The synchrotron-self-Compton spectrum of relativistic blast waves at large Y

Recent analyses of multiwavelength light curves of gamma-ray bursts afterglows point to values of the magnetic turbulence well below the canonical $\sim1\,$\% of equipartition, in agreement with theoretical expectations of a micro-turbulence generated in the shock precursor, which then decays downstream of the shock front through collisionless damping. As a direct consequence, the Compton parameter $Y$ can take large values in the blast. In the presence of decaying micro-turbulence and/or as a result of the Klein-Nishina suppression of inverse Compton cooling, the $Y$ parameter carries a non-trivial dependence on the electron Lorentz factor, which modifies the spectral shape of the synchrotron and inverse Compton components. This paper provides detailed calculations of this synchrotron-self-Compton spectrum in this large $Y$ regime, accounting for the possibility of decaying micro-turbulence. It calculates the expected temporal and spectral indices $\alpha$ and $\beta$ customarily defined by $F_\nu\,\propto\,t_{\rm obs}^{-\alpha}\nu^{-\beta}$ in various spectral domains. This paper also makes predictions for the very high energy photon flux; in particular, it shows that the large $Y$ regime would imply a detection rate of gamma-ray bursts at $>10\,$GeV several times larger than currently anticipated.Comment: 13 pages, 6 figures, to appear in MNRA

Simple Proof Of A Known Result In Random-Walk Theory

Mathematic

Parental Gifts: Father-Son Dedications and Dialogues in Roman Didactic Literature

published or submitted for publicatio

Relativistic shock acceleration and some consequences

This paper summarizes recent progresses in our theoretical understanding of particle acceleration at relativistic shock waves and it discusses two salient consequences: (1) the maximal energy of accelerated particles; (2) the impact of the shock-generated micro-turbulence on the multi-wavelength light curves of gamma-ray burst afterglows.Comment: 10 pages,1 figure. To appear in the Proceedings of the HEPRO IV (High Energy Phenomena in Relativistic Outflows) Conference (Heidelberg, Germany, July 2013), eds. F. Rieger and F. Aharonian, in Int. J. Mod. Phys. Conf. Se

Inhomogeneous extragalactic magnetic fields and the second knee in the cosmic ray spectrum

Various experiments indicate the existence of a second knee around energy E=3.10^{17} eV in the cosmic ray spectrum. This feature could be the signature of the end of the galactic component and of the emergence of the extragalactic one, provided that the latter cuts off at low energies. Recent analytical calculations have shown that this cut-off could be a consequence of the existence of extragalactic magnetic fields: low energy protons diffuse on extragalactic magnetic fields and cannot reach the observer within a given time. We study the influence of inhomogeneous magnetic fields on the magnetic horizon, using a new semi-analytical propagation code. Our results indicate that, at a fixed value of the volume averaged magnetic field , the amplitude of the low energy cut-off is mainly controled by the strength of magnetic fields in the voids of the large scale structure distribution.Comment: 15 pages, 10 figures. Version to appear in PRD (minor changes

Relativistic Fermi acceleration with shock compressed turbulence

This paper presents numerical simulations of test particle Fermi acceleration at relativistic shocks of Lorentz factor Gamma_sh = 2-60, using a realistic downstream magnetic structure obtained from the shock jump conditions. The upstream magnetic field is described as pure Kolmogorov turbulence; the corresponding downstream magnetic field lies predominantly in the plane tangential to the shock surface and the coherence length is smaller along the shock normal than in the tangential plane. Acceleration is nonetheless efficient and leads to powerlaw spectra with index s = 2.6-2.7 at large shock Lorentz factor Gamma_sh >> 1, markedly steeper than for isotropic scattering downstream. The acceleration timescale t_acc in the upstream rest frame becomes a fraction of Larmor time t_L in the ultra-relativistic limit, t_acc ~ 10 t_L/Gamma_sh. Astrophysical applications are discussed, in particular the acceleration in gamma-ray bursts internal and external shocks.Comment: 11 pages; 10 figures; submitted to MNRA

Annex A5 : A model of the stochastic convergence between euro area business cycles.

A new non-linear parametric model, the Stochastic Cyclical Convergence Model (SCCM), is used for measuring the convergence of business cycles between euro area countries and the euro area aggregate. The model combines unobserved component models with time-varying parameter models. The convergence between the two cycles is characterised by two time-varying parameters, the phase-shift and a weight, which is related to the phase-adjusted correlation. A Kalman filter-based iterative procedure is used for the model estimation. SCCM models are applied to the GDP of euro area countries, the United Kingdom and of the euro area aggregate over the period 1963:1-2002:4. When the euro was launched, the convergence was already achieved for most of euro area countries, but Finland, Greece and Ireland had still not converged in 2002:4. The British cycle is also divergent with a lead equal to 3 quarters in 2002:4 and a weight equal to 0.6 in 2002:4. UK shocks have asynchronous asymmetric effects and this suggests that it would be delicate for the UK to join the euro area.convergence;synchronisation;business cycles;multivariate unobserved components models;time-varying parameter models;Kalman filter;