Reflection Spectroscopy of the Black Hole Binary XTE J1752−223 in Its Long-stable Hard State

• Published in: The Astrophysical journal 2018-09, Vol.864 (1), p.25
• Main Authors: García, Javier A., Steiner, James F., Grinberg, Victoria, Dauser, Thomas, Connors, Riley M. T., McClintock, Jeffrey E., Remillard, Ronald A., Wilms, Jörn, Harrison, Fiona A., Tomsick, John A.
• Format: Article
• Language: English
• Subjects: Accretion disks; accretion, accretion disks; Astrophysics; atomic processes; black hole physics; Black holes; Constraint modelling; Corona; Emissivity; Inclination; line: formation; Noise spectra; Physical properties; Proportional counters; Reflection; Spectral analysis; Spectroscopy; Spectrum analysis; X-rays: individual (XTE J1752−223)
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aad231

We present a detailed spectral analysis of the black hole binary XTE J1752−223 in the hard state of its 2009 outburst. Regular monitoring of this source by the Rossi X-ray Timing Explorer mission provided high signal-to-noise spectra along the outburst rise and decay. During one full month this source stalled at ∼30% of its peak count rate at a constant hardness and intensity. By combining all the data in this exceptionally stable hard state, we obtained an aggregate proportional counter array spectrum (3-45 keV) with 100 million counts, and a corresponding high energy X-ray timing experiment spectrum (20-140 keV) with 5.8 million counts. Implementing a version of our reflection code with a physical model for Comptonization, we obtain tight constraints on important physical parameters for this system. In particular, the inner accretion disk is measured very close in, at Rin = 1.7 0.4 Rg. Assuming Rin = RISCO, we find a relatively high black hole spin (a* = 0.92 0.06). Imposing a lamppost geometry, we obtain a low inclination (i = 35° 4°), which agrees with the upper limit found in the radio (i < 49°). However, we note that this model cannot be statistically distinguished from a non-lamppost model with a free emissivity index, for which the inclination is markedly higher. Additionally, we find a relatively cool corona (57-70 keV) and large iron abundance (3.3-3.7 solar). We further find that properly accounting for Comptonization of the reflection emission improves the fit significantly and causes an otherwise low reflection fraction (∼0.2-0.3) to increase by an order of magnitude, in line with geometrical expectations for a lamppost corona. We compare these results with similar investigations reported for GX 339−4 in its bright hard state.