TeV halos and the role of pulsar wind nebulae as sources of cosmic ray positrons

TL;DR

This paper analyzes TeV halos around pulsar wind nebulae, especially Geminga, to understand cosmic ray positron sources, pair transport, and implications for particle acceleration, based on recent HAWC observations.

Contribution

It provides new insights into pair transport near pulsars, constraints on pair spectra, and the role of TeV halos in cosmic ray physics, supported by recent observational data.

Findings

Suppressed diffusion extends 20-50 pc around pulsars.

Constraints on pair spectra consistent with PWN models.

Implications for proton acceleration in pulsar environments.

Abstract

The recent detection of the Geminga PWN by HAWC in the multi-TeV band allows us to infer precious information about the transport of pairs in the immediate surroundings of the pulsar and on the spectrum of pairs contributed by a Geminga-like pulsar to the spectrum of pairs in the cosmic radiation. Moreover, this detection allows us to address the issue of how typical are the so-called TeV halos associated to PWNe. Our calculations confirm the need to have suppressed diffusion in a region of at least $20-50\,$pc around the pulsar, and are used here to infer precious constraints on the spectrum of pairs accelerated at the termination shock: more specifically, we discuss the conditions under which such a spectrum is consistent with that typically expected in a PWN and how it gets modified once it escapes the halo. Finally, we discuss the implications of the existence of a TeV halo around Geminga in terms of acceleration of protons in the pulsar environment, a topic of profound relevance for the whole field of particle acceleration and physics of pulsars.