Time evolution of the X-ray and gamma-ray fluxes of the Crab pulsar

TL;DR

This study analyzes 20 years of X-ray and gamma-ray data from the Crab pulsar, revealing a long-term decrease in flux and a correlation between X-ray luminosity and spin-down power, enhancing understanding of pulsar emission evolution.

Contribution

It provides the first long-term analysis of the Crab pulsar's high-energy flux evolution and its correlation with spin-down power using extensive RXTE and Fermi data.

Findings

X-ray flux in 5-60 keV decreases over time.

Gamma-ray flux shows a similar but statistically insignificant decreasing trend.

X-ray luminosity correlates with spin-down power as L_X ∝ L_sd^{1.6±0.3}.

Abstract

We studied the evolution of the X-ray and gamma-ray spectra of the Crab pulsar utilizing the 11-year observations from the Rossi X-ray Timing Explorer (RXTE) and 9-year observations from the Fermi Gamma-ray Space Telescope (FGST). By fitting the spectrum of each observation, we obtained the corresponding flux, and then analysed the long term evolution of the X-ray (or gamma-ray) luminosities as well as their correlations with the spin down power of the pulsar. The X-ray flux in 5-60 keV obtained by the Proportional Counter Array (PCA) of RXTE decreases with a rate of (-2.4+/-0.4)*10^(-14) erg cm^(-2) s^(-1) per day. The X-ray flux in 15-250 keV obtained by the High Energy X-ray Timing Experiment (HEXTE) of RXTE and the gamma-ray flux in 0.1-300 GeV by the Large Area Telescope (LAT) onboard FGST show similar decreasing trend, but are unsignificant statistically. The 5--60 keV X-ray luminosity L_(X) is correlated with the spin down power L_(sd) by L_(X) propto L_(sd)^(1.6+/-0.3), which is similar to the statistical results for young pulsars.