A Study of the Correlation between the Amplification of the Fe Kα Line and the X‐Ray Continuum of Quasars due to Microlensing

Abstract

The observed enhancement of the Fe Kα line in three gravitationally lensed QSOs (MG J0414+0534, QSO 2237+0305, H1413+117) is interpreted in terms of microlensing, even when equivalent X-ray continuum amplification is not observed. In order to interpret these observations, first we studied the effects of microlensing on quasars spectra, produced by straight fold caustic crossing over standard relativistic accretion disk. The disk emission was analyzed using the ray tracing method, considering Schwarzschild and Kerr metrics. When the emission is separated in two regions (an inner disk corresponding to the Fe Kα line and an outer annulus corresponding to the continuum, or vice-versa) we find microlensing events which enhance the Fe Kα line without noticeable amplification of the X-ray continuum, but only during a limited time interval. Continuum amplification is expected if a complete microlensing event is monitored. Second, we studied a more realistic case of amplification by caustic magnification pattern. In this case we could satisfactorily explain the observations if the Fe Kα line is emitted from the innermost part of the accretion disk, while the continuum is emitted from a larger region. Also, we studied the chromatic effects of microlensing, finding that the radial distribution of temperature in the accretion disk, combined with microlensing itself, can induce wavelength dependent variability of ∼ 30% for microlenses with very small masses. All these results show that X-ray monitoring of gravitational lenses is a well suited method for studying of the innermost structure of AGN accretion disks.

Observational effects of strong gravity in vicinity of supermassive black holes

“…• (see [8] and references therein). The inner radius R in of the disk can not be smaller than the radius of the marginally stable orbit R ms , that corresponds to R ms = 6R g (gravitational radius R g = GM/c 2 , where G is gravitational constant, M is the mass of central BH, and c is the velocity of light) in the Schwarzschild metric and to R ms = 1.23R g in the case of the Kerr metric with angular momentum parameter a = 0.998.…”

Time Delays in the Gravitationally Lensed Quasar H1413+117 (Cloverleaf)

“…Microlensing variations in H1413+117 may shed light on the nature and structure of the source quasar (e.g., Lewis & Belle 1998;Popović et al 2006). The three time-delay measurements in Section 3 and the new data on the lens (mass and redshift) in Section 4 are useful tools for analyses of microlensing variability.…”

Influence of gravitational microlensing on broad absorption lines of QSOs: The case of the Fe Kα line

“…In several previous papers (Popović et al, 2001(Popović et al, , 2003Popović et al, 2006a;Popović et al, 2006b;Jovanović and Popović, 2007;Jovanović et al, 2008;Jovanović and Popović, 2009) we have shown that the effect of strong gravitational lensing can have influence on the intensity and shape of Fe Kα line. Consequently, this effect can be used as a probe for the structure of the innermost part of lensed quasars.…”

“…To select the outer radius R out of the disk, we take into account some recent investigations of the Fe Kα line profile showing that it should be emitted from the innermost part of the disk which outer radius is within several tens of R g (see e.g. Popović et al, 2006a, and references therein). Therefore, in our numerical simulations we adopted the following disk parameters: inclination i = 35 o , inner and outer radii R in = R ms and R out = 20 R g , emissivity index q = −2.5 and angular momentum of central BH a = 0 (Schwarzschild metric).…”