Fürst, F.Tomsick, J. A.Yamaoka, K.Dauser, T.Pottschmidt, Katjaet al2023-08-312023-08-312016-11-22Fürst, F., J. A. Tomsick, K. Yamaoka, T. Dauser, J. M. Miller, M. Clavel, S. Corbel, et al. “GRS 1739-278 Observed at Very Low Luminosity with XMM-Newton and NuSTAR.” The Astrophysical Journal 832, no. 2 (November 2016): 115. https://doi.org/10.3847/0004-637X/832/2/115.https://doi.org/10.3847/0004-637X/832/2/115http://hdl.handle.net/11603/29489Authors: - F. Fürst, J. A. Tomsick, K. Yamaoka, T. Dauser, J. M. Miller, M. Clavel, S. Corbel, A. Fabian, J. García, F. A. Harrison, A. Loh, P. Kaaret, E. Kalemci, S. Migliari, J. C. A. Miller-Jones, K. Pottschmidt, F. Rahoui, J. Rodriguez, D. Stern, M. Stuhlinger, D. J. Walton, and J. WilmsWe 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⊙). The broadband X-ray spectrum between 0.5 and 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 Γ = 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 Rᵣₑfₗ = 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 et al., 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 RᵢₛCₒ) at the 90% confidence limit. These values depend strongly on the assumptions and we discuss possible systematic uncertainties.7 pagesen-USThis item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.Text