Multi-wavelength emission region of gamma-ray emitting pulsars

TL;DR

This study uses the outer gap model to analyze the emission regions of gamma-ray pulsars across multiple wavelengths, revealing how emission altitude varies with pulsar inclination and affecting pulsar population statistics.

Contribution

It introduces a method to determine emission region altitude from multi-wavelength data, incorporating observational constraints and suggesting modifications to pulsar population models.

Findings

Outer gap model explains multi-wavelength pulse behavior.

Emission altitude depends on inclination angle.

Low inclination pulsars have emission regions at very low altitudes.

Abstract

Using the outer gap model, we investigate the emission region for the multi-wavelength light curve from energetic pulsars. We assume that gamma-ray and non-thermal X-ray photons are emitted from a particle acceleration region in the outer magnetosphere, and UV/optical photons originate above that region. We assume that gamma-rays are radiated only by outwardly moving particles, whereas the other photons are produced by particles moving inward and outward. We parameterize the altitude of the emission region as the deviation from the rotating dipole in vacuum and determine it from the observed multi-wavelength pulse profile using the observationally constrained magnetic dipole inclination angle and viewing angle of the pulsars. We find that the outer gap model can explain the multi-wavelength pulse behavior by a simple distribution of emissivity, and discuss the possibility of further improvement. From observational fitting, we also find a general tendency for the altitude of the gamma-ray emission region to depend on the inclination angle. In particular, the emission region for low inclination angle is required to be located in very low altitude, which corresponds to the inner region within the last-open field line of rotating dipole in vacuum. This model suggests a modification of statistics about observed gamma-ray pulsars. Number of the sources with low inclination and viewing angles increases compared with previous estimate.