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Active Galactic Nuclei : I

Active Galactic Nuclei : I. Keith Arnaud NASA Goddard University of Maryland. AGN Overview. First identified as bright (blue) point-like emission from the centers of some galaxies. Now characterized in most cases by strong optical emission lines from photoionized material.

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Active Galactic Nuclei : I

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  1. Active Galactic Nuclei : I Keith Arnaud NASA Goddard University of Maryland COSPAR Workshop, Udaipur 2003

  2. AGN Overview • First identified as bright (blue) point-like emission from the centers of some galaxies. Now characterized in most cases by strong optical emission lines from photoionized material. • Come in a bewildering number of types - Quasars, Seyfert 1, Seyfert 2, Bl Lac, Liner, NLAGN, NLSy1, BLRG,… • Powered by accretion onto a supermassive (106-108Mo) black hole (other processes may also be significant). • Seen both near (our Galactic Center) and far (z > 6). • Excellent background light sources - Ly alpha forest, gravitational lenses,… COSPAR Workshop, Udaipur 2003

  3. Spectrum of Mkn 421 COSPAR Workshop, Udaipur 2003 Takahashi et al. 1998

  4. Fundamental Questions • Where does the emission come from and how is accretion energy converted to radiation. • Why are there so many different types of AGN and how are they related. Is there a unified model ? Can we draw an H-R diagram for AGN ? • What is the relationship between the massive black hole (MBH) and the host galaxy ? Which forms first and what causes the excellent correlation between black hole mass and bulge velocity dispersion. • Do all galaxies have MBH ? If so, why are they not all AGN ? How long does AGN activity last ? What is the connection with starbursts ? COSPAR Workshop, Udaipur 2003

  5. Is G.R. correct in the vicinity of a MBH ? The strong gravity limit. • Why do some AGN have jets ? What are jets made of ? What powers and collimates them ? COSPAR Workshop, Udaipur 2003

  6. The importance of X-ray observations • AGN are easy to find in X-rays. Away from the Galactic plane most X-ray sources are AGN. Many X-ray selected AGN show weak or no optical signatures. • X-rays come from very close to the MBH. The most rapid variability is seen in X-rays. • The only spectral lines observed that come from close to the MBH are in the X-ray band. The strongest line is from Fe at ~6.4 keV but other lines have been observed. • All types of AGN are strong X-ray sources. • We can “X-ray” the material around AGN using the emission from close to the MBH as a background source. COSPAR Workshop, Udaipur 2003

  7. Blazar Schematic view of AGN central engine Sy 2 Torus Disk Narrow line region Broad line region Jet Padovani & Urry 1995 Sy 1 COSPAR Workshop, Udaipur 2003

  8. X-ray emission from around the MBH COSPAR Workshop, Udaipur 2003

  9. Reflection and Fluorescence • The MBH is surrounded by an accretion disk. Suppose that X-rays are generated above the disk. • We observe some photons directly. • Others hit the accretion disk. Some are reflected. Some eject an inner shell electron from an atom to give fluorescent line emission. COSPAR Workshop, Udaipur 2003

  10. NGC 4945 direct fluorescence reflected COSPAR Workshop, Udaipur 2003 Madejski et al. 2000

  11. Reflected X-ray Spectra COSPAR Workshop, Udaipur 2003

  12. Reflection from neutral slab COSPAR Workshop, Udaipur 2003

  13. Reflection from an ionized slab Increasing ionization COSPAR Workshop, Udaipur 2003

  14. Reflection and Fluorescence • The MBH is surrounded by an accretion disk. Suppose that X-rays are generated above the disk. • We observe some photons directly. • Others hit the accretion disk. Some are reflected. Some eject an inner shell electron from an atom to give fluorescent line emission. • X-rays from parts of the disk moving towards us are blue-shifted due to Doppler and red-shifted due to gravity. Emission from regions moving away from us is red-shifted by both effects. • We see a line with a red wing. The shape depends on the disk inclination and distribution of X-ray emission over the disk. COSPAR Workshop, Udaipur 2003

  15. ASCA observation of MCG 6-30-15 COSPAR Workshop, Udaipur 2003

  16. Fluorescence line from disk around Kerr black hole COSPAR Workshop, Udaipur 2003

  17. Effect of changing emission profile of disk COSPAR Workshop, Udaipur 2003

  18. Effect of changing black hole spin COSPAR Workshop, Udaipur 2003

  19. The effect of MBH spin COSPAR Workshop, Udaipur 2003

  20. ASCA 1994 and 1997 observations Time-averaged Snapshot COSPAR Workshop, Udaipur 2003

  21. Chandra observation of NGC 5548 Yaqoob et al. 2001 COSPAR Workshop, Udaipur 2003

  22. Location of Fe K line in NGC 5548 Line origin is outer BLR or molecular torus. Yaqoob et al. 2001; BLR results from Peterson & Wandel 1999 COSPAR Workshop, Udaipur 2003

  23. Comparison of ASCA and Chandra COSPAR Workshop, Udaipur 2003

  24. Narrow Fe-K lines with Chandra Padmanabhan & Yaqoob 2002 COSPAR Workshop, Udaipur 2003

  25. Complex Fe line in NGC 5506 Neutral line Ionized line Matt et al. 2001 COSPAR Workshop, Udaipur 2003

  26. XMM observations of Sy 1 Reeves 2002 COSPAR Workshop, Udaipur 2003

  27. More Sy 1s from XMM Reeves 2002 COSPAR Workshop, Udaipur 2003

  28. Mkn 841 narrow line variability 15 hours later Petrucci et al. 2002 COSPAR Workshop, Udaipur 2003

  29. XMM observation of MCG 6-30-15 Requires emission peaked near MBH Wilms et al. 2001 COSPAR Workshop, Udaipur 2003

  30. Mean profile from XMM MCG 6-30-15 “long look” Fabian et al. 2002 COSPAR Workshop, Udaipur 2003

  31. Difference between bright and faint spectra of MCG 6-30-15 Line varies with continuum. Fabian et al. 2002 COSPAR Workshop, Udaipur 2003

  32. Chandra and XMM observation of NGC 3516 Turner et al. 2002 COSPAR Workshop, Udaipur 2003

  33. Model for NGC 3516 Turner et al. 2002 COSPAR Workshop, Udaipur 2003

  34. Flares above the accretion disk Reynolds & Young COSPAR Workshop, Udaipur 2003

  35. Fe K line results from Chandra and XMM • The Chandra HETG can resolve narrow (few 1000 km/s) lines. • A narrow line is seen in many objects. This must be subtracted from the broad line when using the line shape to estimate disk parameters. • NGC 5548 : line width => origin in either BLR or the molecular torus. • A systematic analysis (in progress) finds broad lines consistent with earlier results using ASCA. COSPAR Workshop, Udaipur 2003

  36. XMM-Newton has observed emission from highly ionized iron in several sources. • Probably from photo-ionized gas (BLR?). It is not clear how common this is. • XMM-Newton observations of MCG-6-30-15 show a very relativistically broadened line. • Wilms et al. claim that most of the emission must come from close to the MBH and this is not possible with standard accretion disk models. • The line may be powered by magnetic extraction of MBH spin energy (Penrose effect). COSPAR Workshop, Udaipur 2003

  37. In MCG-60-30-15 (at least) the iron line does not lag the continuum as would be predicted by simple reflection models. • If the emission comes from very close to the MBH then we do not expect a simple relation between line and continuum. • Joint Chandra and XMM-Newton observations of NGC 3516 find evidence for sharp line-like features within the broad line. • Lines may be due to flares covering small sections of the disk. COSPAR Workshop, Udaipur 2003

  38. What is required next • Systematic studies of Fe lines from many objects with both Chandra HETG and XMM-Newton EPIC. • Longer observations to study time variability. • High resolution spectroscopy at Fe K energies with higher sensitivity than available with the Chandra HETG (Astro-E2). • Observations extending to higher energies - we need to accurately measure the continuum and determine the amount of reflected emission (Chandra+RXTE, Astrosat). COSPAR Workshop, Udaipur 2003

  39. COSPAR Workshop, Udaipur 2003

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