2. Gamma Ray Bursts: open issues  Brief history  Power  Short history of the paradigm: internal vs external shocks  Afterglows: external shocks  The spectral-energy relations  GRBs for cosmology Gabriele Ghisellini – Osservatorio di Brera

3. Gamma-Ray Bursts: The story begins Treates banning nuclear tests between USA and USSR in early 60s VELA Satellites: X and soft  -ray detectors Klebesadel R.W., Strong I.B., Olson R., 1973, Astrophysical Journal, 182, L85 `Observations of Gamma-Ray Bursts of Cosmic Origin’ Brief, intense flashes of  -rays

5. Shortest 6 ms GRB 910711 Longest ~2000 s GRB 971208 Paciesas et al (2002) Briggs et al (2002) Koveliotou (2002) SHORT LONG Short – Hard Long - Soft Two flavours, long and short

6. Spectra Non thermal spectra featureless continuum power-laws - peak in F power-laws - peak in F F ~ E  F ~ E  E peak

7. 1997: The BeppoSAX satellite Slewing in several hours Italian-Dutch “Satellite per l’ Astronomia X” Instruments Wide Field Cameras: 5% of sky – positioning ~ 4’ 5% of sky – positioning ~ 4’ + Narrow Field Instruments arcmin resolution NFI

8. Discovery of first afterglow! GRB 28 9702 3 March 28 February

9. Optical id. host galaxy: redshifts Cosmological origin ! ~120 / 3000 with z: <0.1 – 6.3 (Batse, SAX, HETE-II, Integral, Swift, …)

10. Huge isotropic equivalent energy! 119 GRBs with z GRB typical Fluence (i.e. time int. flux) is 10 -8 – 10 -4 erg/cm 2 (1keV – 10 MeV) Assume Isotropy Energy and Power

11. GRB are powerful AGN: L < 10 48 erg/sAGN: L < 10 48 erg/s SN: L < 10 45 erg/s (in photons)SN: L < 10 45 erg/s (in photons) GRB: L < 10 53 erg/sGRB: L < 10 53 erg/s Planck power: Mc 2 c 5 R g /c G = = 3.6x10 59 erg/s

12. “first light” & PopIII chemical evolution large scale structures cover the epoch of re-ionization Star Formation Rate Probes of far universe SNIa

13. Huge energy Small Volume Fireball Invented even before knowing that GRBs are cosmological….

14. A short history of fireballs 1978 Cavallo & Rees: fireball: photons trapped by their own pairs 1978 Rees: internal shocks in M87 to transport energy along the jet 1986 Paczynski: Cosmological GRB  L=10 51 erg/s and T~1 MeV 1986 Goodman: T obs remains T during expansion. Doppler balances adiabatic cooling 1992 Pure fireball made by   e+e-. Focussing by gravitation

15. NS e+e-

16. A short history of fireballs 1978 Cavallo & Rees: fireball: photons trapped by their own pairs 1978 Rees: internal shocks in M87 to transport energy along the jet 1986 Paczynski: Cosmological GRB  L=10 51 erg/s and T~1 MeV 1986 Goodman: T obs remains T during expansion. Doppler balances adiabatic cooling 1992 Pure fireball made by   e+e-. Focussing by gravitation 1992 Dirty fireball polluted by baryons. Re-conversion of bulk kinetic into radiation through shocks with external medium 1994 Internal shocks due to shells moving with different 

17. Why internal shocks? Spikes have same duration A process that repeats itself

18. Relativ. e - + B: synchrotron?? Relativ. e - + B: synchrotron Shell still opaque Shell still opaque “The” model: Internal/External Shocks Rees-Meszaros-Piran

19. Progenitors Host galaxies Faint (m R ~ 25 ) galaxies Sites of star formation Low metallicities Bloom et al. 2002 GRBs associated with SN (Ib,c) SN afterglow Matheson et al. 2003 Afterglow re-brightening A few spectroscopic ident. (underluminous?)

20. Progenitors core collapse of massive stars (M > 30 M sun ) long GRBs Collapsar or Hypernova (MacFadyen & Woosley 1999) GRB simultaneous with SN Supranova – two-step collapse (Vietri & Stella 1998) GRB delayed by few months-years Discriminants: host galaxies, location within host, duration, environment, redshift distribution,... compact object mergers (NS-NS, NS-BH) short GRBs ?

21. The engine Accreting torus Formation of a spinning BH + dense torus, sustaining B ~ 10 14 -10 15 G Extraction BH spin energy (0.29 M BH c 2 ) Extract E > 10 52 erg t GRB ~ 10 4 t dyn

22. Jets

23. Jet half opening angle Jet effect  , Surf.  Relativistc beaming: emitting surface  1/    1/   1/ Log(t) Log(F) Jet break  >> 1/

24. Israel et al. 1999 GRB Jet measure “Jet break” Jet break time t break Jet opening angle

25. “True” energetics Frail et al. 2001 Isotropic equivalent energy E true = E iso (1 – cos ) Bloom et al. 2003 E p e a k w a s n o t c o n s i d e r e d …

26. Amati et al. 2002 9+2 BeppoSAX GRBs E peak  E iso 0.5 Peak energy – Isotropic energy Correlation E peak (1+z)

27. Nava et al. 2006; Ghirlanda et al. 2007 “Amati” (62) “Ghirlanda” (25) 1- cos  jet

28. Ghirlanda, Ghisellini, Lazzati & Firmani 2004 Luminosity distance redshift GRBs can be used as cosmological RULERS ! Supernovae GRBs

29. Problems: 1: Efficiency

30. Efficiency=Radiated/total energy Only the RELATIVE kinetic energy can be used! Shells of equal masses Shells of equal energies  final ~ (  1  2 ) 1/2  final ~ (  1  2 ) 1/2 Dynamical efficiency (%) 5%

31. Piro astro-ph/0001436 A lot of kinetic energy should remain to power the afterglow A lot of kinetic energy should remain to power the afterglow SAX X-ray afterglow light curve Prompt

32. Willingale et al. 2007 SWIFT

33. E afterglow < E prompt E afterglow ~ 0.1 E prompt

34. Problems: 2: Early “afterglow”

35. Good old times Piro astro-ph/0001436

36. Now: a mess GRB 050904 z=6.29

37. Panaitescu 2006 X Opt.

38. X-ray and optical behave differently X-rays: steep-flat-steep TATA Is this “real” afterglow? i.e. external shock?

39. Early (normal) prompt: Early (normal) prompt:  >>1 /  j Late prompt: Late prompt:  >1 /  j Late prompt: Late prompt:  =1 /  j Late prompt: Late prompt:  <1 /  j ”real” after- glow Ghisellini et al. 2007

40. Long lasting engine?? R s /c ~ 10 -4 s (for a 10 solar mass BH)R s /c ~ 10 -4 s (for a 10 solar mass BH) Even 10 s are 10 5 dynamical timesEven 10 s are 10 5 dynamical times Two-phase accretion?Two-phase accretion?

41. Conclusions “Paradigm”: internal+external shocks, synchrotron for both: it helps, but it is limiting Efficiency is an issue Efficiency is an issue Progenitors for long: done. For short: not yet Progenitors for long: done. For short: not yet Central engine? How long does it live? Central engine? How long does it live? GRBs as probes of the far universe (continue…) GRBs as probes of the far universe (continue…)

43. There can be a Black Body … but Time resolved spectra Time integrated spectrum The same occurs for ALL GRBs detected by BATSE and with WFC Ghirlanda et al. 2007b

44. Memory

45. E peak =509 keV E peak =503 keV E peak = 416 keV Time [sec] cts/sec E peak = 390 keV EF(E) GRB spectrum evolves with time within single bursts Ghirlanda PhD thesis

46. phot /cm^2 sec Hard to Soft evolution E pea k   E peak,  t),  t) Decrease independent of the rise and decay of the flux

47. E pea k   time Tracking evolution Photon flux Correlated with E peak (t),  (t),  (t)

48. By construction, internal shocks should all be equal. Then, why does the spectrum evolve?

49. Spectra Spectra Fishman & Meegan 1995   E peak

50. Prompt radiation: Synchrotron?

51. Energy spectrum of a cooling electron Fast cooling + synchro: E( ) -1/2 N( ) -3/2

52. Typical synchrotron frequency syn = 3.6x10 6 B  2  /(1+z)  Hz syn = 3.6x10 6 B  2  /(1+z)  Hz Magnetic field from: L B =  B L kin R 2  2 B 2 c =  B L shell Size from: R ~ R 0  2 (internal shock) Electron energy from:  m e c 2 =  e m p c 2 (  ’-1) ~  e m p c 2  B L shell   R 0 B B ~ 1/21/2  ~  e m p /m e

53. Synchrotron  -ray emission?  B  e L kin,shell,50 h syn ~ 400 keV 1/221/2  3 R 0,7 (1+z) 2 t cool ~ 10 - 7  e (  /100) MeV MeV 23sec  Extremely short - No way to make it longer  t cool << t dynamical ~ 10 -2 sec  It must be short, if not, how can the flux vary?

54. 0.2 ms More than exponential

55. -2 -1 0 1 Low energy photon power law index N(E) = kE -  Preece et al. F ~ 1/3 F ~ -1/2

57. Can it be rescued by:  Reacceleration? No, in ISS e- are accelerated only once  Adiabatic losses? No, too small regions would be involved, too much IC  Self absorption? No, lots of e- needed, too much IC  Self Compton? No, t cool too small even in this case

58. Clustering of the optical luminosities

59. Flux vs observed time  =0.48 Nardini et al. 2006

60. Luminosity vs rest frame time  =0.28 Nardini et al. 2006

61. Swift GRBs

62. 3 21 5 27 Pre-Swift +Swift Dark??

63. Lx @ 12 hours pre-Swift (19) Including Swift (30)

64. G1=100, G2=200

65. Thompson, Meszaros & Rees 2007 At R ~ R star the fireball dissipates part of its energy  BB L ~  2 L iso   2 ~ L/L iso L iso ~ R 2   2 T’ 4 ~ ( R/  2  T 4 ~ ( R/  2  T 4  L iso ~ R 2 (L /L iso )T 4  E peak ~ L iso 1/2 L -1/4

66. A short history of fireballs

70. Short Bursts

71. The spectrum of short bursts harder softer

72. Log Epeak Log  short long Ghirlanda et al. 2004 because harder because  is harder, E peak is the same or even smaller

73. Density

74. Star forming regions are dense

75. GRB – Afterglow – Temporal Properties GRB emission in X, Optical Panaitescu & Kumar

76. Why densities are so small?

77. Firmani et al. 2004 L -1.5+-0.05

80. No corr.

82. L x > L opt L opt more clustered than L x v c between optical and X-rays ~same values of  B,  e, E k,iso moderate cooling (small  B ) large Comptonization y parameter different p

83. Universal energy reservoir? Bloom et al. 2003 Frail et al. 2001 Best n from fits Frail et al. 2001

84. Same energy, different angles?

85. Structured jets view  view jet  jet E(  )=const E (  )= E 0  -2  L) = kL -2

86. Universal E peak ? Preece et al. ~200 keV, observer frame BATSE

87. HETE II

88. X-ray flashes Amati et al. +Lamb et al. The “Amati et al.” relation E peak = 100 keV E iso,52 + E iso = E true /  2 E peak = 1/  1/2