Constraining the production of cosmic rays by pulsars

TL;DR

This study investigates gamma-ray halos around young pulsars using Fermi-LAT data to assess their role in producing galactic cosmic rays, finding limited evidence for such halos and suggesting pulsars are not the dominant source.

Contribution

The paper provides the first systematic search for gamma-ray halos around a selected set of young pulsars using 7-year Fermi-LAT data, constraining their contribution to cosmic rays.

Findings

Extended gamma-ray emission possibly indicating halos was found only around PSR J0007+7303.

The luminosity of this potential halo aligns with the energy expected from cosmic ray injection (~10^{50} erg).

Bounds on gamma-ray halo luminosity imply pulsars are a subdominant source of galactic cosmic rays in the GeV-TeV range.

Abstract

One of the possible sources of hadronic cosmic rays (CRs) are newborn pulsars. If this is indeed the case, they should feature diffusive gamma-ray halos produced by interactions of CRs with interstellar gas. In this paper we try to identify extended gamma-ray emission around young pulsars, making use of the 7-year Fermi-LAT data. For this purpose we select and analyze a set of eight pulsars that are most likely to possess detectable gamma-ray halos. We find extended emission that might be interpreted as a gamma-ray halo only in the case of PSR J0007+7303. Its luminosity accords with the total energy of injected cosmic rays $\sim 10^{50}$ erg, although other interpretations of this source are possible. Irrespectively of the nature of this source we put bounds on the luminosity of gamma-ray halos which suggest that pulsars' contribution to the overall energy budget of galactic CRs is subdominant in the GeV-TeV range.