A Radio and X-ray Study of Particle Acceleration in Centaurus A’s Jet Joanna Goodger University of...

A Radio and X-ray Study of A Radio and X-ray Study of Particle Acceleration in Particle Acceleration in

Centaurus A’s JetCentaurus A’s Jet

Joanna GoodgerJoanna GoodgerUniversity of HertfordshireUniversity of Hertfordshire

SupervisorsSupervisors: Martin Hardcastle and Judith Croston: Martin Hardcastle and Judith Croston

CollaboratorsCollaborators: Kraft, Jordan, Juett, Evans, Forman, : Kraft, Jordan, Juett, Evans, Forman, Sarazin, Sivakoff, Birkinshaw, Worrall, Brassington, Sarazin, Sivakoff, Birkinshaw, Worrall, Brassington,

Harris, Jones, Murray, Raychaudhury, Woodley Harris, Jones, Murray, Raychaudhury, Woodley

Joanna Goodger: Particle Acceleration in Centaurus AJoanna Goodger: Particle Acceleration in Centaurus A08/06/08 Radio Galaxies in the Chandra Era08/06/08 Radio Galaxies in the Chandra Era

OverviewOverview Introduction to

Centaurus A and its jet

Previous X-ray results

Radio results

Current X-ray work

What next… 1` 1.1kpc


Centaurus A’s JetCentaurus A’s Jet

X-ray emission from the knots and diffuse emission indicate regions of current particle acceleration

Coincident radio emission tells us about the structure, dynamics and evolution

Previous work has detected motions in some but not all of the radio knots prompting monitoring in the radio and X-ray

The presence of stationary and moving knots could indicate both local shocks and compressions in the fluid flow. Studying the variability in simultaneous radio and X-ray observations gives us insights into the nature of these knots.

1kpc


”

Hardcastle et al. 2007, ApJ 670, L81

Flat X consistent with shock acceleration coupled with rapid downstream expansion losses while RX > X

suggests that particle acceleration is localized to small sub-regions of the jet.

Particle AccelerationParticle Acceleration

S


” ”Emission is dominated by the extended filamentary emission, consistent with a diffuse acceleration mechanism. (Kraft et al. 2006, ApJ 641, 158)



S



1 kpc


” X-ray spectral steepening not synchrotron losses due to spatial scales being too large; believed to be a progressive loss of efficiency in high energy particle acceleration.

Several Regimes of Particle Acceleration along the jet

S


Particle AccelerationParticle AccelerationWorrall et al. 2008, ApJ 670, L81

A significant difference in inner and outer radial region knots (below, left and right) has prompted further investigation into a spectral index dependence on jet radial position.

Photon Index (+1)

NH (

102

2)

cm-2


Date Band Config.

19912002200320042006200720072007

XXXXXCXK

A & BA & BA + PTA + PTA + PTAAA & B

Multi-frequency radio data quasi-simultaneous to Chandra Very Large Project taken in the Summer of 2007

Radio DataRadio DataSix epochs of VLA data showing clear motion of knots and diffuse material downstream in the jet.

Proposal submitted recently for another epoch in early 2009.


A1B

A2A

A1A

SJ2

SJ3

A1E

A1C

A1D

SJ1

A3AA3B

A4A5AA6A

Compact KnotsCompact Knots

A2B

Compact Knots:

Some knots move along the jet (A1B) with velocities of ~0.6c

Others appear stationary (A1A, A2A etc).

Some increase in flux with time (SJ1), however there is lower level variability in other knots


Radio Proper MotionsRadio Proper Motions

A1A - Stationary A1B - Moving

These are examples of a stationary knot (left) and a moving knot (right).

The observed motions are consistent with those previous published in Hardcastle et al. 2003.


Radio VariabilityRadio Variability

SJ1

SJ1:

Stationary, but shows strong variability, increasing in flux by a factor of two in the last 4 epochs.


Radio VariabilityRadio Variability

Other knots show less dramatic changes increasing or decreasing by 10-20% over 15 years.

A1B

A1C

A2A

A1A


PolarizationPolarization

Polarization vectors for the group A knots from 2002



Q U

To determine if the polarization varies over the monitoring program, we constructed residuals of the Q and U stokes parameters (2007 – 2002)

In the A2 group, the vectors appear to swing from positive (black) to negative (white) at opposite ends of the group; either due to motion, real change in polarisation or variability in the flux of the knot.

A2 GroupA1 Group



A1E

- Constant Total Intensity- Increasing Fractional Polarization Intensity- Constant Q/U Ratio

change in fractional polarization with constant position angle.

Total Intensity

Fractional Pol.

Q/U



A2B

- Constant Total Intensity- Constant Fractional Polarization Intensity- Increasing Q/U Ratio

change position angle with constant fractional polarization.

Total Intensity

Fractional Pol.

Q/U



A2D

- Constant Total Intensity- Constant Fractional Polarization Intensity- Varying Q/U ratio

changing position angle and constant fractional polarization.

Total Intensity

Fractional Pol.

Q/U


X-ray knotsX-ray knots

G groupF group

EX1 and EX2

C group

B group

A group

Counterjet knots


X-ray CounterpartsX-ray Counterparts

11/40 X-ray knots have radio counterparts

11/20 radio knots have X-ray counterparts

X-rayX-ray RadioRadio

AX1AAX1A A1AA1A

AX1CAX1C A1CA1C

AX2AX2 A2AA2A

AX3AX3 A3AA3A

AX4AX4 A3BA3B

AX5AX5 A5AA5A

AX6AX6 A6AA6A

BX2BX2 B1AB1A

BX4BX4 B2B2

SJX1bSJX1b SJ3SJ3

SX1aSX1a S1S1


X-ray VariabilityX-ray Variability

The lack of radio counterpart and its proximity to the edge of the jet suggest that AX2a is a coincidently positioned LMXB

20072004


X-ray VariabilityX-ray VariabilitySX1

SX1’s flat spectrum and lack of radio counterpart mean we cannot rule it out as a LMXB unrelated to the jet.


X-ray VariabilityX-ray VariabilityCX3 gradually increases in flux from 2000, being undetected in the 1999 observation.

Unfortunately, we have not detected a radio counterpart.

This is also one of the less compact X-ray knots.


A1A X-ray variability is in sync with the observed radio variability, increasing gradually on long time scales.

X-ray VariabilityX-ray Variability

A1A


SummarySummary

- Long term variability (eg. A1A)

- Consistent, in sync, changes in the flux in both X-ray and radio suggest changes in the magnetic field strength and/or particle density

No changes in particle acceleration as this would produce stronger X-ray variability.

- Combined with non-movement in the radio, this is consistent with a model where these stationary knots are local standing shocks.

- Short term variability (eg. CX3 and SX1)

- Flares in X-ray or radio on timescales shorter than the light crossing time, suggest change in unresolved sub-regions or beaming.

- Changes in the polarization would also fit this picture.

- No radio flaring of this type has been observed, and no flaring X-ray knot has a radio counterpart.


Future WorkFuture Work

To investigate the properties of the inner jet further we plan to To investigate the properties of the inner jet further we plan to

Refine our method for measuring the proper motions of the radio knotsRefine our method for measuring the proper motions of the radio knots

Determine the broadband spectra, using our multi-frequency radio data, of the Determine the broadband spectra, using our multi-frequency radio data, of the knots and diffuse material in the jetknots and diffuse material in the jet

Further investigate the spectral properties of the knots as a function of their Further investigate the spectral properties of the knots as a function of their position in the jetposition in the jet

Investigate the spectral properties of the narrow innermost jet in radio and X-rayInvestigate the spectral properties of the narrow innermost jet in radio and X-ray

Search for optical and infra-red counterpart to the knotsSearch for optical and infra-red counterpart to the knots

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A Radio and X-ray Study of Particle Acceleration in Centaurus A’s Jet Joanna Goodger University of...

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