X-ray Eclipse Mapping Constrains the Binary Inclination and Mass Ratio of Swift J1858.6-0814. (arXiv:2205.05571v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Knight_A/0/1/0/all/0/1">Amy H. Knight</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ingram_A/0/1/0/all/0/1">Adam Ingram</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Middleton_M/0/1/0/all/0/1">Matthew Middleton</a>
X-ray eclipse mapping is a promising modelling technique, capable of
constraining the mass and/or radius of neutron stars (NSs) or black holes (BHs)
in eclipsing binaries and probing any structure surrounding the companion star.
In eclipsing systems, the binary inclination, $i$, and mass ratio, $q$ relate
via the duration of totality, $t_{e}$. The degeneracy between $i$ and $q$ can
then be broken through detailed modelling of the eclipse profile. Here we model
the eclipses of the NS low-mass X-ray binary Swift J1858.6$-$0814 utilising
archival NICER observations taken while the source was in outburst. Analogous
to EXO 0748$-$676, we find evidence for irradiation driven ablation of the
companion’s surface by requiring a layer of stellar material to surround the
companion star in our modelling. This material layer extends $sim 7000 –
14000$ km from the companion’s surface and is likely the cause of the extended,
energy-dependent and asymmetric ingress and egress that we observe. Our fits
return an inclination of $i sim 81^{circ}$ and a mass ratio $q sim 0.14$.
Using Kepler’s law to relate the mass and radius of the companion star via the
orbital period ($sim$ 21.3 hrs), we subsequently determine the companion to
have a low mass in the range $0.183 M_{odot} leq M_{cs} leq 0.372 M_{odot}$
and a large radius in the range $1.02 R_{odot} leq R_{cs} leq 1.29
R_{odot}$. Our results, combined with future radial velocity amplitudes
measured from stellar absorption/emission lines, can place precise constraints
on the component masses in this system.
X-ray eclipse mapping is a promising modelling technique, capable of
constraining the mass and/or radius of neutron stars (NSs) or black holes (BHs)
in eclipsing binaries and probing any structure surrounding the companion star.
In eclipsing systems, the binary inclination, $i$, and mass ratio, $q$ relate
via the duration of totality, $t_{e}$. The degeneracy between $i$ and $q$ can
then be broken through detailed modelling of the eclipse profile. Here we model
the eclipses of the NS low-mass X-ray binary Swift J1858.6$-$0814 utilising
archival NICER observations taken while the source was in outburst. Analogous
to EXO 0748$-$676, we find evidence for irradiation driven ablation of the
companion’s surface by requiring a layer of stellar material to surround the
companion star in our modelling. This material layer extends $sim 7000 –
14000$ km from the companion’s surface and is likely the cause of the extended,
energy-dependent and asymmetric ingress and egress that we observe. Our fits
return an inclination of $i sim 81^{circ}$ and a mass ratio $q sim 0.14$.
Using Kepler’s law to relate the mass and radius of the companion star via the
orbital period ($sim$ 21.3 hrs), we subsequently determine the companion to
have a low mass in the range $0.183 M_{odot} leq M_{cs} leq 0.372 M_{odot}$
and a large radius in the range $1.02 R_{odot} leq R_{cs} leq 1.29
R_{odot}$. Our results, combined with future radial velocity amplitudes
measured from stellar absorption/emission lines, can place precise constraints
on the component masses in this system.
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