29 March 2005 John G. Learned GRB Gamma Ray Bursts An Ongoing Mystery, Evolving Quickly John G. Learned University of Hawaii with slides from many folks, Particularly Kevin Hurley and Guido Barbiellini

29 March 2005 John G. Learned GRBs First Seen 1967 Vela satellites, Seeking atom bomb tests Secret at first Clearly a lot of Energy, depending upon distance and solid angle of emission Distance, years of debate: Very local? Galaxy halo? Not so far away? Cosmic Scale?

29 March 2005 John G. Learned CGRO-BATSE Tagged Many Distribution: Isotropic By early 90’s became clear Not associated with our galaxy: no clustering in plane no tilt towards GC Still models for near solar system Sentiment towards cosmological distances BATSE could not tag fast enough or with sufficient accuracy (1’) for telescopes

29 March 2005 John G. Learned Beppo-SAX Does the Job in 1997

29 March 2005 John G. Learned THREE INTERESTING GAMMA- RAY BURST/SUPERNOVA PARAMETERS Beaming Factor ~340 ( )

29 March 2005 John G. Learned SOME ABSOLUTELY INCONTROVERTIBLE GRB PROPERTIES THAT NO REASONABLE PERSON COULD POSSIBLY DISAGREE WITH 1.There are two morphological classes of GRBs, long bursts (~20 s duration) and short bursts (~0.2 s duration) 2.Counterparts and redshifts have been found for many long bursts 3.No counterpart or redshift has been found for any short burst 4.Most of the long bursts display long-wavelength (radio and optical) “afterglows”; but some of them have no detectable optical or radio counterparts (“dark” bursts) 5.There is good evidence which links some long bursts to the deaths of massive stars K. Hurley, Moriond 2005

29 March 2005 John G. Learned 6.The energy spectra of the long bursts form a continuum, from X- ray flashes (with few or no γ-rays), X-ray rich bursts, and GRBs 7.There is no experimental evidence to suggest that any class of burst (long/short, X-ray rich, dark) has a different origin, or a different spatial distribution, from any other class – but there are many theories which do suggest different origins. 8.The energy spectra of the long bursts form a continuum, from X- ray flashes (with few or no γ-rays), X-ray rich bursts, and GRBs 9.There is no experimental evidence to suggest that any class of burst (long/short, X-ray rich, dark) has a different origin, or a different spatial distribution, from any other class – but there are many theories which do suggest different origins

29 March 2005 John G. Learned SHORT BURST

29 March 2005 John G. Learned LONG BURST

29 March 2005 John G. Learned THE GRB DURATION DISTRIBUTION SHORT BURSTS (~25%) LONG BURSTS ~75% HARDER ENERGY SPECTRA SOFTER ENERGY SPECTRA WE ONLY KNOW ABOUT THE ORIGIN OF THE LONG BURSTS

29 March 2005 John G. Learned ENERGY SPECTRA OF THE LONG BURSTS    …OBSERVED UP TO 18 GeV E peak ~100’s of keV

29 March 2005 John G. Learned THE ENERGY SPECTRA OF THE LONG BURSTS FORM A CONTINUUM, FROM SOFT-SPECTRUM X-RAY FLASHES TO HARD-SPECTRUM GAMMA-RAY BURSTS (BeppoSAX, HETE) X-RAY FLASH GAMMA-RAY BURST E peak ~keV   E peak ~200 keV

29 March 2005 John G. Learned GAMMA-RAY BURSTS ARE FOLLOWED BY X-RAY AFTERGLOWS… BeppoSAX: Costa et al T 0 +8h T 0 +2d 1-10 keV 1’

29 March 2005 John G. Learned …OPTICAL AFTERGLOWS… Pandey et al. 2004

29 March 2005 John G. Learned …AND RADIO AFTERGLOWS Time after GRB970508, days Flux density, μJy Frail et al. 2003

29 March 2005 John G. Learned FIREBALL MODEL   ISM INTERNAL SHOCK  RAYS EXTERNAL SHOCK X-RAYS OPTICAL RADIO 20 km 1-6 AU AU

29 March 2005 John G. Learned SIMULTANEOUS OPTICAL/GAMMA-RAY EMISSION HAS NOW BEEN DETECTED TWICE GRB (BATSE) ROTSE (

29 March 2005 John G. Learned GRB (INTEGRAL) RAPTOR (

29 March 2005 John G. Learned (z=0.8424) (z=1.0964) (z=2.0335) GRB HOST GALAXIES Aren’t pretty; but they are normal Not active galaxies Indistinguishable from field galaxies with similar ages

29 March 2005 John G. Learned REDSHIFT DISTRIBUTION OF 34 LONG GAMMA- RAY BURSTS LOWEST REDSHIFT=0.104 (INTEGRAL, GRB031203); HIGHEST=4.5 (IPN, GRB000131); AVERAGE=1.4 ONLY ONE REDSHIFT HAS BEEN MEASURED FOR AN X- RAY FLASH z=0.25

29 March 2005 John G. Learned GRB ENERGETICS Isotropic gamma-ray energies range from >10 51 to >10 54 erg Two possibilities for liberating large amounts of energy: 1.Merging neutron stars (short bursts?) 2.Collapsars (also called hypernovae, or energetic supernovae; long bursts) In either case, beaming is also required; there is observational evidence in afterglow light curves that it occurs in some cases

29 March 2005 John G. Learned THE OPTICAL AFTERGLOW CAN GIVE INFORMATION ABOUT BEAMING OBSERVER TIME AFTERGLOW INTENSITY BREAK

29 March 2005 John G. Learned BEAMING CAN TURN GRBs INTO (MODEL- DEPENDENT) STANDARD CANDLES Beaming angles range from ~1º to ~25º; average ~ 4º Distribution of energy assumed uniform within the beam Energy ~ 1.3x10 51 erg Isotropic energies, no beaming Corrected for beaming Frail et al. 2001

29 March 2005 John G. Learned HOW IS THE ENERGY DISTRIBUTED?  keV  rays: 65% keV X-rays: 7% 3Optical: 0.1% 4Radio ? 5MeV/GeV/TeV ? >10%? 6Gravitational radiation ?  keV  rays: 7% keV X-rays: 9% 3Optical: 2% 4Radio: 0.05% DURING THE BURSTAFTERGLOW

29 March 2005 John G. Learned GRB – THE “POSTER CHILD”* FOR THE GRB-SUPERNOVA CONNECTION GRB was a bright (top 1%) nearby (z=0.17) burst, discovered by HETE It is the best-studied GRB to date (>>100 observations) Its optical afterglow light curve and spectrum point to an underlying supernova component (SN2003dh) These signatures have been observed before in numerous GRBs, starting with GRB (=SN1998bw, peculiar Type Ic – the previous poster child), but GRB is the most convincing case *Poster child n. A child afflicted by some disease or deformity whose picture is used on posters to raise money for charitable purposes

29 March 2005 John G. Learned Matheson et al Optical afterglow spectrum resembles that of SN1998bw Broad, shallow absorption lines imply large expansion velocities Afterglow light curve can be decomposed into two components: power law decay + supernova  Some long GRB’s are associated with the deaths of massive stars (>30M  ) Stanek et al. 2003

29 March 2005 John G. Learned MYSTERY OF THE OPTICALLY DARK BURSTS DARK BURSTS Fox et al. 2003

29 March 2005 John G. Learned THE MYSTERY OF THE OPTICALLY DARK BURSTS IS BEING SOLVED 35% of the GRBs detected by BeppoSAX and the IPN had no detectable optical counterparts – why? 1.Absorbed by dust within the host galaxy? 2.Intrinsically faint and/or rapidly fading? 3.High redshift? Only ~10% of the bursts detected by HETE are optically dark –HETE gets positions out to the astronomers faster than BeppoSAX and the IPN did –Swift is now doing the same, and carrying out optical observations within minutes –Some Swift bursts do appear to be optically dark Confirmed by observation? Not so far

29 March 2005 John G. Learned OBSERVATIONS OF SWIFT BURSTS DARK BURSTS       

29 March 2005 John G. Learned WHAT ARE X-RAY FLASHES? 1.GRBs observed away from the jet axis? 2.Explosions with less relativistic ejecta? 3.GRBs at high redshift? We have only one XRF redshift (XRF020903, z=0.251); in this case, the answer is clearly 2 (Soderberg et al. 2004)

29 March 2005 John G. Learned ARE THE SHORT GRBS NEARBY MAGNETAR FLARES? GIANT FLARE FROM SGR RHESSI DATA Giant flares begin with ~0.2 s long, hard spectrum spikes Their energy can be ~10 47 erg The spike is followed by a pulsating tail with ~1/1000 th of the energy Viewed from a large distance, only the initial spikes would be visible They would resemble the short GRBs Swift can detect them out to 100 Mpc Are all short GRBs magnetar flares? –Uncertainties are the progenitors of magnetars and the number-intensity relation for giant flares

29 March 2005 John G. Learned CONCLUSIONS Good evidence now links some of the long GRBs to Type Ic supernovae and the deaths of massive stars The origin of one X-ray flash has been determined – but does this explain all of them? The origin of the short bursts is probably the most outstanding mystery – neutron star/neutron star mergers, magnetar flares in nearby galaxies, both, something else? The mystery of the dark bursts is being solved – but are some at high redshift? GRB’s are bright enough to be detected out to z>10 – but are they actually generated there? HETE, INTEGRAL, and Swift may solve these mysteries

29 March 2005 John G. Learned GRB UHE cosmic ray acceleration; Quantum gravity Mass extinctions, morbid curiosity of the general public Early universe, reionization Merging neutron stars, GW Stellar collapse

29 March 2005 John G. Learned

29 March 2005 John G. Learned THE E peak -E isotropic energy RELATION Amati (2002) found that the peak energy in a GRB spectrum is related to the isotropic equivalent energy: E peak  E iso 0.52 (BeppoSAX results) Lamb (2004) has begun to extend this relation down to the XRF’s using HETE results: the relation holds also for XRF’s There are still several possible explanations for this, but in any case it strongly suggests that XRF’s and GRB’s are related

29 March 2005 John G. Learned B field Vacuum Breakdown Blandford-Znajek mechanism Blandford & Znajek (1977) Brown et al. (2000) Barbiellini & Longo (2001) Barbiellini, Celotti & Longo (2003)

29 March 2005 John G. Learned Vacuum Breakdown Polar cap BH vacuum breakdown Figure from Heyl 2001 The GRB energy emission is attributed to an high magnetic field that breaks down the vacuum around the BH and gives origin to a e  fireball. Pair production rate

29 March 2005 John G. Learned Two phase expansion Phase 1 (acceleration and collimation) ends when: Assuming a dependence of the B field: this happens at Parallel stream with Internal “temperature” The first phase of the evolution occurs close to the engine and is responsible of energizing and collimating the shells. It ends when the external magnetic field cannot balance the radiation pressure.

29 March 2005 John G. Learned Two phase expansion Phase 2 (adiabatic expansion) ends at the radius:  Fireball matter dominated: R 2 estimation Fireball adiabatic expansion The second phase of the evolution is a radiation dominated expansion.

29 March 2005 John G. Learned Jet Angle estimation Figure from Landau-Lifšits (1976) Lorentz factors Opening angle Result: The fireball evolution is hypothized in analogy with the in-flight decay of an elementary particle.

29 March 2005 John G. Learned Energy Angle relationship Predicted Energy-Angle relation The observed angular distribution of the fireball Lorentz factor is expected to be anisotropic.

29 March 2005 John G. Learned Spectral Energy correlations Amati et al. (2002) Ghirlanda et al. (2004)

29 March 2005 John G. Learned GRB for Cosmology Ghirlanda et al. (2004)

29 March 2005 John G. Learned GRB for Cosmology Ghirlanda et al. 2005

29 March 2005 John G. Learned Testing the correlations (Band and Preece 2005)

29 March 2005 John G. Learned GRB fluence distribution GRB RATE  SFR Madau & Pozzetti 2000 FLUENCE DISTRIBUTION USING AMATI RELATION By random extraction of Epeak (Preece et al. 2000) and GRB redshift for a sample of GRBs we reproduce bright GRB fluence distribution. Bosnjak et al. (2004)

29 March 2005 John G. Learned Testing the correlations Ghirlanda et al. astro-ph/

29 March 2005 John G. Learned SN- GRB connection SN 1998bw - GRB chance coincidence O(10 -4 ) (Galama et al. 98) SN evidence

29 March 2005 John G. Learned GRB : the “smoking gun”? (Matheson et al. 2003)

29 March 2005 John G. Learned Bright and Dim GRB (Connaughton 2002) Q = cts/peak cts  BRIGHT GRB  DIM GRB

29 March 2005 John G. Learned GRB tails Connaughton (2002), ApJ 567, 1028 Search for Post Burst emission in prompt GRB energy band Looking for high energy afterglow (overlapping with prompt emission) for constraining Internal/External Shock Model Sum of Background Subtracted Burst Light Curves Tails out to hundreds of seconds decaying as temporal power law  = 0.6  0.1 Common feature for long GRB Not related to presence of low energy afterglow

29 March 2005 John G. Learned GRB tails Sum of 400 long GRB bkg subtracted peak alligned curve Connaughton 2002

29 March 2005 John G. Learned GRB tails Connaughton 2002 Dim Bursts Bright Bursts

29 March 2005 John G. Learned Bright and Dim Bursts 3 equally populated classes Bright bursts –Peak counts >1.5 cm -2 s -1 –Mean Fluence 1.5  erg cm -2 Dim bursts –peak counts < 0.75 cm -2 s -1 –Mean fluence 1.3  erg cm -2 Mean fluence ratio = 11

29 March 2005 John G. Learned Recent evidence Piro et al. (2005) GRB

29 March 2005 John G. Learned Effect of Attenuation Epeak Egamma E p ~ E g 0.7 E p ~ E g Preliminary Tau = Caution: scaling fluence and Epeak

29 March 2005 John G. Learned Effects on Hubble Plots Luminosity distance Redshift Reducing the scatter Preliminary

29 March 2005 John G. Learned Effects on Hubble Plots Luminosity distance Redshift Preliminary

29 March 2005 John G. Learned Conclusions Cosmology with GRB requires: –Spectral Epeak determination –Measurement of Jet Opening Angle –Evaluation of environment material Waiting for Swift results

29 March 2005 John G. Learned COMPARISON OF CURRENT MISSIONS FOV, sr # BURSTS/ YEAR LOCALIZATION ACCURACY IPN4π4π1005’HETE ’ INTEGRAL ’ Swift ’ NO ONBOARD FOLLOWUP X-RAYS? OPTICAL? NO YES Should be an exciting year for GRB results!