Reflection Modeling of the Black Hole Binary 4U~1630$-$47: the Disk Density and Returning Radiation

Abstract

We present the analysis of X-ray observations of the black hole binary 4U~1630$-$47 using relativistic reflection spectroscopy. We use archival data from the RXTE, Swift, and NuSTAR observatories, taken during different outbursts of the source between $1998$ and $2015$. Our modeling includes two relatively new advances in modern reflection codes: high-density disks, and returning thermal disk radiation. Accretion disks around stellar-mass black holes are expected to have densities well above the standard value assumed in traditional reflection models (i.e., $n_{\mathrm{e}}\sim 10^{15}\mathrm{c}{\mathrm{m}}^{-3}$). New high-density reflection models have important implications in the determination of disk truncation (i.e., the disk inner radius). This is because one must retain self-consistency in the irradiating flux and corresponding disk ionization state, which is a function of disk density and system geometry. We find the disk density is $n_{\mathrm{e}}\ge 10^{20}\mathrm{c}{\mathrm{m}}^{-3}$ across all spectral states. This density, combined with our constraints on the ionization state of the material, implies an irradiating flux impinging on the disk that is consistent with the expected theoretical estimates. Returning thermal disk radiation -- the fraction of disk photons which bend back to the disk producing additional reflection components -- is expected predominantly in the soft state. We show that returning radiation models indeed provide a better fit to the soft state data, reinforcing previous results which show that in the soft state the irradiating continuum may be blackbody emission from the disk itself.

20 pages, 6 figures, 6 tables, Accepted by ApJ

References in corpus (13)

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Cited by in corpus (10)

• Towards more accurate synthetic reflection spectra: improving the calculations of returning radiation
• Reflection and timing study of the transient black hole X-ray binary MAXI J1803-298 with NuSTAR
• MAXI and NuSTAR observations of the faint X-ray transient MAXI J1848-015 in the GLIMPSE-C01 Cluster
• X-ray spectral correlations in a sample of Low-mass black hole X-ray binaries in the hard state
• The long-stable hard state of XTE J1752-223 and the disk truncation dilemma
• An Insight-HXMT view of the mHz quasi-regular modulation phenomenon in the black hole X-ray binary 4U 1630-47
• A NuSTAR and Swift View of the Hard State of MAXI J1813-095
• The Spin of a Newborn Black Hole: Swift J1728.9-3613
• Proof of principle X-ray reflection mass measurement of the black hole in H1743-322
• Accretion Geometry of Black Hole X-ray Binaries: Insights from X-ray Observations