Gamma-Ray Bursts

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Gamma-Ray Bursts

• Aurélien Bouvier

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about me
- Name Aurélien Bouvier - Nationality bloody
french - Position slave for the Fermi team -
Interest jumping out of a perfectly functioning
airplane

• If you pretend being interested in the stuff
  about me, Ill click on the link below
• Video

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Outline

• A bit of history
• GRB observations up to year 2000
• On the theory side (as if I understood)
• Beginning of a new era Swift-Fermi observations

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GRBs - Discovery (1967-1973)

• US Vela Nuclear test detection satellites

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GRB, tell me who you are

• GRBs remained a complete mystery for almost 30
  years !
• More than 150 different theories
• Magnetic flares
• Black Hole evaporation
• Anti-matter accretion
• Deflected AGN jet
• Magnetars, Soft Gamma-Ray Repeaters (SGRs)
• Mini BH devouring NS
• ..

• message from the Aliens

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Compton Gamma-Ray Observatory (CGRO)

• CGRO launched in 1991(orbit above atmospheric
  absorption)

• BATSE (20 keV-1 MeV)
• extremely sensitive gamma-ray detector
  (scintillator)
• EGRET (20 MeV-30 GeV)
• Pair production detector
• looked at the whole sky
• GRB detection rate 1 GRB/day
• thousands of GRBs detected over the whole
  mission

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BATSE results

• 2 populations of GRBs
• Short-Hard / Long-Soft Bursts

Burst duration
Hardness-duration diagram
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GRB lightcurve / spectrum

• Non thermal prompt emission
• Best spectral fit smoothly joining broken power
  law
• Compactness problem
• Emitting region optically
• thin if emitting material
• has Lorentz factor gt 100
• -gt Ultrarelativistic outflow
• (fastest bulk flow in the
• universe)

Briggs et al. 1999
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BATSE results

• Isotropic distribution
• -gt rules out most galactic model
• Galactic (SGRs in a halo surrounding our galaxy)
  Versus Extragalactic origin

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Galactic vs Cosmological origin

• BeppoSAX GRB 970228
• 1st X-ray/Optical afterglows detected
• Host galaxy was identified at z 0.7 !

GRBs are extragalactic !
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Consequence of cosmological origin of GRBs

• Tremendous isotropic-equivalent energy
• 1050 -1054 ergs released in a short time scale
  only in the form of gamma-rays.
• (sun 1033 erg/sec supernova 1051 ergs on a
  month time scale)
• GRBs have been observed up to z 6.3
• -gt hope to use GRB as cosmological tool (similar
  as Type Ia supernovae)

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Evidence of a jet

• Energetic argument the release of isotropic
  energy in the form of gamma-rays is a real
  theoretical nightmare
• Evidence of jet-like emission in the optical
  afterglow lightcurve (but not so widespread)
• Rate of GRBs 1 GRB/galaxy/100,000 years

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High energy behavior

• Little is known about GRB emission above 10 MeV
• EGRET detected a handful of burst but statistics
  is quite poor to draw any paradigm from it
• GRB940217? 18 GeV photons detected up to 90
  minutes after trigger

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Progenitors

• Long-Soft bursts Collapsar model
• Death of a massive (gt 40 Msun), rotating,
  low-metallicity star

• Massive for a core-collapse forming a BH
• Rotating to drive a pair of jet along the
  rotation axis
• Low-metallicity to retain mass an angular
  momentum

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Evidence for the core collapse model

• Long-Soft Bursts located in star forming region
  (irregular galaxies, arms of spiral galaxies)
  were massive stars are always found

• Supernovae connection
• Bump observed in the optical
• afterglow
• Connection with Type Ib/c
• (core-collapse supernovae)

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Progenitors

• Short-Hard Bursts NS-NS (NS-BH) merger

• NS-NS (NS-BH) in a binary system will loose
  energy through gravitational waves
• The 2 objects will get closer until tidal forces
  rip the NS apart and matter falls into a BH.
• The process has ms timescale

• Evidence for the merger model are less striking
• Afterglow localized outside older galaxies
• Good candidate for gravitational wave detection
• Other progenitor still possible (giant magnetar
  flares)

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Fireball model

• Prompt outburst phase (gamma-ray/x-ray) internal
  shocks in the relativistic blast wave.
• Afterglow (x-ray, optical, radio)
• external shock of the cooling fireball with the
  surrounding medium.

Note this is independent of the type of
progenitor
Note 2 this is just the leading candidate (for
good reasons?), many more are out there
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What else are GRB useful for?

• GRB is one of the leading candidate for the
  production of Ultra-relativistic CR (gt1018
  eV-1020 eV)

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Whats now?

• Swift
• Very fast X-ray/optical afterglow observations
• Short GRBs
• Detection of flares
• Naked eye bursts
• Peak magnitude 5.8

• TeV telescopes (Magic, Veritas, HESS),
  gravitational wave interferometers (LIGO, LISA),
  Neutrino detectors (Amanda, ANTARES)

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Fermi

• Fermi CGRO big brother
• GBM (BATSE) 10 keV-20 MeV
• LAT (EGRET) 20 MeV- 300 GeV

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Fermi GRB results

• 7 GRBs detected with the LAT instrument
• The big one
• GRB 080916C
• Lots of gt100 MeV emission
• Delayed high-energy emission
• No significant rising HE component
• Long high-energy extended emission (up to 23 min
  after onset)

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Some cool stuff this allows us to do

• Constraint on minimum bulk Lorentz factor (from
  opacity argument)
• ?min 860 (/-40)

• Quantum gravity
• test for possible energy dependence of the speed
  of light
• 13.2 GeV photon detected 16.5 sec after trigger
• Conservative lower limit on the quantum gravity
  mass (assuming linear energy scaling) MQGgt (1.50
  /- 0.20) x 1018 GeV/c2

Pulsar (Kaaret 99)
GRB (Ellis 06)
GRB (Boggs 04)
AGN (Biller 98)
AGN (Aharonian 08)
GRB080916C
Planck mass
min MQG (GeV)
1.8x1015
0.9x1016
1.8x1017
7.2x1017
4x1016
1.5x1018
1017
1019
1.2x1019
1018
1015
1016
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Philosophical note

• Some studies show that Gamma-Ray Bursts might
  have been responsible for Mass Extinction of life
  on Earth !

And theres still people telling me my research
is useless !!! Well ok maybe it is )