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Unifying afterglow diversity

Unifying afterglow diversity. Gabriele Ghisellini INAF-Osservatorio Astronomico di Brera - Italy. with the help of G.Ghirlanda and M. Nardini. X-ray and optical often behave differently. optical. T A. X-ray. Is this “real” afterglow? i.e. external shock?. ~same spectrum. What is T A ?.

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Unifying afterglow diversity

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  1. Unifying afterglow diversity Gabriele Ghisellini INAF-Osservatorio Astronomico di Brera - Italy with the help of G.Ghirlanda and M. Nardini

  2. X-ray and optical often behave differently optical TA X-ray Is this “real” afterglow? i.e. external shock? ~same spectrum What is TA ?

  3. 2 Component model • Component 1: Standard afterglow. Standard=forward shocks in the ISM (e.g. Panaitescu & Kumar 2000) • Component 2: Completely phenomenological. Used for the “flat-steep” part of the light curve. Constant SED (minimum # of parameters). • Both components emit optical and X-rays

  4. X-ray optical

  5. Standard afterglow theory (Panaitescu & Kumar 2000) Optical Afterglow X-ray Afterglow

  6. Component 2: completely phenomenological at this stage Component 2 Component 2

  7. aflat asteep

  8. Sum Sum

  9. X-ray optical

  10. X-ray Afterglow Optical Afterglow

  11. Component 2 Component 2

  12. aflat asteep

  13. Sum Sum

  14. Good fits for all 33 GRBs in the sample • What is “component 2”?

  15. asteep ~5/3 Decay index of steep part of comp 2

  16. ~70 Swift GRBs with z X-rays

  17. t-5/3

  18. t-5/4

  19. Comp 2 Ghisellini+ 2009

  20. t-5/3 Lazzati+ 2008 From averaging the luminosity of flares in different GRBs

  21. t-5/3 M from fallback MacFadyen+ 2001

  22. M from fallback Zhang Woosley Heger 2008 Fallback lasts for quite a long time 103 104 105 106 Time [s]

  23. Fallback Prolonged activity of the central engine • Can we explain TA?

  24. Early (normal) prompt: G>>1/qj Strong, erratic Smooth Late prompt: G>1/qj After the early prompt, the central engine decreases energy and decreases G monotonically Late prompt: G=1/qj Late prompt: G<1/qj ”real” after-glow Ghisellini et al. 2007 R~1013 cm

  25. Early (normal) prompt: G>>1/qj TA Late prompt: G>1/qj Tjet Late prompt: G=1/qj Late prompt: G<1/qj ”real” after-glow Ghisellini et al. 2007 R~1013 cm

  26. Conclusions • 2 components can explain the diversity • Component 2 can be associated with the prolonged activity of the entral engine • Fallback is long  late prompt “forever” • Flares as accretion of denser chunks of fallback material • TA can be explained • Next…

  27. NEXT (Marco Nardini): • Can we also explain the presence/absence of jet breaks?

  28. L ~ GMout ~ t-a3 t-a2 Flux G ~ t-Da/2 t-a3 TA Mout ~ t-(a3+a2)/2 Time

  29. L ~ GMout ~ t-a3 Very cheap L~ Maccr ? t-a2 Flux G ~ t-Da/2 t-a3 TA Mout ~ t-(a3+a2)/2 Time Long lasting engine with two-phase accretion? 1: Very dense torus, large B-field, erratic. 2: Less dense material, smaller B-field, smoother accretion – Fallback?

  30. Tests • SEDs vs light curves X-rays optical Log nFn Log n

  31. Tests • SEDs vs light curves • Some GRBs with no plateau: achromatic breaks?

  32. Tests • SEDs vs light curves • Some GRBs with no plateau: achromatic breaks? • Late ‘jump’ in X-ray light-curves revealing real X-ray afterglow TA Jump=end of late prompt X-ray Flux Time

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