Gamma-Ray Bursts:Gamma-Ray Bursts:The Biggest Explosions Since the Big BangThe Biggest Explosions Since the Big Bang
Edo BergerEdo Berger
Talk Outline
• History and basic observational facts
• Basic Physics: compactness & baryon loading
• The fireball model, afterglows, and jets
• The progenitors of long GRBs
• The progenitors of short GRBs
• GRBs as a powerful cosmological tool
Cosmic Cannon: How an Exploding Star Could Fry EarthBy Robert Roy Britt/Space.com
Gamma-Rays
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Limited Nuclear Test Ban Treaty, 1963
… to prohibit, to prevent, and not to carry out any nuclear weapon test explosion:
(a) in the atmosphere; beyond its limits, including outer space; or under water …
The Vela Satellites
(1963-1970)
The First Gamma-
Ray Burst
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Uncertainty in distance by a factor of one billion
Where Do GRBs Come From?
(1973-1993)
135 theories, less than 100 GRBs!
Short duration, intense energy:New type of supernova? Giant stellar flares?Matter/anti-matter annihilation? Neutron stars? Black holes?
Gamma-Ray Bursts from the
Milky Way
The Compton Gamma-Ray Observatory
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GRBs do not come from the disk of the Milky Way
The “Great Debate” (1995)
“The Distance Scale to Gamma-Ray Bursts”
Bohdan PaczynskiDon Lamb
Galactic Cosmological
The Shapley–Curtis Great Debate (1920) on the “Scale
of the Universe”
Long
Short
Two types of gamma-ray bursts
To solve the GRB mystery it is essential to:• Determine accurate positions• Deliver positions to observers rapidly
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(April 30, 1996)
Delivery time of ~hours
Positions 100x more accurate than BATSE
BeppoSAX
(October 9, 2000)
HETE-2
The Swift Satellite & Future Missions
UV/Optical Telescope
Burst Alert Telescope
X-Ray Telescope
• Event rate ~100/yr• Positions ~1-5”• Lifetime ~2015
GLAST
• 8 keV - 300 GeV• ~150/yr• Launch 10/2007
EXIST• 5-600 keV• All-sky per orbit• 10x Swift sensitivity• ~500-1000/yr• Launch >2015
The First Afterglow (February 28, 1997)
5 hours 3 days
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Afterglows in Visible Light
The Distance to Gamma-Ray Bursts
Low speed(Nearby)
High speed(Far away)
n
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8 billion light-years away
oxygen carbon magnesiumhydrogen
22 sec 47 sec 73 sec
280 sec 450 sec
The Fireball Model(a mini Big Bang, or a super nuclear bomb)
The Compactness & Baryon Loading Problems
⇒ acceleration, thermalization
⇒ thermal GRB
>1051 erg of MeV γ−rays in a few seconds (small region, cδt)
⇒ Fireball: a region optically thick due to electron-positron pair production (e1e2 > mec2 )
The Compactness & Baryon Loading Problems
€
τγγ =f ppσ T Fd 2
mec2R2
~ 1013 Γ−2α
Γ 4~ 1013Γ 6 ⇒ Γ >100
Relativistic motion
The kinetic energy of the baryons is converted to radiation via shocks - internal or external variability points to internal shocks
But...
How do we get only 10-5 Mo in an astrophysical context?
Time
Bri
ghtn
ess
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Courtesy: Tsvi Piran / Hebrew University
The Fireball Model
CollapsarCoalescence
BaryonicMagnetic
Internal ShocksMagnetic instability
External Shock
Εngine energy transport conversion to γ−rays afterglow
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Compact Object Mergers
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BH+NS
Collapsing Massive Stars
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Afterglow Physics
Un-shocked ISM
shocked ISM
Ejecta
CD FS
2 1
γ
N(γγ-p
From the afterglow we can determine the energy, density & geometry
Collimation (“Jets”)
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Energy ReleaseWith jet corrections, we find a narrow distribution of gamma-ray enegy:
Eγ ~ 1.3 1051 erg
Eγiso
Eγ
θjet
The fraction coupled to Γ varies widely.
Quantity is the same, quality differs
Energy Release
Soderberg et al. 2003
Wainwright, Berger & Penprase 2007, ApJ
Long GRBs are Associated with Star Formation
Star Nurseries
GRB 030329: The Rosetta StoneSaturday 3:38 am
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GRBs result from the death of massive stars
Long
Short
Two types of gamma-ray bursts
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LIGO
The Dark Ages of the Universe
GRB Absorption Spectroscopy
Comparison to quasars:
• No proximity effect on galactic scales
• Small impact parameter
• In star forming regions
• Bright(er) [ind. of z]
• High(er) redshift
• Fade away
Redshift Distribution
EB et al. 2005, ApJ
GRB 050505: z = 4.275EB et al. 2006, ApJ
log NH =
22.1 0.1
[S/H] =-1.2 0.06 Z
GRB 050505: Progenitor Properties
CIV extends over ~1000 km/s *
⇒ WR wind from the progenitor
SiIV absorption sensitive to mass and metallicity (Leitherer & Lamers 1991)
⇒ WC Wolf-Rayet star: Z < 0.1Z M < 25 M
* QSOs: correlation length <500 km/s (Rauch et al. 1996)
EB et al. 2006, ApJ
GRB-DLAsEB et al. 2006, ApJ & in prep.
Cosmic ReionizationFan et al. 2005
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Gnedin et al.
Neutral Fraction > 3x10-4
⇐
GRBs and Reionization
Kawai et al. 2005
z = 6.295
log NH ~ 21.3
Z ~ 0.1 Z
xH < 0.6
GRBs
Conclusions
• GRBs require a source of at least 1051 erg (similar to supernovae), but coupled to only 10-5 solar masses
• Very high Lorentz factors are required
• The outflow is collimated in jets
• The progenitors of long GRBs are massive stars
• The progenitors of short GRBs are likely NS-NS or BH-NS binaries
• GRBs are a powerful cosmological tool