2011/05/02 by Farid Rahoui, Julia C. Lee, Sebastian Heinz +4 · 4 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Bremsstrahlung #Emission spectrum #Jet (fluid) #Spectral line #Spectral shape analysis #Stars #Supergiant #Synchrotron #Synchrotron radiation #astro-ph.HE
paper · pdf · doi:10.1088/0004-637x/736/1/63
46 pages, 10 figures, 8 tables. Accepted for publication in ApJ
arxiv created 2011/05/02 · openalex publication_date 2011/07/06 · arxiv updated 2015/05/28 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We report on a Spitzer /InfraRed Spectrograph (mid-infrared), RXTE /PCA+HEXTE (X-ray), and Ryle (radio) simultaneous multiwavelength study of the microquasar Cygnus X-1, which aimed at an investigation of the origin of its mid-infrared emission. Compact jets were present in two out of three observations, and we show that they strongly contribute to the mid-infrared continuum. During the first observation, we detect the spectral break—where the transition from the optically thick to the optically thin regime takes place—at about 2.9 × 10 13 Hz. We then show that the jet's optically thin synchrotron emission accounts for Cygnus X-1's emission beyond 400 keV, although it cannot alone explain its 3–200 keV continuum. A compact jet was also present during the second observation, but we do not detect the break, since it has likely shifted to higher frequencies. In contrast, the compact jet was absent during the last observation, and we show that the 5–30 μm mid-infrared continuum of Cygnus X-1 stems from the blue supergiant companion star HD 226868. Indeed, the emission can then be understood as the combination of the photospheric Rayleigh–Jeans tail and the bremsstrahlung from the expanding stellar wind. Moreover, the stellar wind is found to be clumpy, with a filling factor f ∞ ≈ 0.09–0.10. Its bremsstrahlung emission is likely anti-correlated to the soft X-ray emission, suggesting an anti-correlation between the mass-loss and mass-accretion rates. Nevertheless, we do not detect any mid-infrared spectroscopic evidence of interaction between the jets and Cygnus X-1's environment and/or the companion star's stellar wind.