Open AccessRadiation spectrum from relativistic slim accretion discs: an effect of photon trapping
Author(s) -
Shimura Toshiya,
Manmoto Tadahiro
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06158.x
Subject(s) - physics , eddington luminosity , astrophysics , accretion (finance) , black body radiation , bremsstrahlung , radiative transfer , photon , intermediate polar , luminosity , radiation , astronomy , white dwarf , nuclear physics , quantum mechanics , stars , galaxy
The vertical structure and the emission spectrum of slim accretion discs around massive black holes are investigated for super‐critical accretion states. A key process is the effect of photon trapping, which is included in the radiative transfer equation. It is found that the local radiation spectrum emitted from the inner region has a typical Comptonized bremsstrahlung form, and deviates significantly from the blackbody and the modified blackbody spectrum. The spectral hardening factor of the local spectrum has a large radial dependence: it takes a value of ∼10 4 (inner region) and ∼3 (outer region). Owing to the effect of photon trapping, the emergent luminosity becomes small compared with the gravitational energy released through viscosity. The effect is remarkable for a large accretion rate and a spin parameter close to unity. In particular, for an extreme Kerr case with an accretion rate of 100 L Edd / c 2 , where L Edd is the Eddington luminosity, the emergent luminosity is approximately 2 per cent of the released energy. A comparison with the standard model is also discussed for an accretion rate under the Eddington limit.