A Wind-disk Self-irradiation Model for Supercritical Accretion

Abstract

Optical emission from actively accreting X-ray binaries is dominated by X-ray reprocessing on the outer disk. In the regime of supercritical accretion, strong radiation will power a massive wind that is optically thick and nearly spherical, and will occult the central hard X-rays from irradiating the outer disk. Instead, thermal emission from the wind will act as a new source of irradiation. Here, we construct a self-irradiation model, in which the inner disk (within the wind photosphere) is completely blocked by the wind, the middle part (between the wind photosphere and scattersphere) is heated by the wind directly, and the outer disk (beyond the wind scattersphere) is heated by photons leaving the scattersphere. The model can adequately fit the UV/optical SED of NGC 247 X-1, a candidate source with supercritical accretion, while the standard irradiation model fails to produce a self-consistent result. The best-fit parameters suggest that the source contains a stellar mass black hole with an accretion rate roughly 100 times the critical value. Remarkably, the UV/optical fitting predicts a wind photosphere that is well consistent with X-ray measurements, although it is an extrapolation over 3 orders of magnitude in wavelength. This implies that supercritical accretion does power a massive wind and the UV/optical data are useful in constraining the wind structure.

The chameleon on the branches: spectral state transition and dips in NGC 247 ULX-1

“…In the same plot, we reproduced the expected kT bb versus R bb relation for a 10 M BH and for a 1.4 M NS according to the calculations of Soria & Kong (2016). Our new values appear compatible with the overall trend found by Urquhart & Soria (2016) and suggest in the outflowing scenario of Soria & Kong (2016) either a massive NS (which is likely given the high accretion rate) or a light stellar-mass BH, though this runs contrary to predictions given in Yao & Feng (2019), who estimated a BH mass in the range 15-60 M based on the fit result of a disk irradiation model (Meier 2012) applied to the UV/optical spectrum of the source.…”

The Chameleon on the branches: spectral state transition and dips in NGC 247 ULX-1

“…In the same plot, we reproduced the expected kT bb versus R bb relation for a 10 M BH and for a 1.4 M NS according to the calculations of Soria & Kong (2016). Our new values appear compatible with the overall trend found by Urquhart & Soria (2016) and suggest in the outflowing scenario of Soria & Kong (2016) either a massive NS (which is likely given the high accretion rate) or a light stellar-mass BH, though this runs contrary to predictions given in Yao & Feng (2019), who estimated a BH mass in the range 15-60 M based on the fit result of a disc irradiation model (Meier 2012) applied to the UV/optical spectrum of the source.…”

Quasi-periodic dipping in the ultraluminous X-ray source, NGC 247 ULX-1

“…Frank et al 1987). For NGC 247 ULX-1, Yao & Feng (2019) derived an > 67 deg via modeling the UV/optical spectral energy distribution (SED) with an irradiation model, providing further evidence for a high inclination viewing angle in this source. Additionally, winds observed in BH or NS X-ray binaries (XRBs) have been mostly observed in sources in which the disc is inclined at a large angle to the line of sight (e.g.…”