Gravitationally distorted P-Cygni profiles from outflows near compact objects

TL;DR

This paper develops a new theory for spectral line profiles near compact objects, accounting for gravitational and Doppler effects, revealing complex distorted P-Cygni profiles that can inform studies of outflows close to neutron stars and black holes.

Contribution

It reformulates P-Cygni profile theory to include gravitational effects, predicting complex line shapes near compact objects, unlike classical profiles.

Findings

Profiles can have multiple absorption and emission components.

Profiles may exhibit both red- and blue-shifted absorption troughs.

Strong gravity causes significant distortions in spectral lines.

Abstract

We consider resonant absorption in a spectral line in the outflowing plasma within several tens of Schwarzschild radii from a compact object. We take into account both Doppler and gravitational shifting effects and re-formulate the theory of P-Cygni profiles in these new circumstances. It is found that a spectral line may have multiple absorption and emission components depending on how far the region of interaction is from the compact object and what is the distribution of velocity and opacity. Profiles of spectral lines produced near a neutron star or a black hole can be strongly distorted by Doppler blue-, or red-shifting, and gravitational red-shifting. These profiles may have both red- and blue-shifted absorption troughs. The result should be contrasted with classical P-Cygni profiles which consist of red-shifted emission and blue-shifted absorption features. We suggest this property of line profiles to have complicated narrow absorption and emission components in the presence of strong gravity may help to study spectroscopically the innermost parts of an outflow.