Transcript Blazar Variability & the Radio Galaxy/Cosmology Interface Paul J. Wiita

Blazar Variability &
the Radio Galaxy/Cosmology
Interface
Paul J. Wiita
Georgia State University, Atlanta, USA
Winter School on Black Hole Astrophysics
APCTP, Pohang, January 17-20, 2006
OUTLINE
• Blazar Basics
• Accretion Disks in AGN
Recent Evidence for their Presence
Basic Timescales
A Few Important Instabilities
Spiral Shocks
• Aspects of Jet Produced Variations
Coherent Emission
Slow Knot Speeds vs. Ultrarelativistic Jets
• Radio Galaxies Trigger Extensive Star
Formation
Spread Magnetic Fields and Metals into IGM
Blazar Characteristics
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Rapid variability at all wavelengths
Radio-loud AGN
BL Lacs show extremely weak emission lines
Optical polarization  synchrotron domination
Double humped SEDs: RBL vs XBL?
Core dominated quasars (optically violently variable
and high polarization quasars) 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)
Long-term Blazar Lightcurve
(Optical monitoring at Colgate U.- Balonek)
Long-term Radio Monitoring
Aller & Aller, U Michigan
Microvariability & Intraday Variability too!
Romero, Cellone & Combi; Quirrenbach et al (2000)
Blazar SED: 3C 279 (Moderski et al. 2003)
Left hump: peak in
mm or FIR, from
synchrotron
Right hump: peak
in gamma-rays,
from Inverse
Compton off seed
photons:
From disk, from jet
itself or from broad
line clouds
Orientation
Based
Unification
Picture
Evidence for Accretion Disks in Blazars
Big blue bump in AO 0235+164
(Raiteri et al. astro-ph/0503312)
More New Evidence for Accretion Disks
Optically thick: hidden
Balmer edge now
claimed to be seen in
several quasars.
• Ton 202 polarized flux with face-on Kerr disk model
fitted to it (Kishimoto et al. 2004)
Why Quasi-Keplerian
and Disk-like?
Quasi-black body fits to disk
spectra
Broad K lines for NLS1s
Variable Double peaked lines
[here H lines:
Strateva et al,
AJ (2003)]
Jets probably require disks
as launching pads
Accretion Flow Geometries
• Quasi-accepted picture:
L/LE determines disk
thickness and extent
toward BH:
very high L/LE 
geometrically &
optically thick
intermediate L/LE 
cold optically thick,
geometrically thin
low L/LE  optically thin
hot flow interior to
some transition
radius.
Key Timescales for Accretion
• With R = r/3RS, a quasi-Keplerian flow, h the
thickness and  the viscosity parameter, the fastest
expected direct variations are on dynamical times of
hours for SMBHs (e.g. Czerny 2004).
tdyn (s)  10 4 R 3 / 2 M 8
M8=MBH/108M

r 
tradial  tdyn  
h 
Radial sound
transmission time
tthermal  tdyn /  10  R M 8
5
2
1 3 / 2
0.1
2
r 
7  r  1 3 / 2
tvisc  t thermal   10    0.1R M 8
h 
10h 
Thermal and viscous
timescales
For thin disks, h0.1r
How fast can the cold disk be removed?
• Transition radius changes, either by evaporation or
substantial outflow
• Either way, disk T must go up to about virial T and
enough energy to do this must be stored
• For an -disk, tevap=tvisc , but more generally,
t evap 
E

 Mc 2
;
kTvir
E r 
;
mH
2
r

4RS
 r 2 
t evap (yr)  1000
 m0.1 M 8
100RS 
For AGN > 103yr, so if disk appears to disappear quickly,
probably from suppression of energy dissipation (I.e., MRI

instability
turned off, perhaps by some ordered B field.)
Longest Timescale?
• Governed by rate at which outer disk is fed
• Probably the rate at which gas is injected into the
core of a galaxy (bars within bars to drive inward?)
• Dominated by galactic mergers (probably major) and
timescales > 107 years; can exceed 108 yr
Does harassment (mere passage) work?
• Does the AGN self-regulate, with its energy injection
halting the inflow of gas? (Hopkins et al. 2005a,b,c)
• Most likely depends on whether quasi-isotropic winds
& star-burst supernovae OR
narrow jets carry off most kinetic energy from AGN.
DISK INSTABILITIES
•  many of them. How many are important,
especially for blazars?
• Radiation pressure instability
• Magneto-rotational instabilities
• Flares from Coronae
• Internal oscillatory modes (diskoseismology)
• Avalanches or Self-Organized Criticality
• Spiral shocks induced by companions or
interlopers
• Key point: even if blazar emission dominated
by jets, disk instabilities may feed into jets
Radiation Pressure Instability
Long known that -disks are unstable if radiation
pressure dominated (Shakura & Sunyaev 1976)
• AGN models should be Prad dominated over a wide
range of accretion rates and radii
• Computed variations are on tvisc(~100RS)
(Janiuk et al. 2000; Teresi et al 2004)
• May have been seen in the microquasar
GRS 1915+105 (over 100’s of sec).
• Scaled to AGN masses: significant outbursts, but
over years to decades all the way from X-rays
through IR.
SPH simulation of Shakura-Sunyaev instability
(Teresi, Molteni & Toscano, MNRAS 2004)
MRI Induced Variations
• Magneto-Rotational Instabilities (e.g. Balbus & Hawley
ApJ, 1991) are commonly agreed to be present
• Probably produce effective disk  ~ 0.01-0.10
Total (solid), magnetic stress (dashed) and fluid (dotted) viscosities at a
disk center (Armitage 1998, ApJL)
 Also produce changes in dissipation and accretion rate
 Some disk clumping, but not destruction (profile changes?)
Turbulence in a Magnetized Disk
Distant views of inner disk @
inclinations of 55 and 80o
•Integrated flux for inclinations of (top to
bottom) 1, 20, 40, 80O for a “hot” simulation
using Zeus and pseudo-Newtonian potential
(Armitage & Reynolds, MNRAS 2003)
Significant fluctuations develop on a few
rotational timescales (hours for 108M).
Spiral Shocks in Disks
• Perturbation by smaller BH can drive spiral shocks
• Significant flux variations ensue on orbital timescales
of the perturber (Chakrabarti & Wiita, ApJ, 1993)
Perturbers w/ 0.1 and 0.001 MBH
Spiral Shocks and Line Variations
• This type of shock provides the best fits to changes in
double hump line profiles seen in about 10% of AGN
(Chakrabarti & Wiita 1994)
Model vs. data for 3C 390.3 H broad lines in 1976 & 1980. Expected variations.
Flares and Coronae
• Plenty of debate over the relative contribution of disk
coronal flares to X-ray (predominantly) and other
band (secondarily) emission and variability.
• Clearly an important piece of the Seyfert variability
but probably usually a small piece of blazar emission.
• Total energy releasable from low density coronal
flares is probably too small unless “avalanche” or
self-organized criticality process is triggered, perhaps
propagating inward within a disk (Mineshige et al. 1994;
Yang et al. 2000); easily produces “correct” PSD.
• But flares can provide low level X-ray variations
visible when other activity is minimal; maybe produce
a bit of optical variability too.
Jet Variations in Blazars
• This is the dominant idea, but it still is not well
modeled.
SOMETHING changes: outflow rate, velocity, Bfield structure. Waves can steepen into shocks.
• Relativistic shocks propagating down jets can explain
much of the gross radio through optical variations via
boosted synchrotron emission.
Accretion disk fluctuations could drive them.
• Turbulence, instabilities, magnetic inhomogeneities
can probably explain the bulk of rapid variations.
• Inverse Compton models:
SSC, External Compton, Mirror Model ,
Decelerating Jets, can explain particular high energy
variations wrt low energy ones, though no model
seems able to cover all observations (multiple IC
photon sources?)
Shock-in-jet model: new components
(Aller, Aller & Hughes 1991)
Turbulence in a Jet  Rapid Variations
(Marscher & Travis 1996)
Synchrotron vs. Coherent Emission
• Do any compact radio sources show intrinsic
TB>1011K?
(More realistic self-absorbed source
equipartition inverse Compton catastrophe limit ~3x1010; Singal &
Gopal Krishna 1985; Readhead 1994)
• IDV at cm  big Lorentz factor is necessary (if
intrinsic) as simple measurements often give TB~1021K
• To avoid it, a size ~ larger is allowed if plasma
approaches us with >> 1. So solid angle up ~2.
• TB intrinsic boosted by  wrt source frame so total help
of 3 available: BUT still need ~103 for enough help
• Such huge ’s prevent too many X-rays, but at the cost
of low synchrotron radiative efficiencies and thus
demand very high jet energy fluxes (Begelman et al. 1994)
But what really produces radio IDV?
• It seems most IDV is due to refractive interstellar
scintillation (e.g., Kedziora-Chudczer et al. 2001)
• Then TB,intrinsic~1013K, so 30 solves this problem
• However, space VLBI couldn’t resolve many of these
sources, so TB could be much higher (Kovalev)
• A recent claim that the blazar J1819+3845 shows
diffractive scintillation    10as and
TB,intrinsic>(>)1014K (Macquart & de Bruyn 2005)
• If true, it demands >103 if incoherent synchrotron
emission is the radiation mechanism, and the energy
problem returns
Coherent Radiation Could Solve Problems
• If strong Langmuir turbulence develops in AGN jets
then coherent mechanisms can produce needed huge
TB without requiring extreme Lorentz factors (e.g., Baker
et al. 1988, Krishan & Wiita 1990, Benford 1992).
• One possibility: a pump field can be scattered off a
collective mode of a relativistic electron beam:
Stimulated Raman Scattering; for a density n, area A,
electron Lorentz factor  and bunching fraction 
L  6.3 10 6 nA 2 6 erg s 1
For n~109cm-3, ~103, A~1032 cm2, ~0.5: Lo ~1046 erg/s
BUT: problems with absorption of masers hard to solve
What Type of Coherent Radiation?
• Above models implicitly assumed plasma> cyclotron but some only
required mild population inversions.
• Begelman, Ergun and Rees (2005) have argued that the opposite,
c p is more likely in blazar jets.
• Employ small-scale magnetic mirrors, arising from hydromagnetic
instabilities, shocks or turbulence:
any could provide good
conditions for numerous transient cyclotron masers to form
• Current into mirror inhibits motion of e’s along flux tube.
Maintaining current demands parallel E field and accelerates e’s
Accelerated e’s along converging flux tubes  population inversion
needed for cyclotron maser
Maser pumped by turning kinetic and magnetic energy into jE work
• Synchrotron absorption is serious but high TB maser photons can
escape from a boundary layer giving TB,obs ~ 2x1015K (/10)4 R
Magnetic Mirror & Cyclotron Maser
Current carrying magnetic
mirror on quasi-force-free
flux rope.
Parallel E field maintains
electron flow through mirror.
Parallel potential + magnetic
mirror turns initial electron
distribution into a horseshoe
shaped one (shell in 3-D)
Conditions: mirror ratio R=5,
Current Jzm=30mA/m2
(Jz0=6mA/m2);
Epar=500 keV,
consistent w/ Te=100 keV &
n=100 cm-3
(Begelman et al. 2005)
Modest Superluminal VLBI Speeds
• Only semi-direct probe of extragalactic jet speed: VLBI
knot apparent motions: > 30% subluminal for TeV
blazars (Piner & Edwards 2004; Giroletti et al. 2004)
•  low ~2-4 contradict usual blazar estimates & IDV
1ES 1959+650
@ 15 GHz
3 epochs
Natural (top) vs.
Uniform (bottom)
weighting
(Piner & Edwards
2004) vapp=-0.1
+/- 0.8 c
TeV Blazars want High Doppler factors
• To avoid excessive photon-photon losses variable
TeV emission demands ultrarelativistic jets
(Krawczynski et al. 2002) with 15<  < 100
• Taking into account IR background absorption
strongly implies 45 <  needed in “unreddened”
emission (e.g. Kazanas; Wagner)
• Evidence for TB,intrinsic > 1013K in IDV sources would
also imply  > 30
• While rare (Lister), some vapp > 25c components are
seen (Piner et al.) in EGRET blazars.
• Substantial apparent opening angles are seen for
some transversely resolved knots.
• GRB models usually want  > 100
How to Reconcile Fast Variations with
Slow Knots?
• Spine-sheath type systems: fast core gives variations
via IC and slower outer layer seen in radio (Sol et al.
1989; Laing et al. 1999; Ghisellini et al. 2004)
• Rapidly decelerating jets between sub-pc (-ray) and
pc (VLBI knot) scales (Georganopoulos & Kazanas 2003)
• Viewing angles to within ~1o could work in an
individual case; but  too many slow knots.
• Differential Doppler boosting across jet of finite
opening angle can make the weighted probable vapp
surprisingly small (Gopal-Krishna, Dhurde & Wiita 2004)
• Motions can reflect pattern, not physical, speeds
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
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
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
1/(3 )
min
TB,obs 
 

 Tmax 
 2 app   2 min  1

2min
2 app
tan   2
 app   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
Radio Lobes in the Quasar Era
The dramatic rise in both star formation rate and quasar
densities back to z > 1 motivates investigation of a
possible causal connection.
Radio lobes affected a large fraction of the cosmic web in
which galaxies were forming at 1.5 < z < 3
1.
Most powerful radio galaxies (RGs) are only detectable
for a short fraction of their total lifetimes, so the volumes
filled by old, invisible, lobes are extremely large.
2.
The co-moving density of detected RGs was roughly
1000 times higher at 2 < z < 3 than at z = 0.
3.
These RG lobes need only fill much of the "relevant
universe", the denser portion of the filamentary structures
containing material that is forming galaxies, not the entire
universe; much easier for these ‘rare’ AGN!
RGs Suffer Restricted Visibility
All recent models of RG evolution (Kaiser et al. 1997; Blundell et
al. 1999 -- BRW; Manolakou and Kirk 2002; Barai & Wiita 2006)
agree that radio flux declines with increasing source size
because of adiabatic losses, and with redshift because of
inverse Compton losses off the CMB.
Jets of power Q0, through a declining power-law density, n(r);
has total linear size D; with a0 the core radius (10 kpc), n0
the central density (0.01 cm-3), and  = 1.5.
 r 
n(r )  n0  
 a0 

1
 t Q0  5  
D(t )  3.6a0  5 
 a0 0 
3
Many properties of low frequency radio surveys (3C, 6C, 7C)
can be fit if typical RG lifetimes are long (up to 500 Myr)
and if the jet power distribution goes as Q0-2.6 (BRW).
For RGs at z > 2, most observable lifetimes () are only a few
Myr, even if the jet lifetimes (T) are 100s of Myr
P-D Tracks for Different Models
(Barai & Wiita 2005)
Radio Luminosity Functions
Powerful (FR II) RGs were nearly 1000 times more common
between redshifts of 2 and 3 (Willott et al. 2001).
RLF is flat for about a decade in radio power P151 > 1025.5 W
Hz–1 sr–1 , where FR II sources are most numerous.
With the correction factor (T/ ~ 50) we find at z = 2.5 the
proper density of of powerful RGs living for T is
 ~ 4 x 10–5(1+z)3 T5 Mpc–3 ( log P151)–1
with T5 = T/(5 x 108 yr).
Integrate over the peak of the RLF and take into account
generations of RGs over the 2 Gyr length of the quasar era.
We find (Gopal-Krishna & Wiita 2001) the total proper density of
intrinsically powerful RGs is about:  = 8 x 10 –3 Mpc-3
Radio Luminosity Function
Willott et al. 2001: FR II vary much more than FR I
Models & Data Agree Adequately
(B&W for MK)
16
The Relevant Universe
The web of
baryons traced by
the WHIM at z=0 in
a 100 Mpc3 box
(Cen 2003)
RGs nearly all form
in these filaments
and so most of the
radio lobes will be
confined to them
Radio Lobes Penetrate the Relevant
Universe
During the quasar era, only a small fraction of the baryons had
yet settled into the proto-galactic cosmic web: roughly 10%
of the mass and 3% of the volume (Cen & Ostriker 1999).
Thus RG lobes have a big impact if they pervade only this
filamentary "relevant universe", with volume fraction
 ~ 0.03.
Assuming BRW parameters and integrating over beam power
and z, we find the fraction of the relevant universe filled
during the quasar era by radio lobes:
= 2.1 T518/7 –1 (5/RT)2, is > 0.1
if T > 250 Myr and RT (RG length to width) ~ 5.
Overpressured Lobes Can Trigger
Extensive Star Formation
RG lobes remain significantly supersonic out to D > 1 Mpc.
Their bow shocks will compress cooler clouds within the
IGM (e.g., Rees 1989; GKW01), triggering extensive star
formation.
Much of the "alignment effect" (McCarthy et al. 1987) is thus
explained.
Recent numerical work that includes cooling (Mellema et al.
2002; Fragile et al. 2003, 2004) confirms that RG shocked cloud
fragments become dense enough to yield massive star
clusters (Choi et al. 2006).
Hence, RGs may accelerate the formation of new galaxies
and in some cases produce them where they wouldn’t have
formed in the standard picture.
Jet/Cloud Interaction Simulation
When cooling is included powerful shocks leave behind
dense clumps that can yield major star clusters (Mellema et al.)
Relativistic
Jet/Cloud
3-D
Simulation
Density,
Pressure,
Lorentz
factor
(Choi, Wiita &
Ryu 2006)
Magnetization of the ICM/IGM
We showed (GKW01) that during the quasar era the RGs could
inject average magnetic fields of 10–8 G into the IGM.
Such field strengths within the filaments are supported by
observations (Ryu et al. 1998; Kronberg et al. 2001).
Very different arguments based on total accretion energy
extracted via BHs and on the assumptions of isotropized
magnetized bubbles also lead to similar conclusions that
significant B fields from AGN can fill much of the IGM
(Kronberg et al. 2001; Furlanetto & Loeb 2001) and can have major
impact on star formation (Rawlings & Jarvis 2004; Silk 2005).
Metalization of the IGM
Substantial metal abundances have been found in Lymanbreak galaxies at z > 3 and in damped Ly- clouds.
Gopal-Krishna & Wiita (2003) have shown that the giant RGs
can sweep up significant quantities of metals from host
galaxies.
These can seed the young galaxies, often triggered by the
lobes, with metals.
Subsequent generations of radio activity could further
disperse metals produced in early generations of stars in
those newly formed galaxies.
CONCLUSIONS
• Accretion disks are present and they must
contribute something to optical, UV, and
X-ray variability in all AGN.
• Jet emission may include or be dominated by
coherent processes.
• We can reconcile slow TeV blazar VLBI
motions with high Lorentz factors.
• Radio galaxies can fill much of the universe in
the quasar era: they can trigger substantial
star formation (even new galaxies) & spread
both metals & magnetic fields into the IGM