Thermal stability of winds driven by radiation pressure in super-Eddington accretion disks. (arXiv:1903.06174v1 [astro-ph.HE])

Thermal stability of winds driven by radiation pressure in super-Eddington accretion disks. (arXiv:1903.06174v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Pinto_C/0/1/0/all/0/1">Ciro Pinto</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mehdipour_M/0/1/0/all/0/1">Missagh Mehdipour</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Walton_D/0/1/0/all/0/1">Dom J. Walton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Middleton_M/0/1/0/all/0/1">Matthew J. Middleton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Roberts_T/0/1/0/all/0/1">Tim P. Roberts</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fabian_A/0/1/0/all/0/1">Andrew C. Fabian</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Guainazzi_M/0/1/0/all/0/1">Matteo Guainazzi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Soria_R/0/1/0/all/0/1">Roberto Soria</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kosec_P/0/1/0/all/0/1">Peter Kosec</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ness_J/0/1/0/all/0/1">Jan-Uwe Ness</a>

It is currently thought that the vast majority of ultraluminous X-ray sources
(ULXs) is powered by neutron stars and stellar-mass black holes accreting at
rates which may exceed the Eddington limit by factors of a few up to hundreds.
At these high accretion rates, radiation pressure is expected to inflate the
accretion disk and drive fast winds at significant fractions of the speed of
light. Evidence of such winds has been found in recent work with
high-resolution grating spectrometers (RGS) aboard XMM-Newton as well as
moderate-resolution detectors. The thick disk structure and the spectral energy
distribution resembling those of a broadened disk significantly differ from
those of thin disk accretors such as sub-Eddington active galactic nuclei and
X-ray binaries. The thermal status of ULX winds, and of super-Eddington
accretors in general, is therefore expected to depart from sub-Eddington
accreting objects. Here we show the first attempt to calculate the
photoionization balance of the winds driven by strong radiation pressure in
thick disks with a focus on ULXs, and the effects of different viewing angles.
We find that the winds are generally in thermally stable equilibrium, but
long-term variations in the accretion rate and the inclination due to
precession may have significant effects on the appearance and stability. These
trends can explain the correlation between the spectral residuals around 1 keV
and ULX spectral state. We also find a possible correlation between the
spectral hardness of the ULX, the wind velocity and the ionization parameter in
support of the general scenario.

http://arxiv.org/icons/sfx.gif