Supercritical colliding wind binaries

LEANDRO ABAROA; GUSTAVO E. ROMERO; PABLO SOTOMAYOR

ASTRONOMY & ASTROPHYSICS. SUPPLEMENT SERIES (PRINT)

EDP Sciences

Año: 2023 vol. 671

0365-0138

Context. Particle-accelerating colliding-wind binaries (PACWBs) are systems that are formed by two massive and hot stars andproduce nonthermal radiation. The key elements of these systems are fast winds and the shocks that they create when they collide.Binaries with nonaccreting young pulsars have also been detected as nonthermal emitters, again as a consequence of the wind–windinteraction. Black holes might produce nonthermal radiation by this mechanism if they accrete at super-Eddington rates. In such cases,the disk is expected to launch a radiation-driven wind, and if this wind has an equatorial component, it can collide with the companionstar yielding a PACWB. These systems are supercritical colliding wind binaries.Aims. We aim to characterize the particle acceleration and nonthermal radiation produced by the collision of winds in binary systemscomposed of a superaccreting black hole and an early-type star.Methods. We estimated the terminal velocity of the disk-driven wind by calculating the spatial distribution of the radiation fieldsand their effect on disk particles. We then found the location of the wind collision region and calculated the timescales of energygain and losses of relativistic particles undergoing diffusive particle acceleration. With this information, we were able to computethe associated spectral energy distribution of the radiation. We calculated a number of specific models with different parameters toexplore this scenario.Results. We find that the interaction of winds can produce nonthermal emission from radio up to tens of GeV, with luminosities inthe range of ∼1033–1035 erg s−1, which for the most part are contributed by electron synchrotron and inverse Compton radiation.Conclusions. We conclude that supercritical colliding wind binaries, such as some ultraluminous X-ray sources and some GalacticX-ray binaries, are capable of accelerating cosmic rays and producing nonthermal electromagnetic emission from radio to γ-rays, inaddition to the thermal components.