Gamma Ray Bursts: a new tool for astrophysics and cosmology?

Guido BarbielliniUniversity and INFN Trieste

Outline

Introduction GRB and cosmology

The Fireball model The Afterglow

External density Iron lines

The Prompt Emission Internal shocks problems

The Progenitor Supranova Collapsars Cannonballs

The fireworks model

BeppoSAX Afterglow detection HST host galaxies images

Gamma-Ray Bursts

Temporal behaviourSpectral shape

Spatial distribution

CGRO-BATSE (1991-2000)

CGRO/BATSE (25 KeV÷10 MeV)

The great debate (1995) Fluence:10-7 erg cm-2 s-1

Distance: 1 GpcEnergy:1051 erg

Distance: 100 kpcEnergy: 1043 erg

Cosmological - Galactic?Need a new type of observation!

GRB: where are they?

Costa et al. (1997)

BeppoSAX and the Afterglows

Kippen et al. (1998) Djorgoski et al. (2000)

• Good Angular resolution (< arcmin)• Observation of the X-Afterglow

• Optical Afterglow (HST, Keck)• Direct observation of the host galaxies• Distance determination

GRB 021004: high precision radiography of ISM from z=2.3

Schaefer et al. 2002

GRB host galaxies and Starburst galaxies

Berger et al 2002

GRB and Cosmology

Schaefer 2003

GRB and Cosmology

Djorgovski et al. 2003

The compactness problem

Light curve variability ~ 1 ms

Non thermal spectra

• Fluence (): (0.1-10) x 10-6 erg/cm2 (/4) • Total Energy: E ~ 1051 ÷ 1052 erg

Briggs et al. (1999)

Very High Optical Depth to pair production

Relativistic motion of the emitting region

The compactness problem

Size Pair fraction

Piran (1999)

The Fireball model

• Relativistic motion of the emitting region• Shock mechanism converts the kinetic energy of the shells into radiation.• Baryon Loading problem

Internal Shocks Source activity Synchrotron Emission Rapid time Variability Low conversion efficiency

External Shock Synchrotron & SSC High conversion efficiency Not easy to justify the rapid variability

The Afterglow model

External Shock scenario Forward + Reverse Shock Jet structure confirmation External density

Blast wave deceleration

Afterglow Theory

Sari, Piran & Narayan (1998)

Afterglow theory

Wijers, Rees & Meszaros (1997) Synchrotron Emission Power Law distribution of e-

Galama et al.(1998)

GRB 970508

GRB 970228

Afterglow Observations

Akerlof et al. (1999)

Reverse shock flash

Covino et al. (1999)

Optical Polarization

GRB 990123

GRB 990510

Afterglow Observations

Frail et al. (1997)

• Radio Scintillation

• Confirmation of Relativistic Motion

GRB 970508

Afterglow Observations

Harrison et al (1999)

Achromatic Break

Woosley (2001)

Jet and Energy Requirements

Frail et al. (2001)

Jet and Energy Requirements

Berger et al. (2003)

GRB 021004: surfing on density waves

Lazzati et al. 2002, Heyl and Perna 2002

Iron Lines

Transient Absorbtion Line

Emission Lines

GRB 990705

Amati et al. (2000)

GRB 991216Piro et al. (2000)

Iron Lines theory

Iron Line Geometry

Vietri et al. (2001)

Internal Shock Scenario

Prompt emission Solve variability problem Spectral evolution

Variability

External Shock variability

Internal Shock variability

Norris et al. (1996)

Rise Time ~ Geometry of the Shell

Decay Time ~ Cooling Time

GRB Light curvePiran (1999)

Spectral Evolution

Spectral variability

alphabeta

Epeak

Preece et al. (2000)

Progenitors

Two populations of GRB? Main models Possible solution?

Progenitors

Short GRB

Long GRB

NS/BH Binary Mergers

Merging of compact objects (NS-NS, NS-BH, BH-BH). These objects are observed in our Galaxy.The merging time is about 108 yr, via GW emission.

Eichler et. al. (1989)

Collapsar model

• Very massive star that collapses in a rapidly spinning BH. • Identification with SN explosion.

Woosley (1993)

Collapsar Model

Jets out of the Envelope

Paczynski (1998)

Ramirez Ruiz et al. (2002)

Supranova

SupraMassive NSBaryon Clean Environment

Salgado et. al. (1994)

Vietri & Stella (1998)

Cannonball

Two stage mechanism

Dar & De Rujula (2000)

Towards a solution?

SN 1998bw - GRB 980425 (Galama et al. 98)

GRB 980326 (Bloom et al. 99)

SN evidence

Towards a solution?Fruchter et al (1999)

Offset from Host Galaxy

Star forming region density

Galama & Wijers (2000)

Towards a solution?

Distance from Host GalaxyFryer et al. (1999)

GRB 011121: “evidence” for collapsar?

Bloom et al. (2002)

GRB 011211: “evidence” for supranova?

Reeves et al. (2002)

GRB 030329: the “smoking gun”?

(Zeh et al. 2003)

GRB 030329: the “smoking gun”?

(Matheson et al. 2003)

Vacuum Breakdown

Charged BHRuffini et al. (1999)

Magnetic Fields and Vacuum Breakdown

Blandford-Znajek mechanismBlandford & Znajek (1977)Brown et al. (2000)Barbiellini, Celotti & Longo (2003)

Guido Barbiellini Guido Barbiellini (University and INFN, Trieste)

Annalisa Celotti Annalisa Celotti (SISSA, Trieste)

Francesco LongoFrancesco Longo (University and INFN, Trieste)

The fireworks model for GRBThe fireworks model for GRB

Available Energy

Blandford-Znajek mechanism for GRB

Blandford & Znajek (1977)Brown et al. (2000)Barbiellini & Longo (2001)

Figure from McDonald, Price and Thorne (1986)

M

ME bhBZ

54103.0

The energetics of the long duration GRB phenomenum is compared with models of a rotating Black Hole (BH) in a strong magnetic field generated by an accreting torus.

Available Energy

Inelastic collision between a rotating BH (10 M)and a massive torus (0.1 M) that falls down onto the BH from the last stable orbit

Conservation of angular momentum:

Available rotational energy:

Available gravitational energy:

Total available energy:

III ttbhbh

3

3232 121

2

1

M

MM

I

IIE bh

bhbh

bhrot bhbh

2,

23

8

3332 cM

M

ME

M

MME t

bh

tbhrot

bh

tbhrot bh

2

3

1

3cM

R

MGM

R

MGME t

bh

bht

bh

bhtgrav

5310 gravrot EEE erg

A rough estimate of the energy extracted from a rotating BH is evaluated with a very simple assumption an inelastic collision between the rotating BH and the torus.

Vacuum Breakdown

Polar cap BH vacuum breakdown

Figure from Heyl 2001

The GRB energy emission is attributed to an high magnetic field that breaks down the vacuum around the BH and gives origin to a e fireball.

Pair production rate

Vacuum Breakdown

Critical magnetic field:

Charge acquired by a BH rotating in an external magnetic field (Wald 1974)

Electric field:

Pair volume:

13105.4 cB Gauss

161022 BJQ C

3

bhRVc

15102E V/cm

The formation of the fireball

Pair density (e.g. Fermi 1966):

Magnetic field density:

Energy per particle:

Energy in plasmoid:

Number of plasmoids:

29108en cm-3

25108BU erg cm-3

40 10 acc erg

4510 Bcplasmoid UVE erg

810Bplasmoid

Bplasmoid E

EN

The energy released in the inelastic collision is available to create a series of plasmoids made of the pairs created and accelerated close to the BH.

The formation of the fireball

Acceleration time scale in E field:

Particle collimation by B field:

Curvature radius:

Randomisation time scale by Compton Scattering in radiation field with temperature T0:

s1010 19

22

acceacc

acc eEc

cmt

s10sinsin

19

acccoll ct

cm)Gauss(

)GeV(103 6

B

E

s10 16accrandt

K101

8T 10

412

0

a

B

After the formation of the plasmoid the particles undergo three processes.

Two phase expansion

Phase 1 (acceleration and collimation) ends when:

Assuming a dependence of the B field: this happens at

Parallel stream with

Internal “temperature”

collrand tt

3 RBcm108

1 R

acc301

1'

1

The first phase of the evolution occurs close to the engine and is responsible of energizing and collimating the shells. It ends when the external magnetic field cannot balance the radiation pressure.

Two phase expansion

Phase 2 (adiabatic expansion) ends at the smaller of the 2 radii:

Fireball matter dominated:

Fireball optically thin to pairs:

R2 estimation Fireball adiabatic expansion

20 Mc

ERR

41

430

0 4

3

ppair TR

ERR

02 50RR

0

2'

'2

1R

R

The second phase of the evolution is a radiation dominated expansion.

Jet Angle estimation

Figure from Landau-Lifšits (1976)

Lorentz factors

Opening angle

Result:

The fireball evolution is hypothized in analogy with the in-flight decay of an elementary particle.

Energy Angle relationship

Predicted Energy-Angle relation

The observed angular distribution of the fireball Lorentz factor is expected to be anisotropic.

GRB 000131

ConclusionsAndersen et al. (2000)

GRB: Gravity at Action

GRB Cosmology