Evolution of the X-ray Profile of the Crab Pulsar

Using the archive data from the Rossi X-ray Timing Explorer ({\sl RXTE}), we have studied the evolution of the X-ray profile of the Crab pulsar in a time span of 11 years. The X-ray profiles, as characterized by a few parameters, changed slightly but significantly in these years: the separation of the two peaks increased with a rate $0.88\pm 0.20\text{textordmasculine}$,per century, the flux ratio of the second pulse to the first pulse decreased with $(3.64\pm 0.86)\times {10}^{-2}$,per century, and the pulse widths of the two pulses descended with $1.44\pm 0.15\text{textordmasculine}$, and $1.09\pm 0.73\text{textordmasculine}$,per century, respectively. The evolutionary trends of the above parameters are similar to the radio results, but the values are different. We briefly discussed the constraints of these X-ray properties on the geometry of the emission region of this pulsar.