Abstract
Relativistic winds of fast-spinning pulsars have been proposed as a potential site for cosmic-ray acceleration from very high energies (VHE) to ultrahigh energies (UHE). We re-examine conditions for high-energy neutrino production, considering the interaction of accelerated particles with baryons of the expanding supernova ejecta and the radiation fields in the wind nebula. We make use of the current IceCube sensitivity in diffusive high-energy neutrino background, in order to constrain the parameter space of the most extreme neutron stars as sources of VHE and UHE cosmic rays. We demonstrate that the current non-observation of 1018 eV neutrinos put stringent constraints on the pulsar scenario. For a given model, birthrates, ejecta mass and acceleration efficiency of the magnetar sources can be constrained. When we assume a proton cosmic ray composition and spherical supernovae ejecta, we find that the IceCube limits almost exclude their significant contribution to the observed UHE cosmic-ray flux. Furthermore, we consider scenarios where a fraction of cosmic rays can escape from jet-like structures piercing the ejecta, without significant interactions. Such scenarios would enable the production of UHE cosmic rays and help remove the tension between their EeV neutrino production and the observational data.
Highlights
10−4 of the neutron star population is required to achieve the ultrahigh energy cosmic ray (UHECR) flux level
In ref. [16], we demonstrated that for magnetars, the energy losses experienced by particles during their flight in the supernova ejecta did not allow their escape at ultrahigh energies, unless the ejecta mass was considerably lower than for standard core-collapse supernovae, or if a mechanism such as a jet was invoked to pierce the envelope
The interactions of cosmic rays within the nebula or supernova ejecta regions should lead to the generation of secondary particles, including high energy neutrinos, which has been suggested as a very powerful test of newborn pulsar scenarios for UHECRs [14]
Summary
Ions (from light to heavy nuclei) can be stripped off the neutron star surface by a combination of strong electric fields and bombardment of particles [31, 32]. In equation (2.1) we assume that the flux of particles being heated by the pulsar follows the Goldreich-Julian rate N GJ, as we consider the scenario that ions only get accelerated in the pulsar wind. Taking into account the neutron-star spin down (assuming a breaking index of 3, corresponding to a spin-down luminosity Lsd = Lp (1 + t/tsd)−1), we consider that cosmic rays are accelerated at a given time t3.5 = t/103.5 s at energy [12, 13]. Channeling the Goldreich-Julian charge density into particles and taking into account the neutron-star spin down rate, one can write the cosmic-ray injection flux [12, 13].
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