Active Galactic Nuclei: Jets and other Outflows

1. Active Galactic Nuclei: Jets and other Outflows To discuss two aspects of AGN Activity (About phenomena on parsec & kpc Scales) Gopal KrishnaNCRA-TIFR, Pune, INDIA Paul J. WiitaGSU, Atlanta, USA KASI-APCTP Joint Workshop (KAW4), Daejeon, Korea (May 17-19, 2006)

2. Peculiar radio (synchrotron) spectrum:Sn  n1/3 Electron energy spectrum: either mono-energetic, or having a low energy cut-off (LEC) Salient examples : Galactic (Sgr A* and the "ARC") Extragalactic (extreme IDV quasar PKS 0405-385) Possible implication of LEC for the bulk motion of quasar jets Interplay of the thermal and relativistic plasma outflows from AGN Three topics Based on: Gopal Krishna, Dhurde & Wiita (ApJ, 615, L81, 2004) Gopal Krishna, Wiita & Dhurde (MNRAS, 2006, in press) Gopal Krishna, Wiita & Joshi, (Submitted, 2006)

3. Early Evidence for LEC in the Nuclear Cores • Lack of Faraday depolarization (from VLBI) gmin ~ 100 • (Wardle 1977; Jones & O'Dell 1977) • More direct recent evidence for LEC • From turnover in the radio spectrum of the eastern hotspot of Cygnus A • (nt ~ 0.1 GHz  gmin~300) • (Joseph et al 2006; Biermann et al. 1995; Carilli et al. 1991) • Near the theoretical estimate for hadronic interactions (gmin ~ 100) • Spectral turnover due to LEC can be more readily seen for superluminal VLBI • radio knots (Because nt is pushed to GHz range due to strong Doppler shift) • (Gopal-Krishna, Biermann & Wiita 2004) • For a wide range of B and , LEC is the main cause of spectral flattening/ turnover (Since LEC becomes effective at higher frequency than SSA) • (Gopal-Krishna, Biermann & Wiita 2004)

4. Bulk Lorenz factor of the jet (j) from the inverted spectrum of the Extreme Intra-day Variable (IDV) Blazar PKS 0405-385 • =1/3 up to nt 230 GHz (Protheroe, 2003) Ref: Duschl & Lesch, 1994 Ref: Protheroe, 2003

5. To avoid excessive photo-photon losses, variable TeV emission demands Ultra-relativistic jets (Krawczynski et al. 2002) with 15 < j < 100 (Mastichiadis & Kirk, 1997; Krawczynski, et al. 2001) Correcting the spectrum for Gamma-ray absorption by the IR background strongly implies j > 50 (e.g., Henri & Saugé, 2006) Evidence for Tb(apparent) > 1013 K in IDV blazars would also suggest j> 50 (for simple quasi-spherical geometry of the source) (e.g., Protheroe, 2003; Macquart & de Bruyn, 2005) For several EGRET blazars, recent VLBI shows: vapp > 25c (hence j > 25) (Piner et al. 2006) GRB models usually require jets with j ~ 100-1000 (e.g., Sari et al., 1999; Meszaros, 2002) Note: Jet formation model (j >30) by Vlahakis & Konigl, 2004) Other Indications of Ultra-High jon Parsec / Sub-Parsec Scale

6. As many as 35% - 50% of the VLBI knots in TeV blazars are found to be stationery or moving subluminally. (Piner & Edwards 2004) The fraction is much lower for a normal blazar population (e.g., Jorstad & Marscher, 2003) (Hence, no serious inconsistency with j ~20-30) Problem Posed by Ultra-High j (> 30) However, a serious inconsistency for TeV blazars

7. Viewing angle () of the jet is within ~ 1o (from our line of sight) (NOT a general explanation: Since only ¼ j2 (~10-4) VLBI knots can appear subluminal) Motion of the knots reflects pattern speed, not physical speed (However, see Homan et al. 2006) A dramatic deceleration of jet between sub-pc and parsec scale (Georganopoulos & Kazanas, 2003) DIFFICULTIES Why deceleration in TeV blazars only (and not in EGRET blazars)? Evidence, in fact, points to acceleration on parsec scale(Piner 2006) Spine-sheath structure of jets:(e.g., Ghisellini et al. 2004) Fast spine produces TeV variability via IC and only the slower outer layer is picked inradio VLBI(observational evidence: Giroletti et al2004) DIFFICULTIES Why a two-component jet needs to be invoked only for TeV blazars? Why don't the shocks produce radio knots even in the fast spine? How to Reconcile Ultra-Relativistic Jets with the Slow Moving Radio Knots?

8. Substantial opening angles are seen for some well-resolved VLBI jets. Good example of conical VLBI jet is M87 (w>10o) (Junor et al., 1999) Consequence of conical jet: For an ultra-relativistic jet, a huge variation of j (i.e., of Doppler boosting factor & apparent motion) would occur across the jet’s cross section Needed: Weighted averaging of bapp by the distribution of flux-boosting A() over the jet's cross section (Gopal Krishna et al, 2004) Remember that while A() varies monotonically with , bapp() does not. Moreover, if the line-of-sight to the core passes through the jet’s cone, then large vector cancellation of app can occur over the jet’s cross section. Possible resolution of the Paradox:Conical (Ultra-Relativistic) Jets

9. Pseudo-colour rendition of the nucleus of M87 at 43 GHz on 3 March 1999. (Junor et al, 1999)

10. Relevant analytical expressions(Gopal Krishna et al. 2004) Sobs=  n ().Sem()d  A()Sem [where, n=3 for radio knots and A()=mean amplification factor] (Fomalont et al. 1991)

11. Conical Jets w/ High Lorentz Factors Weighted app vs  for • = 100, 50, 10 and opening angle = 0,1,5 and 10 degrees, With blob 3 boosting Probability of large app can be quite low for high  if opening angle is a few degrees

12. High Gammas Yet Low Betas • app vs  for jet and prob of app >  for opening angles = 0, 1, 5, 10 degrees and  = 50, 10 (continuum 2 boosting) • Despite high  in an effective spine population statistics are OK • Predict transversely resolved jets show different app

13. Thus, even a radio knot moving with the ultra-relativistic spine of the jet would frequently appear to move subluminally (we believe this is the case of TeV blazars). This will happen even for viewing angles () significantly larger than 1/j (Hence, not so unlikely) Effective beaming angle is the same as the jet’s opening angle (5º to 10º) ( >> 1/j). Usually, this is associated with canonical jets (=0) of j=5 to 10. Hence, ultra-relativistic conical jets are also consistent with FR I radio galaxies being the parent population of BL Lacs. Some key Implications

14. Dynamical interaction between thermal and relativistic outflows from AGN(Evidence from Radio Morphology) In several RGs, the inner edges of the two radio lobes are sharply truncated Thus, strip-like central gaps are seen in the radio bridges Typical dimensions of central gaps: Width~30 kpc (0.5 Mpc) Inference: The huge strip-like gap seen between the radio lobe pair betrays the presence of a “Superdisk" made of denser material (Gopal-Krishna & Wiita 2000; Gopal-Krishna & Nath 2001) Since the sharp edges can only be seen from a favorable viewing angle, superdisk should be a fairly common feature Previous Interpretations of the Radio Gaps, in general: Back-flowing synchrotron plasma in the radio lobes is blocked by the ISM of the parent galaxy (ISM arising from stellar winds and/or captured disk galaxies) Buoyancy led outward squeezing of the lobe plasma by the ISM

15. 4C14.27 3C192 3C33 Ref: DRAGN Atlas (P. Leahy) 3C381 3C401

16. Need for an Alternative Interpretation • Radio gaps in some RGs are extremely wide: upto 0.5 Mpc (PKS 0114-476) • Often the parent galaxy is seen at one edge of the radio gap (In some cases, even outside the gap, i.e., within a lobe): (3C 16, 3C19) (Saripalli et al. 2002) (DRAGN atlas (P.Leahy)

17. Dynamical Interaction of the radio lobes with a powerful thermal wind outflowing from the AGN (GK, Wiita & Joshi 2006) Emerging Pieces of Evidence: Thermal winds (vw>103 km/s) and mass outflow of ~1 M/yr are generic to AGN (e.g., Soker & Pizzolato 2005; Brighenti & Mathews 2006) For example, in ADIOS model, accretion energy mostly ends up in a thermal wind (Blandford & Begelman 1999) Thus, relativistic jet pair and non-relativistic wind outflow seem to co-exist (e.g., Binney 2004; Gregg et al. 2006) Evidences: Absorption of AGN's continuum, seen in UV and X-ray bands (review by Crenshaw et al. 2003) Wind outflow probably PRECEDES the jet ejection and lasts for tw > ~ 108 yrs (e.g., Rawlings 2003; Gregg et al. 2006) Mechanical luminosity of the wind can greatly exceed AGN’s bolometric luminosity (Churazov et al. 2002; Peterson & Fabian 2005) Wind outflow is quasi-spherical, while the jets are well collimated (e.g., Levine & Gnedin 2005) A Plausible mechanism for the radio gaps

18. The Basic Model: Sequence of Events • Wind outflow from AGN blows an expanding bubble of metal-rich, hot gas • Later, the AGN ejects a pair of narrow jets of relativistic plasma • The jets rapidly traverse the wind bubble and often come out of the bubble • From then on, the high-pressure backflow of relativistic plasma in the radio lobes begins to impinge on the wind bubble, from outside • This sideways compression of expanding wind bubble by the two radio lobes transform the bubble into a fat pancake, or superdisk • AGN's hot wind escapes through the superdisk region, normal to jets • The superdisk is "frozen" in the space. It manifests itself as a strip-like central emission gap in the radio bridge • Meanwhile, the galaxy can continue to move within the cosmic web It can move ~ 100 kpc in ~ 300 Myr, with a speed of ~ 300 km/s • Thus, in about 108 years the parent galaxy can even reach the edge of the radio emission gap (sometimes, even cross over into the radio lobe: eg., 3C16, 3C19) • Now onwards, the two jets propagate through very different types of ambient media (wind material and radio lobe plasma)

19. The Basic Model: Sequence of Events

20. Modelling the dynamics of the bubble and the jets(Gopal Krishna, Wiita & Joshi 2006) (Uses the analytical works of Levine & Gnedin 2005; Scannapieco & Oh 2004; Kaiser & Alexander 1997) Asymptotic (equilibrium) radius of the wind bubble:

21. For the jet starting a time tj after the onset of the AGN wind: Catch-up time (tc): when jet catches up with the bubble’s surface: Catch up length of the jet After catching up[tc>t >(tj+j)]: Assumption: Jet stops advancing when the AGN switches off.

22. Gopal Krishna, Wiita & Joshi, 2006

23. Determining bulk Lorentz factors, , and misalignment angles, , are difficult for all jets Often just set  =1/ , the most probable value Flux variability and brightness temperature give estimates: Finding Jet Parameters S = change in flux over time obs Tmax= 3x1010K app from VLBI knot speed  is spectral index

24. Inferred Lorentz factors can be well below the actual ones Inferred viewing angles can be substantially underestimated, implying deprojected lengths are overestimated Inferred opening angles of < 2o can also be underestimated IC boosting of AD UV photons by ~10 jets would yield more soft x-rays than seen (“Sikora bump”) but if >50 then this gives hard x-ray fluxes consistent with observations So ultrarelativistic jets with >30 may well be common Conical Jets Also Imply

25. Inferred Lorentz Factors inf vs.  for =100, 50 and 10 for =5o P() and < inf>

26. Inferred Projection Angles • Inferred angles can be well below the actual viewing angle if the velocity is high and the opening angle even a few degrees • This means that de-projected jet lengths are overestimated

27. Part I: Modest opening angles (5º – 10º) of AGN jets can explain the jet Lorenz factor paradox of TeV blazars Thus, the frequently observed subluminal motion of VLBI knots can be reconciled with the ultra-high bulk Lorenz factors (j >30 – 50) inferred from rapid TeV and radio flux variability. Some further consequences of this picture are discussed in our second paper(Gopal Krishna, Wiita & Durde, MNRAS, 2006, in press.) Part II: Dynamical interaction between thermal (wind) and non-thermal (jet) outflows resulting from the AGN activity, gives rise to fat pancake or superdisk shaped regions. The metal-rich in which hot wind material filling the superdisk escapes to hundreds of kpc, roughly orthogonal to the radio axis. Superdisks manifest their presence by causing strip-like emission gaps in the middle of radio bridges. Conclusions

28. Thank you