Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2610.28751

A new view of the cosmic-ray knee after LHAASO

Carmelo Evoli
View original source ↗Read source document ↗Export metadata ↓

Abstract

Recent LHAASO measurements offer a new view of the cosmic-ray knee by combining the all-particle spectrum and mean logarithmic mass with proton and light-component spectra across the PeV region. This contribution reviews these results and their implications for Galactic acceleration and transport. Approximately charge-ordered proton and helium knees coexist with different spectral evolution, while their turnover shapes constrain source populations and escape mechanisms. These measurements anchor an elemental ``ladder'' that, extended to heavier nuclei, will be crucial for establishing how far the Galactic component persists and where the Galactic--extragalactic transition takes place.

Explore related subjects

astro-ph.HE

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Carmelo Evoli. 2026-10-20. A new view of the cosmic-ray knee after LHAASO. https://arxiv.org/abs/2610.28751

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

The Deep Newtonian Regime in Late-Time Blast Waves: Inevitable Transition and Distinct Flux Signatures

In many astrophysical transients, outflows drive shocks into the ambient medium, accelerating electrons to non-thermal energy distributions that produce broadband synchrotron emission. At late times, even initially collimated relativistic jets evolve into quasi-spherical Newtonian blastwaves. As the shock decelerates, the post-shock internal energy per particle decreases; below a critical velocity $β_{\rm DN} \approx 0.2$, only a fraction $ξ_e < 1$ of electrons are accelerated to relativistic energies, defining the deep Newtonian (DN) regime. We develop a unified analytic framework for synchrotron emission in this phase, applicable to both single-velocity and stratified ejecta. For gamma-ray burst afterglows in a uniform medium, the DN transition occurs at $t_{\rm DN} \approx 3.7\,E_{51}^{1/3} n_0^{-1/3}$~yr, yielding a shallower decay by $δα= 6(p-2)/5$ relative to standard Newtonian predictions. For kilonova remnants ($E_0 = 10^{50.5}$~erg, $M_{\rm ej} = 0.1\,M_\odot$), the DN phase begins prior to deceleration; neglecting it underestimates radio flux by factors of $\sim 3$--$5$ during coasting and even more thereafter. Magnetar-boosted remnants ($E \sim10^{52}$~erg) should reach $\sim$\,10\,--\,100\,$μ$Jy at 3~GHz at $\sim$\,40\;Mpc, though limits on GW170817 already disfavor a long-lived millisecond magnetar. In core-collapse supernovae in a wind medium ($ρ\!\propto\!r^{-k}$), the peak luminosity remains constant during coasting, while $ν_{\rm pk} \propto t^{-1}$; for SN~2023ixf, we find $k = 1.29 \pm 0.14$. The DN spectral energy distribution typically satisfies $ν_m\!<\!ν_{\rm sa}\!<\!ν_c$, peaking at sub-GHz frequencies where LOFAR and SKA-low are most sensitive. Even non-detections place robust constraints on ambient density and outflow energetics.

astro-ph.HE↗
arXiv2026

Spectral energy-loss bump and $γ$-ray pulsar halos

The parent electron spectrum of $γ$-ray pulsar halos is determined by continuous injection and radiative energy losses, with the nonlinear nature of the latter expected to produce an age-dependent energy-loss bump in the halo spectrum. We demonstrate that the broadband $γ$-ray spectrum of the Geminga halo measured by Fermi-LAT and HAWC is consistent with this expectation. Its energy-loss bump appears in the GeV region and is primarily produced by electrons injected at the earliest stage. Therefore, fitting the data allows us to constrain parameters governing early electron injection, such as the pulsar braking index $n$ and initial spin period $P_0$. In addition, we show that another crucial condition for explaining the Geminga halo spectrum is a power-law index of the injection spectrum close to $1$, consistent with the X-ray observations of the Geminga pulsar wind nebula. Currently, no significant energy-loss bump has been detected in the spectrum of the Monogem halo; based on this, we also place preliminary constraints on $n$ and $P_0$ of Monogem. This work demonstrates that pulsar halo spectra can be used not only to constrain electron injection parameters, but also to provide independent estimates of certain intrinsic pulsar properties.

astro-ph.HE↗
arXiv2026

Signatures of Lorentz violation in the bright ring for Sgr A* images from radiatively inefficient accretion flows

We have investigated the effects of Lorentz violation (LV) on the bright ring in Sgr A* images illuminated by the 230 GHz thermal synchrotron emission from radiatively inefficient accretion flows around a rotating LV black hole within the low-energy Hořava gravity framework. Our results reveal that the LV parameter reduces the bright ring diameter yet increases its width, luminosity, azimuthal asymmetry and orientation angle. A higher spin parameter strengthens the LV-induced effects on the bright ring properties. Increasing disk thickness reduces the ring diameter and enhances the LV parameter's effects on this diameter. The ring width shows no systematic dependence on the disk thickness. These quantities of the bright ring display similar trends against the black hole spin and the LV parameter for the rotating LV black hole. Using EHT observational data of Sgr A*, we find that, at fixed disk thickness, the parameter-space map illustrates that the bounded range of the LV parameter first broadens and then contracts with the growing black hole spin, and shifts toward smaller LV parameter values. In addition, the LV parameter narrows the bounded range of black hole spin: negative LV parameter values shift this range to a higher spin, while positive values shift it to a lower spin. Finally, we probe effects of the LV parameter on the peak position value and the width of the primary image and the $n=1$ photon ring for the rotating LV black hole. The peak positions and their widths nearly always decrease with the LV parameter. The peak position differences for various LV parameters are more pronounced for a purely Keplerian accretion flow. In addition, the primary image and the $n=1$ photon ring produced by purely radially free-falling flows are broader than their counterparts generated by purely Keplerian flows.

astro-ph.HE↗