1. Fe K  Line in AGN Shane Bussmann AGN Class 4/16/07

2. Importance of Fe K  High energy astrophysics  study accretion disks around BHs Emission feature arises close to BH  probe strong gravity effects, compare to predictions from GR  determine BH properties

3. The Standard Model Haardt et al. 1997Wilms et al. 2004 Accretion system: thin disk + corona

4. Production of Fe K  Comptonized photons irradiate accretion disk with power law spectrum Compton reflection hump –30 keV peak –absorption/flourescent line emission  Fe K  ~ 6.4 keV Lightman & White, 1988 Fe K  Power law input

5. Fe K  : Relativistic Effects Doppler shift: symmetric, double- peaked profile Relativistic beaming: enhance blue peak relative to red peak Gravitational redshift: smearing blue emission into red Fabian 2006

6. Fe K  : Ionization Effects Higher ionization parameter attenuates flourescence emission Low ionization parameter allows forest of lines; relativistic effects then smear these lines together Fabian 2006

7. Light Bending Model X-ray source located at height h s above accretion disk (e.g. the base of a spin-driven magnetic jet) Variation in h s with time leads to variation in flux –Low h s = region I –High h s = region III –Intermediate h s = region II Low h s allows gravity to bend light onto accretion disk, reducing continuum flux while enhancing reflection features Miniutti & Fabian 2004

8. MCG-6-30-15: Poster Child S0 Seyfert 1 D = 37 Mpc M BH ~ 1-20 x 10 6 M sun ASCA: first detection of relativitistically- broadened Fe K  Complex variability! Energy (keV) Fe K  Relativistic broadening Tanaka et al. 1995

9. Fe K  Analysis Issues Continuum subtraction (Fabian et al. 1995) Alternative emission mechanisms –Comptonization: expect break in continuum at 20 keV (not seen, Zdziarski et al. 1995) –Jets/outflows: no blue shifted emission; radio quiet; OVII absorber  v flow,abs << v OF –Photoelectric/resonance absorption of blue wing: blue emission falls off too quickly –Spallation converts Fe to lower Z metals: ASCA should have resolved these lines

10. MCG-6-30-15: ASCA Results Line profile consistent with –Emission from 3R s < r < 10Rs –Disk inclination ~ 30 o –Flux profile ~ r -3 Significant variability

11. MCG-6-30-15: ASCA Variability 1994: large flaring event w/ narrow line close to E0  large radii 1997: large flaring event w/ most emission redshifted  small radii 1994 Deep minimum (DM) state: continuum drops, very broad, red line: R < 3R s  constrain rotation! Reynolds et al. 2003 1994 1997 Time-avg Peculiar DM

12. Measurement of BH Spin Assuming some distribution of flux within a disk truncated at r ms, r ms 0.94 Problem: if emission is allowed to originate within r ms (the plunging region), redshifts can grow arbitrarily large  MUST understand astrophysics of inner accretion disk Fabian 2006 Use line profile to differentiate between Schwarzchild and Kerr BH

13. Schwarzschild vs. Kerr 1.Geometrically thick outer disk corona Irradiates surface of plunging region, producing X- ray reflection signatures 2.Accretion flow within plunging region not dissipationless Inner corona could produce X-ray reflection signature  ASCA data consistent with both Schwarzschild and Kerr BHs (Reynolds & Begelman 1997)

14. MCG-6-30-15: XMM-Epic Part 1 Observations in DM state agree w/ ASCA Improved sensitivity: Schwarzschild case requires all flourescence to originate within R s < r < 1.5R s  very unlikely Successive 10 ks frames show iron line flux proportional to 2-10 keV continuum flux Wilms et al. 2001 100 ks, 2000 June

15. MCG-6-30-15: XMM-Epic Part 2 Observations in normal, higher continuum state Variability in 2-10 keV band continuum flux Iron line flux does NOT change with continuum flux 325 ks, 2001 July 31–2001 August 5 Fabian et al. 2002

16. Line vs. Continuum Variability Difference spectrum = high flux – low flux, normalized by power law continuum No iron line feature: reflection component relatively constant Reflection component saturates at high continuum fluxes Larsson et al. 2007 Difference Spectrum

17. Physical Significance Models suggest a ~ 1 –rapidly spinning BHs can experience a magnetic torque by the fields threading the accretion disk at r ms –steepest dissipation profiles obtained when magnetic torque applied completely at r ms Steep emissivity index of ionized disk (~r -6 ) consistent with magnetic torquing  Accretion disk might be extracting BH spin energy!

18. Results from Suzaku Consistent with XMM data –variable power-law continuum –harder constant component with broad iron line and reflection hump E (keV) 3 8 Miniutti et al. 2006

19. Need for High Spectral Resolution Broad iron lines typically observed in spectra with signatures of absorption by circumnuclear plasma (warm absorber) –Fe K  line might just be leftover continuum –XMM data can’t rule this out (Kinkhabwala 2003) –Prediction: K-shell absorption features between 6.4-6.6 keV Reynolds 2007

20. Chandra/HETG Data Left: Power-law continuum + broad iron line + narrow fluorescent line of FeI + resonant absorption lines of FeXXV and FeXXVI Right: Power-law continuum + warm absorber Reynolds 2007 Deep absorption feature at 6.5 keV

21. Comparison to Light Bending Model Low flux = regime I, normal flux = regime II, high flux = regime III Variability timescale consistent Regime II: variable continuum + constant reflection component Disk emissivity in the form of broken power law (steeper in inner disk) Iron line EW and continuum anti-correlated in normal state Low flux states have broader line that correlates with continuum Reflection component dominates more as flux decreases Iron line in high flux states narrower than low flux states

22. Fe K  in other Seyferts ACSA-era state of the art: composite spectrum from 18 sources (top) Excluding MCG-6-30-15 and NGC 4151 does not alter fit (bottom) Several day long integration necessary for high S/N Nandra et al. 1997

23. Two More Seyferts NGC 3516 –red wing tracks continuum flux –blue wing variability uncorrelated with continuum –Absorption line at 5.9 keV could result from infall of material onto BH NGC 4151 –Iron line profile more variable than continuum –5 years later, opposite true

24. NGC 5548 Very narrow iron line in ASCA data Chandra data show narrow core of line originates a substantial distance from BH –Removing this component produces significantly smaller inner radius –Affects inclination of disk Reynolds & Nowak 2003 XMM data show non-detection  transitory broad Fe lines?

25. NGC 5548 Variability Simultaneous ASCA & RXTE observations –Iron line flux (ASCA) constant while continuum source varies –Continuum reflection (RXTE) increases with continuum flux Counter-intuitive: different facets of same phenomenon should be correlated Reynolds & Nowak 2003  Flux-correlated changes in ionization state of disk? Fe EW Reflection normalization

26. Seyferts: Summary Fe K  from relativistic accretion disk is generic feature of Seyfert I objects Understanding line variability very important Nandra et al. (2006): XMM observations of 30 Seyfert 1’s broadly consistent with results from ASCA

27. Fe K  in other AGN Low luminosity AGN example: NGC 4258 –ASCA: Narrow iron line  r > 50 R s –XMM: non-detection  variable on year-long timescale, iron line originates in accretion disk Typical LLAGN do not show broadened iron line (but S/N is low)

28. Fe K  in HLAGN Fe K  EW decreases for L x > 10 44-45 erg s -1 Highly ionized disks possible explanation Nandra et al. 1997

29. Fe K  and Radio-loud AGN Fe K  ideal way to study central engines of radio-loud and radio-quiet AGN Result: broad iron lines are generally weak or absent in radio-loud sources –Beamed jet swamps Seyfert-like X-ray spectrum –Hot, radiatively inefficient, optically thin inner disk –Radiatively efficient and optically thick inner disk, but highly ionized

30. Fe K  From Galactic BHCs Inner accretion disk similar in AGN and GBHC (GBHC disk more highly ionized) Characteristic timescales very different –AGN t visc ~ tens of years –GBHC t visc ~ days to weeks –Can study changes with accretion rate by observing GBHC

31. Remaining Issues Narrow Fe K  lines ubiquitous, clear broad lines not: requires iron overabundance? EW depends on Eddington ratio? What is the nature of the illuminating X-ray source? How does it change height? Interpretation of complex, time-varying broad iron lines in context of BH spin

32. Future Prospects Next generation missions with larger collecting area and higher spectral res. will obtain significantly larger sample of broad iron line sources Transient relativistic iron line features  dynamical effects near BH Con-X and XEUS will do these both locally and at high redshift –Cosmic history of SMBHs –Reverberation mapping of X-ray flares: test GR in strong field limit