Reflected iron line from a source above a Kerr black hole accretion disc

Abstract

In this paper we present a fully relativistic approach to modelling both the continuum emission and the reflected fluorescent iron line from a primary X‐ray source near a Kerr black hole. The X‐ray source is located above an accretion disc orbiting around the black hole. The source is assumed to be a static point source located on an arbitrary position above the disc, on or off the axis of rotation. We carry out Monte Carlo simulations in order to estimate the iron line spectrum as well as its equivalent width. Because of the gravitational lensing effect, an enhancement of the iron line is expected when the primary source is located close to the central black hole. We find that for a source located on the axis of rotation the enhancement is relatively modest. An observer at inclination 30° would measure an equivalent width of ∼300 eV in the extreme case of a maximally rotating black hole and a source located at height 1.5 gravitational radii from the centre. This corresponds to an equivalent width enhancement factor of about 2 compared with the classical value where no lensing effect comes into play. However, when allowing the source to be located off the axis of rotation, much stronger enhancement can be obtained. In the extreme case of a maximally rotating black hole and a source located just above the approaching side of the disc, an observer at inclination 30° could measure an equivalent width as high as ∼1.5 keV (i.e., ∼10 times the classical value). We also find that observers located at high inclination angles observe a stronger line than observers at low inclination angles.

On the origin of the broad, relativistic iron line of MCG–6-30-15 observed by XMM-Newton

“…Martocchia et al 2000). When allowing the source to be located off the axis of rotation, an even stronger enhancement can be obtained (Dabrowski & Lasenby 2001).…”

Probing variability patterns of the Fe K line complex in bright nearby AGNs

“…Moreover, recent results point towards an origin in small emitting regions within the inner accretion disk (e.g. IMF04, Tombesi et al 2007;Petrucci et al 2007), as predicted by several models, such as the "hot" orbiting spot model (Nayakshin & Kazanas 2001;Dovčiak et al 2004) or the lamppost model (Martocchia & Matt 1996;Dabrowski & Lasenby 2001;. Unfortunately, despite the unprecedented sensitivity of current X-ray telescopes, attempts to test these models are hampered by the too fine spectral features that are predicted (Goosmann et al 2007).…”

Towards Gravitating Discs Around Stationary Black Holes

“…Certain spectral features (the iron Kα line in particular) of some active galactic nuclei (a celebrated example is the Seyfert 1 galaxy MCG-6-30-15) have been interpreted as originating as close to the very centre as a few to a few dozens of Schwarzschild radii, 8 so they may well represent data from the strongest fields ever met (see [107] for a review, and e.g. [266,267,155,88] for models and interpretation issues). The iron lines have already been discovered in the X-ray spectrum of several Galactic microquasars ( [224] and references therein).…”