High energy tails of pulsar gamma-ray emission

TL;DR

This study analyzes high-energy gamma-ray spectra of four pulsars to determine whether curvature emission or inverse-Compton scattering better explains their emission tails above 10 GeV, finding no definitive preference for either model.

Contribution

It provides the first comparative spectral analysis of multiple pulsars' high-energy tails, testing two competing emission models with current data.

Findings

Both models fit the data equally well for all four pulsars.

No firm conclusion can be drawn about the spectral shape above 10 GeV.

Crab pulsar uniquely favors a power-law spectrum over an exponential cutoff.

Abstract

We perform spectral analyses of four bright $\gamma$-ray pulsars: PSR J0007+7303, Vela, Geminga and PSR J2021+3651 concentrating on the high-energy tails, defined as emission above 10\,GeV. The two competing models of pulsar $\gamma$-ray emission predict qualitatively different spectra well above the break energy: curvature emission predicts an exponential cut-off in the spectra, while the inverse-Compton scattering mechanism favors a power-law. We perform fits to the phase-averaged spectral energy distributions for each of the four pulsars. We find that in all cases both models fit the data equally well---the present data set does not allow any firm claim to be made about the shape of the spectra above 10\,GeV. In no case is the power-law fit or exponential cut-off fit significantly preferred over the other. The Crab pulsar remains the only known pulsar in which the power-law fit is clearly preferred over the exponential cut-off.