We report on two years of flux and spin evolution monitoring of 1E 1048.1 - 5937 , a 6.5-s X-ray pulsar identified as a magnetar .
Using Swift XRT data , we observed an X-ray outburst consisting of an increase in the persistent 1–10 keV flux by a factor of 6.3 \pm 0.2 , beginning on 2011 December 31 ( MJD 55926 ) .
Following a delay of \sim 100 days , the magnetar entered a period of large torque variability , with \dot { \nu } reaching a factor of 4.55 \pm 0.05 times the nominal value , before decaying in an oscillatory manner over a time scale of months .
We show by comparing to previous outbursts from the source that this pattern of behavior may repeat itself with a quasi-period of \sim 1800 days .
We compare this phenomenology to periodic torque variations in radio pulsars , finding some similarities which suggest a magnetospheric origin for the behavior of 1E 1048.1 - 5937 .