Anomalous X-ray Pulsar 1E 1048.1–5937: Long-Lived Pulsed Flux Flares and Short-Lived Torque Variations

We report on continued monitoring of the Anomalous X-ray Pulsar 1E 1048.1– 5937 using the Rossi X-ray Timing Explorer. We show that this pulsar has exhibited significant pulsed flux variability. The principal features of this variability are two pulsed X-ray flares. Both flares lasted several months and had well resolved few-week-long rises, a phenomenon not previously reported for this class of object. The epochs of the flare peaks were MJD 52227.8± 8.3 and 52444.4± 7.0. Both flares had shorter rise than fall times. The first and second flares had peak values 1.99±0.31 and 3.12±0.45 times the quiescent pulsed flux, respectively. We estimate a total 2–10 keV energy release of ∼ 2.0× 10 erg and ∼ 2.0× 10 erg for the first and second flare, respectively (for a distance of 3 kpc). We also report large (factor of 10) changes to the pulsar’s spin-down rate on time scales of weeks to months, shorter than has been reported previously. We find marginal evidence for correlation between the flux and spin-down rate variability, with probability of non-random correlation 4%. We discuss the implications of our findings for AXP models. Subject headings: pulsars: general — X-rays: general — pulsars: individual (1E 1048.1–5937)