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

The anomalous X-ray pulsar 4U 0142+61 was observed with Suzaku on 2007 August 15 for a net exposure of ∼100 ks, and was detected in a 0.4 to ∼70 keV energy band. The intrinsic pulse period was determined to be 8.68878±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 Γ_h ∼ 0.9 when the soft component is represented by the resonant cyclotron scattering model, and its high-energy cutoff is constrained as >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 × 10³⁵ erg s^-1 and 6.8 × 10³⁴ erg s^-1, respectively. Their sum becomes ∼10³ 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.