CEA Exploses Csmicas de Raios Gama GammaRay Bursts
CEA Explosões Cósmicas de Raios Gama (Gamma-Ray Bursts) João Braga – INPE n n n breve história dos GRBs Beppo. SAX: afterglows galáxias hospedeiras e redshifts modelos para os progenitores resultados recentes (HETE) SWIFT, MIRAX e o futuro Nova Física no Espaço 2003
CEA History July 1967: Vela satellites detect strong gamma ray signals coming from space 16 peculiar events of cosmic origin short (~s) photon flashes with E > 100 Me. V ð publication only in 1973 (classified before that) ð Phenomenology of bursts before the 90’s: ð ð almost no association with known objects statistically poor distribution no clue
History CEA Burst of March 5 th, 1979 n intense -ray pulse (0. 2 s), ~100 times as intense as any previous burst n SNR N 49 in LMC (~10, 000 ys) n 8 s oscillations in ~200 s (softer emission) Nature of GRBs associated with Galactic neutron stars: n rapid variability compact object (light-seconds) n cyclotron lines @ tens of ke. V B ~ 1012 G : = e. B/mc n emission lines @ hundreds of Ke. V redshifted 511 ke. V zobs = z 0 (1 – 2 GM/c 2 R) n periodicity rotation of a NS : R 3 < (GM/4 2) T 2
CEA • • BATSE – COMPTON GRO launched on 1991 - ~10 years 2704 bursts (~1 each day) Isotropic distribution - No concentration towards LMC, M 31 or nearby clusters - No dipole and quadupole moments • • No spectral lines No periodicity Hundreds of models proposed
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CEA • BATSE – COMPTON GRO Bimodal distribution — most are longer than 2 s Euclidean — ~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
CEA Soft Gamma Ray Repeaters SGR Burst of March 5 th, 1979 (SGR 0526 -66) n SNR N 49 in LMC (~10, 000 ys) SOFT GAMMA RAY REPEATERS bursts repeat in random timescales (normally hundreds of times) (4, maybe 5 objects known) n n soft spectra (E 100 ke. V) n short duration (~100 ms) n Galactic “distribution”, associated with SNRs n possibly associated with magnetars and AXPs
CEA Soft Gamma Ray Repeaters SGR
CEA Beppo. SAX and Afterglows Beppo. SAX: WFC 4 narrow field instruments (. 1 to 300 ke. V; ~arcminute res. ) Wide Field Camera (2 to 28 ke. V; 200 x 200 ; 5’; coded-mask) Gamma Ray Burst Monitor (60 to 600 ke. V; side shield)
Beppo. SAX and Afterglows CEA 97 Feb 28: GRB 970228 n n Discovered by GRBM and WFC NFIs observe 1 SAX J 0501. 7+1146 First clear evidence of a GRB X-ray tail Non-thermal spectra X-ray fluence is 40% of -ray fluence
CEA n n Beppo. SAX and Afterglows Beppo. SAX and RXTE discovered several other afterglows Optical transients: n n 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
CEA GRB 990123 z=1. 6 Keck OT spectrum HST image: host is an irregular, possibly merging system
CEA GRBs observed by Beppo. SAX
CEA GRB 011121
CEA GRB 011121
CEA n Host galaxies Optical IDs distant galaxies (low luminosity, blue) n n n ~30 measured redshifts All in the z = 0. 3 – 4. 5 range, with the exception of GRB 980425, possibly associated with SN 1998 bw @ z = 0. 008 OT is never far from center
CEA redshifts GRB 990123 z=1. 6 Keck OT spectrum
CEA redshifts Energy (isotropy)
CEA redshifts & cosmology
Types of Bursts CEA Long and short bursts: the normal ones. Bimodal distribution; short bursts are harder and have no counterparts; almost all long bursts have X-ray afterglows. Dark bursts: long bursts with X-ray afterglows but no optical or radio afterglows (½ of them). Possible explanations: u u Absorption in the host galaxy They are beamed away from the observer X-ray flashes (XRF’s): little or no emission above ~ 25 ke. V. Possibly related to X-ray rich GRBs.
CEA Burst Class Types of Bursts Percentage of all bursts Typical duration (sec) Initial Afterglow gamma. X-ray emission Long (normal) 25% 20 Long (dark) 30% 20 Long (X-ray rich or XRF) 25% 30 short 20% 0. 3 Afterglow optical emission no Absent or weak no ? ?
CEA Progenitors Long GRBs are probably associated with massive and short-lived progenitors GRBs may be associated with rare types of supernovae n Hypernovae: colapse of rotating massive star black hole accreting from a toroid n Collapsar: coalescence with a compact companion GRBs and SN-type remnant
CEA Progenitors Short GRBs - ? ? associated with mergers of compact objects ð SGRs in external galaxies ð phase transition to strange stars ð
CEA The fireball model Observed fluxes require 1054 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 quasithermal, and events wouldn’t be much longer than ms. Solution: fireball shock model: model shock waves will inevitably occur in the outflow (after fireball becomes transparent) reconvert Ek into nonthermal particle and radiation energy.
CEA n n n 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 Ge. V 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
CEA The fireball model
CEA n. Bipolar The cannonball model jets of highly relativistic cannon balls are launched axially in core-collapse SNe n. The CB front surfaces are collisionally heated to ~ke. V as they cross the SN shell and the wind ejecta from the SN progenitor n. A gamma-ray pulse in a GRB is the quasithermal radiation emitted when a CB becomes visible, boosted and collimated by its highly relativistic motion n. The afterglow is mainly synchrotron radiation from the electrons the CBs gather by going through the ISM
HETE CEA High Energy Transient Explorer space. mit. edu/HETE Ø First dedicated GRB mission, X- and -rays Equatorial orbit, antisolar pointing launched on Oct 9 th, 2000 - Pegasus 3 instruments, 1. 5 sr common FOV Ø SXC (0. 5 -10 ke. V) - < 30” localization WXM (2 – 25 ke. V) - < 10’ localization FREGATE (6 -400 ke. V) - sr localization Rapid dissemination ( 1 s) of GRB positions Ø Ø (Internet and GCN)
CEA HETE
CEA HETE Investigator Team MIT George R. Ricker (PI) Geoffrey Crew John P. Doty Al Levine Roland Vanderspek Joel Villasenor LANL Edward E. Fenimore Mark Galassi UC Santa Cruz Stanford Woosley RIKEN UC Berkeley Masaru Matsuoka Kevin Hurley Nobuyuki Kawai J. Garrett Jernigan Atsumasa Yoshida UChicago CESR Donald Q. Lamb Jean-Luc Atteia Carlo Graziani Gilbert Vedrenne INPE Jean-Francois Olive João Braga Michel Boer CNR CNES Graziella Pizzichini Jean-Luc Issler TIRF SUP’AERO Christian Colongo Ravi Manchanda
CEA Ground station network
CEA n n n HETE results 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 (10 o x 20’ strip) Cross-correlation with Ulysses time history IPN annulus (radius 60 o ± 0. 118 o) intersection gives error region with 310 arcmin 2 centered at ~ 22 h 55 m 30 s, ~ 40052’
CEA GRB 010921
CEA GRB 010921 n Highly symmetric at high energies n Lower S/N for WXM due to offset n Durations increase by 65% at lower energies n Hard-to-soft spectral evolution n Peak energy flux in the 4 -25 ke. V band is 1/3 of 50 -300 ke. V n Peak photon flux is ~4 times higher in the 4 -25 ke. V
CEA GRB 010921 n Long duration GRB n X-ray rich, but no XRF (high 50 -300 ke. V flux) n z = 0. 450 isotropic energy of 7. 8 x 1051 erg ( M=0. 3, =0. 7, H 0=65 km s-1 Mpc-1) - less if beamed n Second lowest z strong candidate for extended searches for possible associated supernova n Final position available 15. 2 h after burst ground-based observations in the first night counterpart established well within HETE-IPN error region
CEA GRB 011211
CEA GRB 020405 n. Highly significant polarization (9. 9%) in the V band measured 1. 3 days after the burst nz = 0. 695 based on emission lines of host galaxy n. High polarization can be due to: line of sight at the very edge of the jet if the magnetic field is restricted to the plane of the shock alignment of the magnetic field over causally connected regions in the observed portion of the afterglow
CEA GRB 020531 n Short, hard GRB detected by FREGATE and WXM on 31 May 2002 n Short, intense peak followed by a marginal peak, which is common on short, hard bursts n T 50 = 360 msec in the 85 – 300 ke. V band n Preliminary localization 88 min after burst, refined IPN localization 5 days after burst RA = +15 h 15 m 04 s, Dec = -19 o 24’ 51” (22 square arcmin hexagonal region) n Follow-up at radio, optical and X-rays n Duration increases with decreasing energy and spectrum evolves from hard to soft ► seem to indicate that short, hard bursts are closed related to long GRBs
CEA n n n n n GRB 021004 detected by Fregate, WXM and SXC duration of ~100 sec (long GRB) GCN position notice (WXM) given 49 s after the beginning of the burst SXC location given 154 min after burst optical afterglow (R) detected in 9 min (15 th mag) HST and Chandra observed in the following day best observed burst so far absorption redshift of 2. 3 (C IV, Si IV, Ly ) unusual brightenings seen in the light curve
CEA n n n GRB 021211 Dark burst Duration of ~2. 5 sec (“ transitional” GRB) GCN position notice (WXM) given 22 s after the beginning of the burst Raptor (LANL) observed 65 sec after burst Optical afterglow extremely faint after 2 hours GRB may have occurred on region with no surrouding gas or dust, so the shock wave had little material to smash into may support the binary merger theory for short GRB
CEA GRB 030115
New missions CEA SWIFT (US): 3 instruments, large area, 250 -300 bursts/yr, coverage from optical to gamma-rays, arcsecond positions, will detect bursts up to z ~20. Will be launched in 2003. INTEGRAL (Europe): launched last year. Several instruments with high energy resolution. EXIST (US): huge area hard X-ray mission for 2010. GLAST (US): large area high energy gamma-ray mission; will study high energy afterglows. To be launched around 2007. MIRAX (Brazil, US, Holland, Germany): broadband imaging (6’) spectroscopy of a large source sample (1000 square degrees) in the central Galactic plane region. Expected to detect ~1 GRB/month. Two hard X-ray cameras and the flight model of the WFC. To be launched in ~2007.
CEA What we do “know” about GRBs so far n Every GRB signals the birth of a sizable stellar-mass black hole somewhere in the observable universe. n Long GRBs occur in star forming galaxies at an average redshift of ~1. n There are now plausible or certain host galaxies found for all but 1 or 2 GRBs with X-ray, optical or radio afterglows positioned with arcsecond precision. n ~30 redshifts have been measured for GRB hosts and/or afterglows, ranging from 0. 25 (or maybe 0. 0085) to 4. 5. n BATSE results and current estimates for beaming imply that GRBs occur at a rate of 1000/day in the universe. n In a few cases, marginal evidence exist for transient X-ray emission lines and absorption features in the prompt and early afterglows.
CEA What to expect in the coming years n Early afterglows will be carefully studied the missing link between the prompt emission and the afterglow will be identified; n The jet configuration will be identified universal structured jet model will be validated by future data; n With accumulation of a large sampe of spectral information and redshifts for GRB/XRF with Swift, we will know a lot more about the site(s) and mechanism(s) for the prompt emission; n Detection of GRB afterglows with z > 6 may provide a unique way to probe the primordial star formation, massive IMF, early IGM, and chemical enrichment at the end of the cosmic reionization era. (Djorgovski et al. 2003); n With Swift, we should get ~120 GRBs to produce Hubble diagrams free of all effects of dust extinction and out to redshifts impossible to reach by any other method (Schaefer 2003).
CEA Open questions n What is the exact nature of the central engine? n Why does it work so intermittently, ejecting blobs with large contrast in their bulk Lorentz factors? n What is the radiation mechanism of the prompt emission? n What is the jet angle? If between 2 o and 20 o, the energy can vary by ~500 (~1050 – 1052 erg) n What is the efficiency of converting bulk motion into radiation?
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