Supercritical colliding wind binaries

Abstract

Context. Particle-accelerating colliding-wind binaries (PACWBs) are systems that are formed by two massive and hot stars and produce 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-wind interaction. 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 companion star 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 systems composed 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 fields and their effect on disk particles. We then found the location of the wind collision region and calculated the timescales of energy gain and losses of relativistic particles undergoing diffusive particle acceleration. With this information, we were able to compute the associated spectral energy distribution of the radiation. We calculated a number of specific models with different parameters to explore this scenario. Results. We find that the interaction of winds can produce nonthermal emission from radio up to tens of GeV, with luminosities in the range of ∼ 10 33 -10 35 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 Galactic X-ray binaries, are capable of accelerating cosmic rays and producing nonthermal electromagnetic emission from radio to γ-rays, in addition to the thermal components.

NuSTAR and XMM-Newton observations of the binary 4FGL J1405.1–6119

“…On the other hand, if the source is in a super-Eddington accretion regime, this would imply that the CO consists of a BH of a few solar masses or a NS with a weak magnetic field. In this case, the X-ray emission from the disk is absorbed by the photosphere of the wind ejected by the same disk (Abaroa et al 2023). This is more consistent with what is observed in the X-ray emission.…”

“…This is more consistent with what is observed in the X-ray emission. The supercritical source may also have an equatorial radio component or equatorial lines with velocities of 10 3 −10 4 km s −1 , as in the case of SS 433, which could be observed in the future (Fabrika et al 2021;Abaroa et al 2023).…”

“…This behavior is also consistent with the presence of a thermal component in the spectra of Epoch 2, which can be explained by the contribution of a thermal inner disk and a reduced nonthermal jet component. In the case of a moderate or low viewing angle, some of the emission from the disk can escape from the central funnel in the wind (Abaroa et al 2023). As for Epoch 1, the contribution to the total flux may be completely dominated by the jet.…”

XMM-Newton observations of the extragalactic microquasar S26 and their implications for PeV cosmic rays

“…In radiative shocks, the gas emits large amounts of thermal radiation. The radii of the shock regions are taken from [3] (we refer to section 3.3 of [5] for characterization of shocks). In what follows, we concentrate only on the backward shock region at the head of the jets -where the radio hotspots were identified by [4]-because we are interested in MQs as cosmic ray generators.…”

“…A key parameter to characterize MQs is the accretion rate of matter onto the compact object, which proceeds in three basic regimes, depending on the relation of the actual accretion rate to the Eddington rate. In super-Eddington regimes, the inner part of the disk launches powerful winds with mass-loss rates similar to the accretion rate [5]. Following the jet-disk symbiosis model [6], the kinetic luminosity of the jet of S26 estimated by [3] implies that the accretion luminosity onto the compact object should be highly super-Eddington, of the order of 𝐿 acc ∼ 𝐿 jet .…”