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

By F. Fürst, J. A. Tomsick, K. Yamaoka, T. Dauser, J. M. Miller, M. Clavel, Stéphane Corbel, A. C. 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. Wilms


International audienceWe 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

Topics: accretion disks, stars: black holes, X-rays: binaries, X-rays: individual (GRS 1739-278), accretion, [ PHYS.ASTR.HE ] Physics [physics]/Astrophysics [astro-ph]/High Energy Astrophysical Phenomena [astro-ph.HE]
Publisher: American Astronomical Society
Year: 2016
DOI identifier: 10.3847/0004-637X/832/2/115
OAI identifier: oai:HAL:insu-01432858v1
Provided by: Hal-Diderot
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