The Soft Gamma-Ray Spectral Variability of Cygnus X-1

By M. McConnell, A. Zdziarski, K. Bennett, H. Bloemen, W. Collmar, W. Hermsen, L. Kuiper, W. Paciesas, B. Phlips, J. Poutanen and 4 more. 2001

190 citations recorded by the source corpus.

We have used observations of Cyg X-1 from the Compton Gamma Ray Observatory and BeppoSAX to study the variation in the MeV γ-ray emission between the hard and soft spectral states, using spectra that cover the energy range from 20 keV up to 10 MeV. These data provide evidence for significant spectral variability at energies above 1 MeV. In particular, whereas the hard X-ray flux decreases during the soft state, the flux at energies above 1 MeV increases, resulting in a significantly harder γ-ray spectrum at energies above 1 MeV. This behavior is consistent with the general picture of galactic black hole candidates having two distinct spectral forms at soft γ-ray energies. These data extend this picture, for the first time, to energies above 1 MeV. We have used two different hybrid thermal/nonthermal Comptonization models to fit broadband spectral data obtained in both the hard and soft spectral states. These fits provide a quantitative estimate of the electron distribution and allow us to probe the physical changes that take place during transitions between the low and high X-ray states. We find that there is a significant increase (by a factor of ~4) in the bolometric luminosity as the source moves from the hard state to the soft state. Furthermore, the presence of a nonthermal tail in the Comptonizing electron distribution provides significant constraints on the magnetic field in the source region.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/66ee614b9d511c4bcca3224f0f42784902efddf1

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. G. Dubus
2. P. Lubiński
3. M. Gilfanov
4. A. Strong
5. LinQing Wen
6. J. Greiner
7. M. Krause
8. J. Poutanen

In Nuclear and High Energy Physics

1. P. Lubiński
2. M. Gilfanov
3. A. Strong
4. J. Greiner
5. G. Dubus
6. A. Zdziarski
7. R. Diehl
8. M. Revnivtsev

Citations in the corpus

• Gamma-ray spectroscopy of Positron Annihilation in the Milky Way (2015, background): “Cyg X-1 is time variable, with a hard, a soft, and possibly an intermediate state (McConnell et al. 2002; Rodriguez et al. 2015).”
• Correlations between X-ray and radio spectral properties of accreting black holes (2002, methodology): “…power-law tail, containing 0.05 of the total e± energy beyond the Maxwellian electron distribution, as suggested C© 2003 RAS, MNRAS 342, 355–372 Downloaded from https://academic.oup.com/mnras/article-abstract/342/2/355/1026896 by guest on 28 July 2018 by the results of McConnell et al. 2002.)”
• Understanding the Long-Term Spectral Variability of Cygnus X-1 with Burst and Transient Source Experiment and All-Sky Monitor Observations (2002, background): “The pointed observations are listed in Table 1 and correspond toMJD 50,226 (RXTE, G99), 50,233–50,234 (ASCA/RXTE, G99), 50,256, 50,338 (BeppoSAX, F01), 50,936–50,937 (BeppoSAX, D01), andMJD 51,091 (BeppoSAX, C.”
• Gamma-ray binaries and related systems (2013, background): “Cyg X-1 is the prominent example, with the power-law extending to 10 MeV in its high/soft X-ray state (McConnell et al. 2002).”