|Speaker||Talk Date||Talk Series|
|Dan Wilkins (IoA)||2 November, 2011||Institute of Astronomy Seminars|
This talk explores how the spectrum of X-ray reflected from the accretion disc in AGN can reveal the illumination pattern (emissivity profile) of the accretion disc by the primary X-ray source. Systematic ray tracing simulations, performed on high performance graphics processing units (GPUs) are used to produce theoretical emissivity profiles due to illumination of the accretion disc for a range of locations and geometries of the X-ray source to discover how the properties of the X-ray source affect the emissivity profile of the accrection disc. Along with measurements of reverberation time lags between the primary continuum and reflected X-rays, this allows constraints to be placed on the location and geometry of the X-ray source in the narrow line Seyfert 1 galaxy 1H 0707-495. The low state of 1H 0707-495 in 2011 in which the spectrum was dominated almost entirely by the reflection from the accretion disc with little or no continuum emission seen is understood in terms of the primary X-ray source collapsing down to a confined region just above the black hole.