arXiv subjects

Valenti Bosch-Ramon

Publications and source records attributed to Valenti Bosch-Ramon.

At least 19 recordsLinked to original sources

arXiv2025

A jet bent by a stellar wind in the black hole X-ray binary Cygnus X-1

Jets provide an important channel for kinetic feedback from accreting black holes into their environment, without which models of the formation of large-scale structure in the universe fail to reproduce the observed properties of galaxies. Hence, an accurate measurement of jet power is critical for understanding black hole growth through accretion and also for quantifying the impact of kinetic feedback. However, the absence of instantaneous jet power measurements has precluded direct comparisons with the accretion luminosity, forcing kinetic feedback models to rely on ad hoc assumptions about how much jet power is released per accreted amount of mass. Here we report the detection of stellar wind-induced bending of the jets in the black hole X-ray binary Cygnus X-1, using 18 years of high-resolution radio imaging. By modeling jet-wind interactions, we determine the current kinetic instantaneous power of the jet to be log$_{10}(L_{\rm jet}/{\rm erg\,s}^{-1}) = 37.3_{-0.2}^{+0.1}$, comparable to the accretion energy determined from its bolometric X-ray luminosity. This result critically places prevailing assumptions about the energetics of black hole powered jets in both galaxy formation simulations, and in scaling models of black hole accretion, on a firm empirical footing.

astro-ph.HE↗

arXiv2025

Probing the detectability of electromagnetic signatures from Galactic isolated black holes

Context: A large number of isolated black holes (IBHs) are expected to populate the Galaxy. However, only one has been confirmed by the analysis of a microlensing event, and no confirmed emission detection from an IBH has been reported so far. Aims: We analysed the detectability of electromagnetic signatures from IBHs moving in the Galaxy. Methods: We considered accretion from the interstellar medium onto an IBH and assumed the formation of an outflow. We modelled the accretion process and the interaction of the outflow with the surrounding medium on large scales, including mechanical feedback on the accretion process. Furthermore, we also calculated the emission from three different regions: the accretion region, the radiation from the outflow medium interaction structure, and the emission of relativistic particles that diffuse in the surrounding medium. Results: Multiwavelength emission associated with Galactic IBHs can be detected in systems moving through a very dense medium. Thermal emission from accretion could be observed in the mid infrared and in hard X rays with current and forthcoming observatories. Thermal and non thermal emission from the outflow medium shock could also be detected in the radio and millimetre ranges. Moreover, detection of the emission from particles diffusing in a dense medium could be feasible in gamma rays. Applying our model to the IBH associated with the gravitational microlensing event MOA2011BLG191 OGLE2011BLG0462, we inferred that radio and infrared detection of the IBH is plausible. Also, we derived that IBHs could be modest Galactic cosmic ray contributors, potentially reaching a 1% contribution at 1 PeV. Finally, by extending our model to primordial black holes, we conclude that efficient leptonic acceleration in their outflow medium interactions would rule them out as a major dark matter component.

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arXiv2024

Investigating the Role of Pre-supernova Massive Stars in the Acceleration of Galactic Cosmic Rays

Galactic cosmic rays (GCRs) constitute a significant part of the energy budget of our Galaxy, and the study of their accelerators is of high importance in modern astrophysics. Their main sources are likely supernova remnants (SNRs). These objects are capable to convert a part of their mechanical energy into accelerated charged particles. However, even though the mechanical energy reservoir of SNRs is promising, a conversion rate into particle energy of 10 to 20% is necessary to feed the population of GCRs. Such an efficiency is however not guaranteed. Complementary sources deserve thus to be investigated. This communication aims to address the question of the contribution to the acceleration of GCRs by pre-supernova massive stars in binary or higher multiplicity systems

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arXiv2024

Two models for the orbital modulation of $\gamma$-rays in Cyg X-3

We model the currently available $\gamma$-ray data from the Fermi Large Area Telescope on Cyg X-3. Thanks to its very strong $\gamma$-ray activity during 2018--2021, the data quality has significantly improved. We study the strong orbital modulation of the $\gamma$-rays observed during at high $\gamma$-ray fluxes. The modulation, as found earlier, is well modeled by anisotropic Compton scattering of the donor blackbody emission by relativistic electrons in a jet strongly misaligned with respect to the orbital axis. We confirm that this model fits well both the average $\gamma$-ray modulation light curve and the spectrum. However, we find that if the jet is aligned with the spin axis of a rotating black hole, it would undergo geodetic precession with the period of $\sim$50 years. However, its presence is ruled out by both the $\gamma$-ray and radio data. Therefore, we consider an alternative model in which the average jet direction jet is aligned, but it is bent to outside the orbit owing to the thrust of the donor stellar wind, and thus precesses at the orbital period. The $\gamma$-ray modulation appears then owing to the variable Doppler boosting of synchrotron self-Compton jet emission. The model also fits well the data. However, the fitted bending angle is much larger than the theoretical one based on the binary and wind parameters as currently known. Thus, both models disagree with important aspects of our current theoretical understanding of the system. We discuss possible ways to find the correct model.

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arXiv2023

The role of supernovae inside AGN jets in UHECR acceleration

Jets of active galactic nuclei are potential accelerators of ultra high-energy cosmic rays. Supernovae can occur inside these jets and contribute to cosmic ray acceleration, particularly of heavy nuclei, but that contribution has been hardly investigated so far. We carried out a first dedicated exploration of the role of supernovae inside extragalactic jets in the production of ultra high-energy cosmic rays. We characterized the energy budget of supernova-jet interactions, and the maximum possible energies of the particles accelerated in those events, likely dominated by heavy nuclei. This allowed us to assess whether these interactions can be potential acceleration sites of ultra high-energy cosmic rays, or at least of their seeds. For that, we estimated the cosmic ray luminosity for different galaxy types, and compared the injection rate of cosmic ray seeds into the jet with that due to galactic cosmic ray entrainment. Since the supernova is fueled for a long time by the luminosity of the jet, the energy of a supernova-jet interaction can be several orders of magnitude greater than that of an isolated supernova. Thus, despite the low rate of supernovae expected to occur in the jet, they could still provide more seeds for accelerating ultra high-energy particles than cosmic ray entrainment from the host galaxy. Moreover, these interactions can create sufficiently efficient accelerators to be a source of cosmic rays with energies $\gtrsim 10$~EeV. Supernova-jet interactions can contribute significantly to the production of ultra high-energy cosmic rays, either directly by accelerating these particles themselves or indirectly by providing pre-accelerated seeds.

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arXiv2023

Achromatic rapid flares in hard X-rays in the $\gamma$-ray binary LS I +61-303

We report on the presence of very rapid hard X-ray variability in the $\gamma$-ray binary LS I +61 303. The results were obtained by analysing NuSTAR data, which show two achromatic strong flares on ks time-scales before apastron. The Swift-BAT orbital X-ray light curve is also presented, and the NuSTAR data are put in the context of the system orbit. The spectrum and estimated physical conditions of the emitting region indicate that the radiation is synchrotron emission from relativistic electrons, likely produced in a shocked pulsar wind. The achromaticity suggests that losses are dominated by escape or adiabatic cooling in a relativistic flow, and the overall behaviour in hard X-rays can be explained by abrupt changes in the size of the emitting region and/or its motion relative to the line of sight, with Doppler boosting potentially being a prominent effect. The rapid changes of the emitter could be the result of different situations such as quick changes in the intra-binary shock, variations in the re-accelerated shocked pulsar wind outside the binary, or strong fluctuations in the location and size of the Coriolis shock region. Although future multi-wavelength observations are needed to further constrain the physical properties of the high-energy emitter, this work already provides important insight into the complex dynamics and radiation processes in LS I +61-303.

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arXiv2023

Unveiling properties of the non-thermal X-ray production in the gamma-ray binary LS 5039 using the long-term pattern of its fast X-ray variability

Gamma-ray binary systems, a subclass of high-mass X-ray binaries, show non-thermal emissions from radio to TeV. While efficient electron acceleration is considered to take place in them, the nature of the acceleration mechanism and the physical environments in these systems have been a long-standing question. In this work, we report on long-term recurrent patterns in the short-term variability of the soft X-ray emission of LS 5039, one of the brightest gamma-ray binary systems. The Neutron star Interior Composition Explorer (NICER) observed LS 5039 four times from 2018 to 2021. By comparing them with the previous Suzaku and NuSTAR long-exposure observations, we studied the long-term evolution of the orbital light curve in the soft X-ray band. Although the observations by NICER and Suzaku are separated by $\sim$14 years, i.e., more than 10^3 orbits, the orbital light curves show remarkable consistency after calculating their running averages with a window width 70 ks. Furthermore, all of the light curves show short-term variability with a time scale of $\sim$10 ks. Since the column density did not vary when the flux changed abruptly, such a short-term variability seems to be an intrinsic feature of the X-ray emission. We propose that the short-term variability is caused by clumps (or inhomogeneities) of the companion star wind impacting the X-ray production site. The observed time scale matches well with the lifetime of the clumps interacting with the pulsar wind and the dynamical time scale of the relativistic intrabinary shock in the pulsar wind scenario.

astro-ph.HE↗

arXiv2022

The major role of eccentricity in the evolution of colliding pulsar-stellar winds

Binary systems that host a massive star and a non-accreting pulsar can be powerful non-thermal emitters. The relativistic pulsar wind and the non-relativistic stellar outflows interact along the orbit, producing ultrarelativistic particles that radiate from radio to gamma rays. To properly characterize the physics of these sources, and better understand their emission and impact on the environment, careful modelling of the outflow interactions, spanning a broad range of spatial and temporal scales, is needed. Full 3-dimensional approaches are very computationally expensive, but simpler approximate approaches, while still realistic at the semi-quantitative level, are available. We present here the results of calculations done with a quasi 3-dimensional scheme to compute the evolution of the interacting flows in a region spanning in size up to a thousand times the size of the binary. In particular, we analyze for the first time the role of different eccentricities in the large scale evolution of the shocked flows. We find that the higher the eccentricity, the closer the flows behave like a one-side outflow, which becomes rather collimated for eccentricity values $\gtrsim 0.75$. The simulations also unveil that the pulsar and the stellar winds become fully mixed within the grid for low eccentricity systems, presenting a more stochastic behavior at large scales than in the highly eccentric systems.

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arXiv2022

Exploring the region encompassing gamma Cygni SNR and MAGIC J2019+408 with the GMRT at 325 and 610 MHz

Gamma Cygni is a young supernova remnant located in the Cygnus region. MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes detected TeV emission (MAGIC J2019+408) to the north-west of this remnant, about 5 arcmin from its border. We want to identify the radio sources within the region encompassing gamma Cygni and MAGIC J2019+408 to shed light on their nature and investigate if these radio sources could be potential contributors to gamma-ray emission. We carried out a detailed study of the data we obtained with a survey of the Cygnus region at 325 and 610 MHz with the Giant Metrewave Radio Telescope (GMRT). We detected several radio sources in the region where the radio and the TeV emission overlap, as well as several areas of enhanced radio emission. In particular, two of these areas of diffuse enhanced emission may correspond to the supernova remnant interacting with a high density region, which seems to be the best candidate for the MAGIC source. Another two radio sources, which may or may not contribute to the gamma rays, are also spatially coincident with the emission peak of the MAGIC TeV source. One of them displays a rather peculiar extended morphology whose nature is completely unknown. We have identified the radio sources overlapping gamma Cygni and MAGIC J2019+408 and have shown that their potential gamma-ray contribution is likely not dominant. In addition, some of the studied sources show peculiar physical characteristics that deserve deeper multi-wavelength observations.

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arXiv2022

3D hydrodynamical simulations of the impact of mechanical feedback on accretion in supersonic stellar-mass black holes

Isolated stellar-mass BH accrete gas, often at supersonic speeds, and can form outflows that can influence the accreted gas. The latter process, known as mechanical feedback, can significantly affect the accretion rate. We use hydrodynamical simulations to assess the impact of mechanical feedback on the accretion rate when the BH moves supersonically through a uniform medium. We carry out 3D hydrodynamical simulations of outflows fueled by accretion that interact with a uniform medium, probing scales similar to and larger than the accretor gravitational sphere of influence. In the simulations the accretor is at rest and the medium moves at supersonic speeds. The outflow power is assumed to be proportional to the accretion rate. The simulations are run for different outflow-medium motion angles and velocity ratios. The impact of different degrees of outflow collimation, accretor size, and resolution is also investigated. In general, the accretion rate is significantly affected by mechanical feedback. The effect is small for outflows perpendicular to the medium motion, and quickly grows for smaller angles. Moreover, the smaller the medium-to-outflow velocity ratio is, the more accretion decreases. On the other hand, the impact of outflow collimation seems moderate. The effect is enhanced when the accretor size is reduced. For a population of BH with random outflow orientations, the average accretion rate drops by (high-low resolution) ~0.2-0.4 and ~0.1-0.2 for medium-to-outflow velocity ratios of 1/20 and 1/100, respectively, when compared to the corresponding cases without outflow. Our results strongly indicate that, on the considered scales, mechanical feedback can easily reduce the energy available from supersonic accretion by a factor of several. This should be taken into account when studying the mechanical, thermal and non-thermal output of isolated BH.

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arXiv2021

Relativistic hydrodynamical simulations of the effects of the stellar wind and the orbit on high-mass microquasar jets

High-mass microquasar jets, produced in an accreting compact object in orbit around a massive star, must cross a region filled with stellar wind. The combined effects of the wind and orbital motion can strongly affect the jet properties on binary scales and beyond. The study of such effects can shed light on how high-mass microquasar jets propagate and terminate in the interstellar medium. We study for the first time, using relativistic hydrodynamical simulations, the combined impact of the stellar wind and orbital motion on the properties of high-mass microquasar jets on binary scales and beyond. We have performed 3-dimensional relativistic hydrodynamic simulations, using the PLUTO code, of a microquasar scenario in which a strong weakly relativistic wind from a star interacts with a relativistic jet under the effect of the binary orbital motion. The parameters of the orbit are chosen such that the results can provide insight on the jet-wind interaction in compact systems like for instance Cyg~X-1 or Cyg~X-3. The wind and jet momentum rates are set to values that may be realistic for these sources and lead to moderate jet bending, which together with the close orbit and jet instabilities could trigger significant jet precession and disruption. For high-mass microquasars with orbit size $a\sim 0.1$~AU, and (relativistic) jet power $L_j\sim 10^{37}(\dot M_w/10^{-6}\,{\rm M}_\odot\,{\rm yr}^{-1})$~erg~s$^{-1}$, where $\dot M_w$ is the stellar wind mass rate, the combined effects of the stellar wind and orbital motion can induce relativistic jet disruption on scales $\sim 1$~AU.

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arXiv2020

Equatorial outflows driven by jets in Population III microquasars

Binary systems of Population III can evolve to microquasars when one of the stars collapses into a black hole. When the compact object accretes matter at a rate greater than the Eddington rate, powerful jets and winds driven by strong radiation pressure should form. We investigate the structure of the jet-wind system for a model of Population III microquasar on scales beyond the jet-wind formation region. Using relativistic hydrodynamic simulations we find that the ratio of kinetic power between the jet and the disk wind determines the configuration of the system. When the power is dominated by the wind, the jet fills a narrow channel, collimated by the dense outflow. When the jet dominates the power of the system, part of its energy is diverted turning the wind into a quasi-equatorial flow, while the jet widens. From the results of our simulations, we implement semi-analytical calculations of the impact of the quasiequatorial wind on scales of the order of the size of the binary system. Our results indicate that Population III microquasars might inject gamma rays and relativistic particles into the early intergalactic medium, contributing to its reionization at large distances from the binary system.

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arXiv2020

Mechanical feedback effects on primordial black hole accretion

Dark matter may consist, at least partially, of primordial black holes formed during the radiation-dominated era. The radiation produced by accretion onto primordial black holes leaves characteristic signatures on the properties of the medium at high redshift, before and after Hydrogen recombination. Therefore, reliable modelling of accretion onto these objects is required to obtain robust constraints on their abundance. We investigate the effect of mechanical feedback, i.e. the impact of outflows (winds and/or jets) on the medium, on primordial black hole accretion, and thereby on the associated radiation. Using analytical and numerical calculations, we study for the first time whether outflows can reduce the accretion rate of primordial black holes with masses similar to those detected by the LIGO-Virgo collaboration. Despite the complexity of the accretion rate evolution, mechanical feedback is able to significantly reduce the primordial black hole accretion rate, at least by an order of magnitude, when outflows are aligned with the motion of the compact object. If the outflow is perpendicular to the direction of motion, the effect is less important but still non-negligible. Outflows from primordial black holes, even rather weak ones, can significantly decrease the accretion rate, effectively weakening abundance constraints on these objects. Our results motivate further numerical simulations with a more realistic setup, which would yield more precise quantitative predictions.

astro-ph.CO↗

arXiv2018

A hydrodynamics-informed, radiation model for HESS J0632$+$057 from radio to gamma rays

Relativistic hydrodynamical simulations of the eccentric gamma-ray binary HESS J0632$+$057, show that the energy of a putative pulsar wind should accumulate in the binary surroundings between periastron and apastron, being released by fast advection close to apastron. To assess whether this could lead to a maximum of the non-thermal emission before apastron, we derive simple prescriptions for the non-thermal energy content, the radiation efficiency, and the impact of energy losses on non-thermal particles, in the simulated hydrodynamical flow. These prescriptions are used to estimate the non-thermal emission in radio, X-rays, GeV, and TeV, from the shocked pulsar wind in a binary system simulated using a simplified 3-dimensional scheme for several orbital cycles. Lightcurves at different wavelengths are derived, together with synthetic radio images for different orbital phases. The dominant peak in the computed lightcurves is broad and appears close to, but before, apastron. This peak is followed by a quasi-plateau shape, and a minor peak only in gamma rays right after periastron. The radio maps show ejection of radio blobs before apastron in the periastron-apastron direction. The results show that a scenario with a highly eccentric high-mass binary hosting a young pulsar can explain the general phenomenology of HESS J0632$+$057: despite its simplicity, the adopted approach yields predictions that are robust at a semi-quantitative level and consistent with multiwavelength observations.

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arXiv2015

The origin of the X-ray-emitting object moving away from PSR B1259-63

A mysterious X-ray-emitting object has been detected moving away from the high-mass gamma-ray binary PSR B1259-63, which contains a non-accreting pulsar and a Be star whose winds collide forming a complex interaction structure. Given the strong eccentricity of this binary, the interaction structure should be strongly anisotropic, which together with the complex evolution of the shocked winds, could explain the origin of the observed moving X-ray feature. We propose here that a fast outflow made of a pulsar-stellar wind mixture is always present moving away from the binary in the apastron direction, with the injection of stellar wind occurring at orbital phases close to periastron passage. This outflow periodically loaded with stellar wind would move with a high speed, and likely host non-thermal activity due to shocks, on scales similar to those of the observed moving X-ray object. Such an outflow is thus a very good candidate to explain this X-ray feature. This, if confirmed, would imply pulsar-to-stellar wind thrust ratios of $\sim 0.1$, and the presence of a jet-like structure on the larger scales, up to its termination in the ISM.

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arXiv2013

Formation of large-scale magnetic structures associated with the Fermi bubbles

The Fermi bubbles are part of a complex region of the Milky Way. This region presents broadband extended non-thermal radiation, apparently coming from a physical structure rooted in the Galactic Centre and with a partly-ordered magnetic field threading it. We explore the possibility of an explosive origin for the Fermi bubble region to explain its morphology, in particular that of the large-scale magnetic fields, and provide context for the broadband non-thermal radiation. We perform 3D magnetohydrodynamical simulations of an explosion from a few million years ago that pushed and sheared a surrounding magnetic loop, anchored in the molecular torus around the Galactic Centre. Our results can explain the formation of the large-scale magnetic structure in the Fermi bubble region. Consecutive explosive events may match better the morphology of the region. Faster velocities at the top of the shocks than at their sides may explain the hardening with distance from the Galactic Plane found in the GeV emission. In the framework of our scenario, we estimate the lifetime of the Fermi bubbles as $2\times10^6$ yr, with a total energy injected in the explosion(s) $> 10^{55}$ ergs. The broadband non-thermal radiation from the region may be explained by leptonic emission, more extended in radio and X-rays, and confined to the Fermi bubbles in gamma rays.

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arXiv2013

Gamma-ray emission from massive stars interacting with AGN jets

Dense populations of stars surround the nuclear regions of galaxies. In active galactic nuclei, these stars can interact with the relativistic jets launched by the supermasive black hole. In this work, we study the interaction of early-type stars with relativistic jets in active galactic nuclei. A bow-shaped double-shock structure is formed as a consequence of the interaction of the jet and the stellar wind of each early-type star. Particles can be accelerated up to relativistic energies in these shocks and emit high-energy radiation. We compute, considering different stellar densities of the galactic core, the gamma-ray emission produced by non-thermal radiative processes. This radiation may be significant in some cases, and its detection might yield valuable information on the properties of the stellar population in the galaxy nucleus, as well as on the relativistic jet. This emission is expected to be particularly relevant for nearby non-blazar sources.

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arXiv2013

Gamma-ray emission from early-type stars interacting with AGN jets

We study the interaction of early-type stars with the jets of active galactic nuclei. A bow-shock will form as a consequence of the interaction of the jet with the winds of stars and particles can be accelerated up to relativistic energies in these shocks. We compute the non-thermal radiation produced by relativistic electrons from radio to gamma-rays. This radiation may be significant, and its detection might yield information on the properties of the stellar population in the galaxy nucleus, as well as on the relativistic jet. This emission is expected to be relevant for nearby non-blazar sources.

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