X-ray Evolution of Pulsar Wind Nebulae

TL;DR

This study reveals that pulsar wind nebulae (PWNe) can expand for up to 100,000 years and that high-energy electrons can escape without significant energy loss, with magnetic fields decreasing over time.

Contribution

It provides new observational evidence of long-term PWN expansion and electron escape, and proposes a decreasing magnetic field model to explain size-age correlations.

Findings

PWNe expand up to ~100 kyrs.

Electrons up to ~80 TeV can escape without energy loss.

Magnetic fields in PWNe decrease over time.

Abstract

During the search for counterparts of very-high-energy gamma-ray sources, we serendipitously discovered large, extended, low surface brightness emission from PWNe around pulsars with the ages up to ~100 kyrs, a discovery made possible by the low and stable background of the Suzaku X-ray satellite. A systematic study of a sample of 8 of these PWNe, together with Chandra datasets, has revealed us that the nebulae keep expanding up to for ~100 kyrs, although time scale of the synchrotron X-ray emission is only ~60 yr for typical magnetic fields of 100 microG. Our result suggests that the accelerated electrons up to ~80 TeV can escape from the PWNe without losing most energies. Moreover, in order to explain the observed correlation between the X-ray size and the pulsar spindwon age, the magnetic field strength in the PWNe must decrease with time.