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

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

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) Costa Metzeger ; z=

Attention: not bolometric for Swift

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

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

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

5th Pillar: Same  t of spikes during the prompt Spikes have same duration A process that repeats itself

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

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

Ideas (and enigmas)

Central Engine Black hole or magnetar, or more exotic? (quark star?) GRBs from quark stars: one-way membrane for baryons, only e+-, photons, B-fields escape… Paczynski & Haensel 2005 MNRAS 362, L4 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).

Magnetic or matter dominated?  ~100 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  Dissipation at large R. Variability through mini- jets or small scale instabilities? (Lyutikov) R~10 9 cm  =? Annihilation

In any case: ~Everybody: At the start: B 0 ~10 15 G for BZ Conversion of Poynting to kinetic Cyclo >m e c 2 Smaller scattering cross section Different E   different B 0 ? Is the funnel useful to collimate? No, it is a myth, short can do without, as well as blazars R~10 6 cm  =? L ~ B 0 2 R 0 2 c/8  ~ B 15 2 R 6 2 erg/s

Efficiency is small. Big prompt/afterglow ratio Even bigger if X-rays are late prompt. GeV relax, but not enough. Internal shocks: collisions within the flow. Dissipate RELATIVE kinetic energy 5% 2/12/12/12/1 Lazzati Willingale Log E afterglow Log E prompt E aft ~ E prompt /10

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

What makes the light we see? we don’t know. 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

Kaneko Nava PhD thesis 2009 Line of death for cooling e- Line of death for non cooling e-

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

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

Log  Log  F Log  F   GBM E peak Spectral-energy correlations

Amati, Ghirlanda, Firmani, Yonetoku… Under attack from the start (selection effects). Fiery replies. Ghirlanda 2009 E p -E iso GRBs “Amati”

Amati, Ghirlanda, Firmani, Yonetoku… Under attack from the start (selection effects). Fiery replies. Ghirlanda 2009 E p -E iso GRBs “Amati”

Amati, Ghirlanda, Firmani, Yonetoku… Under attack from the start (selection effects). Fiery replies. Ghirlanda 2009 E p -E γ 1.03 E p -E iso GRBs 29 GRBs “Amati” “Ghirlanda”

Yet we see the “E peak -L” correlation in single GRBs Luminosity [erg/s] E peak [keV] Rate Ghirlanda E peak =k L 1/2 FERMI-GBM This is not due to selection effects.!!

High energy

Hurley et al EGRET: 100 MeV-10 GeV 18 GeV

GG Fermi: 100 MeV GeV

short

Log  Log  F Log  F    GBM LAT

 vs   vs   Log  Log  F Log  F    GBM LAT

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

Adiabatic fireballs: L bolom = a t -1 Radiative fireballs: L bolom = b t -10/7

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

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

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e+ e- e

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Time Time

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

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

Different component 30 GeV0.1 GeV Average Time resolved 0.5-1s  F( ) [erg/cm 2 /s] Energy [keV] Abdo et al 2009 If LAT and GBM radiation are cospatial:  >1000 to avoid photon-photon absorption If  >1000: deceleration of the fireball occurs early  early afterglow! If  >1000: large electron energies  synchrotron afterglow!

Ghirlanda t2t2t2t2 t -1.5 Fermi-LAT

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

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

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

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

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

FERMI GRBs & TIME INTEGRATED correlations

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/ photons: large entropy (# of photons per particle),   >1 For the afterglow : when it is forward shock it is synchrotron, but when it is late prompt… we don’t know.

Isotropic or collimated? Attention: not bolometric for Swift

Isotropic or collimated? Strongest argument: Ghirlanda relation  <100 Nava+ 2006; Ghirlanda “Amati” “Ghirlanda” 1- cos  jet

For long GRBs: Wolf-Rayet? Isolated or binary? (to give angular momentum). What triggers the SN, if a BH forms? The jet? In all SN Ic? For short: merging NS-NS?

Isotropic or collimated? But this?  No jet breaks  <100

E peak (1+z) Ghirlanda, Ghisellini & Lazzati 2004  r   E peak (1+z) Peak energy vs. True energy E peak  E true 0.7

Homogeneous density Nava et al. 2006

Wind-like density Nava et al “ L o r e n t z i n v a r i a n t ” N  ~ c o n s t ~