April 1st, 2009 SASS 1

Gamma-Ray BurstsGamma-Ray BurstsAurélien Bouvier

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

SASS 23

Philosophical notePhilosophical 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… :)