A Radio and X-ray Study of Particle Acceleration in Centaurus A’s Jet Joanna Goodger University of...
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Transcript of 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
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
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
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
”
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
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
” ”Emission is dominated by the extended filamentary emission, consistent with a diffuse acceleration mechanism. (Kraft et al. 2006, ApJ 641, 158)
Hardcastle et al. 2007, ApJ 670, L81
Particle AccelerationParticle Acceleration
S
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
Particle AccelerationParticle Acceleration
1 kpc
Hardcastle et al. 2007, ApJ 670, L81
” 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
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
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
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
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.
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
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
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
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.
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
Radio VariabilityRadio Variability
SJ1
SJ1:
Stationary, but shows strong variability, increasing in flux by a factor of two in the last 4 epochs.
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
Radio VariabilityRadio Variability
Other knots show less dramatic changes increasing or decreasing by 10-20% over 15 years.
A1B
A1C
A2A
A1A
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
PolarizationPolarization
Polarization vectors for the group A knots from 2002
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
PolarizationPolarization
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
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
PolarizationPolarization
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
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
PolarizationPolarization
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
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
PolarizationPolarization
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
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
X-ray knotsX-ray knots
G groupF group
EX1 and EX2
C group
B group
A group
Counterjet knots
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
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
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
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
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
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.
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
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.
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
A1A X-ray variability is in sync with the observed radio variability, increasing gradually on long time scales.
X-ray VariabilityX-ray Variability
A1A
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
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.
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
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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