Spectral Break of Energetic Pulsar Wind Nebulae Detected with Wideband X-ray Observations

TL;DR

This study detects spectral breaks in the hard X-ray spectra of several energetic pulsar wind nebulae, revealing insights into their emission mechanisms and spectral properties across a broad energy range.

Contribution

First wideband X-ray spectral analysis of multiple PWNe revealing spectral breaks and their potential correlations with pulsar properties.

Findings

Spectral breaks found in four PWNe, with energies between 4-14 keV.

No significant correlation between break energy and pulsar spin-down or age.

Possible correlation between photon index change and pulsar X-ray efficiency.

Abstract

Pulsar wind nebulae (PWNe) are one of the most energetic galactic sources with bright emissions from radio waves to very high-energy gamma-rays. We perform wideband X-ray spectroscopy of four energetic PWNe, N157B, PSR J1813-1749, PSR J1400-6325, and G21.5-0.9, with the Suzaku, Chandra, NuSTAR, and Hitomi observatories. A significant spectral break or cutoff feature is found in the hard X-ray band for all the samples, except for N157B. The break energies in the broken power-law fitting are in the range of 4--14 keV, whereas the cutoff energies in the cutoff power-law fitting are at 22 keV or higher. The break or cutoff energy does not show a significant correlation with either the spin-down energy or characteristic age of the hosting pulsars. A possible correlation is found between the photon index change in the broken power-law fitting and the X-ray emitting efficiency of the pulsars, although its significance is not high enough to be conclusive. We discuss what determines the break parameters based on simple models.