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E. Pian - INAF, Trieste Astronomical Observatory

Santorini, 1 September 2005. Multiwavelength Spectral Properties of Gamma-Ray Bursts. E. Pian - INAF, Trieste Astronomical Observatory. Outline. Spectral evolution of prompt event. Transition between multiwavelength prompt event and afterglow.

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E. Pian - INAF, Trieste Astronomical Observatory

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  1. Santorini, 1 September 2005 Multiwavelength Spectral Properties of Gamma-Ray Bursts E. Pian - INAF, Trieste Astronomical Observatory

  2. Outline Spectral evolution of prompt event Transition between multiwavelength prompt event and afterglow Diagnostic of circumburst medium from spectroscopy of the optical flash X-ray Flashes

  3. Spectral evolution of prompt event 2-26 keV 40-700 keV Frontera et al. 2000

  4. More on spectral evolution

  5. When does the afterglow start? I(E,t)  S(t1,t2) = fluence R(t1,t2)  S(t1,t2) / S(t2,) = = K(1,2)[ ]

  6. Transition between Prompt event and Afterglow in the 2-10 keV range Solid curve: Best fit (K>1) Dashed curve: Expected curve Assuming no Spectral softening Between GRB and afterglow

  7. GRB920723 Burenin et al. 1999 Tkachenko et al. 2000 See also GRB980923, Giblin et al. 1999

  8. radio GRB990510 Harrison et al. 1999; Wijers et al. 1999 optical Pol. flux

  9. WFC last peak  = 1 NFI GRB990510  = 2 Pian et al 2001

  10. WFC NFI GRB990510

  11. Synthetic spectra From external Shock model Ec Em Sari et al. 1998

  12. Time behavior of peak energy

  13. GRB990123 WFC MECS 2-10 keV 15-28 keV PDS Maiorano et al. 2004 Corsi et al. 2004

  14. GRB990123 (z = 1.6) Fruchter et al. 1999

  15. GRB041219a: Optical flash from internal shocks RAPTOR Internal shock ROTSE-I Reverse shock Akerlof et al. 1999; Vestrand et al. 2005

  16. Optical Flashes Guidorzi et al. 2005

  17. GRB050502a z = 3.793 Liverpool 2m telescope + Robonet consortium Forward shock in ISM In variable density Environment Guidorzi et al. 2005

  18. X-ray Flashes

  19. XRF030723 Fynbo et al. 2004 Soderberg et al. 2004 Tominaga et al. 2004

  20. X-Ray Flashes: • High z  unlikely • large viewing angle • low bulk Lorentz factor (dirty fireball) • high bulk Lorentz factor • low contrast in bulk Lorentz factor

  21. XRF020427 BSAX WFC WFC MECS CXO GRBM z ≾ 1 • > 200 Epeak < 5.5 keV Amati et al. 2004

  22. Summary Hard-to-soft evolution of prompt gamma-ray event. Peak Energy decreases while external shock develops Afterglow starts at ~50% of GRB duration. Transition is Seen in gamma- and X-ray spectra. Timing of afterglow May different from GRB Optical flashes: diagnostic of early emission processes (GRB990123; GRB041219a) and circumburst medium (GRB050502a) XRF: intrinsic difference vs viewing angle. At least some XRFs may be GRBs with a narrow distribution of Lorentz factors (XRF020427), and with low contrast in the colliding shells

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