A model for high-mass microquasar jets under the influence of a strong stellar wind

Context. High-mass microquasars (HMMQs) are systems from which relativistic jets are launched. At the scales of several times the binary system size, the jets are expected to follow a helical path caused by the interaction with a strong stellar wind and orbital motion. Such a trajectory has its influence on the non-thermal emission of the jets, which also depends strongly on the observing angle due to Doppler boosting effects. Aims: We explore how the expected non-thermal emission of HMMQ jets at small scales is affected by the impact of the stellar wind and the orbital motion on the jet propagation. Methods: We studied the broadband non-thermal emission, from radio to gamma rays, produced in HMMQ jets up to a distance of several orbital separations, taking into account a realistic jet trajectory, different model parameters, and orbital modulation. The jet trajectory is computed by considering momentum transfer with the stellar wind. Electrons are injected at the position where a recollimation shock in the jets is expected due to the wind impact. Their distribution along the jet path is obtained assuming local acceleration at the recollimation shock, and cooling via adiabatic, synchrotron, and inverse Compton processes. The synchrotron and inverse Compton emission is calculated taking into account synchrotron self-absorption within the jet, free-free absorption with the stellar wind, and absorption by stellar photons via pair production. Results: The spectrum is totally dominated by the jet over the counter-jet due to Doppler boosting. Broadband emission from microwaves to gamma rays is predicted, with radio emission being totally absorbed. This emission is rather concentrated in the regions close to the binary system and features strong orbital modulation at high energies. Asymmetric light curves are obtained owing to the helical trajectory of the jets.Fil: Molina, E.. Universidad de Barcelona; EspañaFil: del Palacio, Santiago. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Bosch Ramon, Valentí. Universidad de Barcelona; Españ

A model for the non-thermal emission of the very massive colliding-wind binary HD 93129A

The binary stellar system HD 93129A is one of the most massive known binaries in our Galaxy. This system presents non-thermal emission in the radio band, which can be used to infer its physical conditions and predict its emission in the high-energy band. We intend to constrain some of the unknown parameters of HD 93129A through modelling the non-thermal emitter, and also to analyse the detectability of this source in hard X-rays and $\gamma$-rays. We develop a broadband radiative model for the wind-collision region taking into account the evolution of the accelerated particles streaming along the shocked region, the emission by different radiative processes, and the attenuation of the emission propagating through the local matter and radiation fields. From the analysis of the radio emission, we find that the binary HD~93129A is more likely to have a low inclination and a high eccentricity. The minimum energy of the non-thermal electrons seems to be between $\sim 20 - 100$MeV, depending on the intensity of the magnetic field in the wind-collision region. The latter can be in the range $\sim 20 - 1500$ mG. Our model is able to reproduce the observed radio emission, and predicts that the non-thermal radiation from HD~93129A will increase in the near future. With instruments such as \textit{NuSTAR}, \textit{Fermi}, and CTA, it will be possible to constrain the relativistic particle content of the source, and other parameters such as the magnetic field strength in the wind collision zone, which in turn can be used to obtain upper-limits of the magnetic field on the surface of the very massive stars, thereby inferring whether magnetic field amplification is taking place in the particle acceleration region.Comment: 11 pages, 9 figures. Accepted for publication in A&

Interacciones de partículas relativistas en vientos estelares

Algunas de las fuentes de rayos gamma galácticas son sistemas binarios en los que una de las componentes es una estrella de gran masa y la otra es una estrella similar o un objeto compacto (ya sea una estrella de neutrones o un agujero negro de masa estelar). Este tipo de binarias presenta emisión no térmica en las bandas de radio y de rayos-X, generada por partículas ultra-relativistas que son aceleradas, generalmente, en ondas de choque fuertes relacionadas con flujos de plasma. Es probable que la radiación proveniente del sistema binario sufra absorción y reprocesamiento en el medio local, por lo que su estudio puede proveer información del emisor y de las propiedades del medio. Además, la investigación de estos objetos puede proporcionar conocimientos de los procesos físicos no térmicos que ocurren en escenarios astrofísicos extremos, con flujos de materia altamente supersónicos, plasma turbulento, campos magnéticos fuertes, campos de radiación intensos y medios densos. El objetivo principal de este trabajo es caracterizar la física de altas energías de binarias de rayos gamma, lo cual permite determinar los procesos radiativos dominantes y testear teorías de aceleración de partículas. Para ello, se incorpora un modelo genérico de los procesos relativistas que ocurren en estos sistemas. En este modelo se considera un mecanismo capaz de inyectar partículas relativistas en un punto del entorno de la estrella de gran masa, las cuales interactúan con el medio circundante produciendo radiación de altas energías. Se desarrolla una herramienta que permite explorar cómo afecta al flujo emitido por el sistema binario la posición del inyector respecto a la estrella, vista por un observador en la Tierra. Teniendo en cuenta las mejoras observacionales presentes y futuras, que posibilitarán un incremento de la cantidad de fuentes observables, es oportuno investigar en detalle los procesos físicos que subyacen a la emisión de este tipo de fuentes. Es aún un problema abierto el poder identificar sin ambigüedades los procesos de emisión y absorción de radiación relevantes en fuentes astrofísicas de altas energías. Los resultados de este trabajo y sus futuras ampliaciones permitirán abordar estudios poblacionales relacionados con parámetros astronómicos hoy en día poco conocidos, tales como la tasa de formación de binarias de gran masa, su vida media y su función de luminosidad. Ésto puede lograrse al establecer cotas aproximadas de la cantidad de fuentes que deberían ser observadas de acuerdo al modelo empleado y contrastarlas con datos empíricos.Some galactic gamma-ray sources are binary systems in which one of the components is a massive star and the companion object is either a similar star or a compact object (i.e. a neutron star or a stellar mass black hole). This type of massive binaries presents non-thermal emission in the radio and X-ray bands, generated by the ultra-relativistic particles accelerated, generally, in strong shock-waves related to plasma flows. Radiation coming from the inner region of the binaries is likely to undergo absorption and reprocessing in the local medium. Its study could provide information on the emitter and the properties of the surrounding medium. Thus, the study of these objects provides knowledge on the non-thermal physical processes ocurring in extreme astrophysical environments, with highly supersonic matter flows, turbulent plasma, strong magnetic fields, intense radiation and a dense medium. The main goal of this work is to characterize the high-energy physics of gamma-ray binaries by modeling their high-energy processes. In this way it is possible to determinate the dominant radiative processes and to test particle acceleration theories. With such a purpose a tool is developed, one capable of providing information of the star wind, the plasma flows interacting with it, the content of matter in such flows and the magnetic fields that they drag. Specifically, we calculate the spectral energy distribution for emitters located in different positions of the binary system, which allows to study the impact of the geometry in the resulting emission from the source. This is done for different cuts of the relevent state parameters. Finally, we use this procedure to produce emissivity maps which are an useful tool for exploring statiscal properties of gamma-ray binaries. Considering the present and future observational developments, which imply an increase in the quantity of observable sources, it is important to investigate in detail the physical processes that underlie the emission on this type of sources. It is still an open problem to unambiguously identify the relevant radiation and absorption processes in high-energy astrophysical sources. The results of this work and its future upgrades will allow poblational studies related to currently unknown parameters, such as the formation rate of massive binaries, their lifespan and their luminosity function. This can be attained by estimating the approximate number of sources detectable with the present instruments (according to the model developed) and comparing it with the empirical data.Facultad de Ciencias Astronómicas y Geofísica

Interacciones de partículas relativistas en vientos estelares

Algunas de las fuentes de rayos gamma galácticas son sistemas binarios en los que una de las componentes es una estrella de gran masa y la otra es una estrella similar o un objeto compacto (ya sea una estrella de neutrones o un agujero negro de masa estelar). Este tipo de binarias presenta emisión no térmica en las bandas de radio y de rayos-X, generada por partículas ultra-relativistas que son aceleradas, generalmente, en ondas de choque fuertes relacionadas con flujos de plasma. Es probable que la radiación proveniente del sistema binario sufra absorción y reprocesamiento en el medio local, por lo que su estudio puede proveer información del emisor y de las propiedades del medio. Además, la investigación de estos objetos puede proporcionar conocimientos de los procesos físicos no térmicos que ocurren en escenarios astrofísicos extremos, con flujos de materia altamente supersónicos, plasma turbulento, campos magnéticos fuertes, campos de radiación intensos y medios densos. El objetivo principal de este trabajo es caracterizar la física de altas energías de binarias de rayos gamma, lo cual permite determinar los procesos radiativos dominantes y testear teorías de aceleración de partículas. Para ello, se incorpora un modelo genérico de los procesos relativistas que ocurren en estos sistemas. En este modelo se considera un mecanismo capaz de inyectar partículas relativistas en un punto del entorno de la estrella de gran masa, las cuales interactúan con el medio circundante produciendo radiación de altas energías. Se desarrolla una herramienta que permite explorar cómo afecta al flujo emitido por el sistema binario la posición del inyector respecto a la estrella, vista por un observador en la Tierra. Teniendo en cuenta las mejoras observacionales presentes y futuras, que posibilitarán un incremento de la cantidad de fuentes observables, es oportuno investigar en detalle los procesos físicos que subyacen a la emisión de este tipo de fuentes. Es aún un problema abierto el poder identificar sin ambigüedades los procesos de emisión y absorción de radiación relevantes en fuentes astrofísicas de altas energías. Los resultados de este trabajo y sus futuras ampliaciones permitirán abordar estudios poblacionales relacionados con parámetros astronómicos hoy en día poco conocidos, tales como la tasa de formación de binarias de gran masa, su vida media y su función de luminosidad. Ésto puede lograrse al establecer cotas aproximadas de la cantidad de fuentes que deberían ser observadas de acuerdo al modelo empleado y contrastarlas con datos empíricos.Some galactic gamma-ray sources are binary systems in which one of the components is a massive star and the companion object is either a similar star or a compact object (i.e. a neutron star or a stellar mass black hole). This type of massive binaries presents non-thermal emission in the radio and X-ray bands, generated by the ultra-relativistic particles accelerated, generally, in strong shock-waves related to plasma flows. Radiation coming from the inner region of the binaries is likely to undergo absorption and reprocessing in the local medium. Its study could provide information on the emitter and the properties of the surrounding medium. Thus, the study of these objects provides knowledge on the non-thermal physical processes ocurring in extreme astrophysical environments, with highly supersonic matter flows, turbulent plasma, strong magnetic fields, intense radiation and a dense medium. The main goal of this work is to characterize the high-energy physics of gamma-ray binaries by modeling their high-energy processes. In this way it is possible to determinate the dominant radiative processes and to test particle acceleration theories. With such a purpose a tool is developed, one capable of providing information of the star wind, the plasma flows interacting with it, the content of matter in such flows and the magnetic fields that they drag. Specifically, we calculate the spectral energy distribution for emitters located in different positions of the binary system, which allows to study the impact of the geometry in the resulting emission from the source. This is done for different cuts of the relevent state parameters. Finally, we use this procedure to produce emissivity maps which are an useful tool for exploring statiscal properties of gamma-ray binaries. Considering the present and future observational developments, which imply an increase in the quantity of observable sources, it is important to investigate in detail the physical processes that underlie the emission on this type of sources. It is still an open problem to unambiguously identify the relevant radiation and absorption processes in high-energy astrophysical sources. The results of this work and its future upgrades will allow poblational studies related to currently unknown parameters, such as the formation rate of massive binaries, their lifespan and their luminosity function. This can be attained by estimating the approximate number of sources detectable with the present instruments (according to the model developed) and comparing it with the empirical data.Facultad de Ciencias Astronómicas y Geofísica

Interacciones de partículas relativistas en vientos estelares

Algunas de las fuentes de rayos gamma galácticas son sistemas binarios en los que una de las componentes es una estrella de gran masa y la otra es una estrella similar o un objeto compacto (ya sea una estrella de neutrones o un agujero negro de masa estelar). Este tipo de binarias presenta emisión no térmica en las bandas de radio y de rayos-X, generada por partículas ultra-relativistas que son aceleradas, generalmente, en ondas de choque fuertes relacionadas con flujos de plasma. Es probable que la radiación proveniente del sistema binario sufra absorción y reprocesamiento en el medio local, por lo que su estudio puede proveer información del emisor y de las propiedades del medio. Además, la investigación de estos objetos puede proporcionar conocimientos de los procesos físicos no térmicos que ocurren en escenarios astrofísicos extremos, con flujos de materia altamente supersónicos, plasma turbulento, campos magnéticos fuertes, campos de radiación intensos y medios densos. El objetivo principal de este trabajo es caracterizar la física de altas energías de binarias de rayos gamma, lo cual permite determinar los procesos radiativos dominantes y testear teorías de aceleración de partículas. Para ello, se incorpora un modelo genérico de los procesos relativistas que ocurren en estos sistemas. En este modelo se considera un mecanismo capaz de inyectar partículas relativistas en un punto del entorno de la estrella de gran masa, las cuales interactúan con el medio circundante produciendo radiación de altas energías. Se desarrolla una herramienta que permite explorar cómo afecta al flujo emitido por el sistema binario la posición del inyector respecto a la estrella, vista por un observador en la Tierra. Teniendo en cuenta las mejoras observacionales presentes y futuras, que posibilitarán un incremento de la cantidad de fuentes observables, es oportuno investigar en detalle los procesos físicos que subyacen a la emisión de este tipo de fuentes. Es aún un problema abierto el poder identificar sin ambigüedades los procesos de emisión y absorción de radiación relevantes en fuentes astrofísicas de altas energías. Los resultados de este trabajo y sus futuras ampliaciones permitirán abordar estudios poblacionales relacionados con parámetros astronómicos hoy en día poco conocidos, tales como la tasa de formación de binarias de gran masa, su vida media y su función de luminosidad. Ésto puede lograrse al establecer cotas aproximadas de la cantidad de fuentes que deberían ser observadas de acuerdo al modelo empleado y contrastarlas con datos empíricos.Some galactic gamma-ray sources are binary systems in which one of the components is a massive star and the companion object is either a similar star or a compact object (i.e. a neutron star or a stellar mass black hole). This type of massive binaries presents non-thermal emission in the radio and X-ray bands, generated by the ultra-relativistic particles accelerated, generally, in strong shock-waves related to plasma flows. Radiation coming from the inner region of the binaries is likely to undergo absorption and reprocessing in the local medium. Its study could provide information on the emitter and the properties of the surrounding medium. Thus, the study of these objects provides knowledge on the non-thermal physical processes ocurring in extreme astrophysical environments, with highly supersonic matter flows, turbulent plasma, strong magnetic fields, intense radiation and a dense medium. The main goal of this work is to characterize the high-energy physics of gamma-ray binaries by modeling their high-energy processes. In this way it is possible to determinate the dominant radiative processes and to test particle acceleration theories. With such a purpose a tool is developed, one capable of providing information of the star wind, the plasma flows interacting with it, the content of matter in such flows and the magnetic fields that they drag. Specifically, we calculate the spectral energy distribution for emitters located in different positions of the binary system, which allows to study the impact of the geometry in the resulting emission from the source. This is done for different cuts of the relevent state parameters. Finally, we use this procedure to produce emissivity maps which are an useful tool for exploring statiscal properties of gamma-ray binaries. Considering the present and future observational developments, which imply an increase in the quantity of observable sources, it is important to investigate in detail the physical processes that underlie the emission on this type of sources. It is still an open problem to unambiguously identify the relevant radiation and absorption processes in high-energy astrophysical sources. The results of this work and its future upgrades will allow poblational studies related to currently unknown parameters, such as the formation rate of massive binaries, their lifespan and their luminosity function. This can be attained by estimating the approximate number of sources detectable with the present instruments (according to the model developed) and comparing it with the empirical data.Facultad de Ciencias Astronómicas y Geofísica

Regiones de colisión de vientos estelares

Las estrellas no son meramente foquitos de luz gigantes . Además de luz (o más apropiadamente, radiación electromagnética) las estrellas liberan grandes cantidades de materia en forma de vientos estelares que, al igual que los vientos en la Tierra, no son más que masas de gas en movimiento -con la salvedad de que son mucho más masivos y calientes, claro está-. En este pequeño artículo nos concentraremos en las estrellas de gran masa de tipo espectral OB o WR, ya que éstas presentan ambientes más extremos y por tanto más interesantes para estudiar desde el punto de vista de la astrofísica de altas energías

Radio observations of evaporating objects in the Cygnus OB2 region

We present observations of the Cygnus OB2 region obtained with the Giant Metrewave Radio Telescope (GMRT) at frequencies of 325 and 610 MHz. In this contribution we focus on the study of proplyd-like objects (also known as free-floating evaporating gas globules or frEGGs) that typically show an extended cometary morphology. We identify eight objects previously studied at other wavelengths and derive their physical properties by obtaining their optical depth at radio-wavelengths. Using their geometry and the photoionization rate needed to produce their radio-continuum emission, we find that these sources are possibly ionized by a contribution of the stars Cyg OB2 #9 and Cyg OB2 #22. Spectral index maps of the eight frEGGs were constructed, showing a flat spectrum in radio frequencies in general. We interpret these as produced by optically thin ionized gas, although it is possible that a combination of thermal emission, not necessarily optically thin, produced by a diffuse gas component and the instrument response (which detects more diffuse emission at low frequencies) can artificially generate negative spectral indices. In particular, for the case of the Tadpole we suggest that the observed emission is not of non-thermal origin despite the presence of regions with negative spectral indices in our maps.Fil: Isequilla, Natacha Laura. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Benaglia, Paula. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Ishwara Chandra, C. H.. National Center For Radio Astrophysics; IndiaFil: del Palacio, Santiago. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin

Gamma rays from jets interacting with BLR clouds in blazars

Context. The innermost parts of powerful jets in active galactic nuclei are surrounded by dense, high-velocity clouds from the broad-line region, which may penetrate into the jet and lead to the formation of a strong shock. Such jet-cloud interactions are expected to have measurable effects on the γ-ray emission from blazars. Aims. We characterise the dynamics of a typical cloud-jet interaction scenario, and the evolution of its radiative output in the 0.1-30 GeV energy range, to assess to what extent these interactions can contribute to the γ-ray emission in blazars. Methods. We use semi-analytical descriptions of the jet-cloud dynamics, taking into account the expansion of the cloud inside the jet and its acceleration. Assuming that electrons are accelerated in the interaction and making use of the hydrodynamical information, we then compute the high-energy radiation from the cloud, including the absorption of γ-rays in the ambient photon field through pair creation. Results. Jet-cloud interactions can lead to significant γ-ray fluxes in blazars with a broad-line region (BLR), in particular when the cloud expansion and acceleration inside the jet are taken into account. This is caused by 1) the increased shocked area in the jet, which leads to an increase in the energy budget for the non-thermal emission; 2) a more efficient inverse Compton cooling with the boosted photon field of the BLR; and 3) an increased observer luminosity due to Doppler boosting effects. Conclusions. For typical broad-line region parameters, either (i) jet-cloud interactions contribute significantly to the persistent γ-ray emission from blazars or (ii) the BLR is far from spherical or the fraction of energy deposited in non-thermal electrons is small.Fil: del Palacio, Santiago. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Bosch Ramon, Valentí. Universidad de Barcelona; EspañaFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de La Plata; Argentin

Gamma-ray binaries beyond one-zone models: an application to LS 5039

Context. Several binary systems hosting massive stars present gamma-ray emission. In most of these systems, despite detailed observational information being available, the nature and the structure of the emitter are still poorly known. Aims. We investigate the validity of the so-called one-zone approximation for the high-energy emitter in binary systems hosting a massive star. In particular, the case of LS 5039 is considered. Methods. Assuming a point-like emitter at rest, the presence of a nearby massive star, and the observed MeV and GeV fluxes as a reference, a non-thermal leptonic model is systematically applied for different locations, magnetic fields, and non-radiative losses. This allows us to identify both the emitter configurations that are most compatible with observations and inconsistencies between model predictions and the available data. Results. In the case of LS 5039, the best parameter combination is fast non-radiative cooling and a low magnetic field. However, discrepancies appear when comparing the model results at the MeV and GeV energy ranges with the observed fluxes. Predictions fail when the orbital motion is included in the analysis, because emitters and energy budgets that are too large are required. Values of X-ray and TeV fluxes that are too high are predicted in such a case, along half of the orbit. Conclusions. We show that the radiation in LS 5039 does not come from only one electron population, and the emitter is likely extended and inhomogeneous with a low magnetic field. We suggest that the emitter moves at relativistic velocities with Doppler boosting playing a significant role.Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí

Interactions of relativistic particles in stellar winds

Several binary systems hosting a massive star and a companion thatis either a similar star or a compact object, present non-thermal emission from radio to gamma-rays. This non-thermal emission is the consequence of the interactions of relativistic particles surrounded by the stellar wind. The main goal of this workis to characterize the high-energy physics of gamma-ray binaries by implementing ageneral modeling for their most important high-energy processes. To thoroughly investigate the effects of the emitter-star-observer geometry on the resultin gradiation, we sistematically applied a non-thermal leptonic model for different locations of the emitter, magnetic fields, and acceleration timescales. The results of this procedure are presented in the form of emissivity maps, which are usefulfor exploring statistical properties of gamma-ray binaries as well as their expected distribution in the galaxy.Fil: del Palacio, Santiago. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Bosch Ramon, Valentí. Universidad de Barcelona. Facultad de Física; España2nd Argentinian-Brazilian Meeting on Gravitation, Relativistic Astrophysics and CosmologyBuenos AiresArgentinaAsociación Argentina de Astronomí