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The ultra-high-energy (UHE) Galactic diffuse gamma-ray emission holds important information on the propagation of cosmic rays in the Galaxy. However, its measurements suffer from a contamination from unresolved sources whose contribution remains unclear. In this Letter, we propose a novel data-driven estimate of the contribution of unresolved pulsar wind nebulae and TeV halos based on the information present in the Australia Telescope National Facility and the LHAASO catalogs. We find that in the inner Galaxy, this contribution is limited to ∼38% ± 10% of the diffuse flux measured by LHAASO at ∼20 TeV in the case where all sources associated to pulsars contribute as unresolved sources, and this fraction drops to less than 21% ± 6% above 100 TeV. In the outer Galaxy, this contribution is always subdominant. In particular, it reaches at most ∼18% ± 2% at 10 TeV and is less than ∼7% ± 1% above ∼25 TeV. We conclude that the UHE Galactic diffuse gamma-ray emission cannot be dominated by unresolved pulsar sources above a few tens of TeV.

Supernova blast wave shock is a very important site of cosmic-ray acceleration. However, the detailed physical process of acceleration, in particular, nonlinear interplay between cosmic-ray streaming and magnetic field amplification, has not been studied under a realistic environment. In this paper, using a unique and novel numerical method, we study cosmic-ray acceleration at supernova blast wave shock propagating in the interstellar medium with well-resolved magnetic field amplification by nonresonant hybrid instability (or Bell instability). We find that the magnetic field is mildly amplified under typical interstellar medium conditions that leads to maximum cosmic-ray energy ≃30 TeV for supernova remnants with age ≃1000 yr consistent with gamma-ray observations. The strength of the amplified magnetic field does not reach the so-called saturation level because the cosmic-ray electric current toward the shock upstream has a finite spatial extent, by which Bell instability cannot experience many e -folding times.

Two-fluid (electron–positron) plasma modeling has shown that inductive acceleration can convert Poynting flux directly into bulk kinetic energy in the relativistic flows driven by rotating magnetized neutron stars and black holes. Here, we generalize this approach by adding an ion fluid. Solutions are presented in which all particles are accelerated as the flow expands, with comparable power channeled into each of the plasma components. In an ion-dominated flow, each species reaches the limiting rigidity, according to Hillas’ criterion, in a distance significantly shorter than in a lepton-dominated flow. These solutions support the hypothesis that newly born magnetars and pulsars are potential sources of ultrahigh energy cosmic rays. The competing process of Poynting flux dissipation by magnetic reconnection is shown to be ineffective in low-density flows in which the conventionally defined electron multiplicity satisfies , where L38 × 1038 erg s−1 is the power carried by the flow in a solid angle Ω, and is the ratio of the ion to lepton power at launch. [ABSTRACT FROM AUTHOR]

We study particle acceleration at the termination shock of a striped pulsar wind by integrating trajectories in a prescribed model of the magnetic field and flow pattern. Drift motion on the shock surface maintains either electrons or positrons on “Speiser” orbits in a ring-shaped region close to the equatorial plane of the pulsar, enabling them to be accelerated to very high energy by the first-order Fermi mechanism. A power-law spectrum results: , where αe lies in the range −1.8 to −2.4 and depends on the downstream turbulence level. For sufficiently strong turbulence, we find αe ≃ −2.2, and both the photon index and the flux of 1–100 keV X-rays from the Crab Nebula, as measured by NuSTAR, can be reproduced. The particle spectrum hardens to αe ≃ −1.8 at lower turbulence levels, which may explain the hard photon index observed by the Chandra X-ray Observatory in the central regions of the Nebula. [ABSTRACT FROM AUTHOR]

We calculate the large-scale cosmic-ray (CR) anisotropies predicted for a range of Goldreich–Sridhar (GS) and isotropic models of interstellar turbulence, and compare them with IceTop data. In general, the predicted CR anisotropy is not a pure dipole; the cold spots reported at 400 TeV and 2 PeV are consistent with a GS model that contains a smooth deficit of parallel-propagating waves and a broad resonance function, though some other possibilities cannot, as yet, be ruled out. In particular, isotropic fast magnetosonic wave turbulence can match the observations at high energy, but cannot accommodate an energy dependence in the shape of the CR anisotropy. Our findings suggest that improved data on the large-scale CR anisotropy could provide a valuable probe of the properties—notably the power-spectrum—of the interstellar turbulence within a few tens of parsecs from Earth. [ABSTRACT FROM AUTHOR]