Estimate of the black-hole mass in NGC 6814 from a relativistic accretion disk scenario

Summary

By using a fully relativistic model for the spectral line produced by a Keplerian disk orbiting a Schwarzschild black hole, we study the temporal behaviour of the line intensity in response to a continuum variation at an extended central source. We compare our results with the observed properties of the Seyfert galaxy NGC 6814, whose X-ray flux has been observed to decrease by a factor of two in ≈ 50 s, while the iron line intensity variations lag continuum variations by 250 s, at the most. Taking the stationary values of the iron line centroid energy and width, and assuming that the line comes from high-ionisation stages of iron (as several indications suggest) we derive that the inner radius of the line-emitting region is between 6 and 30r _g (r _g =GM/c ²), the inclination is ≤40°, while the mass of the central object is constrained to 8·10⁴ L ₄₃<M<3.9·10⁶ M _⊙(L ₄₃ is the accretion luminosity in units of 10⁴³ erg s⁻¹).