Past exam of the astrophysics course of the University of Oxford / 2015 / 2 / b

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- Solution b

Solution

Using

M = 1.4 M_{⊙}

,

R = 1 0^{4}

m and the stated opacity gives

L_{Edd} = 2.06 \times 1 0^{31} W, \dot{M}_{Edd} = 1.11 \times 1 0^{15} kg s^{- 1} = 1.76 \times 1 0^{- 8} M_{⊙} y r^{- 1} .

If the observed X-rays represent isotropic, radiatively efficient surface accretion power, then

\frac{M ˙}{M ˙ _{Edd}} = \frac{L _{X}}{L _{Edd}} = 48.6, \dot{M} ≃ 5.38 \times 1 0^{16} kg s^{- 1} .

A bolometric correction, beaming, radiation advected into the flow or energy carried by a wind would change the mapping from the measured band luminosity to the supplied mass rate. This estimate keeps the assumptions needed for comparison with the torque calculation.

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