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Gamma-Ray Bursts: the Most Violent Explosions in the Universe Once Upon a Time, … Gamma-rayGamma-ray bursts:bursts: TheThe mostmost violentviolent explosionsexplosions inin thethe UniverseUniverse Olivier Godet [email protected] Presentation available at: http://userpages.irap.omp.eu/~ogodet/ 2015-01-05 Outlines Brief history of Gamma-ray bursts & main discoveries Properties of Gamma-ray bursts • What does the prompt emission tells us? • What does the afterglow emission tell us? GRB model GRB progenitors & host galaxies Opened questions Interests of GRBs in astrophysics & fundamental physics • Cosmology • Quantum gravity The future for the GRB study • Instrumental roadmap in the next 10 years and beyond • The SVOM mission • Non-photonic messengers & instruments Gamma-ray bursts: The most violent explosions in the Universe Once upon a time, … • There were « nice » US militaries that launched the Vela satellites to spy on thermonuclear explosions on Earth by badass soviet soldiers. • However, they detected nothing from Earth, but some brief and intense flashes of Gamma-ray photons from the sky. • At first, they thought that nuclear wars might rage on other worlds … • First GRB publication : Klebesadel et al. 1973, ApJ, 185, L85 “Observations of Gamma-Ray Bursts of Cosmic Origin” New astrophysical phenomenon Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Main missions & main discoveries (1) •1991-2000: deep study of the prompt Gamma-ray emission with BATSE (Burst And Transient Source Experiment) on the Compton Gamma-Ray Observatory CGRO • No multi-wavelength counterpart due to poor localization • ~ 1 GRB detected per day during 9 years • GRBs are isotropically distributed on the sky • Non thermal spectra One of the 8 BATSE modules • two types of GRBs: long (>2 s) & short (< 2 s) BATSE, Paciesas et al. 1999; Preece et al. 2000; Band et al. 1993; Kouveliotou et al. 1993 Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Main missions & main discoveries (2) • Revolution in 1997: detection of first multi-wavelength afterglow emission by Beppo-SAX thanks to an innovative instrumentation (combination wide-field high-E instrument & narrow field instruments) Beppo-SAX • Detection of GRB afterglows a few hours after the detection in Gamma- rays • Redshift measurement (i.e. distance of the source) • Afterglow emission from radio to X-rays for long GRBs • Afterglow emission lasts from days to weeks (sometimes months/years) • The emission drops quickly in flux. • Lightcurves display powerlaw segments & chromatic/achromatic breaks • … (Costa et al. 1997; Djorgovski et al. 1997 ;Metzger et al. 1997) Panaitescu & Kumar 2004 Gamma-ray bursts: The most violent explosions in the Universe Main missions & main discoveries (3) •2000-2006: Study of a new class of GRBs, the X-Ray Flashes with main photon energy below 50 keV • Provide arcmin accuracy position to world community in a few tens of seconds • XRFs are long and soft GRBs showing the same properties. • Dark GRBs are not completely dark. • … High Energy Transient Explorer Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Main missions & main discoveries (4) • Since 2004: Swift era (same strategy as Beppo-SAX, but faster and more sensitive instruments) •Detection of > 800 GRBs •Characterization of the early afterglow, a time interval that was at the time not yet observed. •First detection of the afterglows of short GRBs redshift, energetics, nature of the progenitor, etc… Swift Temporal gap Prompt emission Afterglow emission Early afterglow Gamma-ray bursts: The most violent explosions in the Universe Main missions & main discoveries (4) • Since 2004: Swift era •Detection of > 800 GRBs •Characterization of the early afterglow, a time interval that was at the time not yet observed. •First detection of the afterglows of short GRBs •Detection of the naked eye burst GRB 080319B ( Racusin et al. 2008) – Peak brightness in optical = 5.3 mag! •... Prompt optical emission Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Main missions & main discoveries (5) • Since 2008: launch of Fermi – observations of GRB prompt emission up to 200 GeV • Constraints on the emission mechanism for prompt emission • Constraints on the dynamics of the ejecta • New spectral feature seen in the spectra of the prompt emission • Delayed/extended high-energy emission (up to GeV) Fermi results: (e.g. Goldstein et al. 2012) Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe PropertiesProperties && naturenature ofof Gamma-rayGamma-ray burstsbursts The game is starting now !! Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe General: distance BATSE: Burst And Transient Source Experiment on the Compton Gamma-Ray Observatory (1991-2000) BATSE, Paciesas et al. 1999 Question: What does the isotropy tell us about the origin of GRBs? Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe General: distance BATSE: Burst And Transient Source Experiment on the Compton Gamma-Ray Observatory (1991-2000) BATSE, Paciesas et al. 1999 Question: What does the isotropy tell us about the origin of GRBs? GRBs are located at cosmological distances. Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe General: distance • GRBs are located at cosmological distances (from z = 0.033 to z = 8.2, maybe 9.4) Jakobsson et al. 2006 GRB 090423, z = 8.2 GRB 090423 with z =8.2 (Tanvir et al. 2009) GRB 080913 with z=6.7 GRB 050904 with z=6.3 (Haislip et al. 2006) z = 8.2 i.e. ~ 625 million years after the Big Bang & light travel ~ 13 Giga years! z = 0.033 i.e. light travel ~ 440 Million years Gamma-ray bursts: The most violent explosions in the Universe General: energetics 1 erg = 10-7 J • Cosmological distances 1 eV = 1.6 10-12 erg 48 55 17 Huge isotropic energy with Eiso = 10 -10 erg 10 erg ~ 2.4 tonnes TNT over a few hundreds of seconds at most! 55 2 For GRB080916C, Eiso ~ 10 erg ~ 5 MSun c !! 40W electric bulb E ~ 1.3 1016 erg over 1 year Supernovae 51 Tsar H-bomb E ~ 10 erg E = 50 Mt TNT ~ 2.1 1024 erg Milky Way L ~ 1044 erg/s Nuclear plant P mean ~ 1 GW Sun 33 E ~ 3 1023 erg 1 km asteroid impact L ~ 4 10 erg/s 50 28 E ~ 6 10 erg over 5 Gyrs over 1 year E ~ 1.3 10 erg Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Gamma-ray variability •Each GRB light-curve is unique. •GRB light-curves are structured and highly variable. •Timescale variability very small (down to 1 ms). •Variability is related to the central source activity. •Assuming δt ~ 0.1 s, then the size of the system is δd ~ c × δt ~ 3x109cm! (Sun Diameter = 1.392x1011 cm). Question: What type of object could then be the central source in GRBs? Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Gamma-ray variability •Each GRB light-curve is unique. •GRB light-curves are structured and highly variable. •Timescale variability very small (down to 1 ms). •Variability is related to the central source activity. •Assuming δt ~ 0.1 s, then the size of the system is δd ~ c × δt ~ 3x109cm! (Sun Diameter = 1.392x1011 cm). Question: What type of object could then be the central source in GRBs? Answer : a compact object (neutron star or black hole) Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe What mechanism powers GRBs? • Cosmological distances 48 55 Huge isotropic energy with Eiso = 10 -10 erg over a few hundreds of seconds at most! • From previous slides, we know the central source is compact – probably a black hole. Question: What mechanism may be able to generate so much energy onto a BH? Gamma-ray bursts: The most violent explosions in the Universe What mechanism powers GRBs? • Cosmological distances 48 55 Huge isotropic energy with Eiso = 10 -10 erg over a few hundreds of seconds at most! • From previous slides, we know the central source is compact – probably a black hole. Question: What mechanism may be able to generate so much energy onto a BH? Answer: accretion of matter – common phenomenon in the Universe Active Galactic Nuclei 39-48 Lbol ~ 10 erg/s E ~ 1053-63 erg over 107-8 yrs (e.g. Urry & Padovani 1995) X-ray binaries 39 Lmax ~ 10 erg/s 52 6 Emax ~ 10 erg over 10 yrs (e.g. Remillard & McClintock 2006) Gamma-ray bursts: The most violent explosions in the Universe What mechanism powers GRBs? • Cosmological distances 48 55 Huge isotropic energy with Eiso = 10 -10 erg over a few hundreds of seconds at most! • From previous slides, we know the central source is compact – probably a black hole. Question: What mechanism may be able to generate so much energy onto a BH? Answer: accretion of matter – common phenomenon in the Universe Even accretion is not able to produce so much energy over such short timescales! To avoid the energy budget crisis, the outflow be collimated as a jet. Active Galactic Nuclei must 39-48 Lbol ~ 10 erg/s E ~ 1053-63 erg over 107-8 yrs (e.g. Urry & Padovani 1995) X-ray binaries 39 Lmax ~ 10 erg/s 52 6 Emax ~ 10 erg over 10 yrs (e.g. Remillard & McClintock 2006) Gamma-ray bursts: The most violent explosions in the Universe Jets (1) • Jets are often associated with accretion phenomena.
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