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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
Active Galactic Nuclei : I

Keith Arnaud

NASA Goddard

University of Maryland

COSPAR Workshop, Udaipur 2003


Agn overview
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


Spectrum of mkn 421
Spectrum of Mkn 421

COSPAR Workshop, Udaipur 2003

Takahashi et al. 1998


Fundamental questions
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


Active galactic nuclei i

COSPAR Workshop, Udaipur 2003


The importance of x ray observations
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


Schematic view of agn central engine

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


X ray emission from around the mbh
X-ray emission from around the MBH

COSPAR Workshop, Udaipur 2003


Reflection and fluorescence
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


Ngc 4945
NGC 4945

direct

fluorescence

reflected

COSPAR Workshop, Udaipur 2003

Madejski et al. 2000


Reflected x ray spectra
Reflected X-ray Spectra

COSPAR Workshop, Udaipur 2003


Reflection from neutral slab
Reflection from neutral slab

COSPAR Workshop, Udaipur 2003


Reflection from an ionized slab
Reflection from an ionized slab

Increasing ionization

COSPAR Workshop, Udaipur 2003


Reflection and fluorescence1
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


Asca observation of mcg 6 30 15
ASCA observation of MCG 6-30-15

COSPAR Workshop, Udaipur 2003



Effect of changing emission profile of disk
Effect of changing emission profile of disk

COSPAR Workshop, Udaipur 2003


Effect of changing black hole spin
Effect of changing black hole spin

COSPAR Workshop, Udaipur 2003


The effect of mbh spin
The effect of MBH spin

COSPAR Workshop, Udaipur 2003


Asca 1994 and 1997 observations
ASCA 1994 and 1997 observations

Time-averaged

Snapshot

COSPAR Workshop, Udaipur 2003


Chandra observation of ngc 5548
Chandra observation of NGC 5548

Yaqoob et al. 2001

COSPAR Workshop, Udaipur 2003


Location of fe k line in ngc 5548
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


Comparison of asca and chandra
Comparison of ASCA and Chandra

COSPAR Workshop, Udaipur 2003


Narrow fe k lines with chandra
Narrow Fe-K lines with Chandra

Padmanabhan & Yaqoob 2002

COSPAR Workshop, Udaipur 2003


Complex fe line in ngc 5506
Complex Fe line in NGC 5506

Neutral line

Ionized line

Matt et al. 2001

COSPAR Workshop, Udaipur 2003


Xmm observations of sy 1
XMM observations of Sy 1

Reeves 2002

COSPAR Workshop, Udaipur 2003


More sy 1s from xmm
More Sy 1s from XMM

Reeves 2002

COSPAR Workshop, Udaipur 2003


Mkn 841 narrow line variability
Mkn 841 narrow line variability

15 hours later

Petrucci et al. 2002

COSPAR Workshop, Udaipur 2003


Xmm observation of mcg 6 30 15
XMM observation of MCG 6-30-15

Requires emission peaked near MBH

Wilms et al. 2001

COSPAR Workshop, Udaipur 2003


Mean profile from xmm mcg 6 30 15 long look
Mean profile from XMM MCG 6-30-15 “long look”

Fabian et al. 2002

COSPAR Workshop, Udaipur 2003


Difference between bright and faint spectra of mcg 6 30 15
Difference between bright and faint spectra of MCG 6-30-15

Line varies with continuum.

Fabian et al. 2002

COSPAR Workshop, Udaipur 2003


Chandra and xmm observation of ngc 3516
Chandra and XMM observation of NGC 3516

Turner et al. 2002

COSPAR Workshop, Udaipur 2003


Model for ngc 3516
Model for NGC 3516

Turner et al. 2002

COSPAR Workshop, Udaipur 2003


Flares above the accretion disk
Flares above the accretion disk

Reynolds & Young

COSPAR Workshop, Udaipur 2003


Fe k line results from chandra and xmm
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


Active galactic nuclei i

  • 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


Active galactic nuclei i

  • 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


What is required next
What is required next continuum as would be predicted by simple reflection models.

  • 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


Active galactic nuclei i

COSPAR Workshop, Udaipur 2003 continuum as would be predicted by simple reflection models.