Jets%20in%20Astrophysics:%20A%20Review

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Jets in AstrophysicsA Review

• J.H. Beall
• Space Sciences Division,
• Naval Research Lab,
• Washington, DC,
• St. Johns College, Annapolis, MD,
• and
• College of Science, GMU, Fairfax, VA

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Outline of Talk Jets are ubiquitous - active
galaxies and quasars - galactic binaries and
microquasars - star-forming regions - clusters
of galaxies Association of jets with accretion
disks Association of jets in supernovae with
GRBs Regarding the disk-jet connection, it is
hard to see how to get around the Eddington limit
by more than an order of magnitude. The
ergosphere around a rapidly rotating black hole
might be a solution to this problem.
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Outline of Talk (continued) Some relevant
historical investigations (from the late
Jurassic) Nature of the spectra, temporal
features, and structure of AGNs and microquasars,
with an emphasis on How these spectra are
obtained and what limitations these methods have
for source models Some thoughts on how to refine
the measurements and why we should be concerned
about these issues.
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But first, some history First detection of
concurrent, multifrequency variability of an AGN
came from Centaurus A (Beall et al., 1978
Ap.J.). Since then, many other sources have been
shown to have evidence of such effects.
Consider Centaurus A...
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Historical radio variability of Cen A at 10.7,
31.4, and 90 GHz
Beall et al. 1978 Ap.J., 219,836.
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Low energy x-ray (2-6 keV) variability of Cen A
Beall et al. 1978 Ap.J. 219, 836
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High energy x-ray (100 keV) variability of Cen A
Beall et al. 1978 Ap.J., 219, 836.
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Historical spectral variability at 100 keV of Cen
A
Beall et al. 1978 Ap.J., 219, 836.
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What sort of source physics does this pattern of
concurrent variability at various radio
frequencies suggest? The spectrum of the Cen A
data is consistent with a self-absorbed (at 10.7
Ghz) synchrotron emitting region, with a
power-law at higher radio frequencies. This
suggested that the source of the emission could
be modelled by van der Laan (1966) expansion,
where relativistic electrons are entrained in the
magnetic field of a diffuse gas that was slowly
expanding. But a careful look at van der Laan's
paper shows that the Cen A data do not match the
picture of an isotropic and isotropically
emitting source consistent with van der Laan
expansion.
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Radio variability of Cen A is not consistent with
van der Laan expansion.
Beall et al. 1978 Ap.J., 219,836.
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van der Laan expansion radio flux time history
for a spherically symmetric, expanding
synchrotron source (van der Laan, 1966)
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van der Laan Expansion successive plots
show evolution of spectrum as the source expands
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For the Cen A data, it was the concurrent
variability that suggested the radio and x-ray
fluxes were created in the same region. This
suggested we could get source parameters from
observations models Synchrotron radiation for
radio sources Optical and infrared from
thermal sources x-ray and high-energy x-rays
from SSC (synchrotron self-Compton) and
external or BBC (blackbody Compton)? Gamma-ra
y production from multiple self-Compton
scattering or hadronic processes (Beall and
Bednarek 1999). Neutrino production from
hadronic interactions of course this
assumed the same emitting region
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As noted for Cen A, the definition of concurrent
and multifrequency are made more problematic by
the different resolutions of the
observatories radio data from VLBI is
milliarcseconds radio data from VLA in
arcseconds Hubble space telescope 0.1 arcseconds
ground based optical telescopes in arcseconds
or tenths of arcseconds optical and IR
interferometers claim milliarcsecond resolution
Chandra x-ray detector has a resolution of 0.5
arcseconds SWIFT x-ray telescope has a
resolution of 18 arcseconds ?-ray detectors
(AGILE, INTEGRAL, SWIFT, and GLAST) have
resolutions of degrees to a few
minutes. HESS, Magic, Whipple, and others have
resolutions of order a few arcminutes.
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But even today, the definition of concurrent
is very unlikely to mean at exactly the same
time. The definition of multifrequency never
means at all possible frequencies.
Usually, Concurrent within a window of time
that is short compared to the expected time
scales for variability of the object. Multifrequ
ency some representation of the frequencies
over which one expects the emission to occur.
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We often rely on assumptions about relative
intensities and variability of core versus jet
luminosities in our estimations of source fluxes
without confirming this independently.
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The problem of anisotropy Nearly all source
models use the assumption of isotropy to make
the calculations of source spectra
tractable. Some anisotropic calculations (see,
e.g., Bednarek, Karakula, Tkaczyk, and
Giovannelli, 1990) have been done and could be
used as a model for future theoretical work.
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Cen A radio and x-ray variability Data are not
consistent with van der Laan expansion. Requires
some mechanism of accelerating or injecting new
particles into the emitting region. Enter
jets, stage right! Definition of a Jet Jets are
linear structures in the sky that seem to be
associated with outflows from central regions of
gravitational collapse. Therefore, we would
expect jets to be associated with accretion
disks.
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Jets can be modelled to test a number of
physical processes Confirmation of special
relativity, both in terms of Doppler boosting
and superluminal expansion. When coupled with
black hole/neutron star origins, jets have
implications for testing general
relativity. Can use observations to test the
connection of galactic jets to jets in AGN and
quasars (over an enormous dynamic range).
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Cen A radio and x-ray resolution is also a
critical consideration. See, e.g., H. Steinle's
webpage at http//www.mpe.mpg.de/hcs/Cen-A/cen-
a-home.html
Burns and Price 6 cm. VLA image 1983, showing
inner lobes (separated by 3.5 arcminutes).
Feigelson et al. 1981 structure showing core
jet in x-ray. Bar 1 arcminute
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AGN schematic
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Multifrequency Image of M87 jet structure with
arcsecond resolution instruments.
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M87 at mas resolution (white bar is .01 pc)?
Junor, Biretti, and Livio, Nature 1999, 401, 892
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Now possible to resolve structure of core vs. jet
as they change over frequency and time using
VLBI data
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BL Lac radio variability and structure. Note
estimates of core vs. jet flux in panel 3, which
separates jets (e.g., jet 2 at 2 mas) from core.
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Microquasars
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Mirabel 's discovery of superluminal jets in a
galactic source (Mirabel and Rodriguez, Nature,
1994) obs of GRS 1915105 (40,000 lt. years
distant). Data taken from VLA observations.
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Cartoon of microquasar binary system
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Galactic Microquasars show much the same
behaviour as Quasars (after Mirabel)?
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Comparison of Microquasars and Quasars (adapted
from Mirabel)?
AGN/Quasar Microquasar
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Comparison of a quasar jet (3C120) and a
microquasar (Sco X-1).
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Differing resolutions can be a problematic issue.
We illustrate this by looking at the spatial and
temporal evolution of one AGN jet (3C120 in VLBI
radio and x-ray) and the microquasar Sco X-1 in
radio light. First, 3C120 - Radio brightness
of the jet shown as contours. - Color-coded
contours represent the intensity of polarized
radio waves. - Strong polarization indicates
well-ordered magnetic fields (the sticks are in
the direction of the magnetic field). - Bright
"knots" appear and move down the jet, with their
polarization changing. - Red area with the black
center represents the accretion disk . - Light
curve shows X-ray brightness varying with time.
When the X-ray brightness decreases, the dark
part of the accretion disk is illustrated as
becoming larger.. About 4 weeks later, the
starting point of the jet gets bright and a new
superluminal knot moves down the jet.
(see, e.g., Marscher 2006)?
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3C120 Red ellipse represents inner accretion
disk via Rossi XTE data, with insert showing
x-ray light curve (see Marscher, 2003). Contours
43 GHz intensity (VLBA). Inset X-ray light
curve (data courtesy of Alan Marscher and
Jose-Luiz Gomez) 1 mas 0.70 pc _at_ D 120 Mpc.
(see Gomez et al. 2000 Science, 289, 2317)?
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Regarding 3c120rx.avi, it is clear that the
resolution of the x-ray data are from the
central region of the source and cannot approach
the mas resolution of the VLBI data (movie
courtesy of Alan Marscher)?
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Sco X-1 frames from movie (see Fomalhaut,
Geldzahler, and Bradshaw, 2001 Ap.J., 558, 283).
For large blobs, v .45c. On this scale, 1
mas 2.8 AU 4.19x1013 cm with Sco X-1 at a
distance, D 2.8 Kpc (9000 light years).
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Jets can travel outward from the central engines
of AGNs to distances gt 100s of kiloparsecs. In
Cen A, the luminosity of the central engine,
maintained over the propagation time scales of
the jet required to form the giant radio lobes,
can supply the energy of 1060 ergs that is
present in those radio lobes (Beall and Rose,
1981). It is possible that the cluster holes in
this CHANDRA image of MS0735 7421, have been
formed by jets,
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Jets in star-forming regions
Jets in Star-forming Regions in Molecular Clouds
There is evidence for accretion disks in the
existence of bipolar outflows and in the
agreement between calculated and observed spectra
in giant molecular clouds. (see, The
Observational Appearance of Protostellar
Accretion Disks," in Beall 1987, Ap.J. 316, 227).
Data on rho Ophiuchus taken from K. Tachihara's
Ph.D. Thesis,

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Calculation of accretion disk thermal spectrum
(after Beall, J.H., 1987 ApJ, 316, 227)?
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Thermal disk spectrum combined with Comptonized,
soft x-ray photons upscattered to hard x-rays
and gamma-rays (adapted from Hannikainen (2005)?
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Comments on Modelling the Jet-Ambient-Medium
Interaction What mechanisms work to deposit
energy in the ambient medium as the jet
propagates through it, and how does the jet
maintain its coherence as it propagates such
remarkable distances? The details of the
interactions of the jet particles with the
ambient medium are left out of magneto-hydrodynami
c codes. The physics of the jet interaction with
the ambient medium almost certainly involves
plasma processes that accelerate and entrain the
ambient medium into the jet structure (more
discussion on Thursday).
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Synchrotron Self-Compton a self-absorbed
synchrotron radio spectrum x-ray and ?-ray
modelled by inverse-Compton processes can yield
source parameters (see e.g., Grindlay
1975, Ghisillini (2002), Konopelko et al., 2003)?
(Grindlay, 1975 Ap.J.)?
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Synchrotron Self-Compton (continued)
(Grindlay, 1975 Ap.J.)?
In the SSC model, the spectrum of the IC photons
mimics that of the original synchrotron spectrum.
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This is also the case when the seed photons are
thermal (blackbody) photons from BLR in AGN.
Beall et al., 1978 Ap.J.
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SED modeled by SSC (Pian, 2007, Ghisillini 2003,
Konopelko et al. 2003 Ap.J. 597,421)?
MKN 501
MKN 421
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Galactic Gamma-Ray Sources - the Search for the
Cosmic Rays sources (after Bartko 2007).
apparent source direction
CR source
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Jets and the detection of UHE Cosmic Rays from
nearby AGNs via the Auger Observatory. Note
water tank element, sans cows.
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The beginnings of astronomy based on cosmic ray
detections from the Pierre Auger
Collaboration,, Science 318, 938 (2007). The
detection of hadrons in this flux is of the
utmost interest to those interested in the
composition of astrophysical jets.
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This is clearly a new and important result.
But it was not quite unexpected. Maury Shapiro
in 1994 in this very room predicted that
sufficiently energetic cosmic rays from nearby
AGN could be directly associated with their point
of origin. It would appear that his conjecture
has come to pass.
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Differing resolutions could be a problematic
issue. Recall the cases of Cen A The spatial
and temporal evolution of one AGN jet (3C120 in
VLBI radio and x-ray), and the microquasar Sco
X-1 in radio light
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Detectors of comparable resolutions yield a
multi-frequency image of M87 jet structure
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Concurrent, multifrequency observations with
similar angular resolutions can help distinguish
jet components from core emissions. Rayleigh
criterion implies modest sizes for optical and
infrared interferometers For a single
telescope, the angular resolution is sin ??
1.22 ?/D, where ??is the wavelength, and D is
the size of the telescope aperture. For an
interferometer, sin ?? ?/D where D is
the maximum spacing between elements.
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What are the limits of optical and IR
resolutions? Optical and IR interferometry at
the VLT
The Very Large Telescope array (VLT) in Chile,
consisting of four Unit Telescopes with main
mirrors of 8.2m diameter and four movable 1.8m
diameter Auxiliary Telescopes. The telescopes can
work together, in groups of two or three, to form
a giant interferometer, the ESO Very Large
Telescope Interferometer.
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Radio interferometry using the VLBA
The VLBA radio telescopes are located at
Mauna Kea, Hawaii ( 1948'04.97?N,
15527'19.81?W)? Owens Valley, California (
3713'53.95?N, 11816'37.37?W)? Kitt Peak,
Arizona ( 3157'22.70?N, 11136'44.72?W)?
Pie Town, New Mexico ( 3418'03.61?N,
10807'09.06?W)? Los Alamos, New Mexico (
3546'30.45?N, 10614'44.15?W)? Fort Davis,
Texas ( 3038'06.11?N, 10356'41.34?W)?
Brewster, Washington ( 4807'52.42?N,
11940'59.80?W)? North Liberty, Iowa (
4146'17.13?N, 9134'26.88?W)? Hancock, New
Hampshire ( 4256'00.99?N, 7159'11.69?W)?
St. Croix, United States Virgin Islands (
1745'23.68?N, 6435'01.07?W)?
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VLA near Socorro, New Mexico

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Ground-Space-Based VLBI gives a factor of 10
better resolution. The VSOP mission is a
Japanese-led project to image radio sources with
sub-milliarcsec resolution by correlating the
signal from the orbiting 8-m telescope, HALCA,
with a global array of telescopes. Twenty-five
percent of the scientific time of this mission is
devoted to a survey of 402 bright, small-diameter
extra-galactic radio sources at 5 Ghz.
(Hiribayashi et al. 2000 PASJ, 52..997H)
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What is the ultimate resolution we can expect
from x-ray and gamma-ray telescopes? G. Bignami,
Director of ASI, said in a recent interview that
it might be possible to fly two satellites in
formation, one with the instruments, and one
with the x-ray mirrors in order to obtain focal
lengths of 40 meters, and access to much higher
energies for an imaging instrument
(Physics Today, May 2007, p. 28).
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Ground based TeV instruments such as the
HESS, MAGIC, and Whipple Observatory are also
important (see, e.g., Bartko, 2007, Santangelo
2007, Konopelko et al. 2005, below).
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Neutrino observatories may help ultimately to
determine the constitution of the jets in
microquasars or AGNs. (table taken from
Beall, 2005)?
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There exists some possibility of combining radio,
optical, and IR data with milliarcsecond
resolution for AGN. This would give us an
equivalent resolving power that we now have with
microquasars at radio, optical, IR, and
x-ray. This will allow more specificity in
determining correlations between signals that
originate from the different processes of nature
in the same source.
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But it appears that when we use these remarkable
instruments, we will still have the problem of
differing temporal and spatial resolutions, and
we will not be free of ambiguities in associating
variable signals in one instrument with those of
another for astrophysical sources.. Finally,
the highly variable and anisotropic nature of
both galactic microquasars and AGN jets suggests
that we apply anisotropic emission models to
these sources whenever possible.
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