X-Ray Emission From The Nuclei of Radio Galaxies Daniel Evans University of Bristol -with- Diana Worrall, Ralph Kraft, Martin Hardcastle, Mark Birkinshaw, Judith Croston, Bill Forman, Christine Jones, Steve Murray

Contents n An introduction to AGN physics n X-ray emission from radio galaxies: the issues n Centaurus A: the nearest AGN n NGC 6251: a counterexample? n Nuclear emission from a sample of 3CRR radio galaxies n Conclusions

What are AGN? n Unresolved nuclear component n Nuclear luminosity > sum of all stars n M BH ~ 10 6 –10 10 M ๏ n Accompanied by strong X-ray emission NGC 3277 NGC 5548NGC XMM

The Central Engine n Accretion flow surrounded by dusty torus

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

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

The Central Engine n Accretion flow surrounded by dusty torus n BB radiation from disk  ‘big blue bump’ n B-field loops  optically thin corona n Isotropic X-rays from Comptonization of disk photons in hot corona n Power law spectrum

Fe K  Production n Reflection of X-rays from an optically thick accretion disk

Fe K  Production n Reflection of X-rays from an optically thick accretion disk

Fe K  Production n Reflection of X-rays from an optically thick accretion disk

Fe K  Production n Reflection of X-rays from an optically thick accretion disk

Fe K  Production n Reflection of X-rays from an optically thick accretion disk

Fe K  Production n Reflection of X-rays from an optically thick accretion disk Fe Kα

Astrophysical Jets 10 pc NGC GHz VLBI Jones et al. (1986) n Anisotropic emission, power law spectrum Relativistic Doppler beaming, dependent on bulk speed ( Γ ), angle to line of sight Relativistic Doppler beaming, dependent on bulk speed ( Γ ), angle to line of sight

Radio Galaxy Nuclei – Two Competing Models n Is the X-ray emission dominated by: n The parsec-scale jet? -or- n The accretion flow?

Jet-Related Emission e.g., Zamorani et al. (1981) 1. For a given optical luminosity, radio-loud quasars are brighter X-ray sources than radio-quiet quasars  An additional component of emission is present in RLQs Three Discoveries:

Jet-Related Emission 2. Dependence of X-ray luminosity and spectrum on beaming angle  A component is anisotropic 3. Correlation between ROSAT soft X-ray and radio fluxes and luminosities  Soft X-ray emission likely jet-related Shastri et al. (1993) Canosa et al. (1999)

Accretion-Related Emission n Have seen that soft ( keV) X-ray emission likely jet related n What about the rest of the X-ray spectrum? Jet or accretion flow? E.g. Gliozzi et al. (2004) claim broadened Fe K  emission and variability on short timescales in NGC 6251 E.g. Gliozzi et al. (2004) claim broadened Fe K  emission and variability on short timescales in NGC 6251 n Would imply accretion-dominated emission d < ct

Summary of Introduction n Emission in the nuclei of AGN consists of: –“Radio-quiet” accretion- related component –“Radio-loud” jet-related component n Which dominates the X- ray emission? –Matter of considerable debate…

Cen A – The Nearest AGN n Brightest extragalactic object in the hard X-ray sky n Closest radio galaxy (d = 3.4 Mpc) n Complex emission n Ideal object to study n Much-studied by earlier X-ray missions n Rich gallery of radio features (jet, lobes, etc.) Chandra keV X-ray

Continuum Spectrum n Attempt to fit a heavily-absorbed (N H  atoms cm -2 ) power-law (Γ  1.7) n Significant residuals below  2.5 keV XMM-Newton MOS2 1 st observation

Continuum Spectrum n Significant improvement with the addition of a second power-law component Component N H (atoms cm -2 ) Γ Hard PL (1.30 ± 0.16) x ± 0.15 Soft PL (3.8 ± 2.0) x (frozen) Key parameters:

Possible Origin of 2 nd PL n VLBI jet? Flux density  5 Jy at 4.8 GHz n X-ray to radio ratio for 2 nd PL and VLBI jet consistent with that of kpc-scale jet and VLA jet n Mildly absorbed soft power law seen in other FRI galaxies with ROSAT Canosa et al. (1999) 0.7 pc Core Tingay et al. (1998)

Fluorescent Line Emission n Chandra HETGS instrument of choice due to its high spectral resolution Fe K  Fe K  Joint HEG+1 and HEG-1 spectrum Fe K  centroid = ± keV (90% c.l.))  fluorescence from cold, neutral material Fe K  centroid = ± keV (90% c.l.))  fluorescence from cold, neutral material Fe K α is broadened Fe K α is broadened (σ = 20 ± 10 eV (90% c.l.))  v ~ 1000 km s -1  r ~ 0.1 pc (M BH = 2 x 10 8 M ๏ )

Geometry Of Emission Region Fe K  line parameters consistent with fluorescence from N H  atoms cm -2 with torus geometry Fe K  line parameters consistent with fluorescence from N H  atoms cm -2 with torus geometry Also consistent with fluorescence from N H ~ atoms cm -2 outside line of sight (Woźniak et al. 1998) Also consistent with fluorescence from N H ~ atoms cm -2 outside line of sight (Woźniak et al. 1998)

Nature of Accretion Flow Galaxy LxLxLxLx L Edd  Bondi Interpretation Cen A 4.8 x x x Hybrid? Sag A* 2.4 x x x Inefficient NGC x x x Inefficient 3C x x x Standard Hybrid inefficient flow/thin disk

Cen A Summary n Emission characterized by a heavily-absorbed power law n Second power-law component necessary, consistent with VLBI jet n Fluorescent lines from cold, neutral material n Molecular torus? n Accretion flow: Hybrid? n More info: Evans et al. (2004), ApJ, 612, 786

NGC 6251 – A Counterexample n z= (d~100 Mpc) FRI-type radio galaxy n Spectacular radio jet extending hundreds of kpc n Opening angle of 7.4 o n X-ray emission from nucleus and three regions of kpc-scale jet n Synchrotron interpretation for kpc- scale jet (Evans et al. 2005) 1 arcmin 30 kpc 1.6 GHz VLA Jones et al. (1986) keV Chandra image with 1.6 GHz VLA contours (Evans et al. 2005)

NGC Results XMM-Newton observation of NGC Gliozzi et al. (2004) claimed broadened Fe K  line-emission XMM-Newton observation of NGC Gliozzi et al. (2004) claimed broadened Fe K  line-emission n Would imply accretion- dominated X-ray emission n New Chandra data + reanalysis of XMM data n Nuclear spectrum well fitted with a featureless, single, unabsorbed power law 1247 Energy (keV) Chandra XMM

NGC 6251 – Fe K  line No evidence of Fe K  emission in Chandra spectrum No evidence of Fe K  emission in Chandra spectrum No significant evidence for Fe K  emission in XMM spectrum No significant evidence for Fe K  emission in XMM spectrum n Already evidence to disfavour accretion-dominated X-ray emission

NGC Interpretation n 1-keV X-ray flux density consistent with ROSAT soft X-ray results n Also consistent with soft power law observed in Cen A n SED double-peaked and modelled by SSC emission n X-ray emission dominated by a jet

Intermediate Summary n Dissimilar spectra for two seemingly similar FRI-type radio galaxies: –Cen A: X-ray emission hard and heavily absorbed (likely accretion-related), accompanied by soft emission –NGC 6251: X-ray emission soft and unabsorbed n Soft emission of Cen A may have the same origin as that of NGC 6251 n Why might they be dissimilar? n Are both accretion-related and jet- related components present in all radio galaxies at varying levels? n Need to study a sample 1247 Energy (keV) Cen A NGC 6251

The 3CRR Sample n Criteria: –178-MHz luminosity density > 10.9 Jy –Declination > 10 o –|b| > 10 o n Advantages: –No orientation bias –Spectroscopic identification –High-resolution radio observations n 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) n 19/38 X-ray observations of low-z 3CRRs, 16 of them with Chandra n Complete spectral analysis of each

The 3CRR Sample VLA (Leahy, Bridle, & Strom) Chandra keV

The 3CRR Sample: Aims n Dominant X-ray emission mechanism: –Accretion Flow: Fe K , variability -or- –Jet: SED, radio-optical-X-ray luminosity correlations n Nature of accretion flow: thin disk? RIAF? n Is the torus ubiquitous? n FRI-FRII dichotomy? Unified AGN scheme:

n Consider L X and L R n Considerable scatter Luminosity-Luminosity Correlations

n Consider L X and L R n Considerable scatter n Much better correlation between components with N H ≤ 5 x n Most components have N H consistent with 0 n Any intrinsic absorption consistent with dust in host galaxy n Origin of X-ray emission in pc-scale jet (outside any torus) Luminosity-Luminosity Correlations N H ≤ 5 x Jet

n Components with N H ~ lie above trendline n As does 3C 390.3, unobscured BLRG All have Fe K  lines All have Fe K  lines n Accretion-dominated and surrounded by a torus? n Soft components of these sources consistent with jet-related trendline n Accretion and jet components present in all radio galaxies at varying levels? n 7/8 are FRIIs, other is Cen A Luminosity-Luminosity Correlations N H ≤ 5 x N H ~ Jet Accretion

n So far: –X-ray emission of FRIIs is heavily absorbed and accompanied by Fe K  lines  accretion-related and viewed through a torus –X-ray emission of FRIs much less absorbed. L X and L R correlations  jet-related emission n Where is the torus in FRIs? Problems with unified models, etc. n Find upper limits to accretion-related emission in FRIs n Data don’t exclude luminosities of ~ ergs/s n Some comparable to, e.g., Cen A (5x10 41 ergs/s) but lower than FRIIs ( ergs/s) A Nuclear FRI/FRII Dichotomy? e.g. 3C 274 (M87)

n Data do not exclude the presence of a torus in FRIs  supports AGN-unification models n FRI nuclei are not simply scaled versions of FRIIs –For a given jet power, FRI nuclei have less efficient accretion flows –Dichotomy in accretion-flow structure of FRIs and FRIIs n The FRI/FRII dichotomy is not just related to differences in the medium into which jet propagates n First evidence of dichotomy from X-ray studies A Nuclear FRI/FRII Dichotomy? Implications: MHD ADAF Simulation Armitage (2004)

Summary n Unobscured (jet-related), and obscured (accretion-related) components present in all radio galaxies at varying levels n Data do not exclude the presence of a torus in FRI-type sources n An FRI/FRII dichotomy exists on nuclear scales