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CEA Explosões Cósmicas de Raios Gama (Gamma-Ray Bursts) breve história dos GRBs breve história dos GRBs BeppoSAX: afterglows BeppoSAX: afterglows galáxias.

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Presentation on theme: "CEA Explosões Cósmicas de Raios Gama (Gamma-Ray Bursts) breve história dos GRBs breve história dos GRBs BeppoSAX: afterglows BeppoSAX: afterglows galáxias."— Presentation transcript:

1 CEA Explosões Cósmicas de Raios Gama (Gamma-Ray Bursts) breve história dos GRBs breve história dos GRBs BeppoSAX: afterglows BeppoSAX: afterglows galáxias hospedeiras e redshifts galáxias hospedeiras e redshifts modelos para os progenitores modelos para os progenitores resultados recentes (HETE) resultados recentes (HETE) SWIFT, MIRAX e o futuro SWIFT, MIRAX e o futuro João Braga – INPE Nova Física no Espaço 2003

2 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 MeV publication only in 1973 (classified before that) Phenomenology of bursts before the 90s: almost no association with known objects statistically poor distribution no clue

3 CEA History Burst of March 5 th, 1979 intense -ray pulse (0.2 s), ~100 times as intense as any previous burst SNR N49 in LMC (~10,000 ys) 8 s oscillations in ~200 s (softer emission) Nature of GRBs associated with Galactic neutron stars: rapid variability compact object (light-seconds) cyclotron tens of keV B ~ G : = eB/mc emission hundreds of KeV redshifted 511 keV z obs = z 0 (1 – 2GM/c 2 R) periodicity rotation of a NS : R 3 < (GM/4 2 ) T 2

4 CEA BATSE – COMPTON GRO launched on ~10 years 2704 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



7 CEA BATSE – COMPTON GRO 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 - E p decreases with time (in the E.f(E) x E plot) Fluence: ~ erg cm -2 long duration and hard spectrum bursts deviate more from a 3-D Euclidean brightness distribution Euclidean

8 CEA Soft Gamma Ray Repeaters SGR Burst of March 5 th, 1979 Burst of March 5 th, 1979 (SGR ) SNR N49 in LMC (~10,000 ys) SOFT GAMMA RAY REPEATERS bursts repeat in random timescales (normally hundreds of times) (4, maybe 5 objects known) soft spectra (E 100 keV) short duration (~100 ms) Galactic distribution, associated with SNRs possibly associated with magnetars and AXPs

9 CEA Soft Gamma Ray Repeaters SGR

10 CEA BeppoSAX and Afterglows BeppoSAX: 4 narrow field instruments (.1 to 300 keV; ~arcminute res.) Wide Field Camera (2 to 28 keV; 20 0 x 20 0 ; 5; coded-mask) Gamma Ray Burst Monitor (60 to 600 keV; side shield) WFC

11 CEA BeppoSAX and Afterglows 97 Feb 28: GRB Discovered by GRBM and WFC NFIs observe 1SAX J First clear evidence of a GRB X-ray tail Non-thermal spectra X-ray fluence is 40% of -ray fluence

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

13 CEA GRB z=1.6 Keck OT spectrum HST image: host is an irregular, possibly merging system

14 CEA GRBs observed by BeppoSAX


16 CEA

17 CEA Host galaxies Optical IDs distant galaxies (low luminosity, blue) ~30 measured redshifts All in the z = 0.3 – 4.5 range, with the exception of GRB , possibly associated with SN z = OT is never far from center

18 CEA redshifts GRB z=1.6 Keck OT spectrum

19 CEA Energy (isotropy) redshifts

20 CEA redshifts & cosmology

21 CEA Types of Bursts Long and short bursts: 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: Dark bursts: long bursts with X-ray afterglows but no optical or radio afterglows (½ of them). Possible explanations: Absorption in the host galaxy They are beamed away from the observer X-ray flashes (XRFs): X-ray flashes (XRFs): little or no emission above ~ 25 keV. Possibly related to X-ray rich GRBs.

22 CEA Types of Bursts Burst Class Percentage of all bursts Typical duration (sec) Initial gamma- ray emission Afterglow X-ray emission Afterglow optical emission Long (normal) 25%20 Long (dark) 30%20 no Long (X-ray rich or XRF) 25%30 Absent or weak no short 20%0.3 ??

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

24 CEA Progenitors Short GRBs Short GRBs - ?? associated with mergers of compact objects associated with mergers of compact objects SGRs in external galaxies SGRs in external galaxies phase transition to strange stars phase transition to strange stars

25 CEA The fireball model Observed fluxes require erg emitted in seconds in a small region (~km) Relativistic expanding fireball (e ±, ) Problem: Problem: energy would be converted into E k of accelerated baryons, spectrum would be quasi- thermal, and events wouldnt be much longer than ms. Solution:fireball shock model Solution: fireball shock model: shock waves will inevitably occur in the outflow (after fireball becomes transparent) reconvert E k into nonthermal particle and radiation energy.

26 CEA The fireball model internal shocks Complex light curves are due to internal shocks caused by velocity variations. synchrotron power-law GeV range Turbulent magnetic fields built up behind the shocks synchrotron power-law radiation spectrum Compton scattering to GeV range. Jetted fireball jet formation 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

27 CEA The fireball model

28 CEA The cannonball model Bipolar jets of highly relativistic cannon balls are launched axially in core-collapse SNe The CB front surfaces are collisionally heated to ~keV as they cross the SN shell and the wind ejecta from the SN progenitor A gamma-ray pulse in a GRB is the quasi- thermal radiation emitted when a CB becomes visible, boosted and collimated by its highly relativistic motion The afterglow is mainly synchrotron radiation from the electrons the CBs gather by going through the ISM

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


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

32 CEA Ground station network

33 CEA HETE results GRB Bright (>80) burst detected on Sept 21, :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 ± o ) intersection gives error region with 310 arcmin 2 centered at ~ 22h55m30s, ~


35 CEA 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 keV Peak photon flux is ~4 times higher in the 4-25 keV

36 CEA GRB Long duration GRB X-ray rich, but no XRF (high keV flux) z = isotropic energy of 7.8 x erg ( M =0.3, =0.7, H 0 =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


38 CEA GRB Highly significant polarization (9.9%) in the V band measured 1.3 days after the burst z = based on emission lines of host galaxy 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

39 CEA GRB Short, hard GRB detected by FREGATE and WXM on 31 May 2002 Short, intense peak followed by a marginal peak, which is common on short, hard bursts T 50 = 360 msec in the 85 – 300 keV band Preliminary localization 88min after burst, refined IPN localization 5 days after burst RA = +15h 15m 04s, Dec = -19 o (22 square arcmin hexagonal region) Follow-up at radio, optical and X-rays 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

40 CEA GRB 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

41 CEA GRB 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


43 CEA New missions SWIFT (US): SWIFT (US): 3 instruments, large area, bursts/yr, coverage from optical to gamma-rays, arcsecond positions, will detect bursts up to z ~20. Will be launched in INTEGRAL (Europe): INTEGRAL (Europe): launched last year. Several instruments with high energy resolution. EXIST (US): EXIST (US): huge area hard X-ray mission for GLAST (US): GLAST (US): large area high energy gamma-ray mission; will study high energy afterglows. To be launched around MIRAX (Brazil, US, Holland, Germany): 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.

44 CEA Every GRB signals the birth of a sizable stellar-mass black hole somewhere in the observable universe. Long GRBs occur in star forming galaxies at an average redshift of ~1. 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. ~30 redshifts have been measured for GRB hosts and/or afterglows, ranging from 0.25 (or maybe ) to 4.5. BATSE results and current estimates for beaming imply that GRBs occur at a rate of 1000/day in the universe. In a few cases, marginal evidence exist for transient X-ray emission lines and absorption features in the prompt and early afterglows. What we do know about GRBs so far

45 CEA Early afterglows will be carefully studied the missing link between the prompt emission and the afterglow will be identified; The jet configuration will be identified universal structured jet model will be validated by future data; 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; 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); 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). What to expect in the coming years

46 CEA What is the exact nature of the central engine? Why does it work so intermittently, ejecting blobs with large contrast in their bulk Lorentz factors? What is the radiation mechanism of the prompt emission? What is the jet angle? If between 2 o and 20 o, the energy can vary by ~500 (~10 50 – erg) What is the efficiency of converting bulk motion into radiation? Open questions

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