Gamma-Ray Bursts

1. Gamma-Ray Bursts Aurélien Bouvier SASS

2. 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

3. 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

4. GRBs - Discovery (1967-1973) • US Vela Nuclear test detection satellites SASS

5. 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) • 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

7. BATSE results • 2 populations of GRBs: • Short-Hard / Long-Soft Bursts Burst duration Hardness-duration diagram SASS

8. 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

9. BATSE 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 • 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 • 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 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 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. Progenitors • Long-Soft bursts: Collapsar model • Death of a massive (> 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 SASS

15. 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) SASS

16. 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…) SASS

17. 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

18. What else are GRB useful for? • GRB is one of the leading candidate for the production of Ultra-relativistic CR (>1018 eV-1020 eV) SASS

19. What’s 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…) SASS

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

21. 8 keV – 260 keV 260 keV – 5 MeV LAT raw LAT > 100 MeV LAT > 1 GeV T0 Fermi: 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) SASS

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

23. 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