Extended gamma-ray sources around pulsars constrain the origin of the positron flux at Earth

TL;DR

This study uses HAWC observations to analyze gamma-ray emissions around pulsars Geminga and PSR B0656+14, finding that their slow diffusion rates make them unlikely sources of the excess positrons detected at Earth.

Contribution

The paper provides new gamma-ray observations around pulsars that constrain particle diffusion, challenging the idea that these pulsars are the main source of cosmic-ray positron excess.

Findings

Pulsars Geminga and PSR B0656+14 are local sources of accelerated leptons.

Particle diffusion around these pulsars is slower than previously thought.

These pulsars are unlikely to be the primary source of the positron excess at Earth.

Abstract

The unexpectedly high flux of cosmic ray positrons detected at Earth may originate from nearby astrophysical sources, dark matter, or unknown processes of cosmic-ray secondary production. We report the detection, using the HighAltitude Water Cherenkov Observatory (HAWC), of extended tera-electron volt gamma-ray emission coincident with the locations of two nearby middle-aged pulsars (Geminga and PSR B0656+14). The HAWC observations demonstrate that these pulsars are indeed local sources of accelerated leptons, but the measured tera-electron volt emission profile constrains the diffusion of particles away from these sources to be much slower than previously assumed. We demonstrate that the leptons emitted by these objects are therefore unlikely to be the origin of the excess positrons, which may have a more exotic origin.