Soft and Hard X-Ray Emissions from the Anomalous X-Ray Pulsar 4U 0142+61 Observed with Suzaku

Abstract

The anomalous X-ray pulsar 4U 0142$+$61 was observed with Suzaku on 2007 August 15 for a net exposure of $\sim\ $100 ks, and was detected in a 0.4 to $\sim\ $70 keV energy band. The intrinsic pulse period was determined to be 8.68878$\ \pm\ $0.00005 s, in agreement with an extrapolation from previous measurements. The broadband Suzaku spectra enabled a first simultaneous and accurate measurement of the soft and hard components of this object by a single satellite. The former can be reproduced by two blackbodies, or slightly better by a resonant cyclotron scattering model. The hard component can be approximated by a power-law of photon index of $\Gamma_{\rm h}$ $\sim\ $ 0.9 when the soft component is represented by the resonant cyclotron scattering model, and its high-energy cutoff is constrained as $\gt\ $180 keV. Assuming an isotropic emission at a distance of 3.6 kpc, the unabsorbed 1-10 keV and 10-70 keV luminosities of the soft and hard components were calculated to be 2.8 $\times$ 10$^{35}\ $erg s$^{-1}$ and 6.8 $\times$ 10$^{34}\ $erg s$^{-1}$, respectively. Their sum becomes $\sim\ $10$^3$ times as large as the estimated spin-down luminosity. On a time scale of 30 ks, the hard component exhibited evidence of variations either in its normalization or pulse shape.