Gamma Ray Bursts: a new tool for astrophysics and cosmology? Guido Barbiellini University 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 behaviour Spectral shape Spatial distribution

CGRO-BATSE ( ) CGRO/BATSE (25 KeV÷10 MeV)

The great debate (1995) Fluence:10 -7 erg cm -2 s -1 Distance: 1 Gpc Energy:10 51 erg Distance: 100 kpc Energy: 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 : 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 erg/cm 2 (  /4  ) Total Energy: E ~ ÷ 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 GRB

Afterglow Observations Akerlof et al. (1999) Reverse shock flash Covino et al. (1999) Optical Polarization GRB GRB

Afterglow Observations Frail et al. (1997) Radio Scintillation Confirmation of Relativistic Motion GRB

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 : surfing on density waves Lazzati et al. 2002, Heyl and Perna 2002

Iron Lines Transient Absorbtion Line Emission Lines GRB Amati et al. (2000) GRB Piro 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 curve Piran (1999)

Spectral Evolution

Spectral variability alpha beta 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 10 8 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 NS Baryon Clean Environment Salgado et. al. (1994) Vietri & Stella (1998)

Cannonball Two stage mechanism Dar & De Rujula (2000)

Towards a solution? SN 1998bw - GRB (Galama et al. 98) GRB (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 Galaxy Fryer et al. (1999)

GRB : “evidence” for collapsar? Bloom et al. (2002)

GRB : “evidence” for supranova? Reeves et al. (2002)

GRB : the “smoking gun”? (Zeh et al. 2003)

GRB : the “smoking gun”? (Matheson et al. 2003)

Vacuum Breakdown Charged BH Ruffini et al. (1999)

Magnetic Fields and Vacuum Breakdown Blandford-Znajek mechanism Blandford & 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 Longo Francesco Longo (University and INFN, Trieste) The 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)  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: 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: Gauss C 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: cm -3 erg cm -3 erg 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 T 0 : 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” 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: R 2 estimation Fireball adiabatic expansion 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 Conclusions Andersen et al. (2000) GRB: Gravity at Action GRB Cosmology