Abstract
Thanks to the good spectral resolution and large effective area of the EPIC/PN instrument on board of XMM-Newton, we have at hand a large number of observations of accreting low-mass X-ray binaries, that allow for the fist time a comprehensive view on the characteristics of the reflection component at different accretion regimes and to probe the effects of a magnetosphere on its formation. We focus here on a comparative analysis of the reflection component from a series of spectroscopic studies on selected sources: 4U 1705-44, observed both in the soft and hard state, the pulsating ms pulsars SAX J1808.4- 3658 and IGR J17511-3057, and the intermittent pulsar HETE J1900-2455. Although the sources can present very similar accretion rates and continuum shapes, the reflection parameters do not generally result the same, moreover the effect of a magnetosphere on the formation of the reflection component appears elusive.
Highlights
Broad iron emission lines have been observed in many low-mass X-ray binaries (LMXBs) hosting both neutron stars (NSs) and black-holes with high statistics and good spectral resolution by the EPIC/PN on board of XMM-Newton
Thanks to the good spectral resolution and large effective area of the EPIC/PN instrument on board of XMM-Newton, we have at hand a large number of observations of accreting low-mass X-ray binaries, that allow for the fist time a comprehensive view on the characteristics of the reflection component at different accretion regimes and to probe the effects of a magnetosphere on its formation
Atoll sources enter the hard state when the luminosity drops below a certain threshold, and the accretion flow close to the NS becomes optically thin
Summary
Broad iron emission lines have been observed in many low-mass X-ray binaries (LMXBs) hosting both neutron stars (NSs) and black-holes with high statistics and good spectral resolution by the EPIC/PN on board of XMM-Newton. There is growing evidence that these lines are formed by reflection of corona/boundary layer photons in the accretion disk and broadened by a combination of dynamical and relativistic effects. The soft state is characterized by high accretion rates (luminosity ≥ 0.1 LEdd), total flux mostly in the 1-10 keV range, spectrum composed of a soft ∼1 keV thermal disk emission and optically thick boundary layer emission. The hard state is, on the contrary, characterized by lower accretion rates, relatively small, or undetected, disk emission and a dominating hard, optically thin, Comptonized component extending well above 10 keV. In both states, a reflection component is present and appears relativistically broadened.
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