Neutron star radius measurement from the ultraviolet and soft X-ray thermal emission of PSR J0437-4715. (arXiv:1904.12114v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Gonzalez_Caniulef_D/0/1/0/all/0/1">Denis Gonzalez-Caniulef</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Guillot_S/0/1/0/all/0/1">Sebastien Guillot</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reisenegger_A/0/1/0/all/0/1">Andreas Reisenegger</a>
We analyze the thermal emission from the entire surface of the millisecond
pulsar PSR J0437-4715 observed in the ultraviolet and soft X-ray bands. For
this, we calculated non-magnetized, partially ionized atmosphere models of
different compositions, and include plasma frequency effects which may affect
the emergent spectrum. This is particularly true for the coldest atmospheres
composed of the heaviest elements (up to a few percent changes in the soft
X-ray flux). Employing a Markov chain Monte Carlo method, we find that the
spectral fits favour a hydrogen atmosphere, disfavour a helium composition and
rule out Fe atmosphere and blackbody models. By using a Gaussian prior on the
dust extinction value, according the latest 3D map of Galactic dust, we found
that the hydrogen atmosphere model results in a neutron star radius
$R_mathrm{NS} = 13.10^{+0.9}_{-0.7}$ km and bulk surface temperature
$T^{infty}_mathrm{eff}=left(2.8pm0.2right)times10^5$ K. Because of the
well known mass of this pulsar, our analysis produces tight constraints on its
radius, and therefore on the properties of ultra-dense matter, by favouring a
stiff equation of state and disfavouring a strange quark composition inside
neutron stars.
We analyze the thermal emission from the entire surface of the millisecond
pulsar PSR J0437-4715 observed in the ultraviolet and soft X-ray bands. For
this, we calculated non-magnetized, partially ionized atmosphere models of
different compositions, and include plasma frequency effects which may affect
the emergent spectrum. This is particularly true for the coldest atmospheres
composed of the heaviest elements (up to a few percent changes in the soft
X-ray flux). Employing a Markov chain Monte Carlo method, we find that the
spectral fits favour a hydrogen atmosphere, disfavour a helium composition and
rule out Fe atmosphere and blackbody models. By using a Gaussian prior on the
dust extinction value, according the latest 3D map of Galactic dust, we found
that the hydrogen atmosphere model results in a neutron star radius
$R_mathrm{NS} = 13.10^{+0.9}_{-0.7}$ km and bulk surface temperature
$T^{infty}_mathrm{eff}=left(2.8pm0.2right)times10^5$ K. Because of the
well known mass of this pulsar, our analysis produces tight constraints on its
radius, and therefore on the properties of ultra-dense matter, by favouring a
stiff equation of state and disfavouring a strange quark composition inside
neutron stars.
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