The Reflection Spectrum of Cygnus X-1 as Measured by NuSTAR
Abstract
Cygnus X-1 is an accreting black hole binary that has been persistently bright throughout the history of X-ray astronomy. Over the years, observations of Cyg X-1 across the electromagnetic spectrum have led to breakthrough results, including dynamical evidence that its compact object is a black hole, measurements indicating that the black hole is rapidly rotating, resolving its compact jet in the radio band, obtaining parallax distance and proper motion measurements, and the discovery of soft and hard spectral states. The NuSTAR satellite has obtained 3-79 keV observations of Cyg X-1, sampling soft, hard, and intermediate states over the past several years. The NuSTAR bandpass, energy resolution, and throughput provide measurements of the Compton reflection component with unprecedented quality, and results have been reported for the soft state (e.g., Tomsick et al. 2014; Walton et al. 2016), the hard state (e.g., Parker et al. 2015; Basak et al. 2017), and the intermediate state (Tomsick et al. 2018). The relativistic distortion of the reflection component depends on the location of the inner radius of the disk and the geometry of the source, and spectral modeling can lead to constraints. However, in some cases, the models also lead to unphysically high iron abundances, and this may be a source of systematic uncertainty for the other model parameters. Here, we investigate possible reasons for the high iron abundances, focusing on detailed modeling of one of the intermediate state Cyg X-1 spectra.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E3408T