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Gamma Ray Bursts As High Energy Transients

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Gamma Ray Bursts As High Energy Transients Gamma Ray Bursts as High Energy Transients L. Angelo Antonelli INAF-Oss. Astronomico di Roma ASI Science Data Center INFN sez. Roma 2 “Tor Vergata” Outline 1) Observation • The discovery • CGRO and the burst characterization • BeppoSAX and the afterglow discovery • SWIFT: deep inside the afterglow era • Fermi and the HE domain 2) Models & Physics • The central engine & emitting processes • Progenitors • The environment Gamma Ray Bursts: the discovery • 1967-1979 Vela 4,5,6 satellites: look for X and gamma rays in order to monitor compliance with the Geneva Limited Nuclear Test Ban Treaty of 1963 (no nuclear tests in space and atmosphere) • 105 km Orbits • Launched in pairs – launched 1963-1969 • Operated until 1979 • All satellites allowed for some localization. Gamma Ray Bursts: the discovery • Vela satellites discovered intense flashes of Gamma rays of cosmic origin. • Due to the military nature of the satellites the discovery was maintained classified until 1973 when it was announced to the GAMMA RAY BURSTS (GRBs) (Klebesadel et al. 1973; Strong et al. 1974) astronomical community. What Gamma Ray Bursts are? Klebesadel et al., 1973 Gamma Ray Bursts: the discovery • Non-imaging Cs-I detectors ≈ 150 keV – 750 keV • Coincident events in light curves • Timing studies/ triangulation ⇒ Cosmic origin In 10 years over 73 burst were observed. Klebesadel, Strong, & Olson (1973) Not only Gamma Ray Bursts • The so called “Vela Incident” (sometimes referred to as the South Atlantic Flash) was an unidentified “double flash" of gamma ray that was detected by a Vela satellite on September 22, 1979. • Probably due to a real nuclear experiment performed nearby to the Prince Edward Islands, it was the only terrestrial explosion recorded by these instruments. Gamma Ray Bursts: after the discovery -Many gamma ray burst detectors equipped a large number of spacecrafts. -Hundreds GRBs were discovered from satellite networks through the 80’s. -No clue on source distance Apollo 15 - Harwit in 1984 in the work “Cosmic Discovery” said: “Remarkably little is known about gamma- ray bursts.” Venera 12 Ulysses The InterPlanetary Network • The InterPlanetary Network (IPN) is a group of spacecrafts located in the Solar System and equipped with gamma-ray burst detectors. • By timing the arrival of a burst at several spacecraft, its precise location can be found. The farther apart the detectors, the more precise the location. Theorists’ Paradise With so few constraints, all sort of models were proposed. • Solar System: comet knots, magnetic reconnection in heliopause, etc. • Galactic: SGR, Neutron Star quakes, Magnetic reconnections, etc. • Cosmological: hypernovae, NS-NS mergers, tidal disruption, AGN, matter-antimatter annihilation, etc. Galactic Solar System Energy Requirements may vary over more than 20 orders of magnitude! Fluence:10-7 erg cm-2 2 Energy = Fluence. x d Distance: 1 Gpc Cosmological Energy:1051 erg Distance: 100 kpc Energy: 1043 erg By 1992, over 100 models Existed! Exploring the GRB Phenomenon: CGRO Compton Gamma Ray Observatory (CGRO) • The second of NASA's great observatories • Operational in 1991-2000 • 4 instruments covering the 30 keV – 30 GeV energy range • BATSE observed ~ 1 GRB/day with few degree accuracy and rapid data dissemination, yielding a wealth of new results What CGRO told us about GRBs ? A sample of GRB light curves • Brief (1ms-100s) intense flashes of Gamma-rays • About 1 per day • A GRB does not repeat. • They are isotropically distributed in the sky • No information are available regarding the luminosity BATSE suggestion for a cosmological origin of GRBs • No evidence for anisotropy in GRB directions (Meegan et al. 1992) • Peak count size distribution deviates from -3/2 size distribution GRB Peak Count Rate Distribution -3/2 N ∝ φp Gamma ray burst characteristics: Light Curves • Wide range of morphologies • ~25% have fast rise, slow decay profile • Durations from ms up to thousands of seconds • No evidence for periodicities • No standard shape Empirical correlations: • Hardness-Intensity • hard-to-soft evolution Gamma ray bursts characteristcs: duration distribution. • GRBs duration distribution is double peaked. It peaks around 0.2 s and 20 s. Two Populations: Short – 0.03-3s Long – 3-1000s (e.g. Briggs et al. 2002) • Short GRBs are harder than long GRBs (e.g. Fishman & Meegan, 1995). Gamma ray bursts characteristics: Energy spectra. −α * E ' * E(2 +α) ' F(E) = A( % exp(− % E < Ebreak 100 ( E % ) & ) peak & GRBs spectra are well fitted by * ' (α −β ) ( % 0 E peak - ( (β −α) % the empirical “Band Function”: F(E) = A/(α − β ) , exp β E ≥ Ebreak 100(2 +α) ( E % . [ ]+ ( * ' % ( ( % % a smoothly broken power-law. ) )100 & & (α − β )E E = peak break (2 +α) (Band et al.,1993) α Ebreak β Epeak Band Function parameters Preece et al. (2000) GRBs spectra properties • The time resolved spectral analysis of GRBs shows a hard-to-soft evolution of the spectrum and the decrease of Epeak (e.g. Frontera et al., 2000). Spectral evolution of GRB 000214 is shown in figure (from Antonelli et al., 2002) Long and Short GRBs spectral properties. Short bursts • Short and Long GRBs have the same spectral shape but Long show differences in values bursts of spectral parameters. (Pecesias et al., 2002) BeppoSAX and the Afterglow Era BeppoSAX & GRBs Afterglow • Launched on April 30, 1996 and switched-off on April 30, 2002, deorbited on April 30, 2003 • First and last observation of a GRB on July 20, 1996 and on April 30, 2002 BeppoSAX & GRBs GRB970111: the 1st fast localization & follow-up of a GRB • Triggered by GRBM and localized by the WFC of BeppoSAX • fast follow-up (16 hrs after the GRB) by the NFI. • In MECS (2-10 keV) image a faint source is detected: F=(1.2±0.3)x10-13 cgs (Feroci, Antonelli, Guainazzi, et al., 1998) GRB970228: the 1st X-ray and Optical afterglow • Fast follow up with NFI (8hr) led to discover a bright unknown X-ray source. • A second pointing 3 days after showed the source (Costa, et al., 1997) faded. Thanks to the good X-ray position an optical fading source could be observed. (Van Paradijs, et al., 1997) GRB970508: the 1st redshift • Images in the 2-10 keV range by the BSAX WFC (10-200 sec after the GRB) and by the BSAX MECS (6 hrs and 3 days). The BSAX observation led the Caltech group to the measurement of the first redshift and Frail et al. to the discovery of the 1st radio afterglow and direct measurement of relativistic expansion Metzeger et al., 1997 GRBs are definitively sources at cosmological distances! GRB970508: direct evidence of relativistic expansion • Discovery of the radio afterglow • Direct evidence of a relativistic expanding source. In the first 3 weeks the radio source exhibited erratic variations that then disappeared. if it is due to diffractive scintillation of radio waves on interstellar electrons, the damping of the fluctuations later on indicates that the source had expanded to a greater size 1 month => 1017 cm knowing source distance, a relativistic velocity is derived (Frail et al., 1997). GRB Redshifts (2000) GRB Redshift Isotropic GRB Redshift Isotropic Energy Energy GRB970228 0.695 5x1051 GRB990308 >1.2? NA GRB970508 0.835 8x1051 GRB990506 1.3 NA GRB970828 0.958 NA GRB990510 1.619 3x1053 GRB971214 3.418 3x1053 GRB990705 0.86 NA GRB980326 1? 3x1051 GRB990712 0.430 NA GRB980329 2 or 3-5 NA GRB991208 0.706 1.3x1053 GRB980425 0.0085 1048 GRB991216 1.02 6.7x1053 GRB980613 1.096 NA GRB000131 4.5 1054 GRB980703 0.966 1x1053 GRB000418 1.118 5x1052 GRB990123 1.600 3x1054 GRB000926 2.066 2.6x1053 GRBs are definitively sources at cosmological distances as well as the most energetic sources in the Universe! Amati Relation between Epk and Eiso Evidence for a strong correlation between Ep and Eiso 0.52±0.06 Epk = kEiso (Lamb et al. 2004) (Amati et al. 2002) • spans 5 orders of magnitude in Eiso and 3 orders of magnitude in Epk Power laws: the hallmark of afterglows -δ • Fx(t) ∝ t , δx≈1.1-1.4 -α • Fx(ν) ∝ ν , αx≈1.1 Prompt domain Afterglow domain GB000926:Piro et al, 01 Simultaneous Optical and X-ray light curves of GB990510 • Late time optical light curves of GRBs afterglow are also decaying following a typical power law behavior. • Decay behavior is not depending on wavelength (with some exception) • GRB 990510: a break in the OT at t=1 day is observed (Harrison et al 99) • BeppoSAX light curve compatible with break 1 10 T-T0(days) (Kuulkers, Antonelli, Kuiper et al., 2000) HOST GALAXIES OF GRB Bluish star-forming galaxies: dwarf irregulars or spiral host galaxies ~ 1/3 dark bursts ⇒ Dusty media? ⇒ Regions of active star formation van Paradijs et al. (2000) The GRB-SN Connection GB980425: in the BeppoSAX error box: SN1998bw (Pian et al99,Kulkarni et al, Galama et al al 98). Exploded within 1 day from the GRB. Chance P=10-4 The GRB-SN Connection • GRB optical counterparts coincident with center or spiral arms of galaxy hosts • Reddened supernova emission in late time optical afterglow spectra • SN bumps in some GRB light curves behavior GRB 980326 (Bloom et al. 99) Bloom et al. (2002) (Della Valle et al. 2003) GRB 030329: the smocking gun Matheson et al. 2004 Stanek et al. 2004 • Optical afterglow spectrum resembles that of SN1998bw • Broad, shallow absorption lines imply large expansion velocities • GRB030329 was a bright (top 1%) nearby (z = 0.17) burst, discovered by HETE-II • Afterglow light curve can be decomposed into two components: • Its optical afterglow light curve and spectrum power law decay + supernova bump point clearly to an underlying supernova Ic (SN1998bw redshifted) component (SN2003dh)
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