Jets in Radio Galaxies and Blazars: Conical Opening Angles and Superdisks

1
Jets in Radio Galaxies and Blazars Conical
Opening Angles and Superdisks

• Paul J. Wiita
• Georgia State University, USA

Peking University, 9 May 2008
2
Outline

• Basic Properties of Blazars
• TeV blazars inverse Compton mechanism boosting
  to the highest energies
• Conical jets vs. cyclindrical jets modest
  opening angles can explain many peculiarities,
  including high Lorentz factors, but slow radio
  knots
• Wide gaps between some lobes in radio galaxies
  imply jets launched after mergers

3
Blazar Characteristics

• Rapid variability at all wavelengths
• Radio-loud AGN
• Optical polarization high ? synchrotron
  domination
• BL Lacs show extremely weak emission lines
• Double humped SEDs RBL vs XBL?
• Core dominated quasars (or FSRQs) clubbed w/ BL
  Lacs to form the blazar class
• Population statistics indicate that BL Lacs are
  FR I RGs viewed close to jet direction (Padovani
  Urry 1992)
• The more powerful Flat Spectrum Radio Quasars are
  FR II RGs viewed nearly along the jet (Padovani
  2007)

4
Microvariability Intraday Variability
tooRomero, Cellone Combi (2000) Quirrenbach
et al (2000)
5
Blazar Spectral Energy Distributions

• Radio/IR/optical is dominated by synchrotron
  emission, with ?e 103-105
• X-ray may be synchrotron if ?e gt 107 or
  Inverse Compton, where ?e 102 is OK
• Gamma-rays likely to be IC and to get TeV
  photons ?e 107 might be needed

BL Lac Boettcher Reimer 2004, ApJ, 609, 576
6
SED of TeV Blazar Mrk 421 in High Low States
(Konopelko et al. 2003, ApJ, 597, 851)
Here x-rays at peak of synchrotron (HBL) and
powerful gamma-rays are modeled by Synchrotron
self-compton process
7
3C 130 3C 449 FR Isz0.109 z0.017
8
Canonical FR II Cygnus A (z0.056)
9
Quasar 3C 175 (z0.770) Only 1
jet seen core relatively more prominent than in
RG
10
VLBA of 3C279 Apparent Superluminal Motionwith
Vapp3.5c really V0.997c at viewing angle of 2
degrees(z 0.536)
11
RG Jets Start off With Relativistic Bulk Motions

• Apparent superluminal motions seen in some FR II
  RGs, especially flat spectrum quasars seen in
  VLBI
• Gross asymmetries seen between jets and
  counter-jets in FR II RGs Doppler favoritism
• Correlated one-sided-ness almost always seen
  between VLBI (pc-scale) and multi-kpc jets
• Only plausible explanation for blazars

12
Jet of Quasar 3C 273 in IR, radio
optical X-ray (Uchiyama et al. 2006, ApJ, 648,
910)
13
Part I Bulk Speeds of AGN Jets

• Big questions
• What is the bulk Lorentz factor ??
• What is the true jet orientation angle ??
• Most of this part is based on three papers
• Gopal-Krishna, Dhurde Wiita, ApJ, 615, L81
  (2004)
• Gopal-Krishna, Wiita Dhurde, MNRAS, 369, 1287
  (2006)
• Gopal-Krishna, Dhurde, Sircar Wiita, MNRAS,
  377, 446 (2007)

14
Estimating Bulk Doppler Factors (?)

• Boosted brightness temperature
• Intraday radio flux variability
• Models of SED of TeV blazars
• Rapid variability of gamma-ray flux
• The most direct measures come from VLBI knot
  motions (but may arise from shock, not bulk,
  velocities)

15
Doppler Factor from ?-ray Variability

• Several blazars show ?obs lt 1 hr for GeV ?-rays
• If stationary source size lt c ?obs
• For corresponding photon densities ?XSSC?ee-
• High cross-section means ?-rays should not escape
• If moving relativistically, then size lt c ? ?obs
• Thus photon opacity can be reduced sufficiently
  if ?100 (e.g., Krawczynski Kirk 2002)
• Also, Gamma-Ray Bursts seem to require
  ?100-1000 (e.g. Sari et al. 1999 Meszaros et
  al. 2002)
• Is there an underlying similarity for AGN and
  GRBs?

16
Direct Estimates from VLBI

• For normal blazars (Piner et al. 2006, ApJ, 640,
  196)
• 0235164 C1 ?app25.67.0 C2 ?app
  8.91.3 C3 ?app 7.94.7
• 0827243 C2 ?app25.64.4 Most are C3
  ?app19.23.7 quite C4 ?app12.37.4 superl
  uminal C5 ?app12.18.1 C6 ?app 3.23.7
• 1406-076 C1 ?app15.613.2 C2
  ?app28.26.6 C3 ?app22.58.9 C4
  ?app15.82.0

17
VLBI Knot Speeds for TeV Blazars (Piner Edwards
2004, ApJ, 600, 115)
Mrk 421 C4 ?app0.040.06 C5
?app0.200.05 C6 ?app0.180.05 C7
?app0.120.06 Mrk 501 C1 ?app0.050.18
C2 ?app0.540.14 C3 ?app0.260.11
C4 ?app-0.020.06 1ES 1959650 C1
?app-0.110.79 C2 ?app-0.210.61 PKS2155
-304 C1 ?app4.372.88 1ES 2344514 C1
?app1.150.46 C2 ?app0.460.43
C3 ?app-0.190.40
Most are subluminal or only modestly superluminal
18
Slow VLBI Knots in PKS 2155-304

• Top row, natural weighting bottom, uniform
  weighting with speeds C1--1.15c, C2--0.46c,
  C3---0.19c (Piner Edwards 2004)

19
How to have Small ?app in TeV Blazars?

• Dramatic deceleration between sub-pc (gamma-ray)
  and pc (radio) scales (Georganopoulos Kazanas
  2003, ApJ, 594, L27) Energetics are difficult
  where does it go?
• Very close alignment of the jet ? lt 0.1o if
  ?100 (statistically unlikely)
• Fast spine (? gt 30) and slow sheath (?3) the
  spine would produce X- and ?-rays, while the
  sheath would yield the radio synchrotron photons
  (e.g. Ghisellini et al. 2005, AA, 432,
  401) Distinctly possible, but not necessary

20
Jets Start Out Wide

• Opening angle vs distance for M87 (Biretta et al.
  2002) and Cen A (Horiuchi et al. 2006)

21
So We Consider Conical Jets

• Assume a uniform radio emitting knot with a
  finite opening angle, which may be comparable to
  the viewing angle, and allow for large values of
  ?, which may be a function of transverse location.

22
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)
23
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 high probability of low ?app
• Predict transversely resolved jets show different
  ?app

24
Apparent Velocities for Conical Jets

• For ? 100 40 sub-luminal (?5o) 70
  sub-luminal (?10o)
• For ? 50 15 sub-luminal (?5o) 30
  sub-luminal (?10o) lt?appgt 6 c (?5o)
• So high ? and low ?app for TeV blazars can be
  reconciled
• Small fraction of blazars must show ?app gt 50
• Both dense VLBI monitoring and unbiased
  interpretation of the data needed to check

25
Inferred Values for ? for Conical Jets
26
Implications of Jet Angle Results

• If jets are moderately conical, the standard
  analysis, which assumes ?0, would lead to
  serious underestimates of the jet orientation
  angle, ? (if ? lt 10o)
• Standard analysis would grossly overestimate the
  deprojection factor, hence the true radio size of
  the jet
• In-situ acceleration of TeV electrons in
  hot-spots may not be needed-- they could be
  transported
• Parent population of blazars is not overpredicted
  even if very high Lorentz factors are assumed

27
Conical Spine-Sheath Jets

• We also consider jets where Lorentz factor varies
• ?(r) ?0exp(-2rq/?)
• q0 for constant ?, q1 for mild transverse
  gradient q2 for strong gradient
• The expectation values of the viewing angles
  decline rapidly with ?0 regardless of the values
  of ? or q.
• But they level off at lt?gt ?/3 when the jets
  become ultrarelativistic (?0 gt 30), particularly
  if ?gt5o

28
Effective Speeds (left) and Doppler Factors
(right)for p3 ?020 (top), ?050 (middle)
?0100(bottom)
29
Results for Spine-Sheath Conical Jets

• Decline of ?eff with ? is faster for knots with
  higher ?.
• For well collimated jets (? lt 0.5o) ?eff for
  uniform ? is typically 1.5-2 times more than for
  q1 and 2-4 times higher for q2.
• Therefore the fastest spine component, close to
  the jet axis, would be concealed in VLBI
  measurements.
• Again, for good collimation, uniform ? jets would
  have 2-4 times larger ?eff compared to stratified
  jets, implying Doppler boost factors 10 times
  greater.
• Different VLBI speeds for different knots in the
  same jet could only mean that surface brightness
  distributions across similar speed knots are
  different.

30
Part II Superdisks in Radio Galaxies

• A small fraction of FR II RGs have lobes with
  large separations (25-30 kpc) and sharp parallel
  inner edges extending (75 kpc or more)
• These huge strip-like gaps imply the presence of
  a superdisk made of denser material
  (Gopal-Krishna Wiita 2000, ApJ,
  529,189)
• Previous Interpretations of the Radio Gaps were
  Either
• 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
• BUT, these wide gaps cannot be explained this
  way the ISM is too small

31
3C192
3C33
4C14.27
Ref DRAGN Atlas (P. Leahy)
3C381
3C401
32
A Plausible Mechanism for the Radio Gaps at High
Redshift

• Dynamical Interaction of radio lobes with a
  powerful thermal wind outflowing from the AGN
  (Gopal-Krishna, PJW, Joshi, 2007, MN, 380,703)
• Key Emerging Pieces of Evidence
• Non-relativistic winds (vwgt103 km/s) and mass
  outflow 1 M?/yr are generic to AGN
  (e.g., Soker Pizzolato 2005
  Brighenti Mathews 2006)
• Thus, relativistic jet pair and non-relativistic
  wind outflow seem to co-exist
• (e.g., Binney 2004 Gregg et al. 2006)
• Evidence 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 can last for tw gt 108 yrs
• (e.g., Rawlings 2003 Gregg et al. 2006)
• Wind outflow is quasi-spherical, while the jets
  are well collimated
• (e.g., Levine Gnedin 2005)

33
The Wind-Jet Model Sequence of Events, 1

• Wind outflow from AGN blows an expanding bubble
  of metal-rich, hot gas into intergalactic medium
• Later, the AGN ejects a pair of collimated jets
  of relativistic plasma
• The jets rapidly traverse the wind bubble and
  often overtake the bubbles boundary
• From then on, the high-pressure backflow of
  relativistic plasma of 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

34
The Wind-Jet Model Sequence of Events, 2

• The 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, within about 108 years the parent galaxy
  can even reach the edge of the radio emission gap
  (sometimes, even cross over into the radio lobe
  e..g., 3C16, 3C19)
• From then onwards, the two jets propagate through
  very different types of ambient media (wind
  material and radio lobe plasma)

35
Jets Overtake Many Bubbles

• Distance where (or if) jets catch up to bubbles
  is a function of relative powers (LJ/LW) and
  delay between wind and jet, tJ
• (a) - (d) go from weak to strong winds, all
  lasting 100 Myr
• Gray bands correspond to realistic lobe energy
  densities

Gopal-Krishna, PJW Joshi, 2007, MNRAS, 380, 703
36
Mergers Can Yield Superdisks at Low-z

• At zlt1, the T104K IGM assumed above isnt
  around instead, RGs emerge into Intracluster
  Medium (ICM) with Tgt107K
• We have just considered this situation in the
  context of very asymmetric RGs with SDs
  (Gopal-Krishna Wiita 2008, New Astr.)
• Of 22 SD-RGs, 16 are substantially asymmetric,
  with central galaxies well offset from center of
  SD, sometimes even inside one lobe

37
Asymmetric SD RGs
(DRAGN atlas, P. Leahy)
(Saripalli et al. 2002)
38
Hot-Spot Asymmetries

• 13 of those 16 have hot-spots more symmetrically
  placed to the SD midplane rather than the host
  galaxy
• Shown is Number of Sources against ratio of
  hotspot distances to SD center (solid) and host
  galaxy (dashed)

39
Mergers of Ellipticals

• Can trigger jet launching
• If smaller galaxy is gt0.1 mass of larger then the
  gas attached to that galaxy is likely to deposit
  its (orbital) angular momentum into the host
  galaxys halo
• This can cause the halo to expand to SD
  dimensions
• The host can get a kick from the merger which,
  along with its random motion can produce
  asymmetries over 10-100Myr

40
Conclusions

• Part I Modest opening angles (5º 10º) of AGN
  jets can resolve the jet Lorenz factor paradox of
  TeV blazars
• 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.
• Conical jets also produce larger central angles
  to line of sight and thus smaller deprojected
  sizes
• Part II Wide strip-like emission gaps are seen
  in some Radio Galaxies and cant be understood as
  arising from backflow onto normal ISM
• _ Dynamical interaction between thermal (wind)
  and non-thermal (jet) outflows resulting from the
  AGN activity, can produce fat pancake or
  superdisk shaped regions at high redshifts.
• Mergers between elliptical galaxies can also
  produce superdisks this is more likely for low-z
  RGs.
• The observed asymmetries in lobe/core distances
  come out of these scenarios

41
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
42
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

43
Inferred Lorentz Factors
?inf vs. ? for ?100, 50 and 10 for ?5o P(?)
and lt ?infgt
44
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

45
Orientation Based Unification Picture
46
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

47
Expectation Values of ? for Conical Jets

• ? (actual) ?(deg) lt ?gt (likely to be
• 10 1 10 inferred from data 5 9.2
  10 7.8
• 50 1 46 5 25 10 17
• 100 1 78 5 34 10 22

48
Conical Jets How Well is ? Recovered?
49
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.
50
Expectation values for ?p2 (left)p3(right)q0
(top)q1(middle)q2(bottom)In each panel?10o
(top) ?5o (middle) ?1o(bottom)
51
Effective Speeds (left) and Doppler Factors
(right)for p2 ?020 (top), ?050 (middle)
?0100(bottom)
52
Modeling 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
53
Key Blazar Conclusions

• Blazars are dominated by emission from jets
• Variations within the jet are Doppler boosted and
  greatly amplified
• TeV blazars almost certainly require very high
  Lorentz factors but often show slow VLBI knots
• Allowing for conical jets means ultrarelativistic
  jet speeds can produce slow apparent speeds, even
  for fast spine--slow sheath structures
• They also produce larger central angles to line
  of sight and thus smaller deprojected sizes