276 research outputs found
Radiation from matter entrainment in astrophysical jets: the AGN case
Jets are found in a variety of astrophysical sources, from young stellar
objects to active galactic nuclei. In all the cases the jet propagates with a
supersonic velocity through the external medium, which can be inhomogeneous,
and inhomogeneities could penetrate into the jet. The interaction of the jet
material with an obstacle produces a bow shock in the jet in which particles
can be accelerated up to relativistic energies and emit high-energy photons. In
this work, we explore the active galactic nuclei scenario, focusing on the
dynamical and radiative consequences of the interaction at different jet
heights. We find that the produced high-energy emission could be detectable by
the current gamma-ray telescopes. In general, the jet-clump interactions are a
possible mechanism to produce (steady or flaring) high-energy emission in many
astrophysical sources in which jets are present.Comment: 4 pages, 2 figures. Accepted for publication in the Proceedings of
the 275 IAU Symposium: "Jets at all Scales", held in Buenos Aires, September
13-17, 201
Formación estelar y rayos gamma
Las estrellas se clasifican de acuerdo a su masa M en masivas (M ≥ 8M⊙) y poco masivas (M ≤ 8M⊙). Entre estas últimas podemos incluir, por ejemplo, al Sol cuya masa es M⊙ ∼ 2 × 10 30 kg 1 . Estas estrellas de baja masa son fáciles de detectar y es por esto que se conoce bastante de su formación y evolución. Sin embargo, no ocurre lo mismo con las estrellas masivas, las cuales se encuentran embebidas en grandes condensaciones de gas y polvo con lo cual la extinción de la luz que emiten es grande y poco llega de ellas a nuestros detectores. Por esta razón el estudio de las estrellas masivas es complejo aunque no por esto menos excitante, siendo la formación de estas estrellas uno de los problemas candentes de la astrofÃsica actual.
Básicamente existen dos modelos posibles para la formación de estrellas masivas. Uno es el que sugiere un mecanismo similar al que opera en las estrellas de baja masa, y el otro es el que sostiene una formación de tipo jerárquica; esto es, primero se formarÃan las estrellas de baja masa y luego, por la coalisción de algunas de éstas, las estrellas masivas.
Observaciones recientes de objetos estelares jóvenes (YSOs por Young Stellar Objects) cercanos sugieren que el primero serÃa el mecanismo elegido por la naturaleza para formar las estrellas de gran masa. Esto es, un proceso de condensación de inhomogeneidades en una nube molecular, con la consecuente formación de un disco a través del cual se acreta material de la nube (disco de acreción) y la ejección de materia a través de flujos (jets) bipolares, serÃa la secuencia de hechos en la formación estelar, para todo el espectro de masas.
En este artÃculo revisaremos la teorÃa y las observaciones con las que cuentan hoy en dÃa los astrónomos para estudiar la formación de las estrellas masivas y luego veremos las especulaciones teóricas que pueden hacerse a partir de lo que se observa y se conoce. En particular, nos concentraremos en la posible emisión en rayos gamma2 de las estrellas masivas en formación
High-energy flares from jet-clump interactions
High-mass microquasars are binary systems composed by a massive star and a
compact object from which relativistic jets are launched. Regarding the
companion star, observational evidence supports the idea that winds of hot
stars are formed by clumps. Then, these inhomogeneities may interact with the
jets producing a flaring activity. In the present contribution we study the
interaction between a jet and a clump of the stellar wind in a high-mass
microquasar. This interaction produces a shock in the jet, where particles may
be accelerated up to relativistic energies. We calculate the spectral energy
distributions of the dominant non-thermal processes: synchrotron radiation,
inverse Compton scattering, and proton-proton collisions. Significant levels of
X- and gamma-ray emission are predicted, with luminosities in the different
domains up to ~ 10^{34} - 10^{35} erg/s on a timescale of about ~ 1 h. Finally,
jet-clump interactions in high-mass microquasars could be detectable at high
energies. These phenomena may be behind the fast TeV variability found in some
high-mass X-ray binary systems, such as Cygnus X-1, LS 5039 and LS I+61 303. In
addition, our model can help to derive information on the properties of jets
and clumpy winds.Comment: Proceeding of the conference "High Energy Phenomena in Massive
Stars". Jaen (Spain), 2-5 February 200
Evidence that particle acceleration in hotspots of FR II galaxies is not constrained by synchrotron cooling
We study the hotspots of powerful radiogalaxies, where electrons accelerated
at the jet termination shock emit synchrotron radiation. The turnover of the
synchrotron spectrum is typically observed between infrared and optical
frequencies, indicating that the maximum energy of non-thermal electrons
accelerated at the shock is ~TeV for a canonical magnetic field of ~100 micro
Gauss. We show that this maximum energy cannot be constrained by synchrotron
losses as usually assumed, unless the jet density is unreasonably large and
most of the jet upstream energy goes to non-thermal particles. We test this
result by considering a sample of hotspots observed at radio, infrared and
optical wavelengths.Comment: 7 pages, 2 figures. To be appear in the proceedings of the conference
"Cosmic ray origin - beyond the standard models" (San Vito di Cadore, Italy,
September 2016
Transient gamma-ray emission from Cygnus X-3
The high-mass microquasar Cygnus X-3 has been recently detected in a flaring
state by the gamma-ray satellites Fermi and Agile. In the present contribution,
we study the high-energy emission from Cygnus X-3 through a model based on the
interaction of clumps from the Wolf-Rayet wind with the jet. The clumps inside
the jet act as obstacles in which shocks are formed leading to particle
acceleration and non-thermal emission. We model the high energy emission
produced by the interaction of one clump with the jet and briefly discus the
possibility of many clumps interacting with the jet. From the characteristics
of the considered scenario, the produced emission could be flare-like due to
discontinuous clump penetration, with the GeV long-term activity explained by
changes in the wind properties.Comment: Contribution to the proceedings of the 25th Texas Symposium on
Relativistic Astrophysics - TEXAS 2010, December 06-10, Heidelberg, German
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.Comment: Accepted for publication on MNRAS (15 pages, 9 figures
Gamma rays from cloud penetration at the base of AGN jets
Dense and cold clouds seem to populate the broad line region surrounding the
central black hole in AGNs. These clouds could interact with the AGN jet base
and this could have observational consequences. We want to study the gamma-ray
emission produced by these jet-cloud interactions, and explore under which
conditions this radiation would be detectable. We investigate the
hydrodynamical properties of jet-cloud interactions and the resulting shocks,
and develop a model to compute the spectral energy distribution of the emission
generated by the particles accelerated in these shocks. We discuss our model in
the context of radio-loud AGNs, with applications to two representative cases,
the low-luminous Centaurus A, and the powerful 3C 273. Some fraction of the jet
power can be channelled to gamma-rays, which would be likely dominated by
synchrotron self-Compton radiation, and show typical variability timescales
similar to the cloud lifetime within the jet, which is longer than several
hours. Many clouds can interact with the jet simultaneously leading to fluxes
significantly higher than in one interaction, but then variability will be
smoothed out. Jet-cloud interactions may produce detectable gamma-rays in
non-blazar AGNs, of transient nature in nearby low-luminous sources like Cen A,
and steady in the case of powerful objects of FR II type.Comment: Accepted for publication in A&A (9 pages, 7 figures
Gamma-rays from the compact colliding wind region in Cyg OB2 #5
In this contribution we model the non-thermal emission (from radio to
gamma-rays) produced in the compact (and recently detected) colliding wind
region in the multiple stellar system Cyg OB2 #5. We focus our study on the
detectability of the produced gamma-rays.Comment: To appear in the proceedings of the 5th International Symposium on
High-Energy Gamma-Ray Astronomy (Gamma2012), held in Heidelberg, July 9-13,
201
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