Gamma-Ray Bursts and the Cold War. In the 1950s, the US and USSR agreed to ban the testing of nuclear weapons.

Transkript

1 Gammablixtar?

2 Gamma-Ray Bursts and the Cold War In the 1950s, the US and USSR agreed to ban the testing of nuclear weapons. How was this verified? Seismic Waves Low Frequency Sound Waves Gamma-Rays Crashed Balloon near Roswell,NM in July 1947 became Roswell Alien! Mogul Project

3 1967/1973 Vela-satelliterna Gammastrålningsutbrott USAs Vela satelliter sändes upp under 60-talet för att registrera ev. kärnvapentester. 1969, hittade man I data från 1967 ett utbrott som inte kom från Jorden. Totalt detekterade Velasatelliterna 73 utbrott. Inget enda av de kom från Jorden.

4 GRBs de kraftigaste explosionerna vi känner till Ljuskurvan i bandet 20 kev - 2 MeV Under en kort tidsperiod skiner de gånger kraftigare än en vanlig Supernova och miljon miljarder gånger starkare än solen. De är i särklass de starkaste objekten på gamma-himmeln. Hur förklarar man gammablixtarna, ljuskurvan och den intensiva γ-strålningen?

5 GRBs The Golden Age for Theory What was known/not known from observations Not Russian tests! Lots of gamma-ray emission No distances: Total energy and location unknown! Too few objects to get spatial distribution!

6 Creativity of Theorists With so few constraints, theorists came up with all Sorts of models relying on a range of physics. Three Classes based on location: Solar System Galactic Cosmological (outside of the Milky Way) SS Galactic Energy = Observed Flux d 2 Energy Requirements Vary over 20 orders Of magnitude! Cosmological

7 By 1992, over 100 models existed! Despite this number, the currently favored model is not on this list!

8 Gamma-Ray Bursts in the Solar System? Lightning in the Earth s atmosphere (High Altitude) Relativistic Iron Dust Grains Magnetic Reconnection in the Heliopause Red Sprite Lightning

9 Gamma-Ray Bursts in the Milky Way? Accretion Onto White Dwarfs Accretion onto neutron stars I) From binary companion II) Comets X-ray Novae Neutron Star Quakes Magnetic Reconnection

10 Cosmological Models? Large distances means large energy requirement (10 51 erg) Event rate rare ( per year in a galaxy) Object can be exotic

11 Cosmological Models? Collapsing WDs Stars Accreting on AGN White Holes Cosmic Strings Black Hole Accretion Disks Binary Mergers Collapsing Stars

12 BATSE - Burst And Transient Spectrometer Experiment on Compton Gamma-Ray Observatory ( ) BATSE Module 8 Detectors Almost Full Sky Coverage Few Degree Resolution keV

13 Gammablixtar Stor variation i ljuskurvor för olika gammablixtar.

14 Gammablixt himmeln Ett par gånger per dag. En blixtkälla återkommer inte. Isotrop fördelning på himlen (ingen speciell riktning) Förväntad fördelning för galaktiska källor. Alltså: Inte galaktiska!

15 Gamma-Ray Burst Durations Two Populations: Short s Long s

16 Afterglow Röntgenobservationer av GRB Upptäcktes 1997 av BeppoSAX första nogranna positionsbestämningen

17 GRB Optical Counterpart Discovered (with corresponding optical localization!)

18 GRB Absorption Lines: z=0.835 Optisk identifiering möjliggjorde observation av spectrum.

19

20 SN 1998bw Galama et al Sollerman et al Fynbo et al. 2000

21 Magnitud i optiskt (R) för afterglow månaderna efter en gammablixt. Ljusökningen efter 10 dagar har identifierats med en supernova. Gammablixtar och supernovor hör ihop!!!!!

22 Black Hole Accretion Disk Models Collapsar (aka hypernova): Supernova explosion of a fast rotating very massive star Iron core collapse forming a black hole; Material from the outer shells accreting onto the black hole Accretion disk => Jets => GRB!

23 Den troliga förklaringen till gammablixtar är alltså att de kommer från de supernovor som resulterar I ett svart hål (hypernovor). Men är detta förklaringen till alla gammablixtar? De korta (<2 sekunder) har ännu inte identifierats) Hypernova Binary neutron star merger

24 GRBs The Historical Perspective 1967: Discovery Vela Satellites : Golden Age for Theorists - no constraints and a world of proposals 1991: Constraining the theories CGRO (BATSE) finds isotropic distribution 1996: Localization BeppoSAX localizes bursts to get redshifts and host-galaxy information 1998: Some GRBs coincident with supernovae

25 Gamma Ray Bursts (GRB) summary Cosmic γ-rays must be observed from above our atmosphere. since the 1960s, satellites have detected strong bursts of γ-rays they occur daily, for a few minutes γ-rays are hard to focus, so determining their direction is tough Since 1997, we have detected the afterglows of GRBs at other wavelengths. we can pinpoint their sources to distant galaxies What they are is still a mystery. best theory: they are hypernovae gigantic supernovae which form black holes most luminous events since the Big Bang Hubble ST image of GRB afterglow in a distant galaxy