Morphology of Relativistically Broadened Line Emission from Axisymmetric Equatorial Accretion Disks

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Main Authors: Gates, Delilah E. A., Truong, Chau, Sahu, Amrita, Cárdenas-Avendaño, Alejandro
Format: Preprint
Published: 2024
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author Gates, Delilah E. A.
Truong, Chau
Sahu, Amrita
Cárdenas-Avendaño, Alejandro
author_facet Gates, Delilah E. A.
Truong, Chau
Sahu, Amrita
Cárdenas-Avendaño, Alejandro
contents Single-frequency emission from an accretion disk around a black hole is broadened into a line profile due to gravitational redshift and the motion of the disk's particles relative to the observer. The ensemble of relativistically broadened emission frequencies from the disk elements forms the spectrum viewed by an observer. Over the past decades, the broadened spectra of accreting systems have been used to constrain the spin of the black hole, the observer's inclination, and the astrophysical model parameters of the system. These inferences are usually made under the assumption that the accretion disk consists of particles orbiting around the black hole on stable circular orbits in the equatorial plane. Under this Standard disk model, in this work, we revisit line profile morphology, i.e., its extent, kinks, and fall-off. We provide a unified analytical explanation for these line profile morphological features, which encode the black hole spin, viewing inclination, and locations of the disk's inner and outer edges. We then show that these features, however, are model-dependent, by parametrically relaxing some of the astrophysical assumptions. In particular, we explore how allowing the disk particles to deviate from stable circular orbits rapidly degenerates the characteristic features of the line profile under the Standard disk model. Our results further demonstrate how sensitive our understanding of black hole and system properties can be to assumptions we make when interpreting these types of measurements.
format Preprint
id arxiv_https___arxiv_org_abs_2411_14338
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle Morphology of Relativistically Broadened Line Emission from Axisymmetric Equatorial Accretion Disks
Gates, Delilah E. A.
Truong, Chau
Sahu, Amrita
Cárdenas-Avendaño, Alejandro
High Energy Astrophysical Phenomena
General Relativity and Quantum Cosmology
Single-frequency emission from an accretion disk around a black hole is broadened into a line profile due to gravitational redshift and the motion of the disk's particles relative to the observer. The ensemble of relativistically broadened emission frequencies from the disk elements forms the spectrum viewed by an observer. Over the past decades, the broadened spectra of accreting systems have been used to constrain the spin of the black hole, the observer's inclination, and the astrophysical model parameters of the system. These inferences are usually made under the assumption that the accretion disk consists of particles orbiting around the black hole on stable circular orbits in the equatorial plane. Under this Standard disk model, in this work, we revisit line profile morphology, i.e., its extent, kinks, and fall-off. We provide a unified analytical explanation for these line profile morphological features, which encode the black hole spin, viewing inclination, and locations of the disk's inner and outer edges. We then show that these features, however, are model-dependent, by parametrically relaxing some of the astrophysical assumptions. In particular, we explore how allowing the disk particles to deviate from stable circular orbits rapidly degenerates the characteristic features of the line profile under the Standard disk model. Our results further demonstrate how sensitive our understanding of black hole and system properties can be to assumptions we make when interpreting these types of measurements.
title Morphology of Relativistically Broadened Line Emission from Axisymmetric Equatorial Accretion Disks
topic High Energy Astrophysical Phenomena
General Relativity and Quantum Cosmology
url https://arxiv.org/abs/2411.14338