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Gamma-Ray Bursts Aurélien Bouvier April 1st, 2009 SASS 1 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: • Video SASS 2 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 SASS 3 GRBs - Discovery (1967-1973) • US Vela Nuclear test detection satellites SASS 4 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 5 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 SASS 6 BATSE results • 2 populations of GRBs: • Short-Hard / Long-Soft Bursts Burst duration Hardness-duration diagram SASS 7 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 SASS 8 BATSE results • Isotropic distribution: -> rules out most galactic model Galactic (SGRs in a halo surrounding our galaxy) Versus Extragalactic origin SASS 9 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 10 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 11 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): SASS • Rate of GRBs ~ 1 GRB/galaxy/100,000 years 12 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 SASS 13 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 SASS 14 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) SASS 15 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 QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. • Good candidate for gravitational wave detection • Other progenitor still possible (giant magnetar flares…) SASS 16 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… SASS 17 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. SASS 18 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…) SASS 19 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. SASS 20 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 SASS 21 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 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 18 1018 1.5x10 SASS Planck mass 1019 1.2x1019 22 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… :) SASS 23