The broad iron line physics: summary and outlook

Abstract

AbstractA brief overview of the ESAC/XMM‐Newton Science Operations Centre Workshop on “Variable and Broad Iron Lines around Black Holes” is presented. Following the relativistic disk‐line theory of accreting black holes, ASCA discovered such broad iron lines from several AGN. XMM‐Newton and Chandra confirmed the ASCA results, but also found more complexities. It was pointed out that poor modelling of the continuum may mimic broad iron line, if ionized absorbers are present. This degeneracy between the broad line and the continuum shape was shown to be resolved by separately determining the continuum and the reflection component with use of an accurate hard X‐ray spectrum obtained with Suzaku. As a result, the relativistic broad iron lines are now robust. Time variations of the primary continuum and the reflection component are often decoupled, the latter varying little. This is explained by the light bending model that applies in the region near to an extreme Kerr hole. The red‐ and/or blueshifted transient iron line features were found with XMM‐Newton, some of which revealed a possible quasi‐periodicity. Such transient features are important dynamical probes of the black hole vicinity. The remaining issues are briefly mentioned. Finally, there is no doubt that the broad line physics continues to be extremely important. Prospects for the future development are discussed, which justify large next‐generation missions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)