Broad iron lines in neutrons stars: dynamical broadening or wind scattering?

Abstract

Broad iron emission lines are observed in many accreting systems from black holes in AGN and X-ray binaries to neutron star low-mass X-ray binaries. The origin of the line broadening is often interpreted as due to dynamical broadening and relativistic effects. However, alternative interpretations have been proposed, included broadening due to Compton scattering in a wind or accretion disk atmosphere. Here we explore the observational signatures expected from broadening in a wind, in particular that the iron line width should increase with an increase in the column density of the absorber (due to an increase in the number of scatterings). We study the data from three neutron star low-mass X-ray binaries where both a broad iron emission line and absorption lines are seen simultaneously, and show that there is no significant correlation between line width and column density. This favors an inner disk origin for the line broadening rather than scattering in a wind.

5 pages, 1 table, 5 figures, accepted for publication in ApJ

References in corpus (14)

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• High-Resolution X-Ray Spectroscopy of the Bursting Pulsar GRO J1744-28
• Broad-band spectral analysis of the accreting millisecond X-ray pulsar SAX J1748.9-2021
• NuSTAR and XMM-Newton broad-band spectrum of SAX J1808.4-3658 during its latest outburst in 2015
• Testing Rate Dependent corrections on timing mode EPIC-pn spectra of the accreting Neutron Star GX 13+1
• Black Hole Spin Measurements Based on a Thin Disc Model with Finite Thickness I. An example study of MCG-06-30-15
• The broadband spectral analysis of 4U 1702-429 using XMM-Newton and BeppoSAX data
• Comprehensive broadband study of accreting neutron stars with Suzaku: Is there a bi-modality in the X-ray spectrum?
• An XSPEC model to explore spectral features from black-hole sources - II. The relativistic iron line in the lamp-post geometry
• Red-skewed K$\alpha$ iron lines in GX 13+1
• Broadband observations of the X-ray burster 4U 1705-44 with BeppoSAX