Gamma-Ray Bursts: The Biggest Explosions Since the Big Bang Edo Berger
Talk Outline History and basic observational facts Basic Physics: compactness & baryon loading The fireball model, afterglows, and jets The progenitors of long GRBs The progenitors of short GRBs GRBs as a powerful cosmological tool
Cosmic Cannon: How an Exploding Star Could Fry Earth By Robert Roy Britt/Space.com
Gamma-Rays
Limited Nuclear Test Ban Treaty, 1963 … to prohibit, to prevent, and not to carry out any nuclear weapon test explosion: (a) in the atmosphere; beyond its limits, including outer space; or under water …
The Vela Satellites ( )
The First Gamma- Ray Burst
Uncertainty in distance by a factor of one billion Where Do GRBs Come From? ( ) 135 theories, less than 100 GRBs! Short duration, intense energy: New type of supernova? Giant stellar flares? Matter/anti-matter annihilation? Neutron stars? Black holes?
Gamma-Ray Bursts from the Milky Way
The Compton Gamma-Ray Observatory
GRBs do not come from the disk of the Milky Way
The “Great Debate” (1995) “The Distance Scale to Gamma-Ray Bursts” Bohdan PaczynskiDon Lamb GalacticCosmological The Shapley–Curtis Great Debate (1920) on the “Scale of the Universe”
Long Short Two types of gamma-ray bursts
To solve the GRB mystery it is essential to: Determine accurate positions Deliver positions to observers rapidly
(April 30, 1996) Delivery time of ~hours Positions 100x more accurate than BATSE BeppoSAX (October 9, 2000) HETE-2
The Swift Satellite & Future Missions UV/Optical Telescope Burst Alert Telescope X-Ray Telescope Event rate ~100/yr Positions ~1-5” Lifetime ~2015 GLAST 8 keV GeV ~150/yr Launch 10/2007 EXIST keV All-sky per orbit 10x Swift sensitivity ~ /yr Launch >2015
The First Afterglow (February 28, 1997) 5 hours3 days
Afterglows in Visible Light
The Distance to Gamma-Ray Bursts Low speed (Nearby) High speed (Far away) n
8 billion light-years away oxygencarbonmagnesiumhydrogen 22 sec47 sec73 sec 280 sec 450 sec
The Fireball Model (a mini Big Bang, or a super nuclear bomb)
The Compactness & Baryon Loading Problems ⇒ acceleration, thermalization ⇒ thermal GRB >10 51 erg of MeV − rays in a few seconds (small region, c t) Fireball: a region optically thick due to electron-positron pair production (e 1 e 2 > m e c 2 )
The Compactness & Baryon Loading Problems Relativistic motion The kinetic energy of the baryons is converted to radiation via shocks - internal or external variability points to internal shocks The unavoidable baryon contamination provides a mechanism for delaying optical thinness and ensuring a high Lorentz factor required for GRB production. The new baryon loading problem is how to get only M But... How do we get only M o in an astrophysical context?
Time Brightness
Courtesy: Tsvi Piran / Hebrew University
The Fireball Model Collapsar Coalescence Baryonic Magnetic Internal Shocks Magnetic instability External Shock Ε ngine energy transport conversion to − rays afterglow
Compact Object Mergers NS+NS BH+NS
Collapsing Massive Stars
Afterglow Physics Un-shocked ISM shocked ISM Ejecta CDFS 21 N( -p From the afterglow we can determine the energy, density & geometry
Collimation (“Jets”)
Energy Release With jet corrections, we find a narrow distribution of gamma-ray enegy: E ~ 1.3 erg E iso EE jet
The fraction coupled to Γ varies widely. Quantity is the same, quality differs Energy Release
Soderberg et al Wainwright, Berger & Penprase 2007, ApJ Long GRBs are Associated with Star Formation Wainwright, EB & Penprase 2007, ApJ
Star Nurseries
GRB : The Rosetta Stone Saturday 3:38 am
GRBs result from the death of massive stars
Long Short Two types of gamma-ray bursts
LIGO
The Dark Ages of the Universe
GRB Absorption Spectroscopy Comparison to quasars: No proximity effect on galactic scales Small impact parameter In star forming regions Bright(er) [ind. of z] High(er) redshift Fade away
Redshift Distribution EB et al. 2005, ApJ
GRB : z = EB et al. 2006, ApJ log N H = 22.1 0.1 [S/H] = -1.2 0.06 Z
GRB : Progenitor Properties CIV extends over ~1000 km/s * WR wind from the progenitor SiIV absorption sensitive to mass and metallicity (Leitherer & Lamers 1991) WC Wolf-Rayet star: Z < 0.1Z M < 25 M * QSOs: correlation length <500 km/s (Rauch et al. 1996) EB et al. 2006, ApJ
GRB-DLAs EB et al. 2006, ApJ & in prep.
Cosmic Reionization Fan et al. 2005Gnedin et al. Neutral Fraction > 3x10 -4 ⇐
GRBs and Reionization Kawai et al z = log N H ~ 21.3 Z ~ 0.1 Z x H < 0.6 GRBs
Conclusions GRBs require a source of at least erg (similar to supernovae), but coupled to only solar masses Very high Lorentz factors are required The outflow is collimated in jets The progenitors of long GRBs are massive stars The progenitors of short GRBs are likely NS-NS or BH- NS binaries GRBs are a powerful cosmological tool