On ultra-high energy cosmic ray acceleration at the termination shock of young pulsar winds

Abstract

Pulsar wind nebulae (PWNe) are outstanding accelerators in Nature, in the sense that they accelerate electrons up to the radiation reaction limit. Motivated by this observation, this paper examines the possibility that young pulsar wind nebulae can accelerate ions to ultra-high energies at the termination shock of the pulsar wind. We consider here powerful PWNe, fed by pulsars born with ∼ millisecond periods. Assuming that such pulsars exist, at least during a few years after the birth of the neutron star, and that they inject ions into the wind, we find that protons could be accelerated up to energies of the order of the Greisen-Zatsepin-Kuzmin cut-off, for a fiducial rotation period P ∼ 1 msec and a pulsar magnetic field B ∼ 10 13 G, implying a fiducial wind luminosity L p ∼ 10 45 erg/s and a spin-down time t sd ∼ 3 × 10 7 s. The main limiting factor is set by synchrotron losses in the nebula and by the size of the termination shock; ions with Z ≥ 1 may therefore be accelerated to even higher energies. We derive an associated neutrino flux produced by interactions in the source region. For a proton-dominated composition, our maximum flux lies slightly below the 5-year sensitivity of IceCube-86 and above the 3-year sensitivity of the projected Askaryan Radio Array. It might thus become detectable in the next decade, depending on the exact level of contribution of these millisecond pulsar wind nebulae to the ultra-high energy cosmic ray flux.

Nonthermal particles and photons in starburst regions and superbubbles

“…He also predicted that the gravitational radiation events should correlate with the bursts of UHECRs and that the Pierre Auger Observatory should see the bursts of CR particles with energy above 10 20 eV once in a few years. Recently, Lemoine et al (2014) proposed that CR protons of energies up to 4 × 10 20 eV can be accelerated at the termination shock of the relativistic pulsar wind for a fiducial pulsar rotation period of one msec and a magnetic field of about 10 13 G.…”

Ultrahigh-Energy Cosmic Rays From the “En Caul” Birth of Magnetars*

“…In our case,  ℓ 1 for the times we consider, as we show explicitly below. This density is in contrast to other work on UHECRs from magnetars in a core-collapse scenario (Fang et al 2012;Lemoine et al 2015) that instead use a Goldreich-Julian density (Goldreich & Julian 1969). Another difference is that Equation (8) assumes that the  e are fairly sub-relativistic.…”

“…Due to this difficulty, we instead consider the energy to which ions can be accelerated just from confinement by magnetic fields within the nebula (Lemoine et al 2015), which gives…”

“…This assumes a Goldreich-Julian injection (Goldreich & Julian 1969) and has mainly been chosen to illustrate the energy constraints on our model. In general, the spectrum could be different depending on the acceleration type (for example, shock acceleration; Lemoine et al 2015) and other additional factors, such as the details of the source population and the magnetic field within the nebula which may also soften the spectrum (e.g., Fang et al 2013). Next, we assume that a fraction of  h 1 cr of the magnetar spin down can be used for UHECR acceleration.…”

“…Thus, for the same reason that we are able to efficiently produce UHECRs, we are also able to not overproduce high-energy neutrinos. We note that there may also be photo-hadronic interactions within the nebula that may also produce neutrinos (Lemoine et al 2015;Fang et al 2016). Since this process is stronger for protons than heavy nuclei, and since our main focus here is on the heavy nuclei as UHECRs, we save such a calculation for future work where the spectra of UHECRs and the non-thermal radiation is computed in more detail.…”