The Pulsed Spectra of Two Extraordinary Pulsars

We report on X-ray monitoring of two isolated pulsars within the same RXTE field of view. PSR J1811-1925 in the young supernova remnant G11.2-0.3 has a nearly sinusoidal pulse profile with a hard pulsed spectrum (photon index Γ ~ 1.2). The pulsar is a highly efficient (~ 1% of spin-down energy) emitter of 2-50 keV pulsed X-rays despite having a fairly typical B ~ 2 × 10¹² G magnetic field. PSR J1809-1943/XTE J1810-197 is a newly discovered slow (P = 5.54 s), apparently isolated X-ray pulsar which increased in flux by a factor of 100 in 2003 January. Nine months of monitoring observations have shown a decrease in pulsed flux of ~ 30% without a significant change in its apparently thermal spectrum (kT ~ 0.7 keV) or pulse profile. During this time, the spin-down torque has fluctuated by a factor of ~ 2. Both the torque and the flux have remained steady for the last 3 months, at levels consistent with a magnetar interpretation.