PASCOS 031 Gamma Ray Bursts – The Brightest Explosions in the Universe Tsvi Piran Hebrew University, Jerusalem  W. Benz  M. Davies  David Eichelr  Philip Hughes  Jonahtan Katz  Shiho Kobayashi  C. Kochaneck  P. Kumar  Mario Livio  Mark Miller  R. Narayan  B. Paczynski  S. Rosswog  Re’em Sari  David Schramm  Jacob Shaham  Wai Mo Suen  F. Thielmann  E. Waxman  Shai Ayal  Ehud Cohen  Jonathan Granot  Ehud Naker  Amotz Shemi

PASCOS 032 THE DISCOVERY  Gamma-Ray Bursts (GRBs) Short (few seconds) bursts of 100keV- few MeV were discovered accidentally by Klebesadal Strong and Olson in 1967 using the Vela satellites (defense satellites sent to monitor the outer space treaty).  The discovery was reported for the first time only in There was an “invite prediction”. S. Colgate was asked to predict GRBs as a scientific excuse for the launch of the Vela Satellites There was an “invite prediction”. S. Colgate was asked to predict GRBs as a scientific excuse for the launch of the Vela Satellites

PASCOS 033  Duration s  Two populations (long and short)  ~ 1 BATSE burst per day  - (a local rate of ~2 Gpc -3 yr -1 )  ~100keV photons  Non thermal Spectrum (very high energy tail,  up to GeV, 500GeV?)  Rapid variability (less than 10ms)  Cosmological Origin  The luminosity of a GRB is comparable to the luminosity of the rest of the Universe combined. GRBsCompton-GRO

PASCOS 034 GRB

PASCOS 035 Why are GRBs so Exciting? GRBs involve the fastest macroscopic relativistic motion observed so far (  >100) GRBs signal (most likely) the fromation of newborn black holes. Sources of GRBs (merging NS or Collapsars) are also sources of Gravitational radiation GRBs are the best cosmological indicators known today for the early (z~5-10) universe. GRBs are the brightest and most luminous objects known today. GRBs are the most relativistic objects known today.

PASCOS : The NY Texas Symposium n Meegan - GRB distribution is isotropic. n Ruderman - First theoretical review:  Cosmological origin ?  Relativistic Motion ?  Galactic origin!?  > 30 models (More models than bursts) - None even remotely relevant. n During the late seventies a consensus formed that GRBs originate on galactic neutron stars.

PASCOS 037  BATSE on Compton - GRO (Fishman et. al.) GRO (Fishman et. al.) discovered that the discovered that the distribution of GRBs distribution of GRBs is isotropic: is isotropic:  GRBs are Cosmological  By now there are redshift measurements for the afterglow of a dozen bursts. 1991: BATSE – The First Revolution 1991: BATSE – The First Revolution

PASCOS 03Tsvi Piran HU8 Revised Energy Estimates The observed fluences are ~ ergs/cm 2 Cosmological corrections ergs (E)  z~1  E~10 52 ergs  GRBs are the (electromagnetically) most luminous objects in the Universe.  For a few second the luminosity of a GRB is comparable to the luminosity of the rest of the Universe.

PASCOS 039 Implications of ergs Need ultrarelativistic motion to get erg out from a compact source within such a short time scale. Need ultrarelativistic motion to get erg out from a compact source within such a short time scale. New Physics?  The FIREBAL MODEL

PASCOS 0310 The Fireball Model The Fireball Model compact source compact source Relativistic Particles  >100 or Poynting flux ~ 10 7 cm Shocks g  rays Goodman; Paczynski; Shemi & Piran, Narayan, Paczynski & Piran; Meszaros & Rees,

PASCOS 0311 Supernova Remnants (SNRs) - the Newtonian Analogue n ~ 10 solar masses are ejected at ~10,000 km/sec during a supernova explosion. n The ejecta is slowed down by the interstellar medium (ISM) emitting x-ray and radio for ~10,000 years.

PASCOS 0312 External Shocks  External shocks are shocks between the relativistic ejecta and the ISM - just like in SNRs. Can be produced by a single explosion.

PASCOS 03Tsvi Piran HU13 A NO GO THEOREM External shocks cannot produce a variable light curve!!! (Sari & Piran 97)

PASCOS 03Tsvi Piran HU14 Implication: Typical* GRBs cannot originate from a single EXPLOSION. This rules out many models: Evaporating mini black holes.Evaporating mini black holes. Discharge of a charged BHDischarge of a charged BH NS -> strange starNS -> strange star Vacuum InstabilityVacuum Instability ………….…………. * Highly variable (there is a small group of smooth bursts which can be explosive)

PASCOS 0315 dT=R/cg 2 = d/c £ D/c =T dT=R/cg 2 = d/c £ D/c =T The observed light curve reflects the activity of the “inner engine”.The observed light curve reflects the activity of the “inner engine”.  Need TWO time scales. To produce internal shocks the source must be active and highly variable over a “long” period.To produce internal shocks the source must be active and highly variable over a “long” period. D =cT =d=cdT=d=cdT Internal Shocks Shocks between different shells of the ejected relativistic matter T dTdTdTdT

PASCOS 0316 Internal shocks can convert only a fraction of the kinetic energy to radiationInternal shocks can convert only a fraction of the kinetic energy to radiation (Sari and Piran 1997; Mochkovich et. al., 1997; Kobayashi, Piran & Sari 1997). (Sari and Piran 1997; Mochkovich et. al., 1997; Kobayashi, Piran & Sari 1997).  It should be followed by additional emission. “It ain't over till it's over” (Yogi Berra) D =cT =d=cdT=d=cdT Internal Shocks  Afterglow

PASCOS ) Compact Source, E>10 51 erg 2) Relativistic Kinetic Energy 3) Radiation due to Internal shocks = GRBs 4) Afterglow by external shocks The Central Compact Source is Hidden The Central Compact Source is Hidden Gamma-Ray Burst: 4 Stages

Inner Engine Relativistic Wind The Internal-External Fireball Model There are no direct observations of the inner engine. The  -rays light curve contains the best evidence on the inner engine’s activity. External Shock Afterglow Internal Shocks  -rays

PASCOS 0319 GRB - The Movie Four Initial shells ISM Afterglow - other colors GRB - yellow flash

PASCOS 03Tsvi Piran HU20 THE FIREBALL MODEL PREDICTED GRB AFTERGLOW (late emission in lower wavelength that will follow the GRB) Rhodas & Paczynksi, Katz, Meszaros & Rees, Waxman, Vietri, Sari & Piran

PASCOS : Afterglow – The Second Revolution  The Italian/Dutch satellite BeppoSAX satellite BeppoSAX discovered x-ray afterglow discovered x-ray afterglow on 28 February 1997 on 28 February 1997 (Costa et. al. 97). (Costa et. al. 97).  Immediate discovery of Optical afterglow (van Paradijs et. al 97).

PASCOS 0322 The Radio Afterglow of GRB (Frail et. al, 97).  Variability:  * Scintillations (Goodman, 97; Frail Kulkarni & Waxman 97) ® Size after one month ~10 17 cm. ® Size after one month ~10 17 cm.  Rising Spectrum at low frequencies:  Self absorption (Katz & Piran, 97; Frail et al 97) ® Size after one month ~ cm.  Relativistic Motion!!! (but  since this is a long time after the explosion

PASCOS 0323 A crash Course in Scintillations Scintillations determine the size of the source in a model independent way. The size (~10 17 cm) is in a perfect agreement with the prediction of the Fireball model.

PASCOS 0324 Afterglow Theory Hydrodynamics: deceleration of the relativistic shell by collision with the surrounding medium (Blandford & McKee 1976) (Meszaros & Rees 1997, Waxman 1997, Sari 1997, Cohen, Piran & Sari 1998) Radiation: synchrotron + IC (?) (Sari, Piran & Narayan 98) Clean, well defined problem. Few parameters: E, n, p,  e,  B initialshell ISM

PASCOS 0325 Comparison with Observations (Sari, Piran & Narayan 98; Wijers & Galama 98; Granot, Piran & Sari 98; Panaitescu & Kumar 02) Radio observations Radio to X-ray

PASCOS 0326 The Early Afterglow and the Optical Flash  The late afterglow observations confirmed relativistic motion.  But what is the value of g during the GRB phase?  100 <  0 = E 0 /M 0 < 10 5  “dirty” “clean”  This could be tested  by early afterglow  observations (Sari &  Piran: Rome, Oct 1998;  Astro-ph/11/1/1999): A very strong optical flash coinciding with the GRB optical x-rays  -rays

Inner Engine Relativistic Wind The Internal-External Fireball Model External Shock Afterglow Internal Shocks  -rays OPTICAL FLASH

PASCOS 0328 GRB The Prompt Optical Flash ROTSE’s detection of a 9 th magnitude prompt optical flash.

PASCOS 0329 The Initial Lorentz Factor  The observations of early afterglow from GRB lead to several independent estimates of the initial Lorentz factor (Sari &Piran, 1999):  The afterglow begins after ~70 sec i ~200  The afterglow begins after ~70 sec   i  ~200  m the synchrotron frequency of the reverse shock, is below the optical bands i ~200  m the synchrotron frequency of the reverse shock, is below the optical bands  i ~200  The ratio m_forward / m_reverse ~ i 2 i ~70  The ratio m_forward / m_reverse ~  i 2  i ~70  This is the first, and so far only, direct measurement of the initial Lorentz factor. It is in agreement with opacity lower limits.  An indirect measurement of ~100 AU from a distance of 6Gpc! ~100 AU from a distance of 6Gpc!

PASCOS 0330 GRB Energies  E tot - The total energy  E  -  Observer  ray energy

PASCOS 0331 The “Efficiency” Factor Total Energy

PASCOS 0332 “Direct” Energy Measurements In bursts with afterglow for which the host galaxy was observed we could estimate the total energy “directly” using the redshift of the host galaxy. In bursts with afterglow for which the host galaxy was observed we could estimate the total energy “directly” using the redshift of the host galaxy. GRB970508Z=

PASCOS 03Tsvi Piran HU33 The Energy Crisis? (E) Totani’s prediction for the energy of GRBs

PASCOS 03Tsvi Piran HU34 How to explain ergs? Once more (now in 1999) GRBs need new Physics

PASCOS 0335 The Resolution of the Energy Crisis The Resolution of the Energy Crisis  E tot - The total energy  E  iso  -  Observed (iostropic)  ray energy Beaming:  E  - Actual  ray energy The two most powerful BeppoSAX bursts are jets (Sari, Piran & Halpern; 1999).

PASCOS 0336 Jets are common in AGN The jet from the core of M87 X-ray jet from the core of Cen A

PASCOS 0337 JETS and BEAMING Jets with an opening angle q expand forwards until g = q -1 and then expand sideways rapidly lowering quickly the observed flux (Piran, 1995; Rhoads, 1997; Wijers et al, 1997; Panaitescu & Meszaros 1998). g = q -1 Particles spreads sideways quickly Radiation is “beamed” into a large cone Particles remain within initial cone Radiation is “beamed” into a narrow cone

PASCOS 0338 GRB II - The Sequel Four Initial shells ISM Afterglow - other colors GRB - yellow flash

PASCOS 0339 GRB The best Jet!       t break = 1.2 days  jet angle = 4 o From Harrison et al 1999

PASCOS 0340

PASCOS 0341 A Sharp (Not Achromatic) Break! * synch emission does not include the effects of cooling.

PASCOS 03Tsvi Piran HU42 The Energy Crisis? (E) Prediction for the energy of GRBs What goes up must go down e.g. NASDAQ

PASCOS 0343 E iso E  (PK) E  (F) E K (PK) Energy Estimates Jimmenez et al Afterglow GRBs Schmidt All GRBs

PASCOS 0344 Redshift and Beaming Energy Determination GRBZ E (× ) > > > < < c

PASCOS 0345 Energy Estimates Frail et al, 01: E   5  ergs FWHM ~ 5 Frail et al, 01: E   5  ergs FWHM ~ 5 PK 01: E   7  ergs FWHM ~11 PK 01: E   7  ergs FWHM ~11 PK 01: E K  2  ergs FWHM ~ 2 PK 01: E K  2  ergs FWHM ~ 2 (PK = Panaitescu & Kumar) Piran, Kumar, Panaitescu Piran, Kumar, Panaitescu & Piro: E K FWHM < 2.5 & Piro: E K FWHM < 2.5 GRBs release a constant amount of energy ~10 51 ergs!!!

PASCOS 03Tsvi Piran HU46 Implications of the Fireball Model

47 Clues on the Inner Engine The inner source is hidden. The observations reflect only the conditions at the fireball.  E tot ~ ergs   < sec  T ~ 30 sec   ~ 200 (“dirty”)  Jets ~ 2 o - 5 o  Rate /yr/galaxy  A compact Object  Prolonged activity: an accretion disk ?  Baryonic Flow ?  Lower energy, higher rates, orphan afterglows  A rare phenomenon Most likely powered by accretion onto a newborn black hole

PASCOS 0348 Routes to a BH-Disk-Jet Different routes can lead to a Black-hole -disk-jet system:  NS/BH-NS merger  BH-WD merger  NS/BH-He core merger  Collapsar Davies et al, 94 Woosley et al, 99 shortLong - LONG - SHORT

PASCOS 0349 Woosley et al., 99 NY Times May 99 Roswog et al, 99 Davies et al, 94

PASCOS 0350 Rates and Distances  One long GRBs per 10 4 (  /0.1) -2 years per galaxy. Beaming factor  One observed long burst per year at D~600 Mpc.  One unobserved burst per year at D~135 (  /0.1) 2/3 Mpc.  Short bursts are most likely at z<0.5 with one short burst per 10 3 (  /0.1) -2 years per galaxy.  One observed short burst per year at D~250 Mpc.  One unobserved short burst per year at D~80(  /0.1) 2/3 Mpc.

PASCOS 0351 GRBs as Beacons for the Universe n GRBs follow the star formation rate. n GRBs and their afterglow can be detected even from Z~10. n 10-25% of GRBs are from Z>5. n GRBs are ideal beacons to explore the early universe – at the time of “first light”. Ly  clouds reionization Star formation rate

PASCOS 0352 GRBs as Tests for Quantum Gravity n Time delay between arrival of high energy photons and low energy photons can yield significant limits of “Lorentz Violation” (Amelino-Camelia, Ellis, Mavromatos, Nanopoulos, Sarkar, 97) (Amelino-Camelia, Ellis, Mavromatos, Nanopoulos, Sarkar, 97)

PASCOS 0353 GRBs in the Galaxy n One GRB per 10 4 years: Results in a double bubble that might be distinguished (for ~1000 years) from a regular SNR. n One GRB towards us per years: May lead to life extinction on earth. May lead to life extinction on earth.