Accretion Rates and Beaming in Ultraluminous X-ray Sources

Abstract

I show that extreme beaming factors $b$ are not needed to explain ULXs as stellar--mass binaries. For neutron star accretors one typically requires $b\sim 0.13$, and for black holes almost no beaming ($b\sim 0.8$). The main reason for the high apparent luminosity is the logarithmic increase in the limiting luminosity for super--Eddington accretion. The required accretion rates are explicable in terms of thermal--timescale mass transfer from donor stars of mass $6 - 10\msun$, or possibly transient outbursts. Beaming factors $\la 0.1$ would be needed to explain luminosities significantly above $10^{40}{L}_{40}$ erg s${}^{-1}$, but these requirements are relaxed somewhat if the accreting matter has low hydrogen content.

MNRAS Letters, in press

References in corpus (1)

• Super-critically accreting stellar-mass black holes as ultraluminous X-ray sources

Cited by in corpus (2)

• Masses, Beaming and Eddington Ratios in Ultraluminous X-ray Sources
• Low metallicity and ultra-luminous X-ray sources in the Cartwheel galaxy