Post on 21-Dec-2015
SASS 2
about me…about me…
• If you pretend being interested in the stuff about me, I’ll click on the link below:
• Video
- Name: Aurélien Bouvier- Nationality: bloody french- Position: slave for the Fermi team- Interest: jumping out of a perfectly functioning airplane
SASS 3
OutlineOutline
• 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
SASS 4
GRBs - Discovery (1967-1973)GRBs - Discovery (1967-1973)
• US Vela Nuclear test detection satellites
SASS 5
GRB, tell me who you are…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
SASS 6
Compton Gamma-Ray Observatory (CGRO)
Compton Gamma-Ray Observatory (CGRO)
• CGRO launched in 1991(orbit above atmospheric absorption)
• BATSE (20 keV-1 MeV):
• extremely sensitive extremely sensitive gamma-ray detector gamma-ray detector ((scintillator))
• EGRET (20 MeV-30 GeV):EGRET (20 MeV-30 GeV):Pair production detectorPair production detector
• looked at the whole skylooked at the whole sky• GRB detection rate ~ 1 GRB/dayGRB detection rate ~ 1 GRB/day• thousands of GRBs detected thousands of GRBs detected over the whole missionover the whole mission
SASS 7
BATSE resultsBATSE results
• 2 populations of GRBs: • Short-Hard / Long-Soft Bursts
Burst duration Hardness-duration diagram
SASS 8
GRB lightcurve / spectrumGRB 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 > 100
-> Ultrarelativistic outflow
(fastest bulk flow in the
universe) Briggs et al. 1999
SASS 9
BATSE resultsBATSE results
• Isotropic distribution:
-> rules out most galactic model
Galactic (SGRs in a halo surrounding our galaxy) Versus Extragalactic origin
SASS 10
Galactic vs Cosmological origin
Galactic vs Cosmological origin
• BeppoSAX: GRB 970228• 1st X-ray/Optical afterglows detected• Host galaxy was identified at z ~ 0.7 !
GRBs are extragalactic !
SASS 11
Consequence of cosmological origin of GRBs
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
-> hope to use GRB as cosmological tool (similar as Type Ia supernovae)
SASS 12
Evidence of a jetEvidence 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
SASS 13
High energy behaviorHigh 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
SASS 14
ProgenitorsProgenitors
• Long-Soft bursts: Collapsar model• Death of a massive (> 40 Msun),
rotating, low-metallicity star:
• MassiveMassive for a core- for a core-collapse forming a BHcollapse forming a BH• RotatingRotating to drive a pair to drive a pair of jet along the rotation of jet along the rotation axisaxis• Low-metallicityLow-metallicity to retain to retain mass an angular mass an angular momentummomentum
SASS 15
Evidence for the core collapse model
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
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• Supernovae connection:•Bump observed in the optical
afterglow
•Connection with Type Ib/c
(core-collapse supernovae)
SASS 16
ProgenitorsProgenitors
• Short-Hard Bursts: NS-NS (NS-BH) merger• NS-NS (NS-BH) in a binary system will NS-NS (NS-BH) in a binary system will loose energy through gravitational loose energy through gravitational waveswaves• The 2 objects will get closer until The 2 objects will get closer until tidal tidal forcesforces rip the NS apart and matter rip the NS apart and matter falls falls into a BHinto a BH..• The process has The process has ms timescalems 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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SASS 17
Fireball modelFireball 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…
SASS 18
What else are GRB useful for?What else are GRB useful for?
• GRB is one of the leading candidate for the production of Ultra-relativistic CR (>1018 eV-1020 eV)
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SASS 19
What’s now?What’s now?
• Swift :• Very fast X-ray/optical afterglow
observations
• Short GRBs
• Detection of flares…
• Naked eye bursts:• Peak magnitude ~ 5.8
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• TeV telescopes (Magic, Veritas, HESS…), gravitational wave interferometers (LIGO, LISA), Neutrino detectors (Amanda, ANTARES…)
SASS 20
FermiFermi
• Fermi: CGRO big brother • GBM (~BATSE): 10 keV-20 MeV
• LAT (~EGRET): 20 MeV- 300 GeV
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SASS 21
Fermi: GRB resultsFermi: GRB results
• 7 GRBs detected with the LAT instrument
The big one:GRB 080916C
Lots of >100 MeV emission
Delayed high-energy emission
No significant rising HE component
Long high-energy extended emission (up to 23 min after onset)
8 keV – 260 keV
260 keV – 5 MeV
LAT raw
LAT > 100 MeV
LAT > 1 GeV
T0
SASS 22
Some cool stuff this allows us to do…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): MQG> (1.50 +/- 0.20) x 1018 GeV/c2
min MQG
(GeV)
1016 1017 10181015 1.8x1015
Pulsar(Kaaret 99)
0.9x1016 1.8x1017 7.2x10174x1016
GRB(Ellis 06)
GRB(Boggs 04)
AGN(Biller 98)
AGN(Aharonian 08)
GRB080916C Planck mass
10191.5x1018 1.2x1019