Black Hole Spin in X-ray Binaries: Giving Uncertainties an $f$. (arXiv:2010.11948v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Salvesen_G/0/1/0/all/0/1">Greg Salvesen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Miller_J/0/1/0/all/0/1">Jonah M. Miller</a>
The two established techniques for measuring black hole spin in X-ray
binaries often yield conflicting results, which must be resolved before either
method may be deemed robust. In practice, black hole spin measurements based on
fitting the accretion disc continuum effectively do not marginalize over the
colour correction factor $f_{mathrm{col}}$. This factor parametrizes spectral
hardening of the disc continuum by the disc atmosphere, whose true properties
are poorly constrained. We incorporate reasonable systematic uncertainties in
$f_{mathrm{col}}$ into the eight (non-maximal) black hole spin measurements
vetted by the disc continuum fitting community. In most cases, an
$f_{mathrm{col}}$ uncertainty of $pm$0.2-0.3 dominates the black hole spin
error budget. We go on to demonstrate that plausible departures in
$f_{mathrm{col}}$ values from those adopted by the disc continuum fitting
practitioners can bring the discrepant black hole spins into agreement with
those from iron line modeling. Systematic uncertainties in $f_{mathrm{col}}$,
such as the effects of strong magnetization, should be better understood before
dismissing their potentially dominant impact on the black hole spin error
budget.
The two established techniques for measuring black hole spin in X-ray
binaries often yield conflicting results, which must be resolved before either
method may be deemed robust. In practice, black hole spin measurements based on
fitting the accretion disc continuum effectively do not marginalize over the
colour correction factor $f_{mathrm{col}}$. This factor parametrizes spectral
hardening of the disc continuum by the disc atmosphere, whose true properties
are poorly constrained. We incorporate reasonable systematic uncertainties in
$f_{mathrm{col}}$ into the eight (non-maximal) black hole spin measurements
vetted by the disc continuum fitting community. In most cases, an
$f_{mathrm{col}}$ uncertainty of $pm$0.2-0.3 dominates the black hole spin
error budget. We go on to demonstrate that plausible departures in
$f_{mathrm{col}}$ values from those adopted by the disc continuum fitting
practitioners can bring the discrepant black hole spins into agreement with
those from iron line modeling. Systematic uncertainties in $f_{mathrm{col}}$,
such as the effects of strong magnetization, should be better understood before
dismissing their potentially dominant impact on the black hole spin error
budget.
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