We report the results obtained from the analysis of XMM-Newton and NuSTAR observations of two ultraluminous X-ray sources (ULXs) located in the galaxies ESO 501-023 and IC 5052. To better understand their nature, we studied the spectral and timing behavior of these sources. We used spectral-timing techniques to investigate the presence of possible pulsations in the data. We did not detect any significant pulsations and set upper limits on the pulsed fraction of < 9% for ESO 501-023 ULX and < 11% for IC 5052 X-1. These sources exhibit typical ULX X-ray spectra and can be well fitted with two thermal components plus a Comptonization tail at high energies. To classify the sources, we compared their spectral parameters with those of other well-known ULXs. Our results show that ESO 501-023 ULX is in the broadened disk state and IC 5052 X-1 is in the hard ultraluminous state. Finally, our results suggest that the sources are likely nonmagnetic, supercritically accreting objects fed by companion stars.

ABSTRACT We report a detailed multi-wavelength study of the supernova remnant G296.5+10.0 using archival data from XMM–Newton and Fermi-LAT complemented with ATCA observations. In the X-ray band, we performed an adaptive smoothing on the double background subtracted images to construct an X-ray mosaic map with six individual observations. Below 2.0 keV, G296.5+10.0 is asymmetrical, with the south-east side of the radio shell brighter than the south-west one. The spatially resolved X-ray spectral study confirms the thermal origin of the plasma, with enhanced metal abundances, probably arising from ejecta material according to the H i and infrared ($140~{\mu \rm m}$) distributions. In the γ-ray band, we analysed 14 years of accumulated Fermi observations below 500 GeV via different fitting processes. To discuss the origin of the γ-ray emission, we compare the GeV results with H i structures probably associated with the SNR and with the radio spectral indices found at various positions towards the radio shell. Moreover, we identified diverse sources candidates to contribute γ-ray emissions observed. Also, we calculated the lepto-hadronic spectral energy distribution of the remnant for synchrotron, inverse Compton, Bremsstrahlung, and proton–proton processes. The emission at low energies can be explained by electron-synchrotron radiation, with a weak magnetic field of $B=25\, {\rm \mu G}$, while the γ-ray data can be explained by hadronic interactions. Employing the reddening-distance method, we computed a distance of 1.4 kpc for the SNR, implying an age of 14 000 yr.

The extragalactic microquasar S26 has the most powerful jets observed in accreting binaries, with a kinetic luminosity of L_ jet∼10^40 erg s^-1. According to the jet-disk symbiosis model, this implies that the accretion power to the stellar black hole at the core of the system should be very super-Eddington, on the order of L_ acc∼ L_ jet. However, the observed X-ray flux of this system, measured by the Chandra and XMM-Newton telescopes, indicates an apparent very sub-Eddington accretion luminosity of L_ X≈ 10^37 erg s^-1, orders of magnitude smaller than the jet power. We present here a preliminary investigation of the relationship between jet and disk power, analyze an X-ray observation of S26 obtained with XMM-Newton, and propose an explanation for the emission. We also examine the acceleration and distribution of the particles to discuss the feasibility of microquasars as potential PeVatron sources, exploring their ability to produce cosmic rays with energies of about 1 PeV or higher.

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.

We have recently proposed that supercritical colliding wind binaries (SCWBs) are suitable scenarios for particle acceleration and nonthermal radiation. In these X-ray binary systems (XRBs), the wind from the companion star collides with the wind ejected from the super-Eddington accretion disk of the stellar black hole. Strong shocks are generated in this collision, leading to the acceleration of particles and subsequent broadband emission through different nonthermal radiative processes. In particular, we estimate luminosities of the order of $L\approx 10^{34}\,{\rm erg\,s^{-1}}$ in the radio band. One of the major components in these processes is the power provided by the super wind expelled from the disk. Furthermore, some properties of the wind photosphere, such as its geometry or its temperature distribution, also contribute to the absorption and reprocessing of the nonthermal radiation. In this work, we perform a more detailed description of the powerful wind launched from the accretion disk, in order to obtain a better understanding of the above-mentioned processes.