NuSTAR and Swift Observations of the Very High State in GX 339-4: Weighing the Black Hole with X-Rays

Abstract

We present results from spectral fitting of the very high state of GX 339-4 with Nuclear Spectroscopic Telescope Array (NuSTAR) and Swift. We use relativistic reflection modeling to measure the spin of the black hole and inclination of the inner disk and find a spin of a={0.95}<SUB>-0.08</SUB><SUP>+0.02</SUP> and inclination of 30° ± 1° (statistical errors). These values agree well with previous results from reflection modeling. With the exceptional sensitivity of NuSTAR at the high-energy side of the disk spectrum, we are able to constrain multiple physical parameters simultaneously using continuum fitting. By using the constraints from reflection as input for the continuum fitting method, we invert the conventional fitting procedure to estimate the mass and distance of GX 339-4 using just the X-ray spectrum, finding a mass of {9.0}<SUB>-1.2</SUB><SUP>+1.6</SUP> {M}<SUB>☉ </SUB> and distance of 8.4 ± 0.9 kpc (statistical errors).