X-ray Emission from Middle-Aged Gamma-Ray Pulsars

TL;DR

This paper investigates whether synchrotron radiation from electrons and positrons in pulsar magnetospheres can explain the observed non-thermal X-ray emissions in middle-aged gamma-ray pulsars, using gamma-ray data and analytical modeling.

Contribution

It provides constraints on the synchrotron radiation mechanism for X-ray emission in middle-aged pulsars, showing it is unlikely to be the dominant process in most cases.

Findings

Synchrotron radiation cannot fully explain X-ray emissions in most middle-aged pulsars.

Photon-photon pair production is less efficient in these pulsars.

The model challenges the synchrotron origin hypothesis for non-thermal X-ray emission.

Abstract

Electrons/positrons produced in a pulsar magnetosphere emit synchrotron radiation, which is widely believed as the origin of the non-thermal X-ray emission detected from pulsars. Particles are produced by curvature photons emitted from accelerated particles in the magnetosphere. These curvature photons are detected as pulsed $\gamma$-ray emissions from pulsars with age $\lesssim10^6$ yr. Using $\gamma$-ray observations and analytical model, we impose severe constraints on the synchrotron radiation as a mechanism of the non-thermal X-ray emission. In most middle-aged pulsars ($\sim10^5-10^6$ yr) which photon-photon pair production is less efficient in their magnetosphere, we find that the synchrotron radiation model is difficult to explain the observed non-thermal X-ray emission.