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Insights on Jet Physics & HighEnergy Emission Processes
from Optical Polarimetry
Eric S. Perlman
Florida Institute of Technology
Collaborators: C. A. Padgett, M. Georganopoulos (UMBC),
F. Dulwich, D. M. Worrall, M. Birkinshaw (Bristol),
A. S. Wilson (UMCP), W. B. Sparks, J. A. Biretta (STScI),
C. O’Dea, S. Baum (RIT) + several others…
Radiation Processes in Jets
e-
Synchrotron radiation
emitted by relativistic
particles in magnetic field
B
Jet “beam”
Inverse-Compton – scattering
interaction between photon and a
relativistic particle that results in a
higher-energy photon.
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).
Important questions:
What does the magnetic field configuration look like?
Does it change as one goes up in energy?
What clues can the magnetic field configuration and ordering give us to radiation and
physical mechanisms involved in producing high-energy emissions?
Perlman et al. 1999
Comparing jet width in
Radio, optical, X-rays…
X-ray jet is narrowest
Optical jet is next
Radio jet is widest
Perlman & Wilson 2005
Stratified jet…
High energy particles nearer jet axis
Low energy particles evenly
distributed
B gets compressed, becomes  to jet
in shocks inside jet
Shocks accelerate particles, so they
brighten optical emission but not
radio
Further development of magnetic
field depends on two scale lengths:
Magnetic field coherence length lB
Perlman et al. 1999
Synchrotron cooling length lcool
lB = lcool
Perlman, Georganopoulos & Kazanas, in progress
lB=2lcool
3C15
Optical and radio jet roughly
similar but optical jet
narrower
2 knots in X-ray, one
coincident with knot C, the
other not coincident with
radio/opt (A’)
Knot A’ X-ray max
corresponds to a feature
seen in UV but not in any
other r/o band
3C 15
 Polarimetry differences more
subtle than M87
 In all X-ray maxima, there
are interesting radio-optical
polzn differences in the
neighborhood
 Resolution marginal
 Optical spectrum hardens
too
 But still indicate stratification
 2-component plasma,
relativistic spine, slower
sheath
 Knot C is a torsional
compression of the jet
where X-ray emission is
triggered
3C 264
 Wide-angle tail type source.
 Bend about 4” from nucleus
 Optical emission dims
markedly after 1”
 X-ray emission both from
inner jet as well as optically
fainter outer jet
3C 264
 Resolution of Chandra data
too low to firmly associate
inner jet X-ray emission
with optical feature
 But polarization anomalies at
0.8” from nuclueus, just upstream of “ring”
 Outer jet emission -optically faint, hard to tell
3C 346
 Kinked jet seen in both
radio and optical
 Major bend may be the
result of the passage of a
companion galaxy
 X-ray emission from ~0.3”
before kink
 Major change in polarization
characteristics near kink
3C 346
 Increase in polarization
near X-ray maximum.
 Small rotation in position
angles, only in optical, at
that point.
 Hardening of optical
spectrum at X-ray max.
 Synchrotron X-ray
emission with associated
compression?
3C 371
3C 371
Optical shows low
polarization in 2 Xray maxima, high
polarization in one.
Significant rotations
seen in optical also
Neither is seen in
radio
Summary
 In all cases, *something* happens in polarimetry at
loci of X-ray emission
 What happens appears different in each jet and each
component
 Usually associated with an increase in radio-optical
polarimetry differences
 Optical spectrum seems to harden at X-ray flux max
 X-ray emission from only a small part of jet “crosssection”
 Optical Polarimetry can serve as a diagnostic for Xray emission mechanism
 This is crying out to be done for higher-power jets!