Phase Evolution of the Crab Pulsar between Radio and X-ray

TL;DR

This study analyzes 11 years of X-ray and 6 years of radio observations of the Crab pulsar, revealing correlated phase behaviors and suggesting that timing noise originates from the pulsar's spin rather than emission region changes or interstellar medium effects.

Contribution

It provides new insights into the origin of timing noise in the Crab pulsar by comparing X-ray and radio phases over long periods, showing their strong correlation and ruling out certain physical causes.

Findings

X-ray and radio phases show similar long-term evolution and short-term variations.

Using Nanshan phases reduces timing noise amplitude and shows no long-term evolution.

Timing noise is likely due to pulsar spin, not emission region changes or interstellar medium effects.

Abstract

We study the X-ray phases of the Crab pulsar utilizing the 11-year observations from the Rossi X-ray Timing Explorer, 6-year radio observations from the Nanshan Telescope, and the ephemeris from Jodrell Bank Observatory. It is found that the X-ray phases in different energy bands and the radio phases from Nanshan Telescope show similar behaviors, including long-time evolution and short-time variations. Such strong correlations between the X-ray and radio phases imply that the radio and X-ray timing noises are both generated from the pulsar spin that cannot be well described by the the monthly ephemeris from the Jodrell Bank observatory. When using the Nanshan phases as references to study the X-ray timing noise, it has a significantly smaller variation amplitude and shows no long-time evolution, with a change rate of $(-1.1\pm1.1)\times10^{-7}$ periods per day. These results show that the distance of the X-ray and radio emission regions on the Crab pulsar has no detectable secular change, and it is unlikely that timing-noises resulted from any unique physical processes in the radio or X-ray emitting regions. The similar behaviors of the X-ray and radio timing noises also imply that the variation of the interstellar medium is not the origin of the Crab pulsar's timing noises, which is consistent with the results obtained from the multi-frequency radio observations of PSR B1540-06.