Time Evolution of the X-Ray and γ-Ray Fluxes of the Crab Pulsar

Abstract

We studied the evolution of the X-ray and γ -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 analyzed the long-term evolution of the X-ray (or γ -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 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 of RXTE and the γ -ray flux in 0.1–300 GeV by the Large Area Telescope onboard FGST show similar decreasing trends but are insignificant statistically. The 5–60 keV X-ray luminosity L X is correlated with the spin-down power L sd by , which is similar to the statistical results for young pulsars.