High Energy Stellar Astrophysics

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High Energy (Stellar) Astrophysics
Any of these

• E gt 1051 erg
• T gt 109 K
• density gt 109 g cm-3
• x-rays or gamma-rays
• ms time variabilty
• strong gravity

• Supernovae
• Pulsars
• Accreting Compact objects neutron
  stars black holes
• Gamma-Ray Bursts

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HEAO survey completed 1978 841 sources mostly
binary stars
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red 100,000 K white 20 million K
ROSAT first pass in 1990 1991
50,000 sources. By 1999 over
150,000 sources had been
catalogued.
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X Ray Binaries

• Two classes based upon mass of companion star
  that is feeding the x-ray emitting compact
  object
• High mass donors (over about 5 solar masses)
  are found in the disk of the galaxy and are
  Population I. The donor star is typically a
  B-type main sequence star or a blue
  supergiant. Roughly 300 are estimated to exist in
  our galaxy. Lifetime lt 108 years. Long
  period. High accretion rate.
• Low mass x-ray binaries contain a donor star of
  lt about 1 solar mass which may be a main
  sequence star. Population II. Found in
  Galactic center, globular clusters, in and
  above disk. Roughly 300 estimated to exist.
  Some exhibit x-ray bursts
• Luminosities in X-rays for both are 1036
  1038 erg s-1

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Cargo Bay
Black Hole Illustration
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Cargo Bay
Some Properties of Black Holes

• Entirely defined by their mass, rotation rate,
  and charge.
• Believed that all the mass is concentrated at
  the center in a small quantum-mechanical
  singularity
• Effective density of stellar mass black holes is
  very high, but there are supermassive black
  holes in active galactic nuclei with
  densities no greater than water. they are
  just very big
• The gravitational field of a black hole close to
  the event horizon is complicated, but by the
  time you are several Schwarzschild radii away,
  it is indistnguishable from that of an
  ordinary (dense) star.

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Cyg X-1 in X-Rays
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Artists Rendition of Cyg X-1
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The spectrum of Cygnus X-1 is non-thermal and
time variable. There is evidence for two
components soft from thin disk
accretion hard quasispherical from a
wind
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Companion
Mass
P (days)
Source
Cygnus X-1 B supergiant
5.6 6-15 LMC X-3B main
sequence 1.7 4-11 A0620-00
(V616 Mon) K main sequence 7.8
4-9 GS2023338 (V404 Cyg) K
main sequence 6.5 gt 6 GS200025
(QZ Vul) K main sequence
0.35 5-14 GS1124-683 (Nova Mus 1991)
K main sequence 0.43 4-6 GRO J1655-40
(Nova Sco 1994) F main sequence 2.4
4-5 H1705-250 (Nova Oph 1977) K main
sequence 0.52 gt 4
2 more
Fraknoi, Morrison, and Wolff p. 328
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Roger Blanford
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Zingale et al. He-detonation at 30
microseconds. v-det 13,000 km/s Density at base
is 108 g cm-3. 3 ms to go from pole to pole. This
unusually high density is not often achieved and
detonation is rare.
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Woosley et al (2004)
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Gamma-Ray Bursts
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A Cosmic Gamma-Ray Burst, GRB for short, is a
brief, bright flash of gamma-rays lasting
typically about 20 seconds that comes from an
unpredictable location in the sky. Some, in
gamma-rays, are as bright as the planet Venus.
Most are as bright as the visible stars. It is
only because of the Earths atmosphere and the
fact that our eyes are not sensitive to
gamma-rays that keeps us from seeing them
frequently. With appropriate
instrumentation, we see about one of these per
day at the Earth. They seem never to repeat
from the same source.
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Nuclear Test Ban Treaty, 1963 First Vela
satellite pair launched 1963
Velar to watch
The Vela 5 satellites were placed in orbit by
the Advanced Research Projects of the DoD and
the AEC. Launched on May 23, 1969 into high
earth orbit (118,000 km), this pair of
satellites and their predecessors, Vela 4,
discovered the first gamma-ray bursts. The
discovery was announced in 1973.
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Typical durations are 20 seconds but there
is wide variation both in time- structure and
duration. Some last only hundredths of a
second. Others last thousands of seconds.
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• Interstellar warfare
• Primordial black hole evaporation
• Flares on nearby stars
• Distant supernovae
• Neutron star quakes
• Comets falling on neutron stars
• Comet anti-comet annihilation
• Thermonuclear explosions on neutron stars
• Name your own ....

uncertainty in distance a factor of one
billion.
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In 1993 there were 135 models
nb. 27, 42, 105, 126
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Most of them involved neutron stars in our own
Galaxy (quakes, comets falling, thermonuclear
runaways, etc.) The expected distribution on the
sky if Galactic neutron stars were responsible
should center around the Galactic equator.
Plane of the MilkyWay Galaxy
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Compton Gamma-Ray Observatory
April 5, 1991 June 4, 2000
BATSE Module
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Bright long bursts are red short fainter bursts
are purple. The rest are intermediate. Note no
correlation with Galactic disk.
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This posed a problem for the models that had GRBs
in our own Galaxy ..


















X









We are not at the center of our galaxy so we
should see more bursts towards the center than
in the opposite direction,









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• Isotropy could mean three things
• Very nearby bursts centered on the Earth
  unlikely
• A very extended spherical halo around the Galaxy
  much bigger than the distance from here to
  the center of the Galaxy
• Bursts very, very far away billions of light
  years

What we really needed was source identifications.
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BeppoSax GRB 970228 (discovered with WFC)
Feb 28, 1997 (8 hr after GRB using MECS)
March 3, 1997 (fainter by 20)
Each square is about 6 arc min or 1/5 the moons
diameter
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GRB 970228
William Hershel Telescope
Isaac Newton Telescope
Groot, Galama, von Paradijs, et al IAUC 6584,
March 12, 1997
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Later ....
Spectrum of the host galaxy of GRB 970228
obtained at the Keck 2 Telescope. Prominent
emission lines of oxygen and neon are indicated
and show that the galaxy is located at a
redshift of z 0.695. (Bloom, Djorgovski, and
Kulkarni (2001), ApJ, 554, 678. See also GCN
289, May 3, 1999.
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From the red shift a distance can be inferred
billions of light years. Far, far outside our
galaxy. From the distance and brightness an
energy can be inferred.
1.6 x 1052 erg in gamma rays alone
This is 13 times as much energy as the sun will
radiate in its ten billion year lifetime, but
emitted in gamma-rays in less than a minute. It
is 2000 times as much as a really bright
supernova radiates in several months.
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Two HST images of GRB 990123. The image on the
left was taken February 8, 1999, the one on the
right March 23, 1999. Each picture is 3.2 arc
seconds on a side. Three orbits of HST time were
used for the first picture two for the second
hence the somewhat reduced exposure.
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The spectrum of host galaxy (Kelson et al, IAUC
7096) taken using the Keck Telescopes gives a
redshift of 1.61. Given the known brightness of
the burst (in gamma-rays) this distance implies
an energy of over several times 1054 erg. About
the mass of the sun turned into pure energy.
Had this burst occurred on the far side of our
Galaxy, at a distance of 60,000 light years, it
would have been as bright in gamma-rays as
the sun. This is ten billion times brighter than
a supernova and equivalent to seeing a one
hundred million trillion trillion megaton
explosion.
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The typical energy is 1053 erg or about 5 of the
mass of the sun turned to pure energy according
to E mc2
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• Gamma-ray bursts are at cosmological distances

Djorgovski et al (2002)
27 Total
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But are the energies required really that great?
Earth
If the energy were beamed to 0.1 of the sky,
then the total energy could be 1000 times less
Earth
Nothing seen down here
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But then there would be a lot of bursts that we
do not see for every one that we do see. About
1000 in fact.
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Quasar 3C 175 as seen in the radio
Quasar 3C273 as seen by the Chandra x-ray
Observatory
Artists conception of SS433 based on
observations
Microquasar GPS 1915 in our own Galaxy time
sequence
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Frail et al. Astrophys. J., (2001), for 17
GRBs with known redshifts and afterglow light
curves.
Using the angles inferred from analyzing the
light curve of the afterglow at various
wavelengths, Frail et al found that an inverse
correlation exists between the apparent energy
of the burst and this angle. Correcting for the
fact that the burst is beamed to a small part of
the sky, they find a typical energy in
gamma-rays is 5 x 1050 erg. For a
reasonable conversion efficiency between
explosion energy and gamma-rays (20), the total
jet energy is about 2 x 1051, not so different
from an ordinary supernova.
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Djorgovski et al (2002)
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Requirements on the Central Engine and its
Immediate Surroundings

• Provide adequate energy to material moving close
  to the speed of light (2 x 1051 erg)
• Collimate the emergent beam to approximately 5
  degrees
• Last approximately 10 s
• Make bursts in star forming regions

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Merging Neutron Stars
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The Collapsar Model (aka the Hypernova)
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Usually massive stars make supernovae. Their iron
core collapses to a neutron star and the energy
released explodes the rest of the star. But what
if the explosion fizzled? What if the iron
core collapsed to an object too massive to be a
neutron star a black hole. A star without
rotation would then simply disappear.... But
what if the star had too much rotation to all
go down the (tiny) black hole? If supernovae are
the observational signal that a neutron star has
been born, what is the event that signals the
birth of a black hole?
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In the vicinity of the rotational axis of the
black hole, by a variety of possible processes,
energy is deposited.
The exact mechanism for extracting this energy
either from the disk or the rotation of the
black hole is fascinating physics, but is not
crucial to the outcome, so long as the energy is
not contaminated by too much matter.
7.6 s after core collapse high viscosity case.
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A 1053 erg event situated 30,000 light years
away (distance from here to the Galactic center)
would give as much energy to the earth in 10
seconds as the sun equivalent to a 200 megaton
explosion. Does it matter having an extra sun in
the sky for 10 seconds? Probably not. This is
spread all over the surface of the earth and the
heat capacity of the Earths atmosphere is very
high. Gamma-rays would deposit their energy
about 30 km up. Some bad nitrogen chemistry
would happen. Noticeable yes, deadly to all
living things No.
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Biological Hazards of Gamma-Ray Bursts
Distance Events
Megatons Results (kpc)
/10 by

• 100 1000 200
  Some ozone damage, EMP
  acid
  rain
• 1 1 10
  20,000 Ozone gone, acid rain,
  blindness
  2nd and 3rd degree
  burns
• 0.1 0.01 0.1 two
  million Shock waves, flash incineration,
  
  tidal waves, radioactivity (14C)
• 
  End of life as we know it.

Depends on uncertain efficiency for conversion
of energetic electrons to optical light