1RXS J170849-400910 is one of four Anomalous X-ray Pulsars which emit persistent luminous radiation in soft X-rays ( < 10 keV ) as well as in hard X-rays ( > 10 keV ) .
In this paper we present detailed spectral and temporal characteristics over the whole X-ray band .
For this purpose data have been used from INTEGRAL , RXTE and XMM- Newton .
The hard X-ray ( > 10 keV ) time-averaged total spectrum , accumulated over four years with the imager IBIS-ISGRI onboard INTEGRAL adding up to 5.2 Ms net exposure , can be described by a power law with a photon index \Gamma = 1.13 \pm 0.06 and extends to \sim 175 keV .
The 20–175 keV flux is ( 7.76 \pm 0.34 ) \times 10 ^ { -11 } erg cm ^ { -2 } s ^ { -1 } which exceeds the 2–10 keV ( unabsorbed ) flux by a factor of \sim 2.3 .
No evidence for a spectral break is found below 300 keV .
Also , no significant long-term time variability has been detected above 20 keV on time scales of 1 and 0.5 year .
Pulsed emission is measured with INTEGRAL up to 270 keV , i.e .
to much higher energies than the total emission , with a detection significance of 12.3 \sigma ( 20–270 keV ) .
The pulse profiles from 0.5 keV up to 270 keV show drastic morphology changes below \sim 20 keV .
Three different pulse components can be recognized in these pulse profiles : 1 ) a hard pulse peaking around phase 0.8 which contributes to the pulse profiles above \sim 4 keV , 2 ) a softer pulse which peaks around phase 0.4 not contributing in the hard X-ray domain and 3 ) a very soft pulse component below 2 keV .
A combined time-averaged pulsed spectrum ( 2.8–270 keV ) from INTEGRAL , RXTE-PCA and HEXTE ( collected over nine years ) can be described with a soft and a hard power-law component : \Gamma _ { { s } } = 2.79 \pm 0.07 and \Gamma _ { { h } } = 0.86 \pm 0.16 .
In the pulsed spectrum extracted from a 25.5 ks net exposure XMM- Newton observation we find a discontinuity between 2 keV and 3 keV .
Above these energies the spectrum is consistent with the spectrum taken with RXTE-PCA .
The pulse profiles and the total-pulsed spectrum prove to be stable over the whole nine-years time span over which the data have been taken .
Also detailed phase-resolved spectroscopy of the pulsed emission confirms the long-term stability as the spectra taken at different epochs connect smoothly .
The phase-resolved spectra reveal complex spectral shapes which do not follow the shape of the total-pulsed spectrum .
The spectral shape gradually changes with phase from a soft single power law to a complex multi-component shape and then to a hard single power law .
The spectrum switches from a very hard ( \Gamma = 0.99 \pm 0.05 ) to a very soft ( \Gamma = 3.58 \pm 0.34 ) single power-law shape within a 0.1-wide phase interval .
The discontinuity measured between 2 keV and 3 keV with XMM- Newton is a result of a curved component .
This component which is most apparent within phase interval 0.7–0.9 significantly contributes in the energy range between 4 keV and 20 keV .
It has a very steep spectrum below 5 keV with a photon index \Gamma \sim - 1.5 .
From the phase-resolved spectra we identify three independent components with different spectral shapes which together can accurately describe all phase-resolved spectra ( 2.8–270 keV ) .
The three shapes are a soft power law ( \Gamma = 3.54 ) , a hard power law ( \Gamma = 0.99 ) and a curved shape ( described with two logparabolic functions ) .
The phase distributions of the normalizations of these spectral components form three decoupled pulse profiles .
The soft component peaks around phase 0.4 while the other two components peak around phase 0.8 .
The width of the curved component ( \sim 0.25 in phase ) is about half the width of the hard component .
After 4U 0142+61 , 1RXS J1708-40 is the second anomalous X-ray pulsar for which such detailed phase-resolved spectroscopy has been performed .
These results give important constraints showing that three dimensional modeling covering both the geometry and different production processes is required to explain our findings .