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A MULTIFREQUENCY STUDY OF DOUBLE-DOUBLE RADIO
GALAXIES
Marek Jamrozy 1 Chiranjib Konar 2, D.J. Saikia
3, Jerzy Machalski 1 1Jagiellonian University,
Kraków, Poland 2IUCAA, Pune, India 3NCRA-TIFR,
Pune, India
LFRU 2008
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For radio galaxies and quasars, an interesting
way of probing their history is via the
structural and spectral information of the
extended lobes. Such studies have provided useful
insights in understanding sources which exhibit
precession or changes in the ejection axis,
effects of motion of the parent galaxy, backflows
from hotspots as well as X-shaped sources and
major interruptions of jet activity.
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Radio galaxies with many lobes
Old slavic idol with many faces
FRII ?

• resolution
• frequency
• array conf.
• int. time

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One of the striking examples of episodic activity
in AGNs are the double-double radio galaxies with
two pairs of radio lobes from two different
cycles of activity.
3C219
High resolution radio imaging ( all sky radio
surveys) has led to the discovery of a rare
class of RGs.
Clarke et al. 1992(ApJ, 385, 173)
DDRG two unequall sized, two sided, double
lobed, edge-brightened (FRII) radio sources
(Schoenmakers et al. 2000, MNRAS, 315, 371)
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Three episods of jet activity
Brocksopp et al. 2007 (MNRAS, 382, 1019)
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There are 14 DDRGs in the literature. They are
mostly GRGs
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• No radio hotspots in the outer lobes
• -gt the jets from AGN do not continuously
• power the radio lobes the activity stops for a
  period and then recommence.
• The interruptions may be related to
• refueling of the central engine
• instabilities in the accretion disk
• jet production mechanism

The newly-formed jets propagate through the
cocoon formed by the earlier cycle of
activity rather than the IGM -gt Numerical
simulation of restarting radio jets Clarke
Burns (1991, ApJ, 369, 308), Kaiser et al.
(2000, MNRAS, 315, 381).
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The aim of our work is to obtain physical
parameters of the old and new lobes of DDRGs on
the basis of a wide range multifrequency radio
observations (GMRT and VLA)

• spectra of the inner and outer lobes
• spectral and dynamical ages
• injection spectra of each cycle of activity
• time scales of episod activity

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J14533308
VLA 4850 MHz
240MHz
330MHz
610MHz
GMRT
1300MHz
(Konar, Saikia, Jamrozy, Machalski, 2006, MNRAS,
372, 693)
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Spectral ageing analysis Assumptions -
magnetic field strength in a given lobe is
constant throughout the energy loss process -
the particles injected into the lobe have a
constant power-law energy spectrum with
spectral index ?inj - the timescale of
isotropisation of pich angles of the particles
is short compared with their radiative lifetime
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?rad50.3 B1/2/(B2BiC2)(?br(1z))1/2
BiC0.318(1z) nT, GHz, Myr
N-lobe trad 47 Myr S-lobe trad 58 Myr Inn
trad lt 2 Myr
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J14533308 Summary
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J11582621
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J18356204 (Konar, Jamrozy, Saikia, Machalski,
in prep.)
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J00413224 (Saikia, Konar,
Kulkarni, 2006, MNRAS, 366, 1391)
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GMRT 240MHz
GMRT 610MHz
J1548-3216
VLA 4860 MHz
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Thank you