A self-consistent model for the long-term gamma-ray spectral variability of Cygnus X-1

Fulvio Melia, Ranjeev Misra

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

The long-term transitions of the black hole candidate Cygnus X-1 (between the states γ1, γ2, and γ3) include the occasional appearance of a strong ∼ MeV bump (γ1), whose strength appears to be anticorrelated with the continuum flux (≲ 400 keV) due to the Compton upscattering of cold disk photons by the inner, hot corona. We develop a self-consistent disk picture that accounts naturally for these transitions and their corresponding spectral variations. We argue that the bump is due to the self-Comptonization of bremsstrahlung photons emitted predominantly near the plane of the corona itself. Our results suggest that a decrease by a factor of ≈ 2 in the viscosity parameter α is responsible for quenching this bump and driving the system to the γ2 state, whereas a transition from γ2 to γ3 appears to be induced by an increase of about 25% in the accretion rate Ṁ. In view of the fact that most of the transitions observed in this source seem to be of the γ23 variety, we conclude that much of the long-term gamma-ray spectral variability in Cygnus X-1 is due to these small fluctuations in Ṁ. The unusual appearance of the γ1 state apparently reflects a change in the dissipative processes within the disk.

Original languageEnglish (US)
Pages (from-to)797-801
Number of pages5
JournalAstrophysical Journal
Volume411
Issue number2
StatePublished - Jul 10 1993

Fingerprint

corona
gamma rays
coronas
viscosity
accretion
photons
bremsstrahlung
quenching
continuums
parameter
rate
cold

Keywords

  • Accretion, accretion disks
  • Black hole physics
  • Radiation mechanisms: miscellaneous
  • Stars: individual (Cygnus x-1)

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

A self-consistent model for the long-term gamma-ray spectral variability of Cygnus X-1. / Melia, Fulvio; Misra, Ranjeev.

In: Astrophysical Journal, Vol. 411, No. 2, 10.07.1993, p. 797-801.

Research output: Contribution to journalArticle

@article{2bcb0b0fbf1749a7817259b0635459d8,
title = "A self-consistent model for the long-term gamma-ray spectral variability of Cygnus X-1",
abstract = "The long-term transitions of the black hole candidate Cygnus X-1 (between the states γ1, γ2, and γ3) include the occasional appearance of a strong ∼ MeV bump (γ1), whose strength appears to be anticorrelated with the continuum flux (≲ 400 keV) due to the Compton upscattering of cold disk photons by the inner, hot corona. We develop a self-consistent disk picture that accounts naturally for these transitions and their corresponding spectral variations. We argue that the bump is due to the self-Comptonization of bremsstrahlung photons emitted predominantly near the plane of the corona itself. Our results suggest that a decrease by a factor of ≈ 2 in the viscosity parameter α is responsible for quenching this bump and driving the system to the γ2 state, whereas a transition from γ2 to γ3 appears to be induced by an increase of about 25{\%} in the accretion rate Ṁ. In view of the fact that most of the transitions observed in this source seem to be of the γ2-γ3 variety, we conclude that much of the long-term gamma-ray spectral variability in Cygnus X-1 is due to these small fluctuations in Ṁ. The unusual appearance of the γ1 state apparently reflects a change in the dissipative processes within the disk.",
keywords = "Accretion, accretion disks, Black hole physics, Radiation mechanisms: miscellaneous, Stars: individual (Cygnus x-1)",
author = "Fulvio Melia and Ranjeev Misra",
year = "1993",
month = "7",
day = "10",
language = "English (US)",
volume = "411",
pages = "797--801",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2",

}

TY - JOUR

T1 - A self-consistent model for the long-term gamma-ray spectral variability of Cygnus X-1

AU - Melia, Fulvio

AU - Misra, Ranjeev

PY - 1993/7/10

Y1 - 1993/7/10

N2 - The long-term transitions of the black hole candidate Cygnus X-1 (between the states γ1, γ2, and γ3) include the occasional appearance of a strong ∼ MeV bump (γ1), whose strength appears to be anticorrelated with the continuum flux (≲ 400 keV) due to the Compton upscattering of cold disk photons by the inner, hot corona. We develop a self-consistent disk picture that accounts naturally for these transitions and their corresponding spectral variations. We argue that the bump is due to the self-Comptonization of bremsstrahlung photons emitted predominantly near the plane of the corona itself. Our results suggest that a decrease by a factor of ≈ 2 in the viscosity parameter α is responsible for quenching this bump and driving the system to the γ2 state, whereas a transition from γ2 to γ3 appears to be induced by an increase of about 25% in the accretion rate Ṁ. In view of the fact that most of the transitions observed in this source seem to be of the γ2-γ3 variety, we conclude that much of the long-term gamma-ray spectral variability in Cygnus X-1 is due to these small fluctuations in Ṁ. The unusual appearance of the γ1 state apparently reflects a change in the dissipative processes within the disk.

AB - The long-term transitions of the black hole candidate Cygnus X-1 (between the states γ1, γ2, and γ3) include the occasional appearance of a strong ∼ MeV bump (γ1), whose strength appears to be anticorrelated with the continuum flux (≲ 400 keV) due to the Compton upscattering of cold disk photons by the inner, hot corona. We develop a self-consistent disk picture that accounts naturally for these transitions and their corresponding spectral variations. We argue that the bump is due to the self-Comptonization of bremsstrahlung photons emitted predominantly near the plane of the corona itself. Our results suggest that a decrease by a factor of ≈ 2 in the viscosity parameter α is responsible for quenching this bump and driving the system to the γ2 state, whereas a transition from γ2 to γ3 appears to be induced by an increase of about 25% in the accretion rate Ṁ. In view of the fact that most of the transitions observed in this source seem to be of the γ2-γ3 variety, we conclude that much of the long-term gamma-ray spectral variability in Cygnus X-1 is due to these small fluctuations in Ṁ. The unusual appearance of the γ1 state apparently reflects a change in the dissipative processes within the disk.

KW - Accretion, accretion disks

KW - Black hole physics

KW - Radiation mechanisms: miscellaneous

KW - Stars: individual (Cygnus x-1)

UR - http://www.scopus.com/inward/record.url?scp=12044250267&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=12044250267&partnerID=8YFLogxK

M3 - Article

VL - 411

SP - 797

EP - 801

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

ER -