SpectroTiming Study of GX 3394 in a Hard Intermediate State
Abstract
We present an analysis of Nuclear Spectroscopic Telescope Array observations of a hard intermediate state of the transient black hole GX 3394 taken in 2015 January. With the source softening significantly over the course of the 1.3 day long observation we split the data into 21 subsets and find that the spectrum of all of them can be well described by a powerlaw continuum with an additional relativistically blurred reflection component. The photon index increases from ∼1.69 to ∼1.77 over the course of the observation. The accretion disk is truncated at around nine gravitational radii in all spectra. We also perform timing analysis on the same 21 individual data sets, and find a strong typeC quasiperiodic oscillation (QPO), which increases in frequency from ∼0.68 to ∼1.05 Hz with time. The frequency change is well correlated with the softening of the spectrum. We discuss possible scenarios for the production of the QPO and calculate predicted inner radii in the relativistic precession model as well as the global disk mode oscillations model. We find discrepancies with respect to the observed values in both models unless we allow for a black hole mass of ∼100 {M}_{⊙ }, which is highly unlikely. We discuss possible systematic uncertainties, in particular with the measurement of the inner accretion disk radius in the relativistic reflection model. We conclude that the combination of observed QPO frequencies and inner accretion disk radii, as obtained from spectral fitting, is difficult to reconcile with current models.
 Publication:

The Astrophysical Journal
 Pub Date:
 September 2016
 DOI:
 10.3847/0004637X/828/1/34
 arXiv:
 arXiv:1604.08644
 Bibcode:
 2016ApJ...828...34F
 Keywords:

 accretion;
 accretion disks;
 stars: black holes;
 Xrays: binaries;
 Xrays: individual: GX 3394;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 10 pages, 8 figures