The X-ray Pulsar PSR J1811–1925 in the historic supernova remnant G11.2–0.3 has a characteristic age over 10 times the age of the remnant .
This likely implies that its current spin period , 65 ms , is close to its birth spin period .
Alternatively , the pulsar may have an unusually high braking index .
We report here on regular Rossi X-ray Timing Explorer / Proportional Counting Array ( RXTE /PCA ) timing observations of the pulsar that were designed to measure its braking index .
We provide a preliminary phase-coherent timing solution which includes a significant \ddot { \nu } .
The braking index we measure is \gg 3 , likely a result of conventional timing noise .
We also report on a preliminary analysis of the pulsar ’ s unusually hard spectrum : we determine a photon index of \Gamma = 1.78 \pm 0.74 , for the pulsed component of the spectra , consistent within the uncertainties with previous ASCA and Chandra observations .
The pulsed emission of PSR J1811–1925 is seen beyond 30 keV , and the pulsations remain sinusoidal up to and beyond this energy .