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Gamma Ray Bursts João Braga - INPE

Gamma Ray Bursts João Braga - INPE. Dark ages of GRBs BATSE/CGRO: some light GRBs x SGRs, magnetars BeppoSAX: afterglows and IDs Progenitors Host galaxies and cosmology HETE, SWIFT and the future. Dark Ages. July 1967: Vela satellites detect gamma ray outbursts

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Gamma Ray Bursts João Braga - INPE

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  1. Gamma Ray BurstsJoão Braga - INPE • Dark ages of GRBs • BATSE/CGRO: some light • GRBs x SGRs, magnetars • BeppoSAX: afterglows and IDs • Progenitors • Host galaxies and cosmology • HETE, SWIFT and the future

  2. Dark Ages • July 1967: Vela satellites detect gamma ray outbursts • 16 peculiar events of cosmic origin short (~s) photon flashes with E > 100 MeV • publication only in 1973

  3. Dark Ages After ~30 ys  only a reasonable idea of what they are • Phenomenology of bursts in the DAs: • almost no association with known objects • statistically poor distribution  no clue

  4. Dark Ages Burst of March 5th, 1979 SNR N49 in LMC (~10,000 ys) 8 s oscillations in ~200 s  Nature of GRBs associated with Galactic neutron stars: rapid variability  compact object (light-seconds) cyclotron lines @ tens of keV  B ~ 1012 G :  = eB/mc emission lines @ hundreds of KeV  redshifted 511 keV zobs = z0 (1 – 2GM/c2 R) periodicity rotation of a NS : R3 < (GM/42) T2

  5. BATSE – COMPTON GRO • ~3000 bursts (~1 each day) • Isotropic distribution - No concentration towards LMC, M31 or nearby clusters - No dipole and quadupole moments • No spectral lines • No periodicity  Hundreds of models proposed

  6. BATSE – COMPTON GRO Euclidean • Bimodal distribution — most are longer than 2 s — ~1/3 are shorter than 2 s • Spectra: combination of two power-laws - spectrum softens with time - Ep decreases with time (in the E.f(E) x E plot) • Fluence:~ 10-6— 10-4 erg cm-2 long duration and hard spectrum bursts deviate more from a 3-D Euclidean brightness distribution

  7. Soft Gamma Ray Repeaters SGR Burst of March 9th, 1979 SNR N49 in LMC (~10,000 ys) 8 s oscillations in ~200 s  SOFT GAMMA RAY REPEATERS bursts repeat soft spectra (E  100 keV) short duration (~100 ms) Galactic “distribution”, associated with SNRs

  8. Soft Gamma Ray Repeaters SGR

  9. Soft Gamma Ray Repeaters SGR

  10. Rotating magnetized neutron stars dE B2 R64 sin2  =   dt 6 c3 Erot= I 2/2 ; P = 2 / dE .  = I   dt . c 3/2 3IPP 1/2  B =    R3 sin 2

  11. Rotating magnetized neutron stars for SGR 0525-66 (5/3/79): ~1 ms 8 s in ~10 kys . • P ~ 3 x 10-11 s s-1 • B ~1015 G !!  MAGNETAR

  12. Rotating magnetized neutron stars Very high fields  Fastspindown  SGRs are young NSs which should still be associated to SNRs

  13. MAGNETARS

  14. MAGNETARS How do the bursts happen? • NS crust brakes due to EM tensions (starquakes) • Alfvén waves injected in the magnetosphere • particle acceleration • optically thick pair plasma forms • gamma-ray emission

  15. MAGNETARS Problems: In 1900+14, RXTE measured a much . smaller P 2 ys before the 1998 active period  EB increased by more than 100%  Spindown is not magnetic and may be due to relativistic winds (no magnetar!)

  16. BeppoSAX and Afterglows • BeppoSAX: - 4 narrow field instruments (.1 to 300 keV; ~arcminute res.) - Wide Field Camera (2 to 25 keV; 200 x 200 ; 5’; coded-mask) - Gamma Ray Burst Monitor (60 to 600 keV; side shield)

  17. BeppoSAX and Afterglows • 97 Feb 28: GRB 970228 • Discovered by GRBM and WFC • NFIs observe 1SAX J0501.7+1146  First clear evidence of a GRB X-ray tail  Non-thermal spectra  X-ray fluence is 40% of -ray fluence

  18. BeppoSAX and Afterglows • BeppoSAX and RXTE discovered several other afterglows • Optical transients: • Observed in appr. ½ of the well localized bursts • GRB 990123 is the only one observed in the optical when the gamma-ray flash was still going on

  19. GRB 990123

  20. GRB 011121

  21. GRB 011121

  22. Host galaxies • Optical IDs  distant galaxies (low luminosity, blue) • ~20 measured redshifts • All in the z = 0.3 – 4.5 range, with the exception of GRB 980425, possibly associated with SN 1998bw @ z = 0.008 • OT is never far from center

  23. redshifts

  24. Progenitors • Long GRBs are probably associated with massive and short-lived progenitors  GRBs may be associated with rare types of supernovae • Hypernovae: colapse of rotating massive star  black hole accreting from a toroid • Collapsar: coalescence with a compact companion  GRBs and SN-type remnant

  25. Progenitors • Short GRBs are probably associated with mergers of compact objects

  26. The fireball model • Observed fluxes require1054 erg emitted in seconds in a small region (~km)  Relativistic expanding fireball (e± , ) Problem:energy would be converted into Ek of accelerated baryons, spectrum would be quasi-thermal, and events wouldn’t be much longer than ms. Solution:fireball shock model: shock waves will inevitably occur in the outflow (after fireball becomes transparent)  reconvert Ek intononthermal particle and radiation energy.

  27. The fireball model • Complex light curves are due to internal shocks caused by velocity variations. • Turbulent magnetic fields built up behind the shocks  synchrotron power-law radiation spectrum  Compton scattering to GeV range. • Jetted fireball: fireball can be significantly collimated if progenitor is a massive star with rapid rotation  escape route along the rotation axis  jet formation  alleviate energy requirements  higher burst rates

  28. High Energy Transient Explorer • First dedicated GRB mission, X- and g-rays • Equatorial orbit, antisolar pointing launched on Oct 9th, 2000 - Pegasus • 3 instruments, 1.5 sr common FOV SXC (0.5-10 keV) - < 30” localization WXM (2 –25 keV) - < 10’ localization FREGATE (6-400keV) -  sr localization • Rapid dissemination ( 1s) of GRB positions (Internet and GCN)

  29. HETE

  30. HETE Investigator Team RIKEN Masaru Matsuoka Nobuyuki Kawai Atsumasa Yoshida MIT George R. Ricker (PI) Geoffrey Crew John P.Doty Al Levine Roland Vanderspek Joel Villasenor UC Berkeley Kevin Hurley J. Garrett Jernigan UChicago Donald Q. LambCarlo Graziani CESR Jean-Luc Atteia Gilbert Vedrenne Jean-Francois Olive Michel Boer INPE João Braga LANL Edward E. Fenimore Mark Galassi CNR Graziella Pizzichini CNES Jean-Luc Issler UC Santa Cruz Stanford Woosley SUP’AERO Christian Colongo TIRF Ravi Manchanda

  31. HETE in the Pegasus

  32. Ground station network

  33. GRB 010921 • Bright (>80) burst detected on Sept 21, 2001 05:15:50.56 UT by FREGATE • First HETE-discovered GRB with counterpart • Detected by WXM, giving good X position (10o x 20’ strip) • Cross-correlation with Ulysses time history  IPN annulus (radius 60o ± 0.118o) • intersection gives error region with 310 arcmin2 centered at  ~ 22h55m30s,  ~ 40052’

  34. GRB 010921

  35. GRB 010921 • Highly symmetric at high energies • Lower S/N for WXM due to offset • Durations increase by 65% at lower energies • Hard-to-soft spectral evolution • Peak energy flux in the 4-25 keV band is 1/3 of 50-300 keV • Peak photon flux is ~4 times higher in the 4-25 keV

  36. Discussion • Long duration GRB • X-ray rich, but no XRF (high 50-300 keV flux) • z = 0.450 isotropic energy of 7.8 x 1051 erg (M=0.3, =0.7, H0=65 km s-1 Mpc-1) - less if beamed • Second lowest z strong candidate for extended searches for possible associated supernova • Final position available 15.2h after burst ground-based observations in the first night  counterpart established well within HETE-IPN error region

  37. Conclusions • GRBs occur at a rate of (no beaming) a few/day/universe or 1/few million ys/average galaxy or ~10-91 cm-3 s-1 (since observed GRBs are detectable out to z ~10) • New missions are very important SWIFT: 3 instruments, 250-300 bursts/yr, coverage from optical to gamma-rays, arcsecond positions, will detect bursts up to z ~20. INTEGRAL, EXIST, MIRAX • Cosmology: burts can proble early universe and some could be related to Pop III stars  metal enrichment and ionization of the primordial gas.

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