Pulse Frequency Fluctuations of Magnetars

Abstract

Using \emph{RXTE}, \emph{Chandra}, \emph{XMM-Newton} and \emph{Swift} observations, we for the first time construct the power spectra and torque noise strengths of magnetars. For some of the sources, we measure strong red noise on timescales months to years which might be a consequence of their outbursts. We compare noise strengths of magnetars with those of radio pulsars by investigating possible correlations of noise strengths with spin-down rate, magnetic field and age. Using these correlations, we find that magnetar noise strengths are obeying similar trends with radio pulsars. On the contrary, we do not find any correlation between noise strength and X-ray luminosity which was seen in accretion powered pulsars. Our findings suggest that the noise behaviour of magnetars resembles that of radio pulsars but they possess higher noise levels likely due to their stronger magnetic fields.