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

Paul J. Wiita

Georgia State University, USA

Peking University, 9 May 2008

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

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)

Microvariability & Intraday Variability tooRomero, Cellone & Combi (2000); Quirrenbach et al (2000)

Blazar Spectral Energy Distributions

• Radio/IR/optical is dominated by synchrotron emission, with e ~ 103-105

• X-ray may be synchrotron if e > 107; or Inverse Compton, where

e ~ 102 is OK• Gamma-rays likely

to be IC and to get TeV photons e ~ 107 might be neededBL Lac: Boettcher & Reimer 2004, ApJ, 609, 576

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 bySynchrotron self-compton process

3C 130 & 3C 449: FR I’sz=0.109; z=0.017

Canonical FR II: Cygnus A (z=0.056)

Quasar: 3C 175 (z=0.770) Only 1 jet seen; core relatively more prominent than in RG

VLBA of

3C279: Apparent

Superluminal Motion

with Vapp=3.5c: really V=0.997c at viewing angle

of 2 degrees(z= 0.536)

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

Jet of Quasar 3C 273 in IR, radio + optical& X-ray (Uchiyama et al. 2006, ApJ, 648, 910)

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)

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)

Doppler Factor from -ray Variability

• Several blazars show obs < 1 hr for GeV -rays

• If stationary source: size < c obs

• For corresponding photon densities: +XSSCe++e-

• High cross-section means -rays should not escape• If moving relativistically, then: size < 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?

Direct Estimates from VLBI

• For normal blazars (Piner et al. 2006, ApJ, 640, 196)

• 0235+164: C1: app=25.6±7.0C2: app= 8.9±1.3C3: app= 7.9±4.7

• 0827+243: C2: app=25.6±4.4 Most are C3: app=19.2±3.7 quite C4: app=12.3±7.4 superluminalC5: app=12.1±8.1C6: app= 3.2±3.7

• 1406-076: C1: app=15.6±13.2C2: app=28.2±6.6C3: app=22.5±8.9C4: app=15.8±2.0

VLBI Knot Speeds for TeV Blazars (Piner & Edwards 2004, ApJ, 600, 115)

Mrk 421: C4: app=0.04±0.06 C5: app=0.20±0.05 C6: app=0.18±0.05 C7: app=0.12±0.06

Mrk 501: C1: app=0.05±0.18 C2: app=0.54±0.14 C3: app=0.26±0.11

C4: app=-0.02±0.06 1ES 1959+650: C1: app=-0.11±0.79

C2: app=-0.21±0.61PKS2155-304: C1: app=4.37±2.881ES 2344+514: C1: app=1.15±0.46

C2: app=0.46±0.43 C3: app=-0.19±0.40

Most are subluminal or only modestly superluminal

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)

How to have Small app in TeV Blazars?

1. Dramatic deceleration between sub-pc (gamma-ray) and pc (radio) scales (Georganopoulos & Kazanas 2003, ApJ, 594, L27)Energetics are difficult; where does it go?

2. Very close alignment of the jet: < 0.1o if =100 (statistically unlikely)

3. Fast spine ( > 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, A&A, 432, 401)Distinctly possible, but not necessary

Jets Start Out Wide

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

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.

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]

ddSS em

n

obsapp

1

5.1 counts; source integral where

sin

:angle viewingofy Probabilit

qdSSdSSN

dAdp

emqememem

q

(Fomalont et al. 1991)

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: high probability of low app

• Predict transversely resolved jets show different app

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)<app> = 6 c (=5o)

• So high and low app for TeV blazars can be reconciled

• Small fraction of blazars must show app > 50• Both dense VLBI monitoring and unbiased

interpretation of the data needed to check

Inferred Values for for Conical Jets

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 < 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

Conical Spine-Sheath Jets

• We also consider jets where Lorentz factor varies (r) = 0exp(-2rq/)

• q=0 for constant , q=1 for mild transverse gradient; q=2 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 <> ~ /3 when the jets become ultrarelativistic (0 > 30), particularly if >5o

Effective Speeds (left) and Doppler

Factors (right)for p=3

& 0=20 (top), 0=50 (middle) 0=100(bottom)

Results for Spine-Sheath Conical Jets

• Decline of eff with is faster for knots with higher .• For well collimated jets ( < 0.5o) eff for uniform is

typically 1.5-2 times more than for q=1 and 2-4 times higher for q=2.

• 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.

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

3C33 4C14.273C192

3C381 3C401

Ref: DRAGN Atlas (P. Leahy)

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 (vw>103 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 w > ~ 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)

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 bubble’s 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

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)

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

Mergers Can Yield Superdisks at Low-z

• At z<1, the T~104K IGM assumed above isn’t around: instead, RGs emerge into Intracluster Medium (ICM) with T>107K

• 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

Asymmetric SD RGs

(Saripalli et al. 2002)

(DRAGN atlas, P. Leahy)

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)

Mergers of Ellipticals

• Can trigger jet launching• If smaller galaxy is >0.1 mass of larger then

the gas attached to that galaxy is likely to deposit its (orbital) angular momentum into the host galaxy’s 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

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 >30 – 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 can’t 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

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:

TB ,obs S

( obs)2

min TB ,obs

Tmax

1/(3 )

2

app 2min 1

2min

tan 2app

2app 2

min 1

S = change in flux over time obs

Tmax= 3x1010K app from VLBI knot speed is spectral index

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 < 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

Inferred Lorentz Factors

inf vs. for =100, 50 and 10 for =5o

P() and < inf>

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

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:

2

2

12

337

31

605

.10

102.3

1103 where,1

104

3103)(

cmdynG

BP

cmznkTnP

erg

E

PMpcR

lobe

bIGMbmIGM

w

exteq

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