Gamma-Ray Bursts: The Biggest Explosions Since the Big Bang Edo Berger

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


(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



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



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


are needed to see this picture.NS+NS

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”)







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





GRBs result from the death of massive stars

Long

Short

Two types of gamma-ray bursts






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



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

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Gamma-Ray Bursts: The Biggest Explosions Since the Big Bang Edo Berger