An appendix summarizes all previous high-energy observations and possible detections of Cygnus X-1 above 1 MeV. In addition to a previously reported episode observed by AGILE in 2009 October during the hard state, we report a weak but important candidate for enhanced emission which occurred at the end of 2010 June (2010 June 30 10:00-2010 July 2 10:00 UT) exactly coinciding with a hard-to-soft state transition and before an anomalous radio flare. We also discuss possible gamma-ray flares detected by AGILE. We discuss theoretical implications of our findings in the context of high-energy emission models of black hole accretion. In particular, we confirm that Cygnus X-1 hosts a rapidly rotating black hole, 0.93≲a, excluding the existence of prominent non-thermal emission above 100 MeV during the soft state of Cygnus X-1. We find excellent consistency for the black hole spin and the iron abundance of the accretion disk, which are expected to remain constant on more » observational timescales. To investigate this variability, we construct a model incorporating both the standard disk-corona continuum and relativistic reflection from the accretion disk, based on prior work on Cygnus X-1, and apply this model to each epoch independently. Despite the basic similarity of the observed spectra, there is clear spectral variability between epochs. We present a multi-epoch hard X-ray analysis of Cygnus X-1 in its soft state based on four observations with the Nuclear Spectroscopic Telescope Array (NuSTAR).
Cygnus x1 accretion disk xray telescope plus#
We find that the blurring parameters are consistent when fitting either just the iron line or the entire broadband spectrum, which is well modeled with a Comptonized continuum plus reflection model. In addition, we find that the line profile has not changed greatly in the switch from soft to hard states, and that the differences are consistent with changes in the underlying reflection spectrum rather than the relativistic blurring. We find a high spin, a small inner disk radius, and a low source height and rule out truncation to greater than three gravitational radii at the 3σ confidence level. Detailed fits to the iron line profile indicate a high level of relativistic blurring, indicative of reflection from the inner accretion disk. to simultaneously measure the black hole spin, more » disk inner radius, and coronal height in a self-consistent manner.
We use the reflection models of García et al. We confirm that the iron line cannot be fit with a combination of narrow lines and absorption features, instead requiring a relativistically blurred profile in combination with a narrow line and absorption from the companion wind. This is the first time this state has been observed in Cyg X-1 with NuSTAR, which enables us to study the reflection and broadband spectra in unprecedented detail. We present simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR ) and Suzaku observations of the X-ray binary Cygnus X-1 in the hard state.
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