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Jet Variability Under the Microscope
Jet Variability Under the Microscope
Eric Perlman - Florida Institute of Technology
Collaborators:Mihai Cara, Sayali Avachat, Raymond Simons, Matt Bourque
(FIT)Markos Georganopoulos (UMBC)
Cade Adams (Georgia and Clemson)Daniel E. Harris (Harvard/Smithsonian CfA)
Eric Clausen-Brown, Maxim Lyutikov (Purdue)Juan P. Madrid (Swinburne)
Lukasz Stawarz (Jagiellonian University and JAXA)C. C. “Teddy” Cheung (NRL)
Bill Sparks, John Biretta (STScI) The HESS, VERITAS and MAGIC TeV Observatory teams
Eric Perlman - Florida Institute of Technology
Collaborators:Mihai Cara, Sayali Avachat, Raymond Simons, Matt Bourque
(FIT)Markos Georganopoulos (UMBC)
Cade Adams (Georgia and Clemson)Daniel E. Harris (Harvard/Smithsonian CfA)
Eric Clausen-Brown, Maxim Lyutikov (Purdue)Juan P. Madrid (Swinburne)
Lukasz Stawarz (Jagiellonian University and JAXA)C. C. “Teddy” Cheung (NRL)
Bill Sparks, John Biretta (STScI) The HESS, VERITAS and MAGIC TeV Observatory teams
OutlineOutline Introduction: What do we know about jets?
Basic PropertiesRadiation MechanismsRelativistic EffectsVariability (and why it is important)
Putting Variability Under the MicroscopeM87: the first RESOLVED variable region!Multiwavelength lightcurves The nucleus & HST-1: two variability modesSpectral and polarimetric variations
ConclusionsTimescales and Particle AccelerationJet Structure and other physics
Introduction: What do we know about jets?Basic PropertiesRadiation MechanismsRelativistic EffectsVariability (and why it is important)
Putting Variability Under the MicroscopeM87: the first RESOLVED variable region!Multiwavelength lightcurves The nucleus & HST-1: two variability modesSpectral and polarimetric variations
ConclusionsTimescales and Particle AccelerationJet Structure and other physics
Stellar Mass NS/BH Binaries: Double star system, neutron star or black hole + main sequence or giant star. Matter accreting from normal star. Flow speeds 0.25-0.95 c.Centers of Galaxies: Matter accreting from interstellar medium onto supermassive black hole. Flow speeds 0.9-0.99c+. Part of “active galactic nucleus” phenomenon.Gamma-Ray Burst: Death throes of a very massive star (>30-50 solar masses); asymmetric explosion drives a relativistic outflow. Flow speeds >0.99c but probably very mass loaded.
Stellar Mass NS/BH Binaries: Double star system, neutron star or black hole + main sequence or giant star. Matter accreting from normal star. Flow speeds 0.25-0.95 c.Centers of Galaxies: Matter accreting from interstellar medium onto supermassive black hole. Flow speeds 0.9-0.99c+. Part of “active galactic nucleus” phenomenon.Gamma-Ray Burst: Death throes of a very massive star (>30-50 solar masses); asymmetric explosion drives a relativistic outflow. Flow speeds >0.99c but probably very mass loaded.
Examples of Relativistic Jets
The Unified AGN ModelThe Unified AGN Model
Supermassive (107-1010 M) black hole. M = 108MRG~2 AU
Accretion disk – thermal UV/X-ray lines from highly ionized atoms (R~3-100 RG)
High velocity (>1000 km/s) broad-line clouds (R~103-4 RG)
Dusty torus, which orbits in/near plane of accretion disk (R~104-5
RG)
Lower velocity (few hundred km/s) narrow-line clouds (R~105-7
RG)
Relativistic jet (Γ ~ 5-30) – may be collimated on ~50 RG
scales, can extend for many kiloparsecs
Observed properties vary with viewing angle
Supermassive (107-1010 M) black hole. M = 108MRG~2 AU
Accretion disk – thermal UV/X-ray lines from highly ionized atoms (R~3-100 RG)
High velocity (>1000 km/s) broad-line clouds (R~103-4 RG)
Dusty torus, which orbits in/near plane of accretion disk (R~104-5
RG)
Lower velocity (few hundred km/s) narrow-line clouds (R~105-7
RG)
Relativistic jet (Γ ~ 5-30) – may be collimated on ~50 RG
scales, can extend for many kiloparsecs
Observed properties vary with viewing angle
Urry & Padovani 1995
Radiation Processes in Jets
Radiation from jets emitted by two processes: synchrotron and inverse-Compton.
For inverse-Compton, the ‘scattered’ photon can be either from within the jet (often called synchrotron self-Compton) or some external source (e.g, the cosmic microwave background or emission line regions).
B
Synchrotron radiation emitted by relativistic particles in magnetic field
e-
Inverse-Compton – scattering interaction between photon and a relativistic particle that results in a higher-energy photon.
Jet “beam”
Biretta et al. 1999
Superluminal motion in quasar jets: an optical illusion
Superluminal motion in quasar jets: an optical illusion
Speed of knot(close to thespeed of light)
Positions of knot when two pictures were taken, one year apart.
Small angle: the knot’s motion is mostly along the line of sight.
Light paths:
B
A
Light path B is shorter than path A. If the knot’s speed is close to the speed of light, B is almost a light-year shorter than A. This “head start” makes the light arrive sooner than expected, giving the appearance that the knot is moving faster than light. (Nothing actually needs to move that fast for the knot to appear to move that fast.)
Not drawn to scale!
Relativistic EffectsRelativistic Effects
Time dilation: appδBlueshifting : νapp= δν“Superluminal” Motion: vapp= v sin θβcosθ
Time dilation: appδBlueshifting : νapp= δν“Superluminal” Motion: vapp= v sin θβcosθ
Curves for Γ = 3,5,8,12
θ
v=βcΓ=(1-β2)-½
δ=[Γ(1β cos θ)]-1
Geometrical distortion: dΩ=dΩ’/δ2
Beaming for Synchrotron and SSC: Lobs=δ4 Lem
For EC: Lobs=δ6Lem/γ2
Variability in JetsVariability in Jets
Jet emission is highly variable. Usually in blazars -- jet seen at very
small angles (our line of sight is nearly along beaming axis)
Relativistic speed confirmed by apparent
Superluminal motion
Typical example: 3C 454.3 (at right)Variable on all timescales
Slow variability & Large flares
Also intraday variabilityBroadband spectrum can
change drastically. However… in most sources the
varying region is unresolved.
Physics not well constrained.
10
Variability and Source Size
Variability and Source Size
Variability timescale implies maximum emission region size scale
)1(
)(105.2)( var
15
z
daytcmr D
b
δ
rb=r´b
Spherical blob in comoving frame
Γ
Doppler Factor1)]1([ Γ δD
Source size from direct observations:
arccos
pcmascm
ddr A
Ab )()10
(227
Source size from temporal variability:
11
Variability and Source Location
Variability and Source Location
Variability timescale implies engine size scale, comoving size scale factor Γ larger and emission location Γ2 larger than values inferred for stationary region
Rapid variability by energizing regions within the Doppler cone
x
Γ
1/Γ
)1(
2 var2 z
ct
c
GMRS
Chandra and HST
The Best-Studied Jet: M87The Best-Studied Jet: M87
Images at right show the M87 jet at radio (bottom) and then in optical and UV (wavelength decreasing as you go up)
Jet is knottier at higher photon energies
Narrowing trend continues all the way up through X-rays
Images at right show the M87 jet at radio (bottom) and then in optical and UV (wavelength decreasing as you go up)
Jet is knottier at higher photon energies
Narrowing trend continues all the way up through X-rays
2 cm
340 nm
230 nm
140 nm
Sparks, Biretta & Macchetto 1996
The M87 Jet (Marshall et al. 2002)
Optical Polarization of the M87 JetOptical Polarization of the M87 Jet
Jet can be very highly polarized -- up to 60%+ in spots Natural for synchrotron emission Position angle of polarization (pictured vectors, rotated 90 degrees to
show B)direction of magnetic field in emitting region
High & low polarization regions correlated with the location of knots Often different in different bands Can give clues to some very interesting physics…
Jet can be very highly polarized -- up to 60%+ in spots Natural for synchrotron emission Position angle of polarization (pictured vectors, rotated 90 degrees to
show B)direction of magnetic field in emitting region
High & low polarization regions correlated with the location of knots Often different in different bands Can give clues to some very interesting physics…
Perlman et al. 1999
Perlman et al. 1999
Perlman & Wilson 2005
Madrid 2009
Variability in the M87 Jet?Variability in the M87 Jet? Yes – dramatic variability!
Giant flare in HST-1 Seen in all bands
Smaller variability in other regions Only opt/X-ray jet where varying
region is isolatedMUCH BETTER CONSTRAINTS ON
PHYSICS Superluminal motion as well
6c in HST-1, decreasing to c at ~12” out
Variability of opt spectrum & polarization will give clues to physics:
Compression/shock/expansion
Acceleration/cooling timescales
Tracing motion of components
Yes – dramatic variability! Giant flare in HST-1
Seen in all bands Smaller variability in other regions
Only opt/X-ray jet where varying region is isolatedMUCH BETTER CONSTRAINTS ON
PHYSICS Superluminal motion as well
6c in HST-1, decreasing to c at ~12” out
Variability of opt spectrum & polarization will give clues to physics:
Compression/shock/expansion
Acceleration/cooling timescales
Tracing motion of components
Harris et al. 2009
A Tale of two componentsA Tale of two components
Two different regions, two different variability behaviors:
HST-1: Giant FlareFlux increased by >100XDominant timescale ~1 year
Nucleus: Numerous smaller flaresLargest variation is a factor 4Timescales ~few months or
lessNot resolved
Two different regions, two different variability behaviors:
HST-1: Giant FlareFlux increased by >100XDominant timescale ~1 year
Nucleus: Numerous smaller flaresLargest variation is a factor 4Timescales ~few months or
lessNot resolved
Optical Lightcurves Optical Lightcurves
Optical and X-ray Variability Closely track one another
Optical and X-ray Variability Closely track one another
Madrid 2009
Where are the Flaring Regions?Where are the Flaring Regions?
Nucleus: innermost few parsecs or smallerVery smooth structure, no obvious “flaring” or motions
HST-1: 0.86” (62 parsecs projected) from nucleusKnotty structure, superluminal motions
Nucleus: innermost few parsecs or smallerVery smooth structure, no obvious “flaring” or motions
HST-1: 0.86” (62 parsecs projected) from nucleusKnotty structure, superluminal motions
Analyzing the lightcurve
Analyzing the lightcurve
Can look for many things, e.g., Does one band flare first?
If so, is there a consistent lag?
Does one band increase faster or slower?
However, the lightcurve contains interesting hints:
X-rays increase, decrease more rapidly to main peakX-rays also contain more month-timescale variability
Can look for many things, e.g., Does one band flare first?
If so, is there a consistent lag?
Does one band increase faster or slower?
However, the lightcurve contains interesting hints:
X-rays increase, decrease more rapidly to main peakX-rays also contain more month-timescale variability
Harris et al. 2009
Analyzing the lightcurve
Analyzing the lightcurve
Quantifying properties in the X-rays.
Use first derivative – as fractional change per year
This is 1/region size for light- travel timeConstrain varying region to <45 light-days from largest derivative.
Quantifying properties in the X-rays.
Use first derivative – as fractional change per year
This is 1/region size for light- travel timeConstrain varying region to <45 light-days from largest derivative.
Harris et al. 2009
Quasi-periodic behavior in HST-1Quasi-periodic behavior in HST-1 Found during the
increasing phase of the flare
No single period, but an increase and decrease was observed every 6-10 months
“Impulsive” acceleration?
Found during the increasing phase of the flare
No single period, but an increase and decrease was observed every 6-10 months
“Impulsive” acceleration?
Harris et al. 2009
Close-up on the flareClose-up on the flare
Optical, X-ray behavior similar
Behavior not monolithic First derivative changes
sign ~2005.5 Secondary flare in 2006
Optical, X-ray behavior similar
Behavior not monolithic First derivative changes
sign ~2005.5 Secondary flare in 2006
Harris et al. 2009
Velocity Structure of HST-1Velocity Structure of HST-1
Four moving components, motions tracked for over three years
One knot – C – split in 2005, coinciding with main flare. Also location of flux peakBirth of a new component
in jet during flare.
Four moving components, motions tracked for over three years
One knot – C – split in 2005, coinciding with main flare. Also location of flux peakBirth of a new component
in jet during flare.
Velocity Structure of HST-1Velocity Structure of HST-1
Four moving components, motions tracked for over three years
One knot – C – split in 2005, coinciding with main flare. Also location of flux peakBirth of a new component
in jet during flare. Fastest components
moved at 4.3 c
Four moving components, motions tracked for over three years
One knot – C – split in 2005, coinciding with main flare. Also location of flux peakBirth of a new component
in jet during flare. Fastest components
moved at 4.3 c
Gamma-ray flaringGamma-ray flaring
Abramowski et al. 2012
Polarization, Spectral
Variability in HST-1
Polarization, Spectral
Variability in HST-1 Strong correlation
between flux, polarization
Very little change in PA Only one region involved
in variability -- fully resolved
Strong correlation between flux, polarization
Very little change in PA Only one region involved
in variability -- fully resolved
Perlman et al. 2011
Strong correlation of polarization with flux
magnetic field involved in particle accel
Complicated relationship between flux and spectral index
Epochs 4-9 – “hard lagging”
Epochs 13-17 – “soft lagging”
The latter is more common; implies shorter acceleration timescales than cooling timescales.
The latter normally requires the opposite relationship … but X-ray is also synchrotron Possibility: most energy losses are
actually in inverse-Comptonizing external photons near Klein-Nishina limit.
Strong correlation of polarization with flux
magnetic field involved in particle accel
Complicated relationship between flux and spectral index
Epochs 4-9 – “hard lagging”
Epochs 13-17 – “soft lagging”
The latter is more common; implies shorter acceleration timescales than cooling timescales.
The latter normally requires the opposite relationship … but X-ray is also synchrotron Possibility: most energy losses are
actually in inverse-Comptonizing external photons near Klein-Nishina limit.
Polarization & Spectral Behavior
Polarization & Spectral Behavior
Perlman et al. 2011
Close-up on the flareClose-up on the flare
Optical, X-ray behavior similar
Behavior not monolithic First derivative changes
sign ~2005.5 Secondary flare in 2006 Switch in fpy, in both X-
ray & optical, corresponded with switch in direction of “looping”
Optical, X-ray behavior similar
Behavior not monolithic First derivative changes
sign ~2005.5 Secondary flare in 2006 Switch in fpy, in both X-
ray & optical, corresponded with switch in direction of “looping”
Harris et al. 2009
ShocksShocks
Compression ratio k
Behavior of Polarization in shockBehavior of Polarization in shock
If shock is localized, planar and perpendicular to jet (as pictured in last plot), MHD predicts a polarization
Our data require a jet bulk Lorentz factor of ~4-5 – consistent with speeds observed in VLBI observations.
Beaming factor can range over a wider range of values
If shock is localized, planar and perpendicular to jet (as pictured in last plot), MHD predicts a polarization
Our data require a jet bulk Lorentz factor of ~4-5 – consistent with speeds observed in VLBI observations.
Beaming factor can range over a wider range of values
P =3+3α5+3α
δ 2 −k2( )sin
2θob
2−δ 2 −k2( )sin
2θob
Perlman et al. 2011
A Tale of two componentsA Tale of two components
Two different regions, two different variability behaviors:
HST-1: Giant FlareFlux increased by >100XDominant timescale ~1 year
Nucleus: Numerous smaller flaresLargest variation is a factor 4Timescales ~few months or
lessNot resolved
Two different regions, two different variability behaviors:
HST-1: Giant FlareFlux increased by >100XDominant timescale ~1 year
Nucleus: Numerous smaller flaresLargest variation is a factor 4Timescales ~few months or
lessNot resolved
Harris et al. 2009
Analyzing the lightcurve
Analyzing the lightcurve
Harris et al. 2009
Larger values of fpy than HST-1 Largest fpy~20 => region
is smaller than ~20 light-days.
Goes along with faster variability in general
Larger values of fpy than HST-1 Largest fpy~20 => region
is smaller than ~20 light-days.
Goes along with faster variability in general
Patterns in the nuclear variability?
Patterns in the nuclear variability?
None seen But … are we
sampling often enough to see them?
Maybe not, given small region size.
None seen But … are we
sampling often enough to see them?
Maybe not, given small region size.
Harris et al. 2009
Gamma-ray flaring
Abramowski et al. 2012
Faster Variability Complex polarization
behavior No obvious correlation
between flux, polarization … unless you look more
carefully No evidence for spectral
index variability
Faster Variability Complex polarization
behavior No obvious correlation
between flux, polarization … unless you look more
carefully No evidence for spectral
index variability
Polarization and Spectral Variability in M87 Jet: Nucleus
Polarization and Spectral Variability in M87 Jet: Nucleus
Perlman et al. 2011
Polarization behavior Polarization behavior
“Loop” in I-P plane – very different from HST-1!
No correlation with EVPA (varies all over the place) or spectral index (near constant)
“Loop” in I-P plane – very different from HST-1!
No correlation with EVPA (varies all over the place) or spectral index (near constant)
Perlman et al. 2011
Dynamics and helical jets
Dynamics and helical jets
Helical jets introduce additional complexity into your jet model
Can introduce a helical distortion
Or velocity variations
Helical jets introduce additional complexity into your jet model
Can introduce a helical distortion
Or velocity variations
I ∝δd2+αk−2B
r−2 2+ 3k2ξ2 − −k2
( )⎡⎣
⎤⎦sin2θ
ob{ }
P =3+3α5+3α
δ 2 −k2( )−3k2ξ2⎡
⎣⎤⎦sin2θ
ob
2−δ 2 −k2( )sin
2θob
+3k2ξ2 sin2θob
I ∝K cos2 ψ +cos2 θ −3 cos θ cos ψ( )2+⎛
⎝⎞⎠
P =3+3α5+3α
−2 +3cos2 ψ( )sin2 θ
5−cos2 θ +cos2 ψ −3cos2 θ cos2 ψ
Perlman et al. 2011
Not shown:Mag. Pitch angle ψShock compression(ratio k)
Nuclear X-ray also synchrotron but more complicated
No correlation with EVPA (varies all over the place) or spectral index (near constant)
Consistent with either: a helical distortion Shock compression in a helical
jet
We favor the latter because of the morphology, known helical morphology of nuclear B field.
Neither one is 100% satisfactory for reproducing EVPA behavior.
Nuclear X-ray also synchrotron but more complicated
No correlation with EVPA (varies all over the place) or spectral index (near constant)
Consistent with either: a helical distortion Shock compression in a helical
jet
We favor the latter because of the morphology, known helical morphology of nuclear B field.
Neither one is 100% satisfactory for reproducing EVPA behavior.
Perlman et al. 2011
Marshall et al. 2010
ConclusionsConclusions
Variability can reveal unique information about jets
We have for the first time isolated a variable region in a jet
HST-1’s Variability was similar to that observed in blazarsX-ray variability was fastest … but spectral behavior complex
Quasi-periodic acceleration during increasing phase
Complex flare shape
Polarization characteristics consistent with a simple shock
Nucleus was also variableFaster variability timescale, smaller region size
No pattern to variability (but are we observing often enough?)
“Loop” in (I,P) plane suggests helical morphology to varying region.
Variability can reveal unique information about jets
We have for the first time isolated a variable region in a jet
HST-1’s Variability was similar to that observed in blazarsX-ray variability was fastest … but spectral behavior complex
Quasi-periodic acceleration during increasing phase
Complex flare shape
Polarization characteristics consistent with a simple shock
Nucleus was also variableFaster variability timescale, smaller region size
No pattern to variability (but are we observing often enough?)
“Loop” in (I,P) plane suggests helical morphology to varying region.
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