Supernovae and GammaRay Bursts

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Supernovae and Gamma-Ray Bursts
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Summary of Post-Main-Sequence Evolution of Stars
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Supernova
Fusion proceeds formation of Fe core.
Subsequent ignition of nuclear reactions
involving heavier elements
M gt 8 Msun
Fusion stops at formation of C,O core.
M lt 4 Msun
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Fusion of Heavier Elements
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126C 42He ? 168O g
168O 42He ? 2010Ne g
168O 168O ? 2814Si 42He
Onset of Si burning at T 3x109 K
? formation of S, Ar,
? formation of 5426Fe and 5626Fe
? iron core
Final stages of fusion happen extremely rapidly
Si burning lasts only for 2 days.
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The Life Clock of a Massive Star (gt 8 Msun)
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Lets compress a massive stars life into one day
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H ? He
1
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Life on the Main Sequence Expansion to Red
Giant 22 h, 24 min. H burning
2
10
9
3
4
8
5
7
6
H ? He
He ? C, O
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1
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2
10
He burning (Horizontal Branch) 1 h, 35 min, 53
s
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3
4
8
5
7
6
5
He ? C, O
H ? He
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12
1
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C ? Ne, Na, Mg, O
2
10
3
9
4
C burning 6.99 s
8
5
7
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C ? Ne, Na, Mg, O
H ? He
Ne ? O, Mg
He ? C, O
Ne burning 6 ms
235959.996
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C ? Ne, Na, Mg, O
H ? He
Ne ? O, Mg
He ? C, O
O ? Si, S, P
O burning 3.97 ms
235959.99997
C ? Ne, Na, Mg, O
H ? He
Ne ? O, Mg
He ? C, O
O ? Si, S, P
Si ? Fe, Co, Ni
The final 0.03 msec!!
Si burning 0.03 ms
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Observations of Supernovae
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Total energy output
DEne 3x1053 erg ( 100 L0 tlife,0)
DEkin 1051 erg
DEph 1049 erg
Lpk 1043 erg/s 109 L0 Lgalaxy!
Supernovae can easily be seen in distant galaxies.
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SN 2006X in M 100 Observed with the MDM 1.3 m
telescope
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Type I and II Supernovae
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Core collapse of a massive star Type II Supernova
Light curve shapes dominated by delayed energy
input due to radioactive decay of 5628Ni
Type II P
Collapse of an accreting White Dwarf exceeding
the Chandrasekhar mass limit ? Type Ia Supernova.
Type II L
Type I No hydrogen lines in the spectrum Type
II Hydrogen lines in the spectrum
Type Ib He-rich Type Ic He-poor
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The Famous Supernova of 1987SN 1987A
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Unusual type II Supernova in the Large Magellanic
Cloud in Feb. 1987
Before
At maximum
Progenitor Blue supergiant (denser than normal
SN II progenitor)
20 M0 lost 1.4 1.6 M0 prior to SN
Evolved from red to blue 40,000 yr prior to SN
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The Remnant of SN 1987A
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Ring due to SN ejecta catching up with pre-SN
stellar wind also observable in X-rays.
vej 0.1 c
Neutrinos from SN1987 have been observed by
Kamiokande (Japan)
Escape before shock becomes opaque to neutrinos ?
before peak of light curve
provided firm upper limit on ne mass mne lt 16 eV
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Remnant of SN1978A in X-rays
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Color contours Chandra X-ray image
White contours HST optical image
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Supernova Remnants
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X-rays
The Crab Nebula Remnant of a supernova observed
in a.d. 1054
The Veil Nebula
Optical
Cassiopeia A
The Cygnus Loop
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Synchrotron Emission and Cosmic-Ray Acceleration
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The shocks of supernova remnants accelerate
protons and electrons to extremely high,
relativistic energies.
?Cosmic Rays
In magnetic fields, these relativistic electrons
emit
Synchrotron Radiation.
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Synchrotron Radiation
Power-law distribution of relativistic electrons
Ne(g) g-p
jn n-a a (p-1)/2
kn n-b b (p4)/2
Opt. thick
In
Opt. thin
n5/2
n-(p-1)/2
n
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Synchrotron Spectra of SNR shocks (I)
Electrons are accelerated at the shock front of
the supernova remnant
Ne Ne(g, t)
.
?Ne/?t -(?/?g)(gNe) Q(g,t)
Q(g,t) Q0 g-q
g-q
Ne (g,t)
Uncooled
Cooled
g-(q1)
g
gc
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Synchrotron Spectra of SNR shocks (II)
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Resulting synchrotron spectrum
Opt. thin, uncooled
Opt. thick
n-(q-1)/2
In
n5/2
Opt. thin, cooled
n-q/2
n
nsy,c nsy (gc)
Find the age of the remnant from t (gc/ggc)
.
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Gamma-Ray Bursts(GRBs)
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Short (sub-second to minutes) flashes of
gamma-rays
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GRB Light Curves
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Long GRBs (duration gt 2 s)
Short GRBs (duration lt 1 s)
Possibly two different types of GRBs Long and
short bursts
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General Properties
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• Random distribution in the sky

• Approx. 1 GRB per day observed

• No repeating GRB sources

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Afterglows of GRBs
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On the day of the GRB
3 days after the GRB
X-ray afterglow of GRB 970228 (GRBs are named by
their date Feb. 28, 1997)
Most GRBs have gradually decaying afterglows in
X-rays, some also in optical and radio.
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1 day after GRB
2 days after GRB
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Optical afterglow of GRB 990510 (May 10, 1999)
Optical afterglows of GRBs are extremely
difficult to localize Very faint ( 18 20
mag.) decaying within a few days.
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Optical Afterglows of GRBs
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Host Galaxy
Long GRBs are often found in the spiral arms
(star forming regions!) of very faint host
galaxies
Optical Afterglow
Optical afterglow of GRB 990123, observed with
Hubble Space Telescope (HST/STIS)
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Energy Output of GRBs
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Observed brightness combined with large distance
implies huge energy output of GRBs, if they are
emitting isotropically E 1054 erg L 1051
erg/s
Energy equivalent to the entire mass of the sun
(E mc2), converted into gamma-rays in just a
few seconds!
another one, observed by us with the MDM 1.3 m
telescope on Kitt Peak!
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Beaming
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Evidence that GRBs are not emitting isotropically
(i.e. with the same intensity in all directions),
but they are beamed
E.g., achromatic breaks in afterglow light curves.
GRB 990510
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Models of GRBs (I)
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Theres no consensus about what causes GRBs.
Several models have been suggested, e.g.
Hypernova
Supernova explosion of a very massive (gt 25 Msun)
star
Iron core collapse forming a black hole
Material from the outer shells accreting onto the
black hole
Accretion disk gt Jets gt GRB!
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Models of GRBs (II)
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Black-hole neutron-star merger
Black hole and neutron star (or 2 neutron stars)
orbiting each other in a binary system
Neutron star will be destroyed by tidal effects
neutron star matter accretes onto black hole
gt Accretion disk gt Jets gt GRB!
Model works probably only for short GRBs.