Studying the inner accretion disk of GX 339-4 with NuSTAR and Swift
Abstract
The latest outburst of the famous transient black-hole binary GX 339-4 at the end of 2013 was intensely monitored by NuSTAR and Swift. Here we present the spectral analysis of four NuSTAR and Swift observations following the rise of the outburst and a final observation at the end of the outburst. During the outburst GX339-4 never left the low-hard state. The NuSTAR data provide excellent data quality to study the reflection component in this state. The iron line shows a significant broadening which is best described by relativistic effects close to the black-hole. If we assume a standard disk with an emissivity index of q=3, the accretion disk seems to be truncated before reaching the ISCO, as expected in the low-hard state. However, if we use a lamp-post geometry for the X-ray corona and self consistently describe the emissivity, the data can be explained by either a truncated accretion disk or a corona located several tens of r_g above the black-hole. Both scenarios show a weak dependence on flux, with the strongest relativistic effects measured at the highest flux phases. We discuss the physical implications of both models.
- Publication:
-
The X-ray Universe 2014
- Pub Date:
- July 2014
- Bibcode:
- 2014xru..confE..75F