Constraint on parameters of the Inverse Compton Scattering model for radio pulsars

TL;DR

This study constrains key parameters of the inverse Compton scattering model for radio pulsars by fitting pulse width data across frequencies, revealing high initial Lorentz factors and significant energy loss in secondary particles.

Contribution

It provides the first detailed parameter constraints for the ICS model in pulsars, linking observational pulse profiles with theoretical particle dynamics.

Findings

Initial Lorentz factor > 4000

Energy loss factor between 20 and 560

Consistent with inner vacuum gap model predictions

Abstract

The inverse Compton scattering (ICS) model can explain various pulse profile shapes and diversity of pulse profile evolution based on the mechanism that the radio emission is generated through inverse Compton scattering between secondary relativistic particles and radio waves from polar gap avalanches. In this paper, we study the parameter space of ICS model for 15 pulsars, which share the common pulse profile evolution phenomena that the pulse profiles are narrower at higher observing frequencies. Two key parameters, the initial Lorentz factor and the energy loss factor of secondary particles are constrained using the least square fitting method, where we fit the theoretical curve of the "beam-frequency mapping" of the ICS model to the observed pulse widths at multiple frequencies. The uncertainty of the inclination and viewing angles are taken into account in the fitting process. It is found that the initial Lorentz factor is larger than 4000, and the energy loss factor is between 20 and 560. The Lorentz factor is consistent with the prediction of the inner vacuum gap model. Such high energy loss factors suggest significant energy loss for secondary particles at altitudes of a few tens to hundreds of kilometers.