The thermal-radiative wind in the neutron star low mass X-ray binary GX 13+1

Kavli Affiliate: Tadayuki Takahashi

| First 5 Authors: Ryota Tomaru, Chris Done, Ken Ohsuga, Hirokazu Odaka, Tadayuki Takahashi

| Summary:

We fit the observed high ionisation X-ray absorption lines in the neutron
star binary GX13+1 with a full simulation of a thermal-radiative wind. This
uses a radiation hydrodynamic code coupled to Monte Carlo radiation transfer to
compute the observed line profiles from Hydrogen and Helium-like iron and
Nickel, including all strong K{alpha} and K{beta} transitions. The wind is
very strong as this object has a very large disc and is very luminous. The
absorption lines from Fe K{alpha} are strongly saturated as the ion columns
are large, so the line equivalent widths (EWs) depend sensitively on the
velocity structure. We additionally simulate the lines including isotropic
turbulence at the level of the azimuthal and radial velocities. We fit these
models to the Fe xxv and xxvi absorption lines seen in the highest resolution
Chandra third order HETGS data. These data already rule out the addition of
turbulence at the level of the radial velocity of ~500 km/s. The velocity
structure predicted by the thermal-radiative wind alone is a fairly good match
to the observed profile, with an upper limit to additional turbulence at the
level of the azimuthal velocity of ~100 km/s. This gives stringent constraints
on any remaining contribution from magnetic acceleration.

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