Red-skewed K$alpha$ iron lines in GX 13+1. (arXiv:1903.11813v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Maiolino_T/0/1/0/all/0/1">T. Maiolino</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Laurent_P/0/1/0/all/0/1">P. Laurent</a> (2,3), <a href="http://arxiv.org/find/astro-ph/1/au:+Titarchuk_L/0/1/0/all/0/1">L. Titarchuk</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Orlandini_M/0/1/0/all/0/1">M. Orlandini</a> (4), <a href="http://arxiv.org/find/astro-ph/1/au:+Frontera_F/0/1/0/all/0/1">F. Frontera</a> (1,4,5) ((1) Ferrara University, Department of Physics and Earth Science, Italy (2) CEA Saclay, France (3) Laboratoire APC, France (4) INAF/Osservatorio di Astrofisica e Scienza dello Spazio (OAS) Bologna, Italy (5) ICRANET, Italy)
Broad, asymmetric, and red-skewed Fe Kalpha emission lines have been observed
in the spectra of low-mass X-ray binaries hosting neutron stars (NSs) as a
compact object. Because more than one model is able to describe these features,
the explanation of where and how the red-skewed Fe lines are produced is still
a matter of discussion. It is broadly accepted that the shape of the Fe Kalpha
line is strongly determined by the special and general relativistic effects
occurring in the innermost part of the accretion disk. In this relativistic
framework, the Fe fluorescent lines are produced in the innermost part of the
accretion disk by reflection of hard X-ray photons coming from the central
source (corona and/or NS surface). We developed an alternative and
nonrelativistic model, called the windline model, that is capable to describe
the Fe line features. In this nonrelativistic framework, the line photons are
produced at the bottom of a partly ionized outflow (wind) shell as a result of
illumination by the continuum photons coming from the central source, and the
red-skewness of the line profile is explained by repeated electron scattering
of the photons in a diverging outflow. Because GX~13+1 is a well-known
disk-wind source, it is a perfect target for testing the windline model and
comparing it to the relativistic one. In order to access the goodness of the
fit and distinguish between the two line models, we used the run-test
statistical method in addition to the canonical $chi^2$ statistical method.
The diskline and windline models both fit the asymmetric GX13+1 Fe line well.
From a statistical point of view, for the two observations we analyzed, the
run-test was not able to distinguish between the two Fe line models, at 5%
significance level.
Broad, asymmetric, and red-skewed Fe Kalpha emission lines have been observed
in the spectra of low-mass X-ray binaries hosting neutron stars (NSs) as a
compact object. Because more than one model is able to describe these features,
the explanation of where and how the red-skewed Fe lines are produced is still
a matter of discussion. It is broadly accepted that the shape of the Fe Kalpha
line is strongly determined by the special and general relativistic effects
occurring in the innermost part of the accretion disk. In this relativistic
framework, the Fe fluorescent lines are produced in the innermost part of the
accretion disk by reflection of hard X-ray photons coming from the central
source (corona and/or NS surface). We developed an alternative and
nonrelativistic model, called the windline model, that is capable to describe
the Fe line features. In this nonrelativistic framework, the line photons are
produced at the bottom of a partly ionized outflow (wind) shell as a result of
illumination by the continuum photons coming from the central source, and the
red-skewness of the line profile is explained by repeated electron scattering
of the photons in a diverging outflow. Because GX~13+1 is a well-known
disk-wind source, it is a perfect target for testing the windline model and
comparing it to the relativistic one. In order to access the goodness of the
fit and distinguish between the two line models, we used the run-test
statistical method in addition to the canonical $chi^2$ statistical method.
The diskline and windline models both fit the asymmetric GX13+1 Fe line well.
From a statistical point of view, for the two observations we analyzed, the
run-test was not able to distinguish between the two Fe line models, at 5%
significance level.
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