Contribution of nuclei accelerated by gamma-ray pulsars to cosmic rays in the Galaxy

Abstract

We consider the galactic population of gamma-ray pulsars as possible sources of cosmic rays at and just above the "knee" in the observed cosmic ray spectrum at 10 15 -10 16 eV. We suggest that iron nuclei may be accelerated in the outer gaps of pulsars, and then suffer partial photo-disintegration in the non-thermal radiation fields of the outer gaps. As a result, protons, neutrons, and surviving heavier nuclei are injected into the expanding supernova remnant. We compute the spectra of nuclei escaping from supernova remnants into the interstellar medium, taking into account the observed population of radio pulsars.Our calculations, which include a realistic model for acceleration and propagation of nuclei in pulsar magnetospheres and supernova remnants, predict that heavy nuclei accelerated directly by gamma-ray pulsars could contribute about 20% of the observed cosmic rays in the knee region. Such a contribution of heavy nuclei to the cosmic ray spectrum at the knee can significantly increase the average value of ln A with increasing energy as is suggested by recent observations.

Gamma-rays from the pulsar wind nebulae

“…The most energetic nuclei can also diffuse out of the nebula. All these processes, adiabatic and collisional losses, fragmentation, escape, have been recently studied in detail by Bednarek & Protheroe (2002) with the purpose to calculate the contribution of pulsar accelerated nuclei to the cosmic rays in the Galaxy. In order to calculate the equilibrium spectra of different types of nuclei inside the nebula at a specific time, we follow the method adopted in Bednarek & Protheroe (2002), and described in detail in Sects.…”

“…2). However, in contrary to Bednarek & Protheroe (2002), who assumed that nuclei are accelerated only by the electric field of the outer gap in the pulsar magnetosphere (Cheng et al 1986), we make use of the model proposed by Gallant & Arons (1994) (see details in Sect. 3 in that paper), in which the nuclei can reach energies corresponding to the significant part of the electric field drop through the pulsar polar cap.…”

“…Therefore, the iron nuclei, extracted from the neutron star surface, are: (1) at first accelerated in the outer gap where they can lose only a small number of nucleons in collisions with the radiation field of the outer gap (see Sect. 4.1 in Protheroe 2002 andProtheroe 1997) and, (2) farther accelerated in the pulsar wind zone to the Lorentz factors γ Fe (Eq. (8)), determined by the pulsar parameters.…”

High energy neutrinos from fast spinning magnetars

“…Sato 1978; Protheroe, Bednarek, & Luo 1998; Bednarek & Protheroe 1997;Bednarek & Protheroe 2002). Neutrinos from slowly rotating magnetars were discussed recently by Zhang et al (2003).…”

“…Ion acceleration in the outer vacuum gap, as a source of high energy neutrinos, was discussed long ago by Sato (1978) and recently by Bednarek & Protheroe (1997) and, as high energy cosmic ray sources, was considered by Bednarek & Protheroe (2002). In those cases, the detailed mechanism of ion injection and constraints by pair production on the acceleration were not discussed.…”