SPH simulations of irradiation-driven warped accretion discs and the long periods in X-ray binaries

TL;DR

This study uses 3D SPH simulations to demonstrate that irradiation-driven warping of accretion discs can explain the long periods observed in X-ray binaries, matching observed luminosities and disc behaviors.

Contribution

First comprehensive 3D SPH modeling showing irradiation-driven warping causes long periods in X-ray binaries, aligning simulations with observations across multiple systems.

Findings

Simulations reproduce observed super-orbital periods and luminosities.

Warp angles up to 18.6 degrees match jet cone observations.

Disc tilts remain below 13 degrees, with maximum warps up to 21 degrees.

Abstract

We present three dimensional smoothed particle hydrodynamics (SPH) calculations of irradiation-driven warping of accretion discs. Initially unwarped planar discs are unstable to the radiation reaction when the disc is illuminated by a central radiation source. The disc warps and tilts and precesses slowly in a retrograde direction; its shape continuously flexes in response to the changing orientation of the Roche potential. We simulate ten systems: eight X-ray binaries, one cataclysmic variable (CV), and a `generic' low mass X-ray binary (LMXB). We adopt system parameters from observations and tune a single parameter: our model X-ray luminosity ($L_{*}$) to reproduce the observed or inferred super-orbital periods. Without exception, across a wide range of parameter space, we find an astonishingly good match between the observed $L_{X}$ and the model $L_{*}$. We conclude irradiation-driven warping is the mechanism underlying the long periods in X-ray binaries. Our Her X-1 simulation simultaneously reproduces the observed $L_{X}$, the "main-" and "short-high" X-ray states and the orbital inclination. Our simulations of SS 433 give a maximum warp angle of $18.6^{\circ}$, a good match to the cone traced by the jets, but this angle is reached only in the outer disc. In all cases, the overall disc tilt is less than $\degrees{13}$ and the maximum disc warp is less than and or equal to $\degrees{21}$.