Search

A large fraction of core-collapse supernovae are thought to result in the birth of a rotation-powered pulsar, which is later observable as a radio pulsar up to great ages. The birth properties of these pulsars, and in particular the distribution of their initial rotation periods, are however difficult to infer from studies of the radio pulsar population in our Galaxy. Yet the distributions of their birth properties is an important assumption for scenarios in which ultra-high-energy cosmic rays (UHECRs) originate in very young, extragalactic pulsars with short birth periods and/or high magnetic fields.Using a model of the very young pulsar wind nebula’s dynamical and spectral evolution, with pulsar wind and accelerated particle parameters assumed similar to those inferred from modeling young pulsar wind nebulae (PWNe) in our Galaxy, we show that X-ray observations of supernovae, a few years to decades after the explosion, constitute a favored window to obtain meaningful constraints on the initial spin-down luminosity of the newly-formed pulsar. We examine the expected emerging PWN spectral component, taking into account the X-ray opacity of the expanding supernova ejecta, and find that it is typically best detectable in < 10 keV X-rays some years after the explosion. We use this framework to assess available X-ray observations and flux upper limits on supernovae, building on the work of Perna et al. (2008). We note that a resulting limit on spin-down luminosity corresponds univocally to a limit on the maximum magnetospheric acceleration potential, irrespective of the specific combination of magnetic field and rotation period that achieves it. We use available X-ray observations of supernovae to place constraints on the birth spin-down luminosity and period distribution of classical pulsars. We also examine the case of magnetars, born with much higher magnetic fields, and show that their much shorter initial spin-down time implies that any plausible signature of young magnetar wind nebulae can only be observed in harder X-ray or gamma-rays. [ABSTRACT FROM PUBLISHER]

In recent years, it has become a well-established paradigm that many aspects of the physics of Pulsar Wind Nebulae can be fully accounted for within a relativistic magnetohydrodynamic description. Numerical simulations have proven extremely successful in reproducing the X-ray morphology of the Crab nebula, down to very fine detail. Radio emission, instead, is currently one of the most obscure aspects of the physics of these objects, and one that holds important information about pulsar properties and their role as antimatter factories. Here, we address the question of radio emission morphology and integrated spectrum from the Crab nebula, by using for the first time an axisymmetric dynamical model with parameters chosen to best reproduce its X-ray morphology. Based on our findings we discuss constraints on the origin of the radio emitting particles. [ABSTRACT FROM AUTHOR]

Context. Observation of Balmer lines from the region around the forward shock of supernova remnants may provide precious information on the shock dynamics and on the efficiency of particle acceleration at the shock. Aims. We calculate the Balmer line emission and the shape of the broad Balmer line for parameter values suitable for SNR 0509-67.5, as a function of the cosmic ray acceleration efficiency and of the level of thermal equilibrium between electrons and protons behind the shock. This calculation aims to use the width of the broad Balmer line emission to infer the cosmic ray acceleration efficiency in this remnant. Methods. We use the recently developed nonlinear theory of diffusive shock acceleration in the presence of neutrals. The semianalytical approach that we developed includes a description of magnetic field amplification as due to resonant streaming instability, the dynamical reaction of both accelerated particles and turbulent magnetic field on the shock, and all channels of interaction between neutral atoms and background plasma that change the shock dynamics. Results. We achieve a quantitative assessment of the CR acceleration efficiency in SNR 0509-67.5 as a function of the shock velocity and different levels of electron-proton thermalization in the shock region. If the shock moves faster than ~4500 km s-1, one can conclude that particle acceleration must be taking place with an efficiency of several tens of percent. For lower shock velocity the evidence of particle acceleration becomes less clear because of the uncertainty in the electron-ion equilibrium downstream. We also discuss the role of future measurements of the narrow Balmer line. [ABSTRACT FROM AUTHOR]

Abstract: We present here a semi-analytical solution of the problem of particle acceleration at non-linear shock waves with a free-escape boundary at some location upstream. This solution, besides allowing us to determine the spectrum of particles accelerated at the shock front, including the shape of the cutoff at some maximum momentum, also allows us to determine the spectrum of particles escaping the system from upstream. This latter aspect of the problem is crucial for establishing a connection between the accelerated particles in astrophysical sources, such as supernova remnants, and the cosmic rays observed at the Earth. An excellent approximate solution, which leads to a computationally fast calculation of the structure of shocks with an arbitrary level of cosmic ray modification, is also obtained. [Copyright &y& Elsevier]

Stationary solutions to the problem of particle acceleration at shock waves in the non-linear regime, when the dynamical reaction of the accelerated particles on the shock cannot be neglected, are known to show a prominent energy flux escaping from the shock towards upstream infinity. On physical grounds, the escape of particles from the upstream region of a shock has to be expected in all those situations in which the maximum momentum of accelerated particles, , decreases with time, as is the case for the Sedov–Taylor phase of expansion of a shell supernova remnant, when both the shock velocity and the cosmic ray induced magnetization decrease. In this situation, at each time t, particles with momenta larger than leave the system from upstream, carrying away a large fraction of the energy if the shock is strongly modified by the presence of cosmic rays. This phenomenon is of crucial importance for explaining the cosmic ray spectrum detected at the Earth. In this paper, we discuss how this escape flux appears in the different approaches to non-linear diffusive shock acceleration, and especially in the quasi-stationary semi-analytical kinetic ones. We apply our calculations to the Sedov–Taylor phase of a typical supernova remnant, including in a self-consistent way particle acceleration, magnetic field amplification and the dynamical reaction on the shock structure of both particles and fields. Within this framework, we calculate the temporal evolution of the maximum energy reached by the accelerated particles and of the escape flux towards upstream infinity. The latter quantity is directly related to the cosmic ray spectrum detected at the Earth. [ABSTRACT FROM AUTHOR]

Abstract: The supernova paradigm for the origin of galactic cosmic rays can be tested using multifrequency observations of both non-thermal and thermal emission from supernova remnants. The smoking gun of hadronic acceleration in these sources can, however, only be provided by the detection of a high energy neutrino signal. Here we apply the theory of non-linear particle acceleration at supernova shocks to the case of the supernova remnant RX J1713.7–3946, which is becoming the stereotypical example of a possible hadronic accelerator after the detection of high energy gamma rays by the HESS telescope. Our aim is twofold: on one hand we want to address the uncertainties in the discrimination between a hadronic and a leptonic interpretation of the gamma ray emission, mainly related to the possibility of a statistical uncertainty in the energy determination of the gamma ray photons in the TeV region. On the other we want to stress how a neutrino telescope would break the degeneracy and provide evidence for efficient cosmic ray acceleration in RX J1713.7–3946. A evidence would require about two years of observation. [Copyright &y& Elsevier]