The Accretion Disk Wind in the Black Hole GRS 1915+105

TL;DR

This study presents a detailed high-resolution spectrum of the black hole GRS 1915+105, revealing a complex, magnetically driven accretion disk wind with multiple components and implications for black hole accretion physics.

Contribution

The paper provides the first detailed high-resolution spectral analysis of the disk wind in GRS 1915+105, identifying multiple wind components and constraining magnetic field strengths involved in wind launching.

Findings

Detection of four wind components in the Fe K band.

Wind launching radii estimated at 10^2-10^4 GM/c^2.

Magnetic field strength inferred to be 10^3-10^5 Gauss.

Abstract

We report on a 120 ks Chandra/HETG spectrum of the black hole GRS 1915+105. The observation was made during an extended and bright soft state in June, 2015. An extremely rich disk wind absorption spectrum is detected, similar to that observed at lower sensitivity in 2007. The very high resolution of the third-order spectrum reveals four components to the disk wind in the Fe K band alone; the fastest has a blue-shift of v = 0.03c. Broadened re-emission from the wind is also detected in the first-order spectrum, giving rise to clear accretion disk P Cygni profiles. Dynamical modeling of the re-emission spectrum gives wind launching radii of r ~ 10^(2-4) GM/c^2. Wind density values of n ~ 10^(13-16) cm^-3 are then required by the ionization parameter formalism. The small launching radii, high density values, and inferred high mass outflow rates signal a role for magnetic driving. With simple, reasonable assumptions, the wind properties constrain the magnitude of the emergent magnetic field to B ~ 10^(3-4) Gauss if the wind is driven via magnetohydrodynamic (MHD) pressure from within the disk, and B ~ 10^(4-5) Gauss if the wind is driven by magnetocentrifugal acceleration. The MHD estimates are below upper limits predicted by the canonical alpha-disk model (Shakura & Sunyaev 1973). We discuss these results in terms of fundamental disk physics and black hole accretion modes.