On the potential of bright, young pulsars to power ultra-high gamma-ray sources

Abstract

The recent discovery of a new population of ultra-high-energy gamma-ray sources with spectra extending beyond 100 TeV revealed the presence of Galactic PeVatrons - cosmic-ray factories accelerating particles to PeV energies. These sources, except for the one associated with the Crab Nebula, are not yet identified. With an extension of 1 degree or more, most of them contain several potential counterparts, including Supernova Remnants, young stellar clusters and Pulsar Wind Nebulae (PWNe), which can perform as PeVatrons and thus power the surrounding diffuse ultra-high energy gamma-ray structures. In the case of PWNe, gamma rays are produced by electrons, accelerated at the pulsar wind termination shock, through the inverse Compton scattering of 2.7 K CMB radiation. The high conversion efficiency of pulsar rotational power to relativistic electrons, combined with the short cooling timescales, allow gamma-ray luminosities up to the level of $L_{\gamma }\sim 0.1\dot{E}$. The pulsar spin-down luminosity, $\dot{E}$, also determines the absolute maximum energy of individual photons: $E_{\gamma \max }\approx 0.9{\dot{E}}_{36}^{0.65}\mathrm{PeV}$. This fundamental constraint dominates over the condition set by synchrotron energy losses of electrons for young PWNe with typical magnetic field of $\approx$100$\mu$G with $\dot{E}\lesssim 10^{37}erg/s$. We discuss the implications of $E_{\gamma \max }$ by comparing it with the highest energy photons reported by LHAASO from a dozen of ultra-high-energy sources. Whenever a PWN origin of the emission is possible, we use the LHAASO measurements to set upper limits on the nebular magnetic field.

accepted for publication in ApJ Letters

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• The LHAASO PeVatron bright sky: what we learned
• Ultra-High-Energy Gamma-Ray Astronomy
• Prospects for a survey of the Galactic plane with the Cherenkov Telescope Array
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• Dissecting the emission from LHAASO J0341+5258: implications for future multi-wavelength observations
• Constraints on the $e^{\pm }$ Pair Injection of Pulsar Halos: Implications from the Galactic Diffuse Multi-TeV Gamma-ray Emission
• Exploring the high energy frontiers of the Milky Way with ground-based gamma-ray astronomy: PeVatrons and the quest for the origin of Galactic cosmic-rays
• Pulsar Wind Nebulae
• Deriving pulsar pair-production multiplicities from pulsar wind nebulae using H.E.S.S. and LHAASO observations
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• HAWC Study of Very-High-Energy $\gamma$-ray Spectrum of HAWC J1844-034
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• An extreme particle accelerator powered by pulsar PSR J1849-0001
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• The Potential for Hadronic Particle Acceleration in Galactic Pulsar Wind Nebulae
• Unraveling the Nature of HAWC J1844-034 with Fermi-LAT Data Analysis and Multi-wavelength Modeling
• Pulsar+escape: the recipe for LHAASO sources ?
• The traveling-PWN modeling attempt on the enigmatic LHAASO dumbbell-like structure
• Investigating the mysterious nature of 1LHAASO J1740+0948u through deep XMM-Newton observations
• Analysis of the Emission and Morphology of the Pulsar Wind Nebula Candidate HAWC J2031+415
• Suppressed diffusion and gamma-ray emission from the Cygnus bubble
• Can a single supernova remnant account for the gamma-ray emission of G106.3+2.7?
• Towards Searching for Photons with Energies beyond the PeV Range from Galactic PeVatrons
• TeV-PeV Gamma-ray and Neutrino Emission in the Galactic Plane