Profiles of spectral lines from failed and decelerated winds from neutron stars and black holes

TL;DR

This paper models spectral line profiles from failed and decelerating winds around neutron stars and black holes, revealing various profile types influenced by gravitational redshift and wind dynamics.

Contribution

It introduces a detailed analysis of spectral line profiles from extended outflows with changing velocities near compact objects, including failed winds and decelerating flows.

Findings

Profiles can be distorted P-Cygni, W-shaped, or inverted P-Cygni.

Inverted P-Cygni profiles can originate from failed winds close to the compact object.

Line profiles depend on the interplay between wind velocity and gravitational redshift.

Abstract

We calculate profiles of spectral lines from an extended outflow from the compact object (a black hole or a neutron star). We assume that the bulk velocity of the flow increases during a short phase of acceleration and then rapidly decreases forming a failed wind. We also study the wind which is only decelerating. We show that depending on the relative strength of the gravitational redshifting line profiles from such winds may be of several types: distorted P-Cygni (emission and blueshifted absorption); W-shaped (absorption-emission-absorption) and inverted P-Cygni (emission-redshifted absorption). The latter case is expected from accretion flows where the velocity is directed inwards; however, we show that inverted P-Cygni profile can be produced by the failed wind, provided the line is formed within several tens of Schwarzschild radii from the compact object.