QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

STSci Nov 28 2007

(Tracey) Jane Turner

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

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

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?

Outline

QuickTime™ and aH.263 decompressor

are needed to see this picture.

Credit: NASA

Black Holes that are switched on are “active”

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)

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”

The Power behind AGN

Simple arguments support that AGN must be powered by accretion on to supermassive black holes

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

–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

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

Thermal Comptonization -> hard X-rays

Copious production of 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 Photoelectric absorption

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

Emission lines & absorption edges result

Fe K most prominent due to

combination of abundance & fluorescence-yield

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

George & Fabian ‘91

X-ray Line ProductionGeorge & 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

Ross & Fabian 2006

X-ray Absorption Line Production

Kaspi et al 2002

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

(Fabian, 2006, AN, 327, 943)

Compton scattering

hump

Iron K Line X-ray

Continuum

Absorption from outflow

Thermal Disk Emission?

SuzakuChandra/XMM

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 KFe K from disk from disk

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

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

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

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

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

sample

6 754 8

Fe K/Reflection

(Nandra et al 1997)

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

“Red wing”

MCG-6-30-15: Poster Child

Energy (keV)

Fe K

“Red wing”

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

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

What about X-ray spectral variability

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

Spectral variability not as predicted

Broad disk line does not vary correlated with continuum

Mkn 766 Miller et al 2007

Seyfert Spectral Variability Behavior

QuickTime™ and aGIF decompressor

are needed to see this picture.

Absorption or Reflection as the origin of the AGN continuum shape?

Ionized ReflectionSmeared Absorption?

Ballantyne et al 2004, Ross & Fabian 2006Gierlinski & Done 2004

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

Iron line does not respond to continuum

Suzaku lightcurve

Light Bending

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.

NGC 1365/XMM, (Risaliti et al. 2005)NGC 3783, XMM, Reeves et al. (2004)

Ambiguity: - X-ray Absorption

Reeves et al 2004

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

NGC 3516 Turner et al 2005

Ambiguity: - X-ray Absorption

Reeves et al 2004

NGC 3783

NGC 3516 Turner et al 2005

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

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

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

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

Kallman et al 2004 NH~ 3x 1023 cm-2, log =2.25

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)

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)

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

Neutral Fe K width ~3000 kms-1

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

Neutral Fe K

Fe XXVI

Fe XXVChandra/HEG

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

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

37%-60%

ALSO explains flux variability

Deep dip is an eclipse event !

2006

Occultation in MCG-6-30-15

Deep dip is an eclipse event !

McKernan & Yaqoob 1998 Occultation by optically-thick cloud explains flux and spectral variability in target low state, including Fe emission line

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)

Partial Covering/Occultation, resurgence of an old idea

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

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)

Partial Covering/Occultation, resurgence of an old idea

Gierlinski & Done 2004 Turner et al 2007

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

(Outflow Schematic; Elvis 2000)

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.

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

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

Are absorbers the only way to get diagnostics from the strong gravity regime?

Fe K fluxcontinuum flux

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

Mkn 766 - Miller et al 2006

Maybe not- broad ionized iron emission line is responding to continuum! 6.7

keV

lin

e

flux

continuum

Fe line/continuum correlated to ~10 ks

Obs

erve

d E

nerg

y /k

eVS/N

6

8

4

Mkn 766 (Turner et al 2006)

Also, line energy varies, tentative period ~165 ks

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

Obs

erve

d E

nerg

y /k

eVS/N

6

8

4

Mkn 766 (Turner et al 2006)

MBH> 5x105M exists within 3.6 x1013cm

€

ΔEE

≈vorbsinθc

≈ sinθrgr

€

torb ≈r

9rg ⎛ ⎝ ⎜

⎞ ⎠ ⎟

3

2

M 8

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

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

Also…new phenomenon discovered

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

HEGHEG

- High - Low

NGC 3516

Mrk 766 Turner et al 2004

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

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

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?

Conclusions• 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