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Araudo A.T.,National Autonomous University of Mexico | Bosch-Ramon V.,University of Barcelona | Romero G.E.,Instituto Argentino Of Radioastronomia | Romero G.E.,National University of La Plata
Monthly Notices of the Royal Astronomical Society | Year: 2013

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 supermassive 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 nonthermal 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. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Del Valle M.V.,Instituto Argentino Of Radioastronomia | Lazarian A.,University of Wisconsin - Madison | Santos-Lima R.,University of Sao Paulo
Monthly Notices of the Royal Astronomical Society | Year: 2016

Galactic cosmic rays are believed to be mostly accelerated at supernova shocks. However, the interstellar magnetic field is too weak to efficiently accelerate galactic cosmic rays up to the highest energies, i.e. 1015 eV. A stronger magnetic field in the pre-shock region could provide the efficiency required. Bell's cosmic ray non-resonant streaming instability has been claimed to be responsible for the amplification of precursor magnetic fields. However, an alternative mechanism has been proposed in which the cosmic ray pressure gradient forms the shock precursor and drives turbulence, amplifying the magnetic field via the small-scale dynamo. Key ingredients for the mechanism to operate are the inhomogeneities present in the interstellar medium. These inhomogeneities are the consequence of turbulence. In this work we explore the magnetic field amplification in different interstellar medium conditions through 3D magnetohydrodynamic numerical simulations. © 2016 The Authors.

Pepe C.,Institute Astronomia y Fisica del Espacio | Pepe C.,CONICET | Pellizza L.J.,Institute Astronomia y Fisica del Espacio | Pellizza L.J.,CONICET | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

In this work we investigate the accretion of cosmological fluids on to an intermediate-mass black hole at the centre of a globular cluster, focusing on the influence of the parent stellar system on the accretion flow. We show that the accretion of cosmic background radiation and the so-called dark energy on to an intermediate-mass black hole is negligible. On the other hand, if cold dark matter has a non-vanishing pressure, the accretion of dark matter is large enough to increase the black hole mass well beyond the present observed upper limits. We conclude that either intermediate-mass black holes do not exist, or dark matter does not exist, or it is not strictly collisionless. In the latter case, we set a lower limit for the parameter of the cold dark matter equation of state. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Romero G.E.,Instituto Argentino Of Radioastronomia | Romero G.E.,National University of La Plata | Vila G.S.,Instituto Argentino Of Radioastronomia | Perez D.,Instituto Argentino Of Radioastronomia
Astronomy and Astrophysics | Year: 2016

Context. Binary systems of supermassive black holes are expected to be strong sources of long gravitational waves prior to merging. These systems are good candidates to be observed with forthcoming space-borne detectors. Only a few of these systems, however, have been firmly identified to date. Aims. We aim at providing a criterion for the identification of some supermassive black hole binaries based on the characteristics of the high-energy emission of a putative relativistic jet launched from the most massive of the two black holes. Methods. We study supermassive black hole binaries where the less massive black hole has carved an annular gap in the circumbinary disk, but nevertheless there is a steady mass flow across its orbit. Such a perturbed disk is hotter and more luminous than a standard thin disk in some regions. Assuming that the jet contains relativistic electrons, we calculate its broadband spectral energy distribution focusing on the inverse Compton up-scattering of the disk photons. We also compute the opacity to the gamma rays produced in the jet by photon annihilation with the disk radiation and take into account the effects of the anisotropy of the target photon field as seen from the jet. Results. We find that the excess of low-energy photons radiated by the perturbed disk causes an increment in the external Compton emission from the jet in the X-ray band, and a deep absorption feature at energies of tens of TeVs for some sets of parameters. According to our results, observations with Cherenkov telescopes might help in the identification of supermassive black hole binaries, especially those black hole binaries that host primaries from tens to hundreds of million of solar masses. © ESO, 2016.

Araudo A.T.,University of Oxford | del Valle M.V.,Instituto Argentino Of Radioastronomia
Nuclear Physics B - Proceedings Supplements | Year: 2014

In addition to efficient particle accelerators in the Galaxy, such as supernova remnants and pulsar wind nebulae, other sources can accelerate particles up to very high energies. We present the case of protostellar jets and runaway stars, where strong shocks act upon electrons and protons through a diffusive process. The detection of synchrotron radio emission from these sources indicates that at least electrons are accelerated in these systems. If protons are accelerated as well, both population of relativistic particles can produce high-energy radiation through a variety of processes. We show results from models of the non-thermal emission, from radio to gamma rays, in these kind of sources. High-energy photons from both protostellar jets and massive runaways might be detectable with the current facilities in the GeV domain, or by the forthcoming Cherenkov arrays. A clear detection would prove that young stars are also cosmic ray accelerators. © 2014 Elsevier B.V.

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