Transcript Document

Gamma-Ray Bursts
Aurélien Bouvier
April 1st, 2009
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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, I’ll click on the
link below:
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Video
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Outline
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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:
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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
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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 > 100
-> Ultrarelativistic outflow
(fastest bulk flow in the
universe)
Briggs et al. 1999
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BATSE results
• Isotropic distribution:
-> 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
-> 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):
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• 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 (> 40 Msun),
rotating, low-metallicity star:
• Massive for a corecollapse 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
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
• 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:
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Afterglow localized outside older galaxies
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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Good candidate for gravitational wave detection
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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
(>1018 eV-1020 eV)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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What’s now?
• Swift :
• Very fast X-ray/optical afterglow
observations
• Short GRBs
• Detection of flares…
• Naked eye bursts:
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
• 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
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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Fermi: GRB results
8 keV – 260 keV
• 7 GRBs detected with
the LAT instrument
260 keV – 5 MeV
The big one:
GRB 080916C
LAT raw
Lots of >100 MeV emission
Delayed high-energy emission
LAT > 100 MeV
No significant rising HE component
Long high-energy extended
emission (up to 23 min after
onset)
LAT > 1 GeV
T0
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Some cool stuff this allows us to do…
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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
Pulsar
GRB
(Kaaret 99) (Ellis 06)
1015
1.8x1015 0.9x1016
1016
AGN
(Biller 98)
4x1016
GRB
AGN
(Boggs 04)(Aharonian 08)
1017
1.8x1017
GRB080916C
min MQG
(GeV)
7.2x1017
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1018 1.5x10
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Planck mass
1019 1.2x1019
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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 there’s still people telling me
my research is useless !!!
Well ok maybe it is… :)
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