Hadronic gamma-ray production in microquasars with equatorial winds

Los microcuasáres son sistemas binarios con emisión en rayos X vinculada a acreción, en los cuales se han detectado chorros de partículas relativistas (jets) a través de su emisión en bandas de radio. La transferencia de masa al objeto compacto puede darse a través del viento ecuatorial de la primaria, cuando ésta es de tipo espectral temprano, como es el caso del microcuásar LSI +61 303. En estos casos se dará inevitablemente una interacción entre el viento estelar y los jets, que puede resultar en la emisión de fotones con muy alta energía. El interés por este escenario resurge a partir de la confirmación de los microcuásares como fuentes detectadas a energías en el rango TeV. Presentamos un modelo para la emisión de rayos gamma que se origina en la interacción de protones relativistas del jet, con los protones fríos de un viento confinado en un disco circunestelar. Se calculó también, en forma simplificada, la emisión de los leptones secundarios. Teniendo en cuenta efectos de opacidad en la fostósfera, hemos podido estimar una curva de luz y un espectro que pueden ser contrastados con las mediciones de observatorios en altas energías como MAGIC o HESS.Microquasars are accreting X-ray binary systems with non-thermal radio jets. When the primary is a highmass early-type star, the compact object accretes from the stellar wind. In some cases, like LS I +61 303, the wind forms an equatorial disk and the secondary moves through it. In such a situation a strong interaction between the relativistic flow and the dense wind material is unavoidable and could result in the generation of high-energy emission. This is particularly interesting since microquasars have been recently confirmed to be high-energy γ-ray sources. We present here a hadronic model for gamma-ray production in this kind of systems, with a specific application to the case of LS I +61 303. We calculate the gamma-ray emission originated in pp interactions between relativistic protons in the jet and cold protons from the wind. The emission from secondary electron-positron pairs is estimated as well. After taking into account opacity effects on the gammarays introduced by the different photons fields, we present high-energy spectral predictions that can be tested with the new generation Cherenkov telescopes like MAGIC and HESSFil: Orellana, Mariana Dominga. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomia; ArgentinaFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomia; Argentin

High-energy gamma-ray production in microquasars

A hadronic model for gamma-ray production in microquasars is presented. Microquasars are galactic binary systems with jets, which have, presumably, hadronic components. We consider a microquasar formed by a neutron star that accretes matter from the equatorial wind of a Be primary star. The collision between the jet, emitted by the compact object, and the dense equatorial disk of the companion massive star is responsible for the gamma-ray production. Gamma-rays result from the decay of neutral pions produced in relativistic pp interactions arising from this collision all along the orbit. Assuming a simple, positional independent set of parameters, our calculations are consistent with a peak of gamma-ray flux at the periastron passage with a secondary maximum near apastron. Under this assumption, gamma-ray signals would be in contrast with the radio/X-ray outbursts which peak clearly after periastron. We finally calculate the opacity of the ambient photon field to the propagation of the gamma-rays. The spectral energy distribution appears strongly attenuated in a wide band (50 GeV - 50 TeV) due to local absorption. These spectral features should be detectable by an instrument like MAGIC through exposures integrated along several periastron passages.Fil: Christiansen, Hugo. Universidade Estadual Do Ceara; BrasilFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomia; ArgentinaFil: Orellana, Mariana Dominga. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomia; Argentin

Supernovas: explosiones estelares

El 2015 fue el Año Internacional de la Luz. En la Universidad Nacional de Río Negro realizamos la segunda Muestra de Fotografía Astronómica que en este caso se centró en un tema de investigación actual: las explosiones de supernovas.Facultad de Ciencias Astronómicas y Geofísica

On the reprocessing of gamma-rays produced by jets

Systems of two very different sizescales are known to produce very high-energy (VHE) radiation in their jets: AGNs and microquasars. The produced VHE photons (Eγ ∼ 1 TeV) can be absorbed by the intense environmental soft photon fields, coming from the companion star (in high mass binaries) or from the accreting material (disk+corona in AGNs), as these are the dominant sources at energies around ∼ (me c2 ) 2/Eγ . Energetic pairs are created by the photonphoton annihilation, and, depending on how efficient are the competing cooling channels, the absorption can lead to a reprocessing by Inverse Compton pair-cascade development. A selfconsistent modeling of these systems as gamma-ray sources should then include, along with the emission and absorption processes, a thorough treatment of the pair cascades. We discuss here on this issue, focusing on our (preliminary) results of numerical simulations devoted to a study case similar to the high-mass microquasar candidate LS 5039.Facultad de Ciencias Astronómicas y Geofísica

On the reprocessing of gamma-rays produced by jets

Systems of two very different sizescales are known to produce very high-energy (VHE) radiation in their jets: AGNs and microquasars. The produced VHE photons (Eγ ∼ 1 TeV) can be absorbed by the intense environmental soft photon fields, coming from the companion star (in high mass binaries) or from the accreting material (disk+corona in AGNs), as these are the dominant sources at energies around ∼ (me c2 ) 2/Eγ . Energetic pairs are created by the photonphoton annihilation, and, depending on how efficient are the competing cooling channels, the absorption can lead to a reprocessing by Inverse Compton pair-cascade development. A selfconsistent modeling of these systems as gamma-ray sources should then include, along with the emission and absorption processes, a thorough treatment of the pair cascades. We discuss here on this issue, focusing on our (preliminary) results of numerical simulations devoted to a study case similar to the high-mass microquasar candidate LS 5039.Facultad de Ciencias Astronómicas y Geofísica

Gamma-Ray Emission From Be/X-Ray Binaries

Be/X-ray binaries are systems formed by a massive Be star and a magnetized neutron star, usually in an eccentric orbit. The Be star has strong equatorial winds occasionally forming a circumstellar disk. When the neutron star intersects the disk the accretion rate dramatically increases and a transient accretion disk can be formed around the compact object. This disk can last longer than a single orbit in the case of major outbursts. If the disk rotates faster than the neutron star, the Cheng-Ruderman mechanism can produce a current of relativistic protons that would impact onto the disk surface, producing gamma-rays from neutral pion decays and initiating electromagnetic cascades inside the disk. In this paper we present calculations of the evolution of the disk parameters during both major and minor X-ray events, and we discuss the generation of gamma-ray emission at different energies within a variety of models that include both screened and unscreened disks.Facultad de Ciencias Astronómicas y Geofísica

On the nature of the episodic gamma-ray flare observed in Cygnus X-1

The high-mass microquasar Cygnus X-1, the best established candidate for a stellar-mass black hole, has been detected in a flaring state at very high energies, E > 200 GeV (Albert et al. 2007). The observation was per- formed by the Atmospheric Cherenkov Telescope MAGIC. It is the first experimental evidence of very high energy emission produced by a galactic stellar-mass black hole. The observed high energy excess occurred in coin- cidence with an X-ray flare. The flare took place at orbital phase = 0.91, being = 1 the moment when the black hole is behind the companion star. In this configuration the absorption of gamma-ray photons produced by photon-photon annihilation with the stellar field is expected to be the highest. We present detailed calculations of the gamma-ray opacity due to pair creation along the whole orbit, and for different locations of the emitter (height above the compact object). We discuss the location of the gamma- ray producing region in Cygnus X-1 and the energetics required to produce the flare.Facultad de Ciencias Astronómicas y Geofísica

On the nature of the episodic gamma-ray flare observed in Cygnus X-1

The high-mass microquasar Cygnus X-1, the best established candidate for a stellar-mass black hole, has been detected in a flaring state at very high energies, E > 200 GeV (Albert et al. 2007). The observation was per- formed by the Atmospheric Cherenkov Telescope MAGIC. It is the first experimental evidence of very high energy emission produced by a galactic stellar-mass black hole. The observed high energy excess occurred in coin- cidence with an X-ray flare. The flare took place at orbital phase = 0.91, being = 1 the moment when the black hole is behind the companion star. In this configuration the absorption of gamma-ray photons produced by photon-photon annihilation with the stellar field is expected to be the highest. We present detailed calculations of the gamma-ray opacity due to pair creation along the whole orbit, and for different locations of the emitter (height above the compact object). We discuss the location of the gamma- ray producing region in Cygnus X-1 and the energetics required to produce the flare.Fil: del Valle, Maria Victoria. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomia; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomia; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Orellana, Mariana Dominga. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomia; Argentina. Universidad de Valparaíso; Chil

Gamma-ray absorption and the origin of the gamma-ray flare in Cygnus X-1

Context. The high-mass microquasar Cyg X-1, the best-established candidate for a stellar-mass black hole in the Galaxy, has been detected in a flaring state at very high energies (VHE), E > 200 GeV, by the Atmospheric Cherenkov Telescope MAGIC. The flare occurred at orbital phase φ = 0.91, where φ = 1 is the configuration with the black hole behind the companion high-mass star, when the absorption of gamma-ray photons by photon-photon annihilation with the stellar field is expected to be highest. Aims. We aim to set up a model for the high-energy emission and absorption in Cyg X-1 that can explain the nature of the observed gamma-ray flare. Methods. We study the gamma-ray opacity due to pair creation along the whole orbit, and for different locations of the emitter. Then we consider a possible mechanism for the production of the VHE emission. Results. We present detailed calculations of the gamma-ray opacity and infer from these calculations the distance from the black hole where the emitting region was located. We suggest that the flare was the result of a jet-clump interaction where the decay products of inelastic p - p collisions dominate the VHE outcome. Conclusions. We are able to reproduce the spectrum of Cyg X-1 during the observed flare under reasonable assumptions. The flare may be the first event of jet-cloud interaction ever detected at such high energies.Facultad de Ciencias Astronómicas y Geofísica