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

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

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

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

Jet-Cloud Interactions in AGNs

Active galactic nuclei present continuum and line emission. The former is produced by the accretion disk and the jets, whereas the latter is originated by gas located close to the super-massive black hole. The small region where the broad lines are emitted is called the broad-line region. The structure of this region is not well known, although it has been proposed that it may be formed by small and dense ionized clouds surrounding the supermassive black-hole. In this work, we study the interaction of one cloud from the broad line region with the jet of the active galactic nuclei. We explore the high-energy emission produced by this interaction close to the base of the jet. The resulting radiation may be detectable for nearby non-blazar sources as well as for powerful quasars, and its detection could give important information on the broad line region and the jet itself.Comment: Proceeding of the conference "High-Energy Gamma-rays and Neutrinos from Extra-Galactic Sources". Heidelberg, 13-16 January 200

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

Particle acceleration and magnetic field amplification in the jets of 4C74.26

We model the multi-wavelength emission in the southern hotspot of the radio quasar 4C74.26. The synchrotron radio emission is resolved near the shock with the MERLIN radio-interferometer, and the rapid decay of this emission behind the shock is interpreted as the decay of the amplified downstream magnetic field as expected for small scale turbulence. Electrons are accelerated to only 0.3 TeV, consistent with a diffusion coefficient many orders of magnitude greater than in the Bohm regime. If the same diffusion coefficient applies to the protons, their maximum energy is only ~100 TeV.Comment: Accepted for publication in ApJ. 6 pages - 2 figures. Minor correction