Transcript The Main Features of the X

The X-ray Universe
Sarah Bank
Presented July 22, 2004
Overview
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X-ray Production Mechanisms
The Sun (in brief)
The Main Features
Supernovae (SNe), Supernova Remnants
(SNRs), and Superbubbles
Active Galactic Nulcei
X-ray Sources
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The three main sources of
astrophysical x-rays
Thermal - bremsstrahlung and line
emission
Synchrotron radiation from relativistic
electrons
Inverse Compton Scattering
Thermal Bremsstrahlung
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Thermal bremsstrahlung or free-free
emission occurs when an e- is
accelerated due to the strong electrical
attraction of a positive ion in a plasma.
Temperatures
above 105 K are
necessary.
http://imagine.gsfc.nasa.gov/docs/science/how_l2/xray_generation.html
Line Emission
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Heavy elements, not fully ionized, can
have inner electrons collisionally excited to
higher energy levels. Upon decay they
emit an X-ray.
http://csep10.phys.utk.edu/astr162/lect/light/bohr.html
Synchrotron/Relativistic e
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Charged particles in a magnetic field are
accelerated around field lines releasing
radiation.
If the particle is relativistic the radiation
undergoes ‘beaming’ and the maximum Ephoton is
then proportional to the field strength and
inversely proportional to the particle’s
momentum.
http://imagine.gsfc.nasa.gov/docs/science/how_l2/xray_generation.html
Inverse Compton Scattering
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A relativistic ecolliding with a low
energy photon can
impart energy
resulting in an Xray.
Seen in SNe and
AGN.
http://venables.asu.edu/quant/proj/compton.html
The Sun
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Turbulence in the convection zone
amplifies magnetic fields to create loops
conducting electric currents, thus heating
the solar corona to X-ray temperatures.
Solar Photosphere ≈ 6000K
Solar Corona ≈ 106 K
Charles & Seward, Exploring the X-ray Universe. Cambridge U. Press, Great Britain©1995
Solar Flare/Loop
The Main
Features
The 1/4
keV
(McCammon,D. et al. (Sept. 2002) ApJ. v.576, no.1,pt.1 p.290-300)
The 3/4
keV
(McCammon,D. et al. (Sept. 2002) ApJ. v.576, no.1,pt.1 p.290-300)
The Features
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The Lockman Hole: a region where absorbing
material, HI and dust, are sparse
Draco Cloud: enhanced soft X-ray region due to a
molecular cloud falling into the plane of the Galaxy
Cygnus Superbubble/Loop: nearby superbubble
from the explosion of many Sne, 14 times the size
(at 400 pc in diameter) of the Cynus Loop, a 20,000
year old SNR emitting thermal bremsstrahlung as
soft x-rays.
North Polar Spur (NPS)/Loop 1: The NPS is a
bright region of the Loop 1 superbubble, a wellknown radio feature.
More Features
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The Virgo Cluster: the cluster of galaxies at the
center of the local supercluster
Galactic Bulge: not well understood, but
definitely consists of some component beyond
the NPS
LMC: a nearby dwarf irregular galaxy
Vela/Puppis SNRs: Vela SNR ~ 1,500 ly away,
11,000 y old and 230 ly in diameter; whereas
Puppis, superimposed on the Vela remnant is ~4
times farther away, but the brightest X-ray
source between 0.5 and 1 keV
Vela and
Puppis
http://heasarc.gsfc.nasa.gov/docs/rosat/gallery/snr_velapup.html
More Features
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Eridanus Enhancement: from the Orion
superbubble, ~1200 ly across, being
energized by stars in the Orion OB1
association
Monogem Ring: a SNR in a low density
region of the Galaxy, thus evolved into a
low surface-brightness remnant
The Crab: a SNR recorded in 1054 and
now observed to contain a 33 ms pulsar
Supernova Remnants
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Type 1: mass transfer onto a white dwarf from a
binary companion resulting in accretion beyond the
Chandrasekhar limit.
Type 2: core collapse of a massive star (~10 Msolar)
that has formed an iron core.
Most profuse X-ray emission during phases 1 & 2.
Thermal x-rays via line emission or bremsstrahlung.
Charles & Seward, Exploring the X-ray Universe. Cambridge U. Press, Great Britain©1995
Superbubbles
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SN - Star Formation - SNe - Superbubble
Not created by a single “super-supernova,” but
by many such events over time.
Dynamite vs. Digger analogy
Charles & Seward, Exploring the X-ray Universe. Cambridge U. Press, Great Britain©1995
Active Galactic Nuclei
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http://www.seds.org/hst/ngc4261.html
The super massive
Black Holes (BHs) at
the centers of galaxies,
actively accrete gas
from the ISM,
cannibalized galaxies,
nearby stars.
An accretion disk
forms, heating the
material, as well as
jets of relativistic
matter at the poles of
the MBH.