The complex accretion geometry of GX339-4 as seen by NuSTAR
Abstract
We present an in-depth spectral analysis of a failed outburst of GX 339-4 in 2013, as observed by NuSTAR and Swift. During this outburst, the source never left the low-hard state and our observations cover Eddington luminosity fractions between 0.9% and 6%. The high quality NuSTAR data allow us to study the weak reflection component in this state. We show that the source very likely has a complex coronal geometry, in which the parts illuminating the accretion disk have a significantly harder spectrum than the observed primary continuum. While we observe a relativistically broadened iron line, the complex corona makes it challenging to put stringent limits on the inner accretion disk radius. The measured values depend strongly on assumptions for the emissivity profile of the accretion disk and we discuss various scenarios. All models, however, clearly require inner disk radii smaller than 100 r_{g}. We compare these spectra to NuSTAR observations of a subsequent full outburst in 2015. We discuss differences in the continuum parameters possibly related to luminosity, which indicate changes in the accretion geometry.
- Publication:
-
The Extremes of Black Hole Accretion
- Pub Date:
- July 2015
- Bibcode:
- 2015ebha.confE..85F