Spectral study of GX 339-4 with TCAF using Swift/XRT and NuSTAR Observation

TL;DR

This study analyzes the spectral properties of GX 339-4 during its 2013 outburst using combined Swift/XRT and NuSTAR data with the TCAF model, revealing the source remained in a hard state and providing insights into accretion flow parameters and black hole spin.

Contribution

First-time fitting of combined NuSTAR and Swift spectra with TCAF, including Fe line broadening analysis and estimation of the Kerr parameter.

Findings

GX 339-4 remained in the hard state during the outburst.

TCAF fitting provided accretion rates and Compton cloud size.

Estimated Kerr spin parameter of the black hole as ~0.99.

Abstract

We fit spectra of galactic transient source GX~339-4 during its 2013 outburst using Two Component Advective Flow (TCAF) solution. For the first time, we are fitting combined NuSTAR and Swift observation with TCAF. We use TCAF to fit 0.8-9.0~keV Swift and 4-79 keV NuSTAR spectra along with the LAOR model. To fit the data we use disk accretion rate, halo accretion rate, size of the Compton cloud and the density jump of advective flows at this cloud boundary as model parameters. From TCAF fitted flow parameters, and energy spectral index we conclude that the source was in the hard state throughout this particular outburst. The present analysis also gives some idea about the broadening of Fe $K_{\alpha}$ with the accretion rate. Since TCAF does not include Fe line yet, we make use of the `LAOR model' as a phenomenological model and find an estimate of the Kerr parameter to be $\sim 0.99$ for this candidate.