New Spectral State of Supercritical Accretion Flow with Comptonizing Outflow
Abstract
Supercritical accretion flows inevitably produce radiation-pressure driven outflows, which Compton up-scatter soft photons from the underlying accretion flow, thereby making hard emission. We performed two-dimensional radiation hydrodynamic simulations of supercritical accretion flows and outflows, while incorporating such Compton scattering effects, and demonstrated that there appears a new hard spectral state at higher photon luminosities than that of the slim-disk state. In this state, as the photon luminosity increases, the photon index decreases and the fraction of the hard emission increases. The Compton y-parameter is on the order of unity (and thus the photon index will be ∼2) when the apparent photon luminosity is ∼30LE (with LE being the Eddington luminosity) for nearly face-on sources. This explains the observed spectral hardening of the ULX NGC 1313 X-2 in its brightening phase, and thus supports the model of supercritical accretion onto stellar-mass black holes in this ULX.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- August 2009
- DOI:
- 10.1093/pasj/61.4.769
- arXiv:
- arXiv:0904.4123
- Bibcode:
- 2009PASJ...61..769K
- Keywords:
-
- accretion;
- accretion disks;
- black hole physics;
- hydrodynamics;
- radiative transfer;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 15 pages, 4 figures, accepted for publication in PASJ