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Post Info TOPIC: IRAS 13224-3809
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RE: IRAS 13224-3809
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Title: Revealing the X-ray source in IRAS 13224-3809 through flux-dependent reverberation lags
Authors: E. Kara, A. C. Fabian, E. M. Cackett, G. Miniutti, P. Uttley

IRAS 13224-3809 was observed in 2011 for 500 ks with the XMM-Newton observatory. We detect highly significant X-ray lags between soft (0.3 - 1 keV) and hard (1.2 - 5 keV) energies. The hard band lags the soft at low frequencies (i.e. hard lag), while the opposite (i.e. soft lag) is observed at high frequencies. In this paper, we study the lag during flaring and quiescent periods. We find that the frequency and absolute amplitude of the soft lag is different during high-flux and low-flux periods. During the low flux intervals, the soft lag is detected at higher frequencies and with smaller amplitude. Assuming that the soft lag is associated with the light travel time between primary and reprocessed emission, this behaviour suggests that the X-ray source is more compact during low-flux intervals, and irradiates smaller radii of the accretion disc (likely because of light bending effects). We continue with an investigation of the lag dependence on energy, and find that isolating the low-flux periods reveals a strong lag signature at the Fe K line energy, similar to results found using 1.3 Ms of data on another well known Narrow-Line Seyfert I galaxy, 1H0707-495.

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Title: Long XMM observation of the Narrow-Line Seyfert 1 galaxy IRAS13224-3809: rapid variability, high spin and a soft lag
Authors: A. C. Fabian, E. Kara, D. J. Walton, D. R. Wilkins, R. R. Ross, K. Lozanov, P. Uttley, L. C. Gallo, A. Zoghbi, G. Miniutti, T. Boller, W. N. Brandt, E. M. Cackett, C.-Y. Chiang, T. Dwelly, J. Malzac, J. M. Miller, E. Nardini, G. Ponti, R. C. Reis, C. S. Reynolds, J. Steiner, Y. Tanaka, A. J. Young

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.

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