Ref HAL: hal-00430342_v1
Ref Arxiv: 0802.2661
Ref. & Cit.: NASA ADS
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Abstract:

Extreme objects such as X-ray binaries, AGN, or $\gamma$-ray bursters harborhigh energy plasmas whose properties are not well understood yet. Not only arethey responsible of the hard X- and $\gamma$-ray emission we observe but alsothey have a strong influence on the main dynamics and energetics of theseobjects themselves. Here we present a new kinetic code that solves theevolution equations for particles and photons around compact objects. Itproduces spectra that will be compared with observations from Simbol-X toconstrain the radiation and acceleration processes in these objects.

Comments: Poster at the international workshop 'Simbol-X: the hard X-ray universe in focus' held in Bologna, 14-16 May 2007. To appear in Memorie della SAIt, 2 pages, 1 figure

Ref HAL: hal-00430340_v1
Ref Arxiv: 0807.3459
DOI: 10.1111/j.1365-2966.2008.14219.x
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46 citations
Abstract:

Fermi acceleration can take place at ultra-relativistic shock waves if theupstream or downstream magnetic field has been remodeled so that most of themagnetic power lies on short spatial scales. The relevant conditions underwhich Fermi acceleration become efficient in the presence of both a coherentand a short scale turbulent magnetic field are addressed. Within the MHDapproximation, this paper then studies the amplification of a pre-existingmagnetic field through the streaming of cosmic rays upstream of a relativisticshock wave. The magnetic field is assumed to be perpendicular in the shockfront frame, as generally expected in the limit of large shock Lorentz factor.In the MHD regime, compressive instabilities seeded by the net cosmic-raycharge in the shock precursor (as seen in the shock front frame) develop on theshortest spatial scales but saturate at a moderate level deltaB/B ~ 1, which isnot sufficient for Fermi acceleration. As we argue, it is possible that otherinstabilities outside the MHD range provide enough amplification to allowsuccessful Fermi acceleration.

Ref HAL: hal-00430336_v1
Ref Arxiv: 0808.1258
DOI: 10.1051/0004-6361:200809982
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43 citations
Abstract:

Modelling the emission properties of compact high energy sources such asX-ray binaries, AGN or gamma-ray bursts represents a complex problem.Contributions of numerous processes participate non linearly to produce theobserved spectra: particle-particle, particle-photon and particle-waveinteractions. In the past decades, numerical simulations have been widely usedto address the key properties of the high energy plasmas present in thesesources. This article presents a code that has been designed to investigatethese questions. It includes most of the relevant processes needed to simulatethe emission of high energy sources. This code solves the time-dependentkinetic equations for homogeneous, isotropic distributions of photons,electrons and positrons. No assumption is made on the shape of thesedistributions. Have been included so far: syn- chrotron self-absorbedradiation, Compton scattering, pair production/annihilation, e-e and e-pCoulomb collisions and some prescriptions for additional particle heating andacceleration. We also present comparisons with earlier works and some examplesto illustrate the code computational capacities. Previous results arereproduced qualitatively but some differences are often found in the details ofthe particle As a first application of the code, we investigate acceleration bysecond order Fermi-like processes and we find that the energy threshold foracceleration has a crucial influence on the particle distribution and theemitted spectrum.

Ref HAL: hal-00430333_v1
Ref Arxiv: 0810.5639
Ref. & Cit.: NASA ADS
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The high energy emission of microquasars is thought to originate from highenergy particles. Depending on the spectral state, the distribution of theseparticles can be thermal with a high temperature (typically 100 keV) ornon-thermal and extending to even higher energy. The properties of high energyplasmas are governed by a rich microphysics involving particle-particlecollisions and particles-photons interactions. We present a new code developed to address the evolution of relativisticplasmas. This one-zone code focuses on the microphysics and solves the coupledkinetic equations for particles and photons, including Compton scattering,synchrotron emission and absorption, pair production and annihilation,bremsstrahlung emission and absorption, Coulomb interactions, and prescriptionsfor additional particle acceleration and heating. It can in particular describemechanisms such a thermalisation by synchrotron self-absorption and Coulombcollisions. Using the code, we investigate whether various acceleration processes, namelythermal heating, non-thermal acceleration and stochastic acceleration, canreproduce the different spectral states of microquasars. Premilinary resultsare presented.

Comments: 9 pages, 6 figures, proceedings of the VII Microquasar Workshop: Microquasars and Beyond, September 1-5 2008, Foca, Izmir, Turkey; accepted for publication in PoS

Ref HAL: hal-00430326_v1
Ref Arxiv: 0810.5640
Ref. & Cit.: NASA ADS
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Abstract:

Accreting sources such as AGN, X-ray binaries or gamma-ray bursts are knownto be strong, high energy emitters. The hard emission is though to originatefrom plasmas of thermal and/or non-thermal high energy particles. Not only doesthis emission allow to probe the unique properties of the matter in an extremeenvironment, but it also has a crucial backreaction on the energetics and thedynamics of the emitting medium itself. Understanding interactions betweenradiation and matter has become a key issue in the modelling of high energysources. Although most cross sections are well known, they are quite complexand the way all processes couple non-linearly is still an open issue. We present a new code that solves the local, kinetic evolution equations fordistributions of electrons, positrons and photons, interacting by radiationprocesses such as self-absorbed synchrotron and brems-strahlung radiation,Compton scattering, pair production/annihilation, and by Coulomb collisions.The code is very general and aimed to modelled various high energy sources. Asan application, we study the spectral states of X-ray binaries, includingthermalization by Coulomb collisions and synchrotron self-absorption. It isfound that the low-hard and high-soft states can be modelled with differentillumination but the same non-thermal acceleration mechanism.

Comments: SF2A-2008: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics Eds.: C. Charbonnel, F. Combes and R. Samadi. Available online at http://proc.sf2a.asso.fr, p.171

Ref HAL: hal-00430249_v1
DOI: 10.1016/j.nuclphysbps.2007.11.019
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Abstract:

On the basis of the extensive air shower (EAS) data obtained by the GAMMA experiment, the energy spectra and elemental composition of the primary cosmic rays are derived in the 1–100 PeV energy range. The reconstruction of the primary energy spectra is carried out using an EAS inverse approach with the hypothesis of power-law primary energy spectra with rigidity-dependent knees. The rigidity-dependent knee feature of the primary energy spectra is displayed at the rigidities ER ~= 2.5±0.2 PeV/Z and ER ~= 3.1–4.2 PeV/Z for the SIBYLL and QGSJET interaction models respectively. Using the event-by-event method of the primary energy evaluation from the measured Nch, Nμ and shower age (s) parameters, the all-particle energy spectrum is also obtained.

Comments: Proceedings of the XIV International Symposium on Very High Energy Cosmic Ray Interactions

Ref HAL: hal-00430148_v1
Ref Arxiv: 0809.0584
DOI: 10.1088/0004-637X/690/2/L101
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86 citations
Abstract:

The High Energy Stereoscopic System (HESS) survey of the Galactic plane hasestablished the existence of a substantial number (~40) of Galactic TeVgamma-ray sources, a large fraction of which remain unidentified. HESSJ0632+057 is one of a small fraction of these objects which is point-like innature(<2' rms), and is one of only two point-like sources that remainunidentified. Follow-up observations of this object with XMM-Newton haverevealed an X-ray source coincident with the TeV source and with the massivestar MWC 148, of the spectral type B0pe. This source exhibits a hard spectrum,consistent with an absorbed power law with Gamma = 1.26 +/- 0.04, and showssignificant variability on hour timescales. We discuss this spatial coincidenceand the implied spectral energy distribution of this object and argue that itis likely a new gamma-ray binary system with a close resemblance to the threeknown members of this class, and in particular to LS I +61 303. Further X-ray,radio and optical observations of this system are needed to firmly establishHESS J0632+057 as a new member of this rare class of Galactic objects.