Gamma-rays from the pulsar wind nebulae

Abstract

Abstract. We investigate the radiation processes inside supernova remnants which are powered by young pulsars. Using a recent model for particle acceleration by the pulsar wind nebulae (PWNe), in which positrons gain energy in the process of resonant scattering by the heavy nuclei, we construct a time-dependent radiation model for the PWNe. In this model, the spectra of relativistic particles, injected inside the nebula, depend on time due to the evolution of the pulsar parameters. Applying a simple model for the evolution of the PWNa, the equilibrium spectra of leptons and nuclei inside the nebula are determined as a function of time, taking into account the energy losses of particles on different processes and their escape from the nebula. We calculate the multiwavelength photon spectra produced by leptons and nuclei and compare them with the observations of the PWNe for which TeV γ-ray emission has been reported, i.e. the Crab Nebula, the Vela Supernova Remnant, and the nebula around PSR 1706-44. It is found that the emission from the Crab Nebula can be well fitted by the composition of the γ-ray emission produced by leptons (below ∼10 TeV) and nuclei (∼10 TeV). The model is further tested by successful fitting of the high energy spectrum from the Vela SNR. In this case, the observed γ-ray emission is mainly due to leptons and the contribution of γ-rays from decay of neutral pions, produced in collision of nuclei, is significantly lower. However, the considered model does not give good fitting to the emission from PSR1706-44 for the likely parameters of this source, unless an additional target for relativistic leptons is present inside the nebula, e.g. the thermal infrared emission. Based on the knowledge obtained from these fittings, we predict the γ-ray fluxes in the TeV energy range from other PWNe, which are promissing TeV γ-ray sources due to their similarities to the γ-ray nebulae, i.e. MSH15-52 (PSR 1509-58), 3C58 (PSR J0205+6449), and CTB80 (PSR 1951+32). Possible detection of these sources by the new generation of Cherenkov telescopes is discussed.

Multi-waveband photons and high energy neutrinos from the Crab nebula

“…In a PWN, leptons are excited by relativistic nuclei and consist of four components: positrons accelerated in a realistic magnetosonic lepton-heavy iron plasma shock, electrons from neutron decay, direct electrons, and secondary electron/positron pairs in a proton-proton interaction (Bednarek & Bartosik 2003). We now give the spectra of the four kinds of leptons and show that the last three components are negligible compared to the first component.…”

“…Jager & Harding 1992; Atoyan & Aharonian 1996;Zhang et al 2008) and hadronic origin models (e.g. Cheng et al 1990;Atoyan & Aharonian 1996;Bednarek & Prothero 1997;Bednarek & Bartosik 2003; a review see Bednarek 2007).…”

“…On the other hand, the selfconsistent, time dependent hadronic-leptonic model has been proposed to account for the high energy processes inside PWNe (e.g. Bednarek & Prothero 1997;Bednarek & Bartosik 2003, 2005. In such a model, heavy nuclei are accelerated in the pulsar magnetosphere, and then suffer partial photo-disintegration in the non-thermal radiation fields of pulsar's outer magnetosphere, leading to the production of relativistic protons and neutrons.…”

“…In this paper we study the production of non-thermal photons and high-energy neutrinos in the Crab nebula based on the model of Bednarek & Protheroe (1997) and Bednarek & Bartosik (2003). In our treatment, we consider the relativistic proton spectrum from both direct proton production and indirect proton production from neutron decay through the disintegration process.…”

“…We also consider four kinds of leptons: the positrons accelerated in a realistic magneto-sonic lepton-heavy iron plasma shock (Hoshino & Arons 1991;Hoshino et al 1992;Gallant & Arons 1994), electrons accompanying neutron decay, direct electrons, and secondary e ± pairs in proton-proton (pp) collisions (We call them nuclei-excited leptons except for the direct electrons, which accompany the nuclei). Different from the work in Bednarek & Bartosik (2003), we include the direct proton contribution which dominates the high-energy end of the proton spectrum, and use the complete form of the positron spectrum (i.e. a Maxwellian distribution plus a power-law tail) given by Hishino et al (1992).…”