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X-Ray Emission From The Nuclei X-Ray Emission From The Nuclei of Radio Galaxiesof Radio Galaxies
Daniel EvansDaniel EvansUniversity of BristolUniversity of Bristol
-with--with-Diana Worrall, Ralph Kraft, Martin Hardcastle, Mark Diana Worrall, Ralph Kraft, Martin Hardcastle, Mark
Birkinshaw, Judith Croston, Bill Forman, Christine Jones, Birkinshaw, Judith Croston, Bill Forman, Christine Jones, Steve MurraySteve Murray
ContentsContents
An introduction to AGN physicsAn introduction to AGN physics X-ray emission from radio galaxies: X-ray emission from radio galaxies:
the issuesthe issues Centaurus A: the nearest AGNCentaurus A: the nearest AGN NGC 6251: a counterexample?NGC 6251: a counterexample? Nuclear emission from a sample of Nuclear emission from a sample of
3CRR radio galaxies3CRR radio galaxies ConclusionsConclusions
What are AGN?What are AGN?
Unresolved nuclear componentUnresolved nuclear component Nuclear luminosity > sum of all starsNuclear luminosity > sum of all stars MMBHBH ~ 10 ~ 1066–10–101010 M M๏๏ Accompanied by strong X-ray emissionAccompanied by strong X-ray emission
NGC 3277 NGC 5548 NGC 6251 - XMM
The Central EngineThe Central Engine
Accretion flow surrounded by dusty torusAccretion flow surrounded by dusty torus
The Central EngineThe Central Engine
Accretion flow surrounded by dusty torusAccretion flow surrounded by dusty torus BB radiation from disk BB radiation from disk ‘big blue bump’ ‘big blue bump’
The Central EngineThe Central Engine
Accretion flow surrounded by dusty torusAccretion flow surrounded by dusty torus BB radiation from disk BB radiation from disk ‘big blue bump’ ‘big blue bump’ B-field loops B-field loops optically thin corona optically thin corona
The Central EngineThe Central Engine
Accretion flow surrounded by dusty torusAccretion flow surrounded by dusty torus BB radiation from disk BB radiation from disk ‘big blue bump’ ‘big blue bump’ B-field loops B-field loops optically thin corona optically thin corona IsotropicIsotropic X-rays from Comptonization of disk photons in hot corona X-rays from Comptonization of disk photons in hot corona Power law spectrumPower law spectrum
Fe KFe K Production Production Reflection of X-rays from an optically thick accretion diskReflection of X-rays from an optically thick accretion disk
Fe KFe K Production Production Reflection of X-rays from an optically thick accretion diskReflection of X-rays from an optically thick accretion disk
Fe KFe K Production Production Reflection of X-rays from an optically thick accretion diskReflection of X-rays from an optically thick accretion disk
Fe KFe K Production Production Reflection of X-rays from an optically thick accretion diskReflection of X-rays from an optically thick accretion disk
Fe KFe K Production Production Reflection of X-rays from an optically thick accretion diskReflection of X-rays from an optically thick accretion disk
Fe KFe K Production Production Reflection of X-rays from an optically thick accretion diskReflection of X-rays from an optically thick accretion disk
Fe Kα
Astrophysical JetsAstrophysical Jets
10 pc
NGC 62515 GHz VLBIJones et al. (1986)
AnisotropicAnisotropic emission, power law spectrum emission, power law spectrum Relativistic Doppler beaming, dependent on bulk speed (Relativistic Doppler beaming, dependent on bulk speed (ΓΓ), angle to ), angle to
line of sightline of sight
Radio Galaxy Nuclei – Two Competing Radio Galaxy Nuclei – Two Competing ModelsModels
Is the X-ray Is the X-ray emission emission dominated by:dominated by:
The parsec-scale The parsec-scale jet?jet?
-or--or- The accretion flow?The accretion flow?
Jet-Related EmissionJet-Related Emission
e.g., Zamorani et al. (1981)
1.1. For a given optical For a given optical luminosity, radio-loud luminosity, radio-loud quasars are brighter X-quasars are brighter X-ray sources than radio-ray sources than radio-quiet quasarsquiet quasars
An additional An additional component of emission component of emission is present in RLQsis present in RLQs
Three Discoveries:Three Discoveries:
Jet-Related EmissionJet-Related Emission
2.2. Dependence of X-ray Dependence of X-ray luminosity and spectrum luminosity and spectrum on beaming angleon beaming angle
A component is A component is anisotropicanisotropic
3.3. Correlation between Correlation between ROSATROSAT soft X-ray and soft X-ray and radio fluxes and radio fluxes and luminositiesluminosities
Soft X-ray emission Soft X-ray emission likely jet-relatedlikely jet-related
Shastri et al. (1993)
Canosa et al. (1999)
Accretion-Related EmissionAccretion-Related Emission
Have seen that soft (0.5-2.4 keV) X-ray emission likely jet Have seen that soft (0.5-2.4 keV) X-ray emission likely jet relatedrelated
What about the rest of the X-ray spectrum? Jet or What about the rest of the X-ray spectrum? Jet or accretion flow?accretion flow?
E.g. Gliozzi et al. (2004) claim broadened Fe KE.g. Gliozzi et al. (2004) claim broadened Fe K emission emission and variability on short timescales in NGC 6251and variability on short timescales in NGC 6251
Would imply accretion-dominated emissionWould imply accretion-dominated emission
d < ct
Summary of IntroductionSummary of Introduction
Emission in the nuclei Emission in the nuclei of AGN consists of:of AGN consists of:– ““Radio-quiet” Radio-quiet”
accretion-related accretion-related componentcomponent
– ““Radio-loud” jet-Radio-loud” jet-related componentrelated component
Which dominates the Which dominates the X-ray emission?X-ray emission?– Matter of Matter of
considerable considerable debate…debate…
Cen A – The Nearest AGNCen A – The Nearest AGN
Brightest Brightest extragalactic object extragalactic object in the hard X-ray skyin the hard X-ray sky
Closest radio galaxy Closest radio galaxy (d = 3.4 Mpc)(d = 3.4 Mpc)
Complex emissionComplex emission Ideal object to studyIdeal object to study Much-studied by Much-studied by
earlier X-ray earlier X-ray missionsmissions
Rich gallery of radio Rich gallery of radio features (jet, lobes, features (jet, lobes, etc.)etc.)
Chandra 0.5-2 keV X-ray
Continuum SpectrumContinuum Spectrum
Attempt to fit a heavily-absorbed (Attempt to fit a heavily-absorbed (NNHH 10 102323 atoms cmatoms cm-2-2) power-law () power-law (ΓΓ 1.7) 1.7)
Significant residuals below Significant residuals below 2.5 keV 2.5 keV
XMM-Newton MOS2 1st observation
Continuum SpectrumContinuum Spectrum
Significant improvement with the addition of a Significant improvement with the addition of a secondsecond power- power-law componentlaw component
ComponeComponentnt
NNHH (atoms cm (atoms cm-2-2)) ΓΓ
Hard PLHard PL (1.30 (1.30 ±± 0.16) x 0.16) x 10102323
1.76 1.76 ±± 0.150.15
Soft PLSoft PL (3.8 (3.8 ±± 2.0) x 10 2.0) x 102222 2 (frozen)2 (frozen)
Key parameters:
Possible Origin of 2Possible Origin of 2ndnd PL PL
VLBI jet? Flux density VLBI jet? Flux density 5 Jy at 4.8 GHz 5 Jy at 4.8 GHz X-ray to radio ratio for 2X-ray to radio ratio for 2ndnd PL and VLBI jet consistent with that of PL and VLBI jet consistent with that of
kpc-scale jet and VLA jetkpc-scale jet and VLA jet Mildly absorbed soft power law seen in other FRI galaxies with Mildly absorbed soft power law seen in other FRI galaxies with
ROSATROSAT
Canosa et al. (1999)Canosa et al. (1999)
0.7 pc
Core
Tingay et al. (1998)Tingay et al. (1998)
Fluorescent Line EmissionFluorescent Line Emission
ChandraChandra HETGS instrument of choice due to its high spectral resolution HETGS instrument of choice due to its high spectral resolution
Fe K
Fe K
Joint HEG+1 and HEG-1 spectrum
Fe KFe K centroid = centroid = 6.4046.404±±0.002 keV (90% 0.002 keV (90% c.l.)) c.l.)) fluorescence fluorescence from cold, neutral from cold, neutral materialmaterial
Fe KFe Kαα is broadened is broadened ((σσ = 20 = 20±±10 eV (90% 10 eV (90% c.l.)) c.l.)) v v ~~ 1000 km s 1000 km s-1-1
r r ~~ 0.1 pc 0.1 pc
(M(MBHBH = 2 x 10 = 2 x 1088 M M๏๏))
Geometry Of Emission RegionGeometry Of Emission Region
Fe KFe K line parameters consistent with fluorescence line parameters consistent with fluorescence from from NNHH 10 102323 atoms cm atoms cm-2 -2 with torus geometrywith torus geometry
Also consistent with fluorescence from Also consistent with fluorescence from NNHH ~~ 10 102424 atoms cmatoms cm-2-2 outside line of sight (Woźniak et al. outside line of sight (Woźniak et al. 1998)1998)
Nature of Accretion FlowNature of Accretion Flow
GalaxyGalaxy LLxx LLEddEdd BondiBondi InterpretationInterpretation
Cen ACen A 4.8 4.8 x x 10104141
2.6 2.6 x x 10104646
2.3 2.3 x 10x 10-3-3 Hybrid?Hybrid?
Sag A*Sag A* 2.4 2.4 x x 10103333
3.3 3.3 x x 10104444
2.4 2.4 x 10x 10-9-9 InefficientInefficient
NGC NGC 44724472
6.4 6.4 x x 10103838
7.2 7.2 x x 10104646
1.4 1.4 x 10x 10-6-6 InefficientInefficient
3C 390.33C 390.3 5.0 5.0 x x 10104444
4.4 4.4 x x 10104646
1.1 1.1 x 10x 10-2-2 StandardStandard
Hybrid inefficient flow/thin disk
Cen A SummaryCen A Summary
Emission characterized by a heavily-Emission characterized by a heavily-absorbed power lawabsorbed power law
Second power-law component Second power-law component necessary, consistent with VLBInecessary, consistent with VLBI jetjet
Fluorescent lines from cold, neutral Fluorescent lines from cold, neutral materialmaterial
Molecular torus?Molecular torus? Accretion flow: Hybrid?Accretion flow: Hybrid? More info: Evans et al. (2004), ApJ, 612, More info: Evans et al. (2004), ApJ, 612,
786786
NGC 6251 – A NGC 6251 – A CounterexampleCounterexample
z=0.0244 (dz=0.0244 (d~100 Mpc) ~100 Mpc) FRI-type FRI-type radio galaxyradio galaxy
Spectacular radio jet extending Spectacular radio jet extending hundreds of kpchundreds of kpc
Opening angle of 7.4Opening angle of 7.4oo
X-ray emission from nucleus X-ray emission from nucleus and three regions of kpc-scale and three regions of kpc-scale jetjet
Synchrotron interpretation for Synchrotron interpretation for kpc-scale jet (Evans et al. 2005)kpc-scale jet (Evans et al. 2005)
1 arcmin
30 kpc
1.6 GHz VLAJones et al. (1986)
0.5-5 keV Chandra image with 1.6 GHz VLA contours (Evans et al. 2005)
NGC 6251 - ResultsNGC 6251 - Results
XMM-Newton observation XMM-Newton observation of NGC 6251. Gliozzi et of NGC 6251. Gliozzi et al. (2004) claimed al. (2004) claimed broadened Fe Kbroadened Fe K line- line-emissionemission
Would imply accretion-Would imply accretion-dominated X-ray dominated X-ray emissionemission
New New ChandraChandra data + data + reanalysis of XMM datareanalysis of XMM data
Nuclear spectrum well Nuclear spectrum well fitted with a featureless, fitted with a featureless, single, unabsorbed single, unabsorbed power lawpower law
1 2 4 7Energy (keV)
Chandra
XM
M
NGC 6251 – Fe KNGC 6251 – Fe K line line No evidence of Fe KNo evidence of Fe K emission in emission in ChandraChandra spectrum spectrum No significant evidence for Fe KNo significant evidence for Fe K emission in XMM spectrum emission in XMM spectrum
Already evidence to disfavour accretion-dominated X-ray emissionAlready evidence to disfavour accretion-dominated X-ray emission
NGC 6251 - InterpretationNGC 6251 - Interpretation
1-keV X-ray flux density consistent with ROSAT soft X-ray results1-keV X-ray flux density consistent with ROSAT soft X-ray results Also consistent with soft power law observed in Cen AAlso consistent with soft power law observed in Cen A SED double-peaked and modelled by SSC emissionSED double-peaked and modelled by SSC emission X-ray emission dominated by a jetX-ray emission dominated by a jet
Intermediate SummaryIntermediate Summary
Dissimilar spectra for two Dissimilar spectra for two seemingly similar FRI-type radio seemingly similar FRI-type radio galaxies:galaxies:– Cen A: X-ray emission hard and Cen A: X-ray emission hard and
heavily absorbed (likely accretion-heavily absorbed (likely accretion-related), accompanied by soft related), accompanied by soft emissionemission
– NGC 6251: X-ray emission soft and NGC 6251: X-ray emission soft and unabsorbedunabsorbed
Soft emission of Cen A may have Soft emission of Cen A may have the same origin as that of NGC the same origin as that of NGC 62516251
Why might they be dissimilar?Why might they be dissimilar? Are both accretion-related and jet-Are both accretion-related and jet-
related components present in related components present in allall radio galaxies at varying levels?radio galaxies at varying levels?
Need to study a sampleNeed to study a sample
1 2 4 7Energy (keV)
Cen A
NG
C 6
251
The 3CRR SampleThe 3CRR Sample
Criteria:Criteria:– 178-MHz luminosity density > 178-MHz luminosity density >
10.9 Jy10.9 Jy– Declination > 10Declination > 10oo
– ||bb| > 10| > 10oo
Advantages:Advantages:– No orientation biasNo orientation bias– Spectroscopic identificationSpectroscopic identification– High-resolution radio High-resolution radio
observationsobservations Select sources with Select sources with zz<0.1<0.1
– Unambiguously spatially Unambiguously spatially separate unresolved nuclear separate unresolved nuclear emission from contaminating emission from contaminating emissionemission
– Rich variety (FRI/FRII, Rich variety (FRI/FRII, broad/narrow lines, large broad/narrow lines, large luminosity range)luminosity range)
19/38 X-ray observations of low-z 19/38 X-ray observations of low-z 3CRRs, 16 of them with 3CRRs, 16 of them with ChandraChandra
Complete spectral analysis of Complete spectral analysis of eacheach
The 3CRR Sample: AimsThe 3CRR Sample: Aims Dominant X-ray emission Dominant X-ray emission
mechanism:mechanism:– Accretion Flow: Accretion Flow:
Fe KFe K, variability, variability
-or--or-– Jet:Jet:
SED, radio-SED, radio-optical-X-ray optical-X-ray luminosity correlationsluminosity correlations
Nature of accretion flow: Nature of accretion flow: thin disk? RIAF?thin disk? RIAF?
IIs the torus ubiquitous?s the torus ubiquitous? FRI-FRII dichotomy?FRI-FRII dichotomy?
Unified AGN scheme:Unified AGN scheme:
Consider Consider LLXX and and LLRR Considerable scatterConsiderable scatter
Luminosity-Luminosity Luminosity-Luminosity CorrelationsCorrelations
5-GHz luminosity density (W Hz-1 sr-1)
1020 1021 1022 1023 1024 1025
1-ke
V lu
min
osity
den
sity
(W
Hz-1
sr-1
)
1013
1014
1015
1016
1017
1018
1019
Consider Consider LLXX and and LLRR Considerable scatterConsiderable scatter Much better Much better
correlation between correlation between components with components with NNHH ≤ 5 x 10≤ 5 x 102222
Most components Most components have have NNHH consistent consistent with 0with 0
Any intrinsic Any intrinsic absorption consistent absorption consistent with dust in host with dust in host galaxygalaxy
Origin of X-ray Origin of X-ray emission in pc-scale emission in pc-scale jet (outside any jet (outside any torus)torus)
Luminosity-Luminosity Luminosity-Luminosity CorrelationsCorrelations
5-GHz luminosity density (W Hz-1 sr-1)
1020 1021 1022 1023 1024 1025
1-ke
V lu
min
osity
den
sity
(W
Hz-1
sr-1
)
1013
1014
1015
1016
1017
1018
1019
NH ≤ 5 x 1022
Jet
Components with Components with NNHH ~ ~ 10102323 lie above trendline lie above trendline
As does 3C 390.3, As does 3C 390.3, unobscured BLRGunobscured BLRG
All have Fe KAll have Fe K lines lines Accretion-dominated Accretion-dominated
and surrounded by a and surrounded by a torus?torus?
Soft components of Soft components of these sources these sources consistent with jet-consistent with jet-related trendline related trendline
Accretion and jet Accretion and jet components present in components present in all radio galaxies at all radio galaxies at varying levels?varying levels?
7/8 are FRIIs, other is 7/8 are FRIIs, other is Cen ACen A
Luminosity-Luminosity Luminosity-Luminosity CorrelationsCorrelations
5-GHz luminosity density (W Hz-1 sr-1)
1020 1021 1022 1023 1024 1025
1-ke
V lu
min
osity
den
sity
(W
Hz-1
sr-1
)
1013
1014
1015
1016
1017
1018
1019
NH ≤ 5 x 1022
5-GHz luminosity density (W Hz-1 sr-1)
1020 1021 1022 1023 1024 1025
1-ke
V lu
min
osity
den
sity
(W
Hz-1
sr-1
)
1013
1014
1015
1016
1017
1018
1019
NH ≤ 5 x 1022
NH ~ 1023
Jet
Accretion
So far:So far:– X-ray emission of FRIIs is heavily X-ray emission of FRIIs is heavily
absorbed and accompanied by absorbed and accompanied by Fe KFe K lines lines accretion-related accretion-related and viewed through a torusand viewed through a torus
– X-ray emission of FRIs much less X-ray emission of FRIs much less absorbed. absorbed. LLXX and and LLRR
correlations correlations jet-related emission jet-related emission
Where is the torus in FRIs? Where is the torus in FRIs? Problems with unified models, Problems with unified models, etc.etc.
Find upper limits to accretion-Find upper limits to accretion-related emission in FRIsrelated emission in FRIs
Data don’t exclude luminosities Data don’t exclude luminosities of ~ 10of ~ 103939-10-104141 ergs/s ergs/s
Some comparable to, e.g., Cen A Some comparable to, e.g., Cen A (5x10(5x104141 ergs/s) but lower than ergs/s) but lower than FRIIs (10FRIIs (104343-10-104444 ergs/s) ergs/s)
A Nuclear FRI/FRII Dichotomy?A Nuclear FRI/FRII Dichotomy?
e.g. 3C 274 (M87)
Data do not exclude the presence of a torus in FRIs Data do not exclude the presence of a torus in FRIs supports AGN- supports AGN-unification modelsunification models
FRI nuclei are FRI nuclei are notnot simply scaled versions of FRIIs simply scaled versions of FRIIs– For a given jet power, FRI nuclei have less efficient accretion flowsFor a given jet power, FRI nuclei have less efficient accretion flows– Dichotomy in accretion-flow structure of FRIs and FRIIsDichotomy in accretion-flow structure of FRIs and FRIIs
The FRI/FRII dichotomy is not just related to differences in the The FRI/FRII dichotomy is not just related to differences in the medium into which jet propagatesmedium into which jet propagates
First evidence of dichotomy from X-ray studiesFirst evidence of dichotomy from X-ray studies
A Nuclear FRI/FRII Dichotomy?A Nuclear FRI/FRII Dichotomy?
Implications:Implications:
MHD ADAF SimulationArmitage (2004)
SummarySummary
Unobscured (jet-related), and obscured Unobscured (jet-related), and obscured (accretion-related) components present (accretion-related) components present in all radio galaxies at varying levelsin all radio galaxies at varying levels
Data do not exclude the presence of a Data do not exclude the presence of a torus in FRI-type sourcestorus in FRI-type sources
An FRI/FRII dichotomy exists on nuclear An FRI/FRII dichotomy exists on nuclear scalesscales