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

TL;DR

This study used Suzaku to observe the anomalous X-ray pulsar 4U 0142+61, providing the first simultaneous broadband measurement of its soft and hard X-ray components, revealing spectral characteristics, luminosities, and variability over 30 ks.

Contribution

It presents the first simultaneous broadband spectral analysis of 4U 0142+61 with Suzaku, modeling soft and hard X-ray components and constraining their properties and variability.

Findings

Soft component modeled by two blackbodies or resonant cyclotron scattering.

Hard component approximated by a power-law with photon index ~0.9 and cutoff >180 keV.

Hard X-ray luminosity is about 10^3 times the spin-down luminosity.

Abstract

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 as 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 \Gamma 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 are calculated as 2.8e+35 erg s^{-1} and 6.8e+34 erg s^{-1}, respectively. Their sum becomes ~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.