jet variability under the microscope

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

http://www.aoc.nrao.edu/~fowen/M87_layout.html

http://www.aoc.nrao.edu/

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




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


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



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



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.



in jet during flare.

Velocity Structure of HST-1Velocity Structure of HST-1



in jet during flare. Fastest components

moved at 4.3 c



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



sign ~2005.5 Secondary flare in 2006 Switch in fpy, in both X-

ray & optical, corresponded with switch in direction of “looping”



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




lessNot resolved




lessNot resolved

Harris et al. 2009



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!


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


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


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.