Detailed high-energy characteristics of AXP 4U 0142+61 - Multi-year observations with INTEGRAL, RXTE, XMM-Newton and ASCA

TL;DR

This study provides a comprehensive multi-year analysis of AXP 4U 0142+61, revealing its spectral shape, energy break, and pulse characteristics across multiple X-ray observatories, indicating a stable emission geometry.

Contribution

It offers the first combined spectral analysis showing a high-energy break and detailed phase-resolved spectroscopy across four major X-ray missions.

Findings

Detection of emission up to 229 keV

Spectral break at approximately 228 keV

Stable emission geometry over years

Abstract

We present detailed spectral and temporal characteristics both in the hard X-ray (>10 keV) and soft X-ray (<10 keV) domains, obtained using data from INTEGRAL, XMM-Newton, ASCA and RXTE. The INTEGRAL time-averaged total spectrum shows a power-law like shape with photon index Gamma = 0.93 +/- 0.06. 4U 0142+61 is detected up to 229 keV and the flux between 20 keV and 229 keV is (15.01 +/- 0.82) x 10^(-11) erg/cm^2/s. Using simultaneously collected data with the spectrometer SPI of INTEGRAL the combined total spectrum yields the first evidence for a spectral break with a peak energy of 228 +65/-41 keV. There is no evidence for significant long-term time variability of the total emission. Pulsed emission is measured with ISGRI up to 160 keV. The 20-160 keV profile shows a broad double-peaked pulse with a 6.2 sigma detection significance. The total pulsed spectrum can be described with a very hard power-law shape with a photon index \Gamma = 0.40 +/- 0.15. We performed phase-resolved spectroscopy over the total high-energy band (2.8-300 keV) and identify at least three genuinely different pulse components with different spectra. The high level of consistency between the detailed results from the four missions is indicative for a remarkable stable geometry underlying the emission scenario.