4U 0142+61 is one of the Anomalous X-ray Pulsars exhibiting hard X-ray emission above 10 keV discovered with INTEGRAL .
In this paper 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 .
Accumulating data collected over four years with the imager IBIS-ISGRI aboard INTEGRAL , the time-averaged total spectrum shows a power-law like shape with photon index \Gamma = 0.93 \pm 0.06. 4U 0142+61 is detected up to 229 keV and the flux between 20 keV and 229 keV is ( 15.01 \pm 0.82 ) \times 10 ^ { -11 } erg cm ^ { -2 } s ^ { -1 } , which exceeds the energy flux in the 2–10 keV band by a factor of \sim 2.3 .
Using simultaneously collected data with the spectrometer SPI of INTEGRAL the combined total spectrum yields the first evidence for a spectral break above 100 keV : Assuming for the spectral shape above 20 keV a logparabolic function the peak energy of 4U 0142+61 is 228 ^ { +65 } _ { -41 } keV .
There is no evidence for significant long-term time variability of the total emission from 4U 0142+61 .
Both the total flux and the spectral index are stable within the 17 % level ( 1 \sigma ) .
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 \pm 0.15 and a 20–150 keV flux of ( 2.68 \pm 1.34 ) \times 10 ^ { -11 } erg cm ^ { -2 } s ^ { -1 } .
To perform accurate phase-resolved spectroscopy over the total X-ray window , we produced pulse profiles in absolute phase for INTEGRAL-ISGRI , RXTE-PCA , XMM- Newton -PN and ASCA-GIS .
The two known pulses in all soft X-ray profiles below 10 keV are located at the same phases .
Three XMM- Newton observations in 2003–2004 show statistically identical profiles .
However , we find a significant profile morphology change between an ASCA-GIS observation in 1999 following a possible glitch of 4U 0142+61 .
This change can be accounted to differences in relative strengths and spectral shapes ( 0.8–10 keV ) of the two pulses .
The principle peak in the INTEGRAL pulse profile above 20 keV is located at the same phase as one of the pulses detected below 10 keV .
The second pulse detected with INTEGRAL is slightly shifted with respect to the second peak observed in the soft X-ray band .
We performed consistent phase-resolved spectroscopy over the total high-energy band 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 .
Finally , we discuss the derived detailed characteristics of the high-energy emission of 4U 0142+61 in relation to three models for the non-thermal hard X-ray emission .