Gamma Ray Bursts: a new tool for astrophysics and cosmology? Guido Barbiellini University and INFN Trieste
Dec 21, 2015
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