GRS 1739-278 observed at very low luminosity with XMM-Newton and NuSTAR

Abstract

We present a detailed spectral analysis of XMM-Newton and NuSTAR observations of the accreting transient black hole GRS 1739-278 during a very faint low hard state at ~0.02% of the Eddington luminosity (for a distance of 8.5 kpc and a mass of 10 M_sun ). The broad-band X-ray spectrum between 0.5-60 keV can be well-described by a power law continuum with an exponential cutoff. The continuum is unusually hard for such a low luminosity, with a photon index of Gamma = 1.39 +/- 0.04. We find evidence for an additional reflection component from an optically thick accretion disk at the 98% likelihood level. The reflection fraction is low with R_refl = 0.043(+0.033,-0.023). In combination with measurements of the spin and inclination parameters made with NuSTAR during a brighter hard state by Miller and co-workers, we seek to constrain the accretion disk geometry. Depending on the assumed emissivity profile of the accretion disk, we find a truncation radius of 15-35 Rg (5-12 R_ISCO ) at the 90% confidence limit. These values depend strongly on the assumptions and we discuss possible systematic uncertainties.

7 pages, 3 figures, accepted for publication in ApJ

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Cited by in corpus (11)

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• Coronal properties of black hole X-ray binaries in the hard state as seen by NuSTAR and Swift
• Evidence for Disk Truncation at Low Accretion States of the Black Hole Binary MAXI J1820+070 Observed by NuSTAR and XMM-Newton
• High-density reflection spectroscopy of black hole X-ray binaries in the hard state
• The black hole X-ray transient Swift J1357.2-0933 as seen with Swift and NuSTAR during its 2017 outburst
• A strongly changing accretion morphology during the outburst decay of the neutron star X-ray binary 4U 1608-52
• Radio/X-ray Correlation in the Mini-Outburts of Black Hole X-ray Transient GRS 1739--278
• X-ray spectral correlations in a sample of Low-mass black hole X-ray binaries in the hard state
• NuSTAR and Swift observations of Swift J1357.2-0933 during an early phase of its 2017 outburst
• Comparing X-ray color selection in separating X-ray binary classes using Color-Color-Intensity diagrams
• Accretion Geometry of Black Hole X-ray Binaries: Insights from X-ray Observations