Long XMM observation of the narrow line Seyfert 1 galaxy IRAS 13224-3809: Rapid variability, high spin and a soft lag

A.C. Fabian, E. Kara, D. Walton, D.R. Wilkins, R.R. Ross, K. Lozanov, P. Uttley, L. Gallo, A. Zoghb et al , 2013, MNRAS 429, 2917-2923

Results are presented from a 500ks long XMM-Newton observation of the Narrow-Line Seyfert 1 galaxy IRAS13224-3809. The source is rapidly variable on timescales down to a few 100s. The spectrum shows strong broad Fe-K and L emission features which are interpreted as arising from reflection from the inner parts of an accretion disc around a rapidly spinning black hole. Assuming a power-law emissivity for the reflected flux and that the innermost radius corresponds to the innermost stable circular orbit, the black hole spin is measured to be 0.988 with a statistical precision better than one per cent. Systematic uncertainties are discussed. A soft X-ray lag of 100s confirms this scenario. The bulk of the power-law continuum source is located at a radius of 2-3 gravitational radii.