Thermal AGN Signatures in Blazars

1. Thermal AGN Signatures in Blazars Eric Perlman Florida Institute of Technology With thanks to: Jill Randall, Sarah McNamara (grad students at FIT working on blazars) Brett Addison (undergrad @FIT working on blazars) Markos Georganopoulos, Paolo Padovani, Paolo Giommi, Anuradha Koratkar, Ian Evans, Demos Kazanas, Elena Pian, Hermine Landt, John Stocke, Travis Rector (collaborators over the years)

2. Outline • Why are we interested? • What constitutes evidence for thermal emission? • What was the first solid evidence for thermal emission in blazars? • What kind of variability signatures should we expect? • What is the current state of the art in evidence for thermal emission from blazars? The existing claims: how do they stack up… This is difficult stuff! • Revisiting the “blazar sequence” & unified models • What might we expect to find in new missions? Are there specific predictions for GLAST? Other wavebands and/or missions?

3. Why are we interested? • AGN are complex beasts Both thermal and non-thermal emission regions Just because observed emission is dominated by one doesn’t mean the other is not there! • So what emits thermally? Accretion Disk Corona (possibly) Torus • These are important elements of unified schemes!

4. What would constitute evidence of thermal emission? Ideally… • Appearance of a relatively narrow-band, blackbody component in simultaneously observed spectrum • Region of spectrum with a “bump” which has different variability characteristics than rest of broadband spectrum • Emission lines from disk, e.g., Fe K Difficult to observe in reality… • Jet is typically ~0.1x power of thermal regions in RL quasars • But…in a blazar with ~5-10 and = that ratio will be at least ~100. • Plus, in at least one of the parent population classes (FR I radio galaxies), thermal emission is intrinsically weak.

5. Underlying Evidence of Thermal Emission? The mere presence of broad and narrow line regions by itself implicates a bright, likely thermal “central engine” Why is this? • For jet to be primary ionizing & exciting source, a cloud must be within the jet’s “beaming cone” VERY SMALL part of BLR solid angle • If -ray flare sites are in BLR and -ray seed photons are from BLR (Sikora/Madejski models), blobs must also be closer to cloud than core by factor [1/(2R)]1/2. See also Celotti, Ghisellini, Fabian (2007)

6. Underlying Evidence of Thermal Emission? The mere presence of broad and narrow line regions by itself implicates a bright, likely thermal “central engine” ….Or does it? • Anticorrelation between R (beaming) and line width (many groups, e.g. Wills & Browne ’86) • 30% covering factor of the accretion disk by the BLR, but still no UV spectra with sharp Ly edge in absorption (Maiolino et al. ’01)

7. Does Superquadratic Variability imply seed photons from outside the jet? In a word: NO! Contrary to claim by Wehrle et al. (1998) and others: SSC naturally produces superquadratic variability when the SSC power is comparable to or higher than that from synchrotron The key: 2nd & higher order scatters This is exactly what is seen in e.g., 3C 279. 234 Power:1:10:100 16 7.1 1 3.2 1 Georganopoulos, Perlman et al. 2008; see our poster!

8. Current view: The GeV emission of blazars is external Compton (EC) scattering off the broad line region (BLR) photons 2 1 • Unavoidable but unobserved marks: • The hump in the synchrotron component • 2. The flat/rising SED of the GeV component • 3. Achromatic variability for the synchrotron hump and the GeV regime. 3 Cooling time as a function of electron energy

9. What other evidence might imply jet interaction with thermal emitting regions? • Internal absorption of gamma-rays caused by interactions with dense narrow-band radiation fields can cause gamma-ray spectra of almost arbitrary hardness • Motivation: hard spectra being found in almost all TeV BL Lacs, including the most distant ones • “Pileup” scenario testable by gamma-ray telescopes • Also could produce neutrino fluxes close to observable by the next generation of high energy neutrino detectors Aharonian et al. 2008

10. Which regions of the AGN? • What might emit thermally? Accretion Disk Corona (possibly) Torus

11. First Solid Evidence of Thermal Emission 3C 279, observed in low state (Pian et al. 1999) • Narrow-band, UV component superposed on broader-band non-thermal emission • Fits blackbody model • Consistent with little or no variability, at least as compared with jet emission • Not seen when object is flaring THERMAL EMISSION FROM DISK

12. First Solid Evidence of Thermal Emission 3C 279, observed in low state (Pian et al. 1999) • Narrow-band, UV component superposed on broader-band non-thermal emission • Fits blackbody model • Consistent with little or no variability, at least as compared with jet emission • Not seen when object is flaring THERMAL EMISSION FROM DISK • Produced diagnostic diagram for when jet or disk would dominate Jet dominated Disk dominated

13. What variability characteristics should we expect? • Look at less jet-dominated objects, e.g. 3C 273 (spectrum at right, Kataoka et al. 2002) Optical-UV dominated by disk Hard X-ray dominated by jet Cross in soft X-rays (Grandi et al. 2004) • Disk varies on longer timescales (months) and less violently (<2X) -- see Ulrich et al. (1993) Similar results in Kaspi et al.(2006, 2007) observations of 7 other quasars • Torus should not vary strongly • Variability should not be strongly frequency dependent & will be uncorrelated with jet

14. Sample-based Efforts Statistical methods • D’Elia et al. (2003): use emission lines to derive BH mass & accretion rate, then predict disk emission ~15% of typical opt/UV emission from FSRQs is thermal Correlation between thermal & nonthermal luminosity No BL Lacs in sample

15. Sample-Based Efforts Modeling of broadband spectra • Maraschi & Tavecchio (2002) modelled multiwaveband + BeppoSAX spectra of 20 blazars inc. some BL Lacs Results qualitatively similar to D’Elia et al. but brighter disks by ~order of magnitude

16. Sample-Based Efforts Modeling of broadband spectra • Wang et al. (2004) use broadband spectra + VLBI maps to find disk + kinetic lum • Relation between Eddington ratio & jet kinetic lum • Used by Punsly & Tingay (2005) to point out PKS0743-67 as extreme

17. Spectral Methods • Sambruna et al. (2007) detected narrow, thermal component in four high z blazars with SWIFT Thermal Component dominated UVOT spectrum Non-thermal emission dominated at higher energies

18. Spectral methods • Idea was applied to HFSRQs by Landt et al. (2008) using XMM & Chandra obs • Several objects thermally dominated, particularly those with low R (e.g., at top) • Claim: optical+UV dominated by disk and torus • However, claim is extended to all HFSRQs including high-R (highly beamed) objects. Interesting idea, but… NOT justified by data (see e.g., objects at bottom)

19. Variability based methods • Look for periods of uncorrelated opt/X-ray or UV/X-ray variability • Two such examples found in PKS 2155-304 low-state SMARTS + RXTE campaigns (Osterman-Mayer et al. 2007)

20. Variability-based Methods • Look for periods of uncorrelated opt/X-ray or UV/X-ray variability • Two such examples found in PKS 2155-304 low-state SMARTS + RXTE campaigns (Osterman-Mayer et al. 2007) • The same may have been found in 2004 XMM observations of 0716+714 (Randall poster) ‘Flickering’ behavior seen in both in the UV/optical Flares seen in the X-rays

21. Spectral & Variability Methods From the 2005 & 2006 3C 454.3 campaigns: • In low state 3C 454.3 shows significant disk emission in blue (Villata et al. 2006) • Both little and big bump contributions can be seen but not separated by variability. • Curvature can also be seen in X-ray spectra (Raiteri et al. 2007)

22. Spectral & Variability Methods From XMM observations of AO 0235+164 (Raiteri et al. 2006): • Spectral curvature in UV-X-ray best explained by big blue bump • Possible detection of a Fe K line but not statistically significant The latter is similar to the case of 0716+714 (Kadler et al. 2005)

23. Eclipse of the accretion disk HST observations of 3C 279 in 2002 (Perlman et al. 2008) • Object was in a moderate state: flux 3-4x higher than in 1992-93 low state Only moderate variability seen • Continuum shape identical to 1992 ~1/3-1/2 of UV continuum from accretion disk, according to Pian diagram • Absorption feature appeared in Ly line during April Not seen in any other observations that year Most consistent explanation: eclipse of the accretion disk!

24. Detection of Fe K emission • Done in two FSRQs: PKS 1136-135 and 1150+497 (Sambruna et al. 2006) Continuum also indicated a mix of disk and jet emission • Continuum emission broken power-law, from jet • From innermost regions of accretion disk • Extension of X-ray “Baldwin Effect” (Nandra et al.) Not strictly thermal but it is from thermal-emitting region.

25. Which regions of the AGN? • What might emit thermally? Accretion Disk Corona (possibly) Torus

26. What should we expect torus emission to look like? • Two spectral signatures IR excess (some of which may also be contributed to by particles in K-N limit) “Bump” in Compton component See simulation at right by Perlman, Addison, Georganopoulos (in progress) • Variablity should be on even longer timescales than disk or corona, if indeed present

27. What about trying to detect the torus? • Not found securely in BL Lacs to date: ISO spectra of BL Lacs mostly well fit by synchrotron (Padovani et al. 2006) Although a few do show some IR excess -- could be from a torus but usually it’s 1-2 points only.

28. What about trying to detect the torus? • Also has not been convincingly demonstrated in more luminous objects • Although … PKS 1830-211 has some evidence for Comptonized torus emission in its broadband spectrum (de Rosa et al. 2005) Consistent with one of the possible explanations for MeV blazars • Also a very broad Fe Kalpha line consistent with emission from innermost regions of disk.

29. Where do we stand? • Thermal emission (or thermal emission regions) in blazars are difficult -- but NOT impossible -- to observe • Good evidence has been found in a number of ways Narrow-band spectral components Spectral curvature Particularly in low states Non-correlated variability behavior Modeling of spectra of samples combined with accretion models Fe K emission • One does have to be careful, though: Superquadratic variability is NOT proof of a link to thermal emission One should not use a paucity of information to infer that a thermal model will work Given the strength of the jet emission, other components need to be eliminated as possible culprits before firm evidence of thermal emission can be cited.

30. Where do unified schemes stand? • Disk emission has been seen in both BL Lacs and FSRQs Strongest evidence is where spectral & variability methods are combined • Corona emission may have been seen in some objects Most likely the culprit where the extra component is in the X-rays -- this is too high frequency for the disk given standard accretion disk models. • Torus emission has not been confirmed yet Suggestive evidence in a few objects For BL Lacs, the parent population may be IR weak and have weak or no tori (e.g., M87, Perlman et al. 2001, 2007). • Overall, pretty good for unified schemes, though (a lot) more work is necessary Given the limited record, this is all preliminary

31. Revisiting the blazar sequence Where does the “blazar sequence” -- which depends on jet dissipation in thermal or thermally excited regions -- stand? • Not good: the overall numbers of LBL/HBL does not agree with the predictions of the blazar scenario (Padovani et al. 2007) • Not good: presence of HFSRQs, very low-freq peaked BL Lacs, spectral index plots (Padovani et al. 2004, Nieppola et al.2007) • But at some level cooling must play a part • Tavecchio & Ghisellini (2008a) revisit the sequence with accretion-based models that do predict HFSRQs plus wider range of properties in other bands Predicts UV/X ‘bumps’ in HFSRQ type objects due to strong disk/corona emission. • Tavecchio & Ghisellini (2008b) models for blazar gamma-ray emission using CLOUDY for seed photons. Important for and testable by GLAST (see also Georganopoulos poster)

32. Prospects for the future • Detection of thermal emission in blazars is important for linking two critical elements of unified scheme models • Blazars are the only objects where we can really probe links between the jet and thermal emission regions. • Important prospects for future missions & telescopes: GLAST, TeV telescopes will be able to test firmly for origin of gamma-ray seed photons (Georganopoulos poster, Ghisellini & Tavecchio 2008b, Aharonian et al. 2008) Con-X will be able to look for thermal disk emission in blazars via Fe K (so far seen in only a few objects) Also -- if the BLR contributes the seed photons for GeV gamma-ray emission we need to monitor Ly  as part of multiwaveband campaigns. Unfortunately this cannot be done with current missions! If primary electrons are from hadronic origin due to pp or pg interactions, we could expect to detect high-energy neutrinos from blazars (Aharonian et al. 2008)