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\large
\vspace{1.7in} 
\centerline{\Red {\underline{\sl ON THE ORIGIN OF THE BROAD }}}
\vskip30pt
\centerline{\Red {\underline{ \sl  RELATIVISTIC IRON LINE OF MCG--6-30-15  }}}
\vskip30pt
\centerline{\Red {\underline{ \sl OBSERVED BY XMM-NEWTON}}}
\vspace{1.5in}


\noindent 
\large
\centerline{\Blue{Andrea Martocchia (1), Giorgio Matt (1)}}
\centerline{\Blue{and  Vladimir Karas (2)}}
\vspace{0.1in}

\normalsize{\sl
\noindent
 1 - Dipartimento di Fisica, Universit\`a degli Studi "Roma Tre", Italy

\noindent
 2 - Astronomical Institute of the Charles University, Prague, Czech Republic }

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\centerline{\fcolorbox{black}{yellow}{Abstract} }
\vskip20pt


\large
The relativistic iron line profile recently observed by XMM-Newton in the spectrum of 
the Seyfert 1
galaxy MCG--6-30-15 (Wilms et al., 2001) is discussed in the framework of a simple lamp-post
model. 
It is shown that the steep disc emissivity, the large line equivalent width and the amount of 
Compton reflection can be self-consistently reproduced in this scenario. 

\normalsize

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\centerline{\fcolorbox{black}{yellow}{Introduction} }
\vskip20pt



Wilms et al. (2001)  recently presented and discussed an extremely broad and red-shifted iron
K$\alpha$ line, detected in the June 11-12, 2000, 100 ksec XMM-Newton observation of
MCG-6-30-15. The line profile is extremely broad and redshifted, indicating that a large fraction
of the emission comes from $r<6r_g$, and that the disc emissivity law is very steep. 
If a simple powerlaw is used for the emissivity, the best-fit powerlaw index is $\beta\sim$4, 
i.e. the dependence
on radius is much steeper than usual in Seyfert galaxies (Nandra et al., 1997). 
In this contribution we show that this emissivity, as well as the observed strong line Equivalent 
Width
(EW$\sim$300 eV) and the amount of Compton reflection ($R\simgt$1), may be reproduced by a model in
which the primary X-ray source - located on the BH symmetry axis at a height $h\sim$a few $r_g$  
(the
gravitational radius) - illuminates the disc. This is the so called lamp-post picture (cp. 
Martocchia \&
Matt, 1996, Petrucci \& Henry, 1997, Bao et al., 1998, Reynolds et al., 1999, Dabrowsky \& Lasenby,
2001). It can be considered a phenomenological scheme appropriate for 
models like those by Henry \& Petrucci (1997) or Agol \& Krolik (2001). 

\Red{ Further details can be found in: Martocchia, Matt \& Karas (2001).}

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\centerline{\fcolorbox{black}{yellow}{An X-ray illuminated disc in Kerr metric } }

\vskip20pt

If the primary source, assumed to be isotropic in its own reference frame, 
is very close to the BH (i.e. $h$ is
small), the illuminating photons' trajectories are strongly bended by the spacetime curvature. The
illuminating flux is thus very anisotropic, and the emission is concentrated in the innermost 
part of the
disc. With decreasing $h$, the effect of light bending, i.e. the anisotropy, increases  
(see \Blue{Figure 1}). This
causes a substantial increase of the fluorescent and  Compton-reflected components, and a 
decrease of the primary continuum. 

The emissivity is derived by means of fully relativistic calculations of the primary 
flux impinging onto
the disc (Martocchia \& Matt 1996, 1997; Martocchia, Karas \& Matt, 2000). Results on the iron line
profiles and underlying Compton-reflected continuum have been presented by Martocchia, Karas \&
Matt (2000). 
  
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\centerline{\fcolorbox{black}{yellow}{Predictions of the model } }

\vskip40pt

\centerline{\Green{1. Emissivity laws }}
\vskip20pt

The radial dependence of the emissivity accounts for the local illuminating flux and incident 
angle; it
depends on $h$ (it steepens when $h$ decreases because of the enhanced anisotropy of the primary
emission) and can be approximated through functions of the form 
$\epsilon(r)=A r^{-B} + C r^{-D}$. Plots of the computed emissivity vs radius, 
and best-fit coefficients for the
approximating formula, have been presented in Martocchia, Karas \& Matt (2000). It is easy to
recognize (see \Blue{Figure 2}) that an emissivity law with $\beta\sim$4, i.e. 
the one derived by Wilms et al. (2001),
may be reproduced in our model with a small height of the primary source: 

\vskip20pt
\centerline{\Red{$h\sim 3 r_g$}}
\vskip20pt
                            
For an emissivity law of this kind, the line profile results to be very broad and 
red-shifted (see \Blue{Figure 3},
and Martocchia, Karas \& Matt, 2000, for details). 
  
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\centerline{\Green{2. Line intensity and Compton reflection }}

\vskip20pt

Due to the high (relativistic) speeds of the disc matter at very low radii, 
the impinging photons as seen
in the matter's frame arrive with high incident angles, and their energy is substantially 
blue-shifted. These effects further increase the amount of fluorescence and reflection. 

For $h\sim3r_g$ our model predicts: 

\vskip20pt
\centerline{\Red{EW $\sim$ 250-300 eV}}
\vskip20pt

  \centerline{\Red{$R\sim4$}} 
\vskip20pt

\noindent
which are consistent with the values found by Wilms et al. (2001). 

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\centerline{\fcolorbox{black}{yellow}{References}
 }

\vskip20pt
\small{
\ref Agol E. \& Krolik J.H. (2000), ApJ 528, 161 

\ref       Bao G., Wiita P.J. \& Hadrava P. (1998), ApJ 504, 58 

\ref       Dabrowski Y. \& Lasenby A.N. (2001), MNRAS 321, 605 

\ref       Henri G. \& Petrucci P.O. (1997), A\&A 326, 87 

\ref       Martocchia A. (2000), ``X-ray Spectral Signatures of Accreting Black Holes'',  
PhD Thesis, SISSA-ISAS, Trieste 

\ref       Martocchia A., Karas V. \& Matt G. (2000), MNRAS 312, 817 

\ref       Martocchia A. \& Matt G. (1996), MNRAS 282, L53 

\ref       Martocchia A. \& Matt G. (1997), in: Proc. of the 12th Italian 
Conference on Gen. Rel. \& Grav. Phys., World Scient. Pub. Co., Singapore 

\ref       Martocchia A., Matt G. \& Karas V. (2001), A\&A, to be submitted 

\ref       Petrucci P.O. \& Henry G. (1997), A\&A 326, 99 

\ref       Reynolds C.S. et al. (1999), ApJ 514, 164 

\ref       Wilms J., Reynolds C.S., Begelman M.C., Reeves J., Molendi S., Staubert R., 
Kendziorra E. (2001), MNRAS 328, L27 
}

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\begin{figure}
\epsfig{file=solidan.eps, height=15.0cm, width=15.0cm}
\caption{
Variation with $h$ of the ratio between the solid angle of the radiation which reaches the equatorial
plane and the same solid angle as it would come out in a flat spacetime, in the assumption that 
the disc
extends up to 1000 $r_g$ and for three values of the BH spin (solid line: $a$=$m$; 
dotted line: $a$=0.5$m$; 
dashed
line: static BH). }
\end{figure}

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\begin{figure}
\epsfig{file=emis_new.ps, height=15.0cm, width=15.0cm, angle=-90 }
\caption{\Black{
Disc emissivity (in arbitrary units) vs. radius (in units of $r_g$) for a source located at 
$h=3r_g$ (solid line)
and $h=4r_g$ (dashed line) in a maximally spinning BH metric. The lower, straight dotted line
corresponds to a power law with $\beta\sim4$. }}
\end{figure}


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\begin{figure}
\epsfig{file=plot3.ps, height=15.0cm, width=15.0cm, angle=-90 }
\caption{\Black{Fe  K$\alpha$ line profiles 
computed with the XSPEC routine {\sc kerrspec} (Martocchia 2000), using
respectively a power-law emissivity with $\beta=4$ (solid line) and a lamp-post 
emissivity with $h=3r_g$ 
(dashed line). All other parameters have been fixed to the best-fit values  
found by Wilms et al. (2001).
Differences between the two plotted models are clearly too small to be detectable by XMM. }}
\end{figure}



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