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

Gamma Ray Bursts: a new tool for astrophysics and cosmology?. Guido Barbiellini Universit y and INFN Trieste. BeppoSAX Afterglow detection. HST host galaxies images. Outline. Introduction GRB and cosmology The Fireball model The Afterglow External density Iron lines

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

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  1. Gamma Ray Bursts:a new tool for astrophysics and cosmology? Guido Barbiellini University and INFN Trieste

  2. BeppoSAX Afterglow detection HST host galaxies images 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

  3. Gamma-Ray Bursts Temporal behaviour Spectral shape Spatial distribution

  4. CGRO-BATSE (1991-2000) CGRO/BATSE (25 KeV÷10 MeV)

  5. GRB: where are they? The great debate (1995) Fluence:10-7 erg cm-2 s-1 Distance: 1 Gpc Energy:1051 erg Distance: 100 kpc Energy: 1043 erg Need a new type of observation! Cosmological - Galactic?

  6. BeppoSAX and the Afterglows • Good Angular resolution (< arcmin) • Observation of the X-Afterglow Costa et al. (1997) • Optical Afterglow (HST, Keck) • Direct observation of the host galaxies • Distance determination Kippen et al. (1998) Djorgoski et al. (2000)

  7. GRB 021004: high precision radiography of ISM from z=2.3 Schaefer et al. 2002

  8. GRB host galaxies and Starburst galaxies Berger et al 2002

  9. GRB and Cosmology Schaefer 2003

  10. GRB and Cosmology Djorgovski et al. 2003

  11. Fluence (): (0.1-10) x 10-6 erg/cm2 (/4) • Total Energy: E ~1051 ÷ 1052 erg The compactness problem Briggs et al. (1999) Light curve variability ~ 1 ms Non thermal spectra

  12. The compactness problem Very High Optical Depth to pair production Size Pair fraction Piran (1999) Relativistic motion of the emitting region

  13. The Fireball model • Relativistic motion of the emitting region • Shock mechanism converts the kinetic energy of the shells intoradiation. • Baryon Loading problem • External Shock • Synchrotron & SSC • High conversion efficiency • Not easy to justify the rapid variability • Internal Shocks • Source activity • Synchrotron Emission • Rapid time Variability • Low conversion efficiency

  14. The Afterglow model • External Shock scenario • Forward + Reverse Shock • Jet structure confirmation • External density Blast wave deceleration

  15. Afterglow Theory Sari, Piran & Narayan (1998)

  16. Afterglow theory GRB 970228 Galama et al.(1998) GRB 970508 • Synchrotron Emission • Power Law distribution of e- Wijers, Rees & Meszaros (1997)

  17. Akerlof et al. (1999) Covino et al. (1999) Optical Polarization Reverse shock flash Afterglow Observations GRB 990123 GRB 990510

  18. Afterglow Observations • Radio Scintillation • Confirmation of Relativistic Motion GRB 970508 Frail et al. (1997)

  19. Afterglow Observations Harrison et al (1999) Achromatic Break Woosley (2001)

  20. Jet and Energy Requirements Frail et al. (2001)

  21. Jet and Energy Requirements Berger et al. (2003)

  22. GRB 021004: surfing on density waves Lazzati et al. 2002, Heyl and Perna 2002

  23. Iron Lines GRB 990705 Emission Lines Amati et al. (2000) Transient Absorbtion Line Piro et al. (2000) GRB 991216

  24. Iron Lines theory Vietri et al. (2001) Iron Line Geometry

  25. Internal Shock Scenario • Prompt emission • Solve variability problem • Spectral evolution

  26. Variability Internal Shock variability External Shock variability

  27. Rise Time ~ Geometry of the Shell Decay Time ~ Cooling Time GRB Light curve Piran (1999) Norris et al. (1996)

  28. Spectral Evolution

  29. Spectral variability Epeak beta alpha Preece et al. (2000)

  30. Progenitors • Two populations of GRB? • Main models • Possible solution?

  31. Progenitors Long GRB Short GRB

  32. 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)

  33. Collapsar model Woosley (1993) • Very massive star that collapses in a rapidly spinning BH. • Identification with SN explosion.

  34. Collapsar Model Ramirez Ruiz et al. (2002) Jets out of the Envelope Paczynski (1998)

  35. Supranova Salgado et. al. (1994) SupraMassive NS Baryon Clean Environment Vietri & Stella (1998)

  36. Cannonball Two stage mechanism Dar & De Rujula (2000)

  37. Towards a solution? SN evidence SN 1998bw - GRB 980425 (Galama et al. 98) GRB 980326 (Bloom et al. 99)

  38. Towards a solution? Fruchter et al (1999) Galama & Wijers (2000) Offset from Host Galaxy Star forming region density

  39. Towards a solution? Fryer et al. (1999) Distance from Host Galaxy

  40. GRB 011121: “evidence” for collapsar? Bloom et al. (2002)

  41. GRB 011211: “evidence” for supranova? Reeves et al. (2002)

  42. GRB 030329: the “smoking gun”? (Zeh et al. 2003)

  43. GRB 030329: the “smoking gun”? (Matheson et al. 2003)

  44. Vacuum Breakdown Ruffini et al. (1999) Charged BH

  45. Magnetic Fields and Vacuum Breakdown Blandford & Znajek (1977) Brown et al. (2000) Barbiellini, Celotti & Longo (2003) Blandford-Znajek mechanism

  46. The fireworks model for GRB Guido Barbiellini (University and INFN, Trieste) Annalisa Celotti (SISSA, Trieste) Francesco Longo (University and INFN, Trieste)

  47. Available Energy • Blandford-Znajek mechanism for GRB 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. Blandford & Znajek (1977) Brown et al. (2000) Barbiellini & Longo (2001) Figure from McDonald, Price and Thorne (1986)

  48. Available Energy 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. • 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

  49. Vacuum Breakdown 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. Polar cap BH vacuum breakdown Pair production rate Figure from Heyl 2001

  50. Gauss C V/cm Vacuum Breakdown • Critical magnetic field: • Charge acquired by a BH rotating in an external magnetic field (Wald 1974) • Electric field: • Pair volume:

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