Active Galactic Nuclei: Jets and other Outflows To discuss two aspects of AGC Activity: Phenomena on

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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)
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Three topics

• 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
  
  

Based on Gopal Krishna, Dhurde Wiita (ApJ,
615, L81, 2004) Gopal Krishna,
Wiita Dhurde (MNRAS, 2006, in press)
Gopal Krishna, Wiita Joshi, (Submitted,
2006)
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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 ? gmin300) (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)
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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
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Other Indications of Ultra-High ?j on Parsec /
Sub-Parsec Scale

• To avoid excessive photo-photon losses, variable
  TeV emission demands Ultra-relativistic jets
  (Krawczynski et al. 2002)
• with 15 lt ?j lt 100
• (Mastichiadis Kirk, 1997 Krawczynski, et al.
  2001)
• Correcting the spectrum for Gamma-ray absorption
  by the IR background strongly implies ?j gt 50
• (e.g., Henri Saugé, 2006)
• Evidence for Tb (apparent) gt 1013 K in IDV
  blazars would also suggest ?jgt 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 gt 25c (hence ?j gt 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 gt30) by Vlahakis
  Konigl, 2004)

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Problem Posed by Ultra-High ?j (gt 30)

• 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)

However, a serious inconsistency for TeV blazars
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How to Reconcile Ultra-Relativistic Jets with
the Slow Moving Radio Knots?

• 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 in radio
  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?

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Possible resolution of the Paradox Conical
(Ultra-Relativistic) Jets

• Substantial opening angles are seen for some
  well-resolved VLBI jets.
• Good example of conical VLBI jet is M87 (wgt10o)
• (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 jets 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 jets cone, then large vector
  cancellation of ?app can occur over the jets
  cross section.

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Pseudo-colour rendition of the nucleus of M87 at
43 GHz on 3 March 1999. (Junor et al, 1999)
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Relevant analytical expressions (Gopal Krishna
et al. 2004)

• Sobs?? ? n (?).Sem(?)d? ? A(?)Sem
• where, n3 for radio knots and A(?)mean
  amplification factor

(Fomalont et al. 1991)
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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

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High Gammas Yet Low Betas

• ?app vs ? for jet and
• prob of ?app gt ? 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

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Some key Implications

• 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 jets
  opening angle ?(5º to 10º) ( gtgt 1/?j).
• Usually, this is associated with canonical
  jets (?0) of ?j5 to 10.
• Hence, ultra-relativistic conical jets are
  also consistent with FR I radio galaxies being
  the parent population of BL Lacs.

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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 Width30 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

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4C14.27
3C192
3C33
Ref DRAGN Atlas (P. Leahy)
3C381
3C401
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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)
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A Plausible mechanism for the radio gaps

• 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 (vwgt103 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 gt 108 yrs
• (e.g., Rawlings 2003 Gregg et al. 2006)
• Mechanical luminosity of the wind can greatly
  exceed AGNs 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)

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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)

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The Basic Model Sequence of Events
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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
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For the jet starting a time tj after the onset of
the AGN wind
Catch-up time (tc) when jet catches up with the
bubbles surface
Catch up length of the jet
After catching up tcgtt gt(tj?j)
Assumption Jet stops advancing when the AGN
switches off.
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Gopal Krishna, Wiita Joshi, 2006
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Finding Jet Parameters

• 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

?S change in flux over time ?obs Tmax
3x1010K ?app from VLBI knot speed ? is
spectral index
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Conical Jets Also Imply

• 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 lt 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 ?gt50 then this gives hard x-ray fluxes
  consistent with observations
• So ultrarelativistic jets with ?gt30 may well be
  common

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Inferred Lorentz Factors
?inf vs. ? for ?100, 50 and 10 for ?5o P(?)
and lt ?infgt
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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

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Conclusions

• 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 gt30 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.

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Thank you