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High energy emission in Gamma Ray Bursts

High energy emission in Gamma Ray Bursts. Gabriele Ghisellini INAF – Osservatorio Astronomico di Brera. “Pillars” of knowledge. Criterion: the most important and not controversial facts constructing the basics of our understanding. 1st Pillar: GRBs are cosmological

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High energy emission in Gamma Ray Bursts

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  1. High energy emission in Gamma Ray Bursts Gabriele Ghisellini INAF – Osservatorio Astronomico di Brera

  2. “Pillars” of knowledge Criterion:the most important and not controversial facts constructing the basics of our understanding

  3. 1st Pillar: GRBs are cosmological (therefore large energetics, but how large? Depends on collimation…). Thanks to BeppoSAX and its team, led by Luigi Piro, and to Paczynski) 970508; z=0.835 970228 Metzeger+ 2007 Costa+ 2007

  4. Attention: not bolometric for Swift

  5. 2nd Pillar: GRBs have large G (From GeV; msec variability; radio scintillation; theory) 090510 970508 Frail+ 1997: G~4 two weeks after Abdo+ 2009; Ghirlanda+ 2010; GG+2010; Ackermann+ 2010: G>1000

  6. 3rd Pillar: Prompt+Afterglow (but X-rays may be late prompt). Energy is NOT released ENTIRELY during the prompt. Prompt SAX X-ray afterglow light curve Before Swift After Swift Piro astro-ph/0001436 Willingale et al. 2007

  7. 4th Pillar: Long & Short But there are exceptions + extended emission SHORT LONG Short – Hard Long - Soft

  8. 5th Pillar: Same Dt of spikes during the prompt A process that repeats itself Spikes have same duration

  9. 6th Pillar: Supernova connection i.e. progenitors. But there are exceptions. Evidence can be gathered only from nearby, under-luminous GRBs. No SN 060614 060218 Campana+ 2006 Della Valle+ 2006 Woosley Bloom 2006

  10. 7th Pillar: Phenomenology of the prompt & “afterglow” Diversity, but some common behavior exists. 2 examples: The total energy of the prompt correlates with peak of the spectrum The early X-ray afterglow is “typical” 1000 steep flares Short Long Log X-ray flux 100 EpeakkeV ? 10 flat steep Eisoerg Log time

  11. Ideas (and enigmas)

  12. Central Engine Black hole or magnetar, or more exotic? (quark star?) Magnetars: Giant flares to explain SGRBs + some short (but numbers are not ok) During the magnetar phase: flat X-ray plateaux Magnetar  BH transition (re-edition of SupraNova). GRBs from quark stars: one-way membrane for baryons, only e+-, photons, B-fields escape… Paczynski & Haensel 2005 MNRAS 362, L4

  13. Magnetic or matter dominated? Internal pressure: Random  bulk  random Disorder  order  disorder “Heavy FB”  optical flash Blandford: bulk  random order  disorder Light “FB”  no opt. flash, no inertia, very large G Dissipation at large R. Variability through mini-jets or small scale instabilities? (Lyutikov) Annihilation R~109 cm G=? G~100

  14. In any case: ~Everybody: At the start: B0~1015 G for BZ Conversion of Poynting to kinetic Cyclo n >mec2 Smaller scattering cross section Different Eg different B0? Is the funnel useful to collimate? No, it is a myth, short can do without, as well as blazars L ~ B02R02c/8p ~ 1051B152R62 erg/s G=? B0~1015 G R~106 cm

  15. Internal shocks: collisions within the flow. Dissipate RELATIVE kinetic energy Lazzati+ 1999 Efficiency is small. Big prompt/afterglow ratio Even bigger if X-rays are late prompt. GeV relax, but not enough. 5% G2/G1 Willingale+ 2007 Log Eafterglow Eaft ~ Eprompt/10 Log Eprompt

  16. Internal shocks: collisions within the flow. Dissipate RELATIVE kinetic energy Efficiency is small. Big prompt/afterglow ratio Even bigger if X-rays are late prompt. GeV relax, but not enough. Deep impacts? Lazzati+ 2009

  17. What makes the light we see? For the prompt: we don’t know. Must be efficient:  short cooling time. If synchro, or IC: F(E) = k E-1/2. SSC even steeper: kE-3/4

  18. Kaneko+ 2006 Nava PhD thesis 2009 Line of death for cooling e- Line of death for non cooling e-

  19. “Afterglows”: X-rays and the optical have often different behaviors. optical Is this “real” afterglow? i.e. external shock? X-ray TA

  20. 2 components? Late prompt+forward shock light curves resemble t-5/3, like rate of fallback material alateprompt ~5/3

  21. Spectral-energy correlations Epeak a b LognFn GBM Logn

  22. Amati, Ghirlanda, Firmani, Yonetoku… Under attack from the start (selection effects). Fiery replies. 97 GRBs Ep-Eiso0.5 “Amati” Ghirlanda 2009

  23. Amati, Ghirlanda, Firmani, Yonetoku… Under attack from the start (selection effects). Fiery replies. q2jet 97 GRBs Ep-Eiso0.5 “Amati” Ghirlanda 2009

  24. Amati, Ghirlanda, Firmani, Yonetoku… Under attack from the start (selection effects). Fiery replies. 29 GRBs Ep-Eγ1.03 q2jet 97 GRBs Ep-Eiso0.5 “Ghirlanda” “Amati” Ghirlanda 2009

  25. Yet we see the “Epeak-L” correlation in single GRBs Rate Ghirlanda+ 2009 This is not due to selection effects.!! Epeak [keV] Epeak =k L1/2 FERMI-GBM Luminosity [erg/s]

  26. High energy

  27. 18 GeV EGRET: 100 MeV-10 GeV Hurley et al. 1994

  28. Fermi: 100 MeV - 100 GeV GG+ 2010

  29. short

  30. a b G Log nFn GBM LAT Log n

  31. a G b Log nFn Log n LAT GBM bvsG avsG G

  32. The 4 brightest LAT GRBs t-10/7 Spectrum and decay: afterglow = forward shock in the circum-burst medium This is puzzling

  33. Adiabatic fireballs: Lbolom = a t-1 Radiative fireballs: Lbolom = b t-10/7

  34. The 4 brightest LAT GRBs t-10/7 Radiative!

  35. The 4 brightest LAT GRBs t-10/7 Radiative?

  36. e

  37. e

  38. e e- e+

  39. e p e- e+

  40. Time Time

  41. GRB 090510 Fermi-LAT • Short • Very hard • z=0.903 • Detected by the LAT up to 31 GeV!! • Well defined timing • Delay: ~GeV arrive after ~MeV (fraction of seconds) • Quantum Gravity? Violation of Lorentz invariance?

  42. precursor 8-260 keV 0.26-5 MeV Delay between GBM and LAT Due to Lorentz invariance violation? LAT all Abdo et al 2009 >100 MeV >1 GeV 31 GeV 0.6s 0.5s Time since trigger (precursor)

  43. 0.1 GeV 30 GeV Average Different component Time resolved 0.5-1s 2 3 nF(n) [erg/cm2/s] If LAT and GBM radiation are cospatial: G>1000 to avoid photon-photon absorption 3 4 Abdo et al 2009 1 If G>1000: deceleration of the fireball occurs early  early afterglow! If G>1000: large electron energies  synchrotron afterglow! Energy [keV]

  44. Fermi-LAT t2 t-1.5 Ghirlanda+ 2010

  45. 0.1-1 GeV Ghirlanda+ 2010 >1 GeV T-T* [s]

  46. ~MeV and ~GeV emission are NOT cospatial. But the ~GeV emission is… No measurable delay in arrival time of high energy photons: tdelay<0.2 s  Strong limit to quantum gravity  MQG > 4.7 MPlanck Ghirlanda+ 2010 T-T* [s]

  47. Conclusions “Paradigm”: internal+external shocks, synchrotron for both: it does not work Fermi/LAT detection  large G Early high energy (and powerful) afterglow Decay suggests radiative afterglows GRB 090510: Violation of the Lorentz invariance? No (not yet)

  48. 4th Pillar: Long & Short (8) Similar spectra, especially for the first second of long Nava+ 2010 Peak Flux Fluence

  49. Energetics Luminosities Amati corr. Yonetoku corr. LONG GRBs LONG GRBs Ghirlanda et al. 2009 Ghirlanda et al. 2009 A2:Short vs Long: < Energetics ; = Luminosities

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