Studying a recurrent nova, RS Ophiuchi, reveals possible source of gamma-rays

The repeated explosions from the recurrent nova RS Ophiuchi (RS Oph) provide favorable environments for accelerating protons to very high energies, a new international study reports. The results suggest a previously unappreciated source of Galactic Cosmic Radiation and constrain models of particle energization, favoring a Hadronic origin of gamma-ray emission over Laptonic emission scenarios. Recurrent novae outbursts, which repeat, arise in binary systems featuring a white dwarf and a main sequence companion star in close orbit, where material is continually stripped from the companion star and transferred the surface of the white dwarf. At irregular intervals, which vary between 10 and 100 years or longer, the buildup of hydrogen on the white dwarf triggers a thermonuclear explosion, which is observed as a nova, some of which emit high-energy gamma rays. However, the origin of such emissions has remained a mystery. Here, the High Energetic Stereoscopic System (H.E.S.S.) Collaboration, an international group of researchers, report observations from the 2021 outburst of the recurrent novae RS Oph. By monitoring the emissions of RS Oph for nearly a month following the outburst, the authors were able to track the nova’s spectral and temporal evolution. By modeling the emission physics, the authors suggest that the expanding shock wave from the RS Oph’s outburst efficiently accelerated protons to gigaelectron volt and teraelectronvolt energies, which could indicate a source of gamma-rays.