tera-electronvolt (TeV) gamma-ray band has been observed from microquasars, indicating the acceleration of relativistic particles. Here we report detection of four microquasars (SS 433, V4641 Sgr, GRS 1915+105, MAXI J1820+070) of spectrum extending to the ultrahigh-energy (UHE; photon energy $E>100$ TeV) band and one microquasar (Cygnus X-1) of spectrum approaching 100 TeV, using the Large High Altitude Air Shower Observatory (LHAASO). Notably, the total emission associated with SS 433 cannot be interpreted with a single leptonic component. In the UHE band, its emission is in spatial coincidence with a giant atomic cloud, which is consistent with a hadronic origin. An elongated source is discovered from V4641 Sgr with the spectrum continuing up to 800 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), suggesting microquasars to be important contributors to Galactic cosmic rays especially around the `knee' region.