Reflections on Accretion Disks

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Reflections on Accretion Disks
David R. Ballantyne TAP Fellow, U. of Arizona
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X-rays from AGN
XMM-Newton Chandra Combined
range of 0.2-12 keV. Both carry gratings to
provide dispersed spectra. Chandra has
sub-arcsecond imaging. XMM-Newton has more than
10? the sensitivity of ASCA.
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Current Spectral Model Overview
Taking into account reflection increases the
intrinsic power law to G?2.
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Spectral Model Reflection

• Ginga found strong Fe Ka emission at 6.4 keV
  (cold iron). This is a fluorescence line.
• No correlation of line strength with
  line-of-sight absorption.
• Ginga also found spectral hardening above 8 keV
• Both features explained by X-ray reprocessing in
  optically-thick material.
• Out of the line-of-sight but would subtend a
  significant solid-angle as seen from the X-ray
  source

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George Fabian (1991) Matt, Perola Piro (1991)
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Ross, Fabian Young (1999)
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• So, where is the reflector?

This makes an interesting prediction
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Spectral Model The Fe Ka line

• What happens to an emission line which
  originates from a spinning disc close to a black
  hole?

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• Shape depends on inner and outer radius of
  emission region, inclination of disc and
  emissivity profile.

Inclination angle.
Fabian et al. (2000)
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• The red-wing primarily determined by inner
  radius
• ? Possible to determine space-time around black
  hole.

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The Case of MCG-6-30-15

• 3.8 day XMM-Newton observation of MCG-6-30-15.
• Highest quality hard X-ray spectrum of a Sy1
  ever made

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• Big problem w/ Fe line interpretation it does
  not vary with the continuum
• In fact, it varies very little at all

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• A new interpretation 2 ionized reflectors from
  different locations on the disc (Ballantyne
  Fabian 2001 Ballantyne, Vaughan Fabian 2003)

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Results of fitting model to the time averaged
spectrum. (Ballantyne et al. 2003)
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• Fit model to 32 10 ks segments.
• Find inner reflector more ionized as flux
  increases.
• Outer reflector remains neutral
• (Ballantyne et al. 2003)

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• This could explain the strange Fe K spectral
  variability

Flare Avg. Minimum
From ASCA (Iwasawa et al 1996)
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• But, model implies unusual geometry, and strong
  energy generation at the inner disk edge.
• Energy extraction from a spinning black hole?
  (Blandford Znajek 1976 Wilms et al. 2001)

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The Superburst from 4U1820-30
Superburst occurred on 1999 September 9. Was
being observed by RXTE/PCA.
Strohmayer Brown (2002)
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Strohmayer Brown (2002)
Line Energy Line Flux Edge Energy Edge depth
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Constant Density Models

• Used extreme He star
• abundances from Pandey
• et al. (2001)
• Models parameterized
• by the ionization parameter

Ballantyne (2004)
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Fitting the Superburst

• have 80 spectra with a 64s integration time
• could fit between 3-40 keV for most of the
  spectra the last 10 or so could only be fit up
  to 15 keV due to the encroaching background
• fit parameters NH (absorbing column density)
• log ? (ionization parameter)
• R (reflection fraction)
• kT (blackbody
  temperature)
• rin (the inner disk radius)
• fixed parameters inclination angle (30 degrees)
• rout 200 GM/c2 (the outer disk
  radius) emissivity index ?3

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Results
Ballantyne Strohmayer (2004)
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