Centaurus A Kraft, Hardcastle, Croston, Worrall, Birkinshaw, Nulsen, Forman, Murray, Goodger, Sivakoff ,Evans, Sarazin, Harris, Gilfanov, Jones

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Centaurus A Kraft, Hardcastle, Croston,
Worrall, Birkinshaw, Nulsen, Forman, Murray,
Goodger, Sivakoff ,Evans, Sarazin, Harris,
Gilfanov, Jones

• Jet
• Southwest Inner Lobe
• Northern Middle Lobe
• Hot ISM

X-ray composite image
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Centaurus A the Nearest Radio Galaxy
Chandra
Kraft et al. 2000, 2001, 2003, 2007,
2008 Hardcastle et al. 2003, 2008 Worrall et al.
2008
VLA
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Multiple Outbursts in Cen A

• Series of outbursts seen in the radio
  (Ekers/Burns, Morganti et al.)
• Nuclear jet
• Inner lobes
• Northern middle lobe
• Linear size to 250 kpc
• Repeated
• AGN outbursts
• spanning 109 yrs

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Centaurus A Bubbles and Jets
Bubble diameter 3 kpc

• Distance 3.7 Mpc 1 18 pc
• New deep (600 ksec) Chandra observation -- PI
  R. Kraft
• Diffuse emission HOT ISM kT0.4 keV ,
• Jet, counter-jet , Lobes, Absorption lanes

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Centaurus A
Jet spans 4.5 kpc from nucleus to northern
lobe and expands with distance from the nucleus
Radio (blue) Chandra X-ray (red)
Lifetime of synchrotron emission of the
ultrarelativistic particles is much less than the
travel time down the jet. (in inner jet 20
years, 60 years beyond knot B). How is kinetic
energy of jets transferred into internal energy
of relativistic plasma in jets?
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Centaurus A Jet
Extended compact knots - Lx (knots) 1039
erg/s 1/3 jet Lx within 1, 2/3 jet Lx
is in knots.
Radio (blue) Chandra X-ray (red)
nucleus
Following M87 jet results where knots are
identified as sites of shocks where magnetic
fields are compressed and particles accelerated
(Sparks et al. Perlman et al.), Cen A knots
may play same role in accelerating
particles (Kraft et al., Hardcastle et al.,
Worrall et al.) Note Gaps between groupings of
knots with only diffuse synchrotron emission.
Particle acceleration distributed throughout jet.
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The Jet in Centaurus A
Many X-ray (blue) knots correspond to radio
(red) knots (Hardcastle et al.2003).

• Differences between positions of radio and X-ray
  knots explained
• by particle aging.

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The Inner Region of the Cen A Jet

• Faint, well-collimated inner jet region detected.
  
• In standard FRI sources, this region is where
  efficient, supersonic flow transports energy up
  to where jet flares and becomes turbulent.
• Could have in situ particle acceleration here.

Chandra (blue) and VLA (red 8.4 GHz)
observations (Hardcastle et al 2003)
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Centaurus A Bubbles and Jets
Bubble diameter 3 kpc

• Counter-jet - several X-ray features with radio
  counterparts (Hardcastle et al )
• Southern lobe - sharp, smooth

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Centaurus A - Southwest Radio Lobe

• Old view -- Emission in shell is from gas swept
  up by expanding lobe
• Model X-ray bubble as driven by expansion of
  radio plasma
• Gas temperature in lobe 2.9 keV (in ISM kT
  0.3 keV)
• Shell gas density 2 10-2 cm-3 (In ISM 2 10-3
  cm-3)
• Shell overpressured (2 10-10 dyn cm-2 in ISM
  10-12, in lobe 10-11)
• Bubble expanding supersonically at Mach 8.5 (2400
  km/sec)

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Centaurus A - Southwest Radio Lobe

• But there were problems with this model !
• Density drop was too large compared to
  temperature change across shock. Inconsistent
  Mach numbers for shock velocity,
• The gas density in shell was too high for swept
  up ISM
• Deep Chandra spectra show southwest region of
  shell is synchrotron and most likely not thermal
  emission (upper region of shell is well fit
  with thermal spectrum).

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Chandra images of Cen A lobes with radio contours
New view -- Southwest X-ray lobe is synchrotron
emission! (NE shell??)
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The Northern Middle Lobe in Cen A

• Series of outbursts seen in the radio
  (Ekers/Burns also see Morganti et al.)
• Nuclear jet
• Inner lobe
• Northern middle lobe
• Linear size to 250 kpc

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Centaurus A
XMM-Newton and Morganti et al (yellow) Burns et
al (green) radio countours
X-ray filament/knots on edge of NRL radio
emission - X-ray knots not correlated with radio
emission Northern middle lobe - poster by Kraft
et al. Previous work - Feigelson et al 1981
(Einstein), Morini et al 1989 (EXOSAT), Morganti
et al 1999 (ASCA).
.
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Centaurus A - Northern Middle Lobe
XMM-Newton MOS 0.5-2 keV raw image
XMM-Newton MOS 0.5-2 keV smoothed, exposure
corrected.
Extended X-ray knots in filament of diffuse
emission Knots are thermal (kT 0.5 keV) LX
(N1) 1039 ergs/s
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Centarus A - Northern Middle Lobe
XMM-Newton MOS
Extended KNOTS are overpressured (and short-lived
3 106 yrs). Must have been recently
shock-heated by jet. NML still being powered by
current AGN outburst.
.

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Centaurus A - Hot ISM
Chandra 0.5-1 keV
Surface brightness discontinuity 3.5 kpc from
nucleus Gas motions in the hot ISM produced by
the recent merger (Kraft et al. 2008
arXiv0803.3595)
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Centaurus A conclusions
Much of emission from SW lobe is synchrotron
In jet, knots may play important reacceleration
role.
NML still powered by jet
Sloshing of hot gas caused by merger
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Thanks