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X-ray Spectroscopy of local AGN: what is really coming from the inner disk?. STSci Nov 28 2007. (Tracey) Jane Turner. Principal Collaborators: Lance Miller (Oxford) James Reeves (Keele) Steve Kraemer (CUA). Outline. Recap - what is an active galactic nucleus

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X-ray Spectroscopy of local AGN: what is really coming from the inner disk?


Nov 28 2007

(Tracey) Jane Turner

Principal Collaborators:

Lance Miller (Oxford)

James Reeves (Keele)

Steve Kraemer (CUA)



Recap - what is an active galactic nucleus

Review - what we can learn about the inner regions of AGN using X-ray data?

Set the scene - what models have developed based on X-ray data?

New - what are the hot new developments and how are they changing our picture?

Summary - what are the open questions?

black holes that are switched on are active
Black Holes that are switched on are “active”

Peterson “An Introduction to Active Galactic Nuclei”

Measurements of gas & stellar kinematics show most/all nucleated galaxies harbor black hole at center (Kormendy & Richstone ‘95, Magorrian et al ‘98, Gebhardt et al 2000)

BH mass scales with galaxy bulge mass so formation linked, although unclear how. Many of these BHs “switched off”

Few % of galaxies - black hole is actively accreting material - releases large amount of energy over broad frequency band, from small region -nucleus - these powerful emitters called active galactic nuclei (AGN)

the power behind agn
Simple arguments support that AGN must be powered by accretion on to supermassive black holesThe Power behind AGN
  • Eddington limit requires self gravity exceeds radiation pressure giving M > 106 M¤
  • Accreting material has angular momentum -forms accretion disk that radiates as gravitational p.e. lost, only way to get enough luminosity from such a small region
  • Accretion disk around a 106 – 108 M¤ black hole emits thermal spectrum - peaks in UV band in agreement with observations

Copious production of X-Rays

UV photons from inner disk Inverse Compton scatter off relativistic electrons in corona

Thermal Comptonization -> hard X-rays

Some X-rays shine back onto disk producing a “reflection spectrum”

Continuum + reflection pass thro’ ionized circumnuclear gas (the “warm absorber”) - that imprints further absorption & emission features on observed spectrum

x ray line production
X-ray Line Production

Photoelectric absorption

(energy dependent) photons are re-emitted via fluorescence or destroyed by Auger de-excitation

Consider X-rays illuminating optically-thick, cold accn disk

Emission lines & absorption edges result

Fe K most prominent due to combination of abundance &


George & Fabian ‘91

x ray line production1
X-ray Line Production

Ross & Fabian 2006

George & Fabian ‘91, Reynolds 1996

Compton Scattering - hard photons scatter with Compton recoil reducing scattered flux above 15 keV

Line energy (6.4-6.97 keV), fluorescence yield depend on ionization

x ray absorption line production
X-ray Absorption Line Production

Compton thin material produces narrow absorption & emission lines - detection depends on our view of gas geometry

Kaspi et al 2002




Absorption from outflow

X-ray Continuum

Iron KLine

Thermal Disk Emission?

Compton scattering hump

(Fabian, 2006, AN, 327, 943)

what are we hoping to learn from x ray studies of agn
What are we hoping to LEARN from X-ray studies of AGN?

Ultimately we hope to understand something fundamental:

- physics in the strong gravity regime Fe K from disk

- black hole accretion/fueling (and hence growth, evolution, structure formation) trace gas near BH -Warm Absorber

How do we get from X-ray data to the physics?


Fe K/Reflection

Profile distorted SR & GR - probe of inner disk/BH


Fe K/Reflection

Profile distorted SR & GR - probe of inner disk/BH


GR Effects on Spectral features

Profile distorted SR & GR - probe of inner disk/BH

Also see GR blurring of absorption features

Line energies, widths, strengths and variability can also tell us about the accretion flow and feedback (disk winds etc)

Smeared absorber - Gierlinski & Done 2004


Fe K/Reflection

Distorted Fe K profiles apparently observed in ASCA data for most nearby AGN

(eg. Fabian et al 1994, Tanaka et al 1995)







(Nandra et al 1997)

“Red wing”

mcg 6 30 15 poster child
MCG-6-30-15: Poster Child

Tanaka et al. 1995, Wilms et al 2000 and many more…

“Red wing”

Fe K

… -but line variability, peak energy and inferred disk inclinations did not match expectations

Energy (keV)

what about x ray spectral variability
What about X-ray spectral variability

Mkn 766 Miller et al 2007

Ummm….but disk derived inclinations don’t match other indicators

Spectral variability not as predicted

Broad disk line does not vary correlated with continuum

absorption or reflection as the origin of the agn continuum shape
Absorption or Reflection as the origin of the AGN continuum shape?

Smeared Absorption?

Ionized Reflection

Ballantyne et al 2004, Ross & Fabian 2006

Gierlinski & Done 2004

light bending
Light bending?

Miniutti & Fabian (2004) suggest continuum source height varies, when contm produced close to disk gravity bends light onto accretion disk, reducing continuum flux while enhancing reflection features

Suzaku lightcurve

Light Bending

Iron line does not respond to continuum


High Resolution Grating Spectroscopy

  • NGC 3783 HETG (Yaqoob et al 2005) red & black - different observations
  • Fe line FWHM ∼1700 km/s
  • Implies emitting gas ~ 70 lt-day from continuum
  • Also Kaspi et al 2002, Netzer et al 2003

Provided Progress: Narrow features resolved - separation of absorption layers & narrow emission components…

iron k shell absorption in seyfert 1s
Iron K-shell Absorption in Seyfert 1s.

NGC 3783, XMM, Reeves et al. (2004)

NGC 1365/XMM, (Risaliti et al. 2005)


Ambiguity: - X-ray Absorption

NGC 3516 Turner et al 2005

Large columns (> 1023 cm-2) of high- gas first suggested from ionized edges in Ginga data (Nandra & Pounds 1994)

Chandra/XMM confirm importance of such gas by detection of narrow absorption lines

Can reduce implied broad red wing (Kinkhabwala 2003)…..

To understand Fe K profiles this gas needs to be accounted for…

NGC 3783

Reeves et al 2004


Ambiguity: - X-ray Absorption

NGC 3516 Turner et al 2005

NGC 3783

Reeves et al 2004

complex variable absorption
Complex & Variable Absorption

Kallman et al 2004

NH~ 3x 1023 cm-2, log =2.25

Components log ~3.5 - 5, NH >> 1023 cm-2 -can we model all curvature with these?

`alternate’ (to diskline) absorption models are not arbitrarilycomplex (e.g. NGC 3516, Turner et al 2005)

Counter claims: Young et al (2005) say cannot thus “explain away” diskline in MCG-6-30-15 strong features ~6.5 keV, not observed

Counter-counter claims: L. Miller et al (2008) say MCG-6 explained without recourse to blurring

HETG, Young et al 2005

chandra xmm ngc 3516 turner et al submitted oct 2007
Chandra/XMM NGC 3516(Turner et al, submitted Oct 2007)

Highly variable light curve and the usual hardening at low flux levels

a highly ionized outflow in ngc 3516 turner et al 2007 in prep
A highly ionized outflow in NGC 3516(Turner et al. 2007, in prep)

Numerous absorption lines, strong (100 eV, EW) lines near 6.7, 6.97 keV rest frame, Fe XXV, XXVI 1s-2p

NH >5x1023 cm-2 vturb=3000 kms-1

more evidence for ionized outflows ngc 3516 turner et al 2007 submitted
More Evidence for ionized outflows:NGC 3516(Turner et al. 2007, submitted)


P-Cygni profile from Fe XXVI. Velocity shift ~2000 km/s

Neutral Fe K width ~3000 kms-1

Neutral Fe K



Observed frame and energies at 6.64, 6.92 (0.02 keV) rules out local (z=0) origin, e.g. WHIM

a highly ionized outflow in ngc 3516 turner et al 2007 in prep1
A highly ionized outflow in NGC 3516(Turner et al. 2007, in prep)


Spectral variability due to changes in covering fraction of intermediate- layer


ALSO explains flux variability

Deep dip is an eclipse event !

occultation in mcg 6 30 15
Occultation in MCG-6-30-15

McKernan & Yaqoob 1998

Occultation by optically-thick cloud explains flux and spectral variability in target low state, including Fe emission line

Deep dip is an eclipse event !


Partial Covering/Occultation, resurgence of an old idea

Can imagine continuum being covered by clouds that don’t cover all the sky, or by an uneven edge of the accretion disk…..the partial-covering absorber idea (Holt et al 1980)

A disk wind? Columns being seen now include Compton-thick blobs so must see some reflection


Partial Covering/Occultation, resurgence of an old idea

Always an appealing alternative to disk reflection, to explain general shapes of AGN spectra and big flux variations (e.g. Boller et al 1997, 2002)

Explains some Galactic black holes (e.g. Dower, Bradt, Morgan 1982, Brandt et al 1996, Tanaka, Ueda and Boller 2003)

Turner et al 2007

Gierlinski & Done 2004

The idea resurfaced with a vengeance because of the complex absorbers revealed by new data

Grating spectroscopy points specifically to a wind origin for the gas

outflows in agn

Outflows (in the form of warm absorbers) are seen in the majority of nearby AGN.

Typically velocities ( from a few 100 km/s to a 1000 km/s, which could carry a few solar masses per year (out to pc scales).

In some higher luminosity AGN strong blue-shifted Fe K absorption features are seen above 7 keV - possible high v outflows at v~0.1c

Outflows can carry significant Kinetic power

Can provide feedback between BH/bulge mass in galaxy.

Outflows in AGN

(Outflow Schematic; Elvis 2000)

Black holes accreting at Eddington or above can produce winds that are optically thick within <100Rg (King & Pounds 2003).

Alternative is magnetic field driving (Kato et al. 2002).

wind parameters
Wind Parameters

Middleton, Done, Gierlinski 2007 from XMM obsns PG QSOs and NLSy1s


Maybe not- broad ionized iron emission line is responding to continuum!

Fe line/continuum correlated to ~10 ks


Fe K flux

continuum flux

Mkn 766 - Miller et al 2006

6.7 keV line flux

Intrinsic link or occultation? Either way, line must originate very close to BH



Mkn 766 (Turner et al 2006)


Observed Energy /keV

Also, line energy varies, tentative period ~165 ks

Orbital Doppler shifts at ~100 rg los velocity ~13,500 km/s





Mkn 766 (Turner et al 2006)


Observed Energy /keV




MBH> 5x105M exists within 3.6 x1013cm

Disk may be best ‘diagnosed’ in Seyfert high-states


Also…new phenomenon discovered

NGC 3516

Narrow Fe emission lines, shifted from rest-energy (Doppler/GR)


First obsn in an AGN - NGC 3516 (Turner et al 2002)

NGC 3516

- High

- Low

Mrk 766 Turner et al 2004

Rapid (tens of ks) flux/energy variability - must be diagnostics of gas very close to BH


Spallation- destruction of Fe enhances Cr & Mn - (Skibo 1997) - line ratios wrong

Precessing jet (cf SS433) - but line widths wrong

Must be Fe, shifted by relativistic effects - diskline/disk wind scenarios?

Emission from disk hotspots integrated over partial orbits at tens-hundreds of rg ? (Turner et al 2002)

  • Large columns of highly ionized gas common in AGN
  • High velocities detected indicate these are outflows -disk winds?
  • Outflows explain much of curvature in X-ray spectra - need to seriously revise out idea about Fe K profiles
  • Feedback can be studied by estimating more outflow rates etc
  • Evidence for Compton-thick gas, some reflection must be present too
  • Variations in covering fraction can explain spectral/flux variability
  • Rapidly varying absorption/emission implies gas at small radii (few rg) so in principal can still study GR
  • Current challenge - obtain enough suitable data to better constrain the complex absorber systems and get to the big science questions