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The Origin of X-Ray Emission in the Nuclei of Radio Galaxies

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The Origin of X-Ray Emission in the Nuclei of Radio Galaxies Powered By Docstoc
					   The Origin of X-Ray Emission in
    the Nuclei of Radio Galaxies



                         Dan Evans (CfA)
                               -with-
  Diana Worrall (U. Bristol), Martin Hardcastle (U. Herts), Ralph
Kraft (CfA), Mark Birkinshaw (U. Bristol), Judith Croston (U. Herts)
                   Contents
•   Brief review of AGN physics & phenomenology
•   Nuclear X-ray emission: accretion flow or jet?
•   The 3CRR sample
•   Is an obscuring torus ubiquitous?
•   A nuclear Fanaroff-Riley dichotomy?
                The Central Engine




•   Accretion flow surrounded by dusty torus
                The Central Engine




•   Accretion flow surrounded by dusty torus
•   BB radiation from disk  ‘big blue bump’
                The Central Engine




•   Accretion flow surrounded by dusty torus
•   BB radiation from disk  ‘big blue bump’
•   B-field loops  optically thin corona
                The Central Engine




•   Accretion flow surrounded by dusty torus
•   BB radiation from disk  ‘big blue bump’
•   B-field loops  optically thin corona
•   Isotropic X-rays from Comptonization of disk photons in hot corona
•   Power law spectrum
                 Fe Ka Production
•   Reflection of X-rays from an optically thick accretion disk
                 Fe Ka Production
•   Reflection of X-rays from an optically thick accretion disk
                 Fe Ka Production
•   Reflection of X-rays from an optically thick accretion disk
                 Fe Ka Production
•   Reflection of X-rays from an optically thick accretion disk
                 Fe Ka Production
•   Reflection of X-rays from an optically thick accretion disk
                 Fe Ka Production
•   Reflection of X-rays from an optically thick accretion disk
                                                                   Fe Kα




                                                         George & Fabian (1991)
                Fe Ka Diagnostics
                                            Fabian et al. (2002)
• Fe Ka lines provide us with
  information about AGN
  processes
   – Centroid – neutral Fe has centroid
     at 6.404 keV, increasing to 6.8 keV
     for highly ionized Fe
   – Profile – broadening, skew gives
     information about proximity to black
     hole
   – Equivalent width – reprocessing
     from accretion flow or torus
Astrophysical Jets in Radio-Loud AGN


                                                            3C 296 (FRI)
                                                            1.5 GHz VLA

                         3C 296




                                                            3C 98 (FRII)
                                                            5 GHz VLA


    What causes the Fanaroff-Riley dichotomy?
                                                Credit: ATLAS of DRAGNs Project
Astrophysical Jets in Radio-Loud AGN




• Anisotropic emission, power law X-ray spectrum
• Relativistic Doppler beaming, dependent on bulk speed (Γ),
  angle to line of sight
• Jet-production mechanism uncertain
  Astrophysical Jets in Radio-Loud AGN
 Chandra commonly resolves kpc-scale X-ray jet emission in nearby RL AGN:




• FRIs  kpc X-ray emission synchrotron in nature (e.g. Hardcastle et al.
  2001, 2003, 2005)
• FRIIs  X-ray emission tends to be inverse-Compton
• What about (unresolved) parsec-scale X-ray jets?
Radio-Galaxy Nuclei – Two Competing Models


• Is nuclear X-ray
  emission dominated by:

• The parsec-scale jet?
          -or-
• The accretion flow?
     Evidence for jet-dominated nuclear X-ray
                      emission
• Correlations between the ROSAT soft X-ray
  and VLA radio core fluxes and luminosities in
  the B2 (Canosa et al. 1999) and 3CRR
  (Hardcastle & Worrall 1999) samples

• Parsec-scale radio emission is jet-generated
  and strongly affected by beaming

• Tight correlations suggest X-ray emission       NGC 6251 - 5 GHz VLBI

  affected by beaming in same manner as radio

• Soft X-ray emission originates in a jet
                                                                10 pc
• Double-peaked SED (modeled with syn+SSC)
                                                          Jones et al. (1986)
Evidence for accretion-dominated nuclear X-ray
                   emission
• Short (~ks) timescale variability in
  broad-line FRII 3C 390.3 (Gliozzi
  et al. 2005)

• Broadened Fe Ka line emission in
  narrow-line FRI NGC 6251 (Gliozzi
  et al. 2004)

• Implies Fe Ka origin in inner
  regions of accretion flow


                                         NGC 6251 - XMM
                                         Gliozzi et al. (2004)
      Summary of Introduction
• X-ray continuum emission in the nuclei of RL AGN consists of:
   – “Radio-quiet” accretion-related component
   – “Radio-loud” jet-related component




        ROSAT

          Chandra/XMM

• Which dominates the X-ray emission?
                   The 3CRR Sample
•   Criteria:
     – 178-MHz luminosity density > 10.9 Jy
     – Declination > 10o
     – |b| > 10o
•   Advantages:
     – No orientation bias
     – Spectroscopic identification
     – High-resolution radio observations
•   Select sources with z<0.1
     – Unambiguously spatially separate
         unresolved nuclear emission from
         contaminating emission
     – Rich variety (FRI/FRII, broad/narrow
         lines, large luminosity range)
•   19/35 X-ray observations of low-z 3CRRs,
    16 of them with Chandra
•   Also include the 3C sources 3C 403, 3C
    405 (Cyg A), & Cen A
•   Complete X-ray spectral analysis of each   VLA (Leahy, Bridle, & Strom)
•   Confirmed with radial-profile analysis
       The 3CRR Sample: Aims
Unified AGN scheme:   1.    Dominant X-ray emission
                            mechanism:
                           – Accretion Flow:
                               Fe Ka, variability
                               -or-
                           –   Jet:
                               SED, radio-optical-X-ray
                               luminosity correlations
                      2.   Nature of accretion flow: thin
                           disk? RIAF?
                      3.   Is the torus ubiquitous?
                      4.   FRI-FRII dichotomy?
  Distribution of intrinsic absorption
• Measure intrinsic absorption                  10

  associated with dominant
  component of X-ray emission
                                                8



• Note that some sources have two
                                                6
  continuum components




                                    Frequency
• Bimodal distribution                          4




• FRIs have low (or no) intrinsic               2


  absorption
                                                0
                                                           <20      21       22        23   24
• FRIIs have NH >   1023   cm-2                                  log NH (atoms cm-2)




• NB BLRG FRII 3C 390.3                              FRI            FRII          3C 390.3
    Origin of intrinsic absorption
• FRI sources with the highest intrinsic absorption are associated
  with host galaxies with circumnuclear disks at high inclinations




• Heavily absorbed emission in FRIIs likely in gas associated with
  dusty torus (c.f. Seyfert 2s)
Luminosity-Luminosity Correlations
                      • Consider LX and LR
                      • Considerable scatter
Luminosity-Luminosity Correlations
                      • Consider LX and LR
                      • Considerable scatter
                      • Strong correlation
                        between components
                        with NH ≤ 5 x 1022
                        (significant at 99.95%)
                      • Apparent in flux-flux too
                      • Suggests X-ray
                        emission affected by
                        beaming in same
                        manner as radio
                      • Origin of X-ray emission
                        in pc-scale jet (outside
                        any torus)
Luminosity-Luminosity Correlations
                      • FRIs are dominated
                        by these
                        components only
                      • FRIIs, although
                        heavily absorbed,
                        also contain these
                        components
                      • Cannot distinguish
                        between jet
                        components in FRIs
                        and FRIIs
Luminosity-Luminosity Correlations
                         • Components with NH ~
                           1023 lie above trendline
                         • As does 3C 390.3,
                           unobscured BLRG
                         • All have Fe Ka lines
                         • Accretion-dominated
                           and surrounded by a
                           torus




              NH ≤ 5 x
              1022


                         • FRIIs are dominated by
                           these components
     Where is the torus in FRIs?
• X-ray emission is jet dominated
  and exists on scales larger than
  any torus
• Cannot determine presence or
  absence of torus directly
• Assume there exists a ‘hidden’
  accretion component obscured
  by a torus of intrinsic absorption
  1023 atoms cm-2
• Find upper limits to luminosity of
  accretion-related emission
• Data don’t exclude luminosities
  of ~ 1039-1041 ergs s-1 (hX,Edd ~
  10-7-10-5)
• Substantially lower than FRIIs,
  LX ~ 1043-1044 ergs s-1 (hX,Edd ~    e.g. 3C 274 (M87)
  10-3-10-2)
         Intermediate Summary
                                                         e.g. 3C 264
• X-ray emission of FRI radio-galaxy                        (FRI)
  nuclei is dominated by a parsec-
  scale jet, with little or no intrinsic
  absorption
• X-ray emission of FRII radio-galaxy
  nuclei is dominated by an accretion
  flow and is heavily absorbed (except
  BLRG 3C 390.3)
• Each FRII also has an unabsorbed         e.g. 3C 403
  component of X-ray emission  jet           (FRII)
  origin
• Cannot rule out a torus in FRIs
• ‘Hidden’ accretion flows in FRIs are
  substantially sub-Eddington (c.f.
  FRIIs)
A Nuclear Fanaroff-Riley Dichotomy?

• Dichotomy in the observed X-ray nuclear
  properties of FRI and FRII radio galaxies
• Why?
• Simple scaling relations?
• Intrinsic dichotomy?
• Three potential models…
Model 1: FRI tori are Compton thick
• Luminous accretion flow
  surrounded by thicker torus than
  FRIIs
• Would give rise to reduced
  observed flux from accretion flow
• Assume NH = 1024 cm-2  hX,Edd ~
  10-6-10-4, still lower than FRIIs
• For FRI and FRII accretion-flow
  efficiencies to match, need extreme
  NH (> 1025 cm-2)
• Ruled out from infrared data (Muller
  et al. 2004, Haas et al. 2004,
  Birkinshaw et al., in prep.)
Model 2: Simple scaling relation
• Relative contribution of accretion-related and jet-related
  emission varies smoothly as a function of total AGN power
                                              FRI     FRII
        Contribution from accretion and jet




                                              Total AGN power

• Intrinsic nuclear dichotomy need not exist
Model 2: Simple scaling relation
• 178-MHz luminosity
  density tracks AGN
  power since it
  correlates reasonably
  well with the narrow-
  line luminosity of AGN
  (Rawlings & Saunders
  1991; Willott et al.
  1999)
• Reasonable underlying correlation. However,
   – Accretion luminosity of 3C 98 (FRII) 1.5 orders of mag. greater than
     3C 338, 3C 465 (FRIs)
   – Why should the transition occur so close to the FRI/FRII boundary?
Model 3: An intrinsic nuclear dichotomy
• Fundamentally different
  accretion mode in FRI and
  FRII nuclei
• Accretion-flow luminosities
  and radiative efficiencies of
  FRIs systematically lower
  than FRIIs
• Widely discussed model:
  hybrid ADAF/thin disk + jet
• Critical mass-accretion rate
  mcrit


                                  Esin et al. (1997)
Model 3: An intrinsic nuclear dichotomy
                                             FRI         FRII
                               LX
• Analogous to XRBs                          Low
                                             state
                                                         High
                                                         state

• Step change in accretion
  luminosity at mcrit
•  At low accretion rates,
  jet still strong and comes
  to dominate


                                                 mcrit           mEdd   m

                                    Esin et al. (1997)
                                    Körding, Falcke, & Markoff (2002)
Model 3: An intrinsic nuclear dichotomy
                                                       FRI         FRII
                                          LX
                                                       Low         High
                                                       state       state




                                                           mcrit           mEdd   m


•   No longer requires an FRI/FRII transition coincidence
•   Important to observe remaining sources that span the FRI/FRII boundary
Model 3: An intrinsic nuclear dichotomy
 How can a dichotomy in the subparsec-scale accretion-
 flow mode influence the kpc-scale deceleration of jets into
 FRI and FRII structures (e.g., Bicknell 1995)?




                                                 “HYMORS” sources
                                             (Gopal-Krishna & Wiita 2000)
                    Summary
• X-ray emission of FRI radio-galaxy nuclei is unabsorbed
  and dominated by a parsec-scale jet
• X-ray emission of FRII radio-galaxy nuclei is heavily
  absorbed and accretion-related
• Each FRII also has an unabsorbed component of X-ray
  emission  jet origin
• Data do not exclude the presence of a heavily
  obscured, accretion-related emission in FRI-type
  sources
• An intrinsic nuclear dichotomy (analogous to XRBs)?
Appendix - Bias
         Appendix - 3C 321




Hardcastle et al. (2004)
Appendix - 3C 388




              Kraft et al. (2006)

				
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posted:10/14/2012
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