2000/01/31 by M. L. McConnell, M. McConnell, J. M. Ryan +12 · 1 citation
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Context (archaeology) #Electron #Gamma ray #Gamma-ray bursts and supernovae #Nuclear physics #Observatory #Optics #Photon #Physics #Spectral index #Spectral line #astro-ph
paper · pdf · doi:10.1086/317128
28 pages, 6 figures, accepted for publication in ApJ. Considerably revised from original submission
arxiv created 2000/06/19 · openalex publication_date 2000/11/10 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The Compton Gamma Ray Observatory ( CGRO ) has observed the Cygnus region on several occasions since its launch in 1991. The data collected by the COMPTEL experiment on CGRO represent the most sensitive observations to date of Cygnus X-1 in the 0.75-30 MeV range. A spectrum accumulated by COMPTEL over 10 weeks of observation time shows significant evidence for emission extending out to several MeV. We have combined these data with contemporaneous data from both BATSE and OSSE to produce a broadband γ-ray spectrum, corresponding to the low X-ray state of Cygnus X-1, extending from 50 keV up to ~5 MeV. Although there is no evidence for any broad-line-like emissions in the MeV region, these data further confirm the presence of a hard tail at energies above several hundred keV. In particular, the spectrum at MeV energies can be described as a power law with a photon spectral index of α = -3.2, with no evidence for a cutoff at high energies. For the 200 keV-5 MeV spectrum, we provide a quantitative description of the underlying electron spectrum, in the context of a hybrid thermal/nonthermal model for the emission. The electron spectrum can be described by a thermal Maxwellian with a temperature of kT e = 86 keV and a nonthermal power-law component with a spectral index of p e = 4.5. The spectral data presented here should provide a useful basis for further theoretical modeling.