What is a Gamma-Ray Burst? Short  -ray flashes E > 100 keV 0.01 < t 90 < 1000s Diverse lightcurves BATSE detected 1/day = 1000 /year/universe Energy ~ f  -1 f  erg Near star forming regions 2 SN Ibc associations Supernova component in lightcurves

Superbowl Burst ms variability + non-thermal spectrum Compactness   GRB Light Curve M = E/  c 2 ~ M sun

GRB CGRO ~1 o 2. BeppoSAX (X-ray) 6-33 hrs hrs ~ 1’ 4. HST 17 days 3. Palomar < 1 day Keck spectrum z=1.60 E iso = 3x10 54 erg ~ M sun c 2 9 th mag flash

135 models (1993) Note: most are Galactic and are ruled out for long bursts

GRB photons are made far away from engine. Can’t observe engine directly in light. (neutrinos, gravitational waves?) Electromagnetic process or neutrino annihilation to tap power of central compact object. Hyper-accreting black hole or high field neutron star (rotating)

Well-localized bursts are all “long-soft” “short-hard” bursts ? Duration (s) hardness Kulkarni et al

NTT image (May 1, 1998) of SN 1998bw in the barred spiral galaxy ESO 184-G82 [Galama et al, A&AS, 138, 465, (1999)] WFC error box (8') for GRB and two NFI x-ray sources. The IPN error arc is also shown. 1) Were the two events the same thing? 2) Was GRB an "ordinary" GRB seen off-axis? SN 1998bw/GRB

Bloom et al (ApJL,2002) GRB991121

see also: Hjorth et al, Fox et al Nature (2003) extremely close = 800 Mpc GRB030329/SN2003DH

SN 1998bw/GRB The supernova - a Type Ic - was very unusual. Large mass of 56 Ni solar masses; (note: jets acting alone do not make 56 Ni) Sollerman et al, ApJL, 537, 127 (2000) McKinzie & Schaefer, PASP, 111, 964, (1999) Extreme energy and mass > erg > 10 Msun Iwamoto et al., Nature, 395, 672 (1998) Woosley, Eastman, & Schmidt, ApJ, 516, 788 (1999) Mazzali et al, ApJ, 559, 1047 (2001) Exceptionally strong radio source Li & Chevalier, ApJ, 526, 716, (1999) Relativistic matter was ejected erg Wieringa, Kulkarni, & Frail, A&AS, 138, 467 (1999) Frail et al, ApJL (2001), astroph Probability favors the GRB-SN association Pian et al ApJ, 536, 778 (2000)

Merging neutron star - black hole pairs Strengths: a) Known event b) Plenty of angular momentum c) Rapid time scale d) High energy e) Well developed numerical models Weaknesses: a) Outside star forming regions b) Beaming and energy may be inadequate for long bursts But this model may still be good for a class of bursts called the “short hard” bursts for which we have no counterpart information yet (SWIFT). Ruffert & Janka, Rosswog et al, Lee et al, Aloy et al

Requirements on the Central Engine and its Immediate Surroundings (long-soft bursts) Provide adequate energy at high Lorentz factor Collimate the emergent beam to approximately 0.1 radians In the internal shock model, provide a beam with rapidly variable Lorentz factor Allow for the observed diverse GRB light curves Last approximately 10 s, but much longer in some cases Explain diverse events like GRB Produce a (Type Ib/c) supernova in some cases Make bursts in star forming regions

GRB central engine : Relativity (SR & GR) Magnetic Fields Rotation (progenitors) Nuclear Physics Neutrinos EOS Turbulence 3D Range of Lengthscales

Muller (1999) “Delayed” SN Explosion acac Accretion vs. Neutrino heating Burrows (2001)

Pre-Supernova Density Structure Woosley & Weaver (1995) Bigger stars: Higher entropy Shallower density gradients

Fryer, ApJ, 522, 413 (1999), Burrows (1999) Bigger stars: 1. Accrete faster & longer 2. Larger binding energy & smaller explosion energy explosionbinding Failure of delayed mechanism

Fukuda (1982) Heger (2000) Stellar Rotation no mass loss Mass loss No B fields

Collapsars Type Mass/sun BH Time Scale Distance Comment I He prompt 20 s all z neutrino-dominated disk II He delayed 20 s – 1 hr all z black hole by fall back III >130 He prompt ~20 s z>10? time dilated, redshifted *(1+z) very energetic, pair instability, low Z A rotating massive star whose core collapses to a black hole and produces an accretion disk. Type I is what we are usually talking about. The 40 solar mass limit comes from assuming that all stars above 100 solar masses on the main sequence are unstable (except Pop III).

IF Two plausible conditions occur: 1. Failure of neutrino powered SN explosion a. complete b. partial (fallback) 2. Rotating stellar cores j > 3 x cm 2 /s THEN Rapidly accreting black hole, (M~0.1 M  /s) fed by collapsing star (t dyn ~ 446 s/  ½ ~ 10 s) Disk formation COLLAPSAR

Collapsar Simulations : pre-SN 15 Msun Helium star Newtonian Hydrodynamics (PPM) alpha viscosity rotation photodisintegration (NSE alpha, n, p) neutrino cooling, thermal + URCA optically thin Ideal nucleons, radiation, relativistic degenerate electrons, positions 2D axisymmetric, spherical grid self gravity, pseudo-Newtonian (PW) R in = 9 R s R out = 9000 R s MacFadyen & Woosley (1999):

Collapsar Disk Animation PPM hydrodynamics, Paczynski-Witta potential, EOS, neutrino cooling, nuclear reactions,  viscosity Stellar collapse w/ rotation. Density structure. No disk, no wind. Note: Accretion shock, funnel clearing, pole to equator density contrast, fluctuating polar density Initial model: 15 M sun Helium (Wolf-Rayet) star evolved with mass loss. R= 8 x 10 8 cm Show inner 1% in radius disk mass =.001 M_sun Low viscosity  =.001

Disk Formation Movie

Accretion Shock, Disk formation t =.75 s Photodisintegration Si,O,C -> free neutrons And protons Enhanced neutrino cooling neutrino coolong allows accretion no cooling=> dynamically unstable CDAF? Could emit GWs but maybe no GRB

 = 0.1 = 0.07 M sun /s = 1.3 x erg/s

spin mass Use 1D neutrino cooled “slim” disk models from Popham et al (1999).

Collapsar results Sustained accretion >10s Sufficient energy Time scale set by He core collapse Disk-feeding time scale not disk-draining Neutrino cooling allows accretion Neutrino annihilation energetically possible –calculable in any case

Funnel geometry channels any fireball. Density contrasts can be huge.

.. E jet = f M acc c 2 MHD T = 5.7 ms E = 5 x erg/s E dep = 2.8 x erg Jet Birth Thermal energy deposition focused by toroidal funnel structure f max ~

Relativistic Jet Movie

Collapsar stages 1.Iron core collapse, disk formation T~10 10 K,  ~10 8 gcm -3, photodisintegration, cooling, pair capture, disk is free nucleons (2 s) 2.Polar density declines to allow jet birth ½  v 3  E dep (2-5 s) 3.Jet tunnels out of star (5 s) Wolf-Rayet 4.Jet powered for ~10 more seconds. Evacuates polar channel and reaches asymptotic speed. (10 s) T_GRB  T_collapse

Red Supergiant R~10 13 cm Blue Supergiant R~10 12 cm Wolf-Rayet Star R~10 11 cm Type Ib or Ic Supernova

Supernovae Ia WD cosmology Type II Hydrogen Type I No Hydrogen Ib, Ic exploding WR thermonuclear old pop. E galaxies core collapse massive stars

Nickel Wind Movie “Nickel Wind” T > 5 x 10 9 K

Fallback in weak SN explosions Shock reaches surface of star but parts of star are not ejected to infinity.

Fallback accretion M ms ~ 25 M sun Same star exploded with a range of explosion energies. Significant accretion for thousands of seconds – days.

If fallback fuels a jet with power fmc 2 May power “hypernova” or long duration GRB Weak supernova shock

Shock breakout X-Ray transient

2. “Brief” jet t engine  t jet Engine dies before jet breakout. Mildly relativistic shock breakout MacFadyen (1999) What made SN1998bw+GRB980425? 1. Accretion powered hypernova w/ Nickel wind MacFadyen (2002) E~ erg, M(Ni)~0.5 M  GRB from  ~3 shock breakout (Tan et al 2001, Perna & Vietri 2002)

Collapsars Can make “long” GRBs in H stripped (WR) stars. t engine > t escape Short bursts may be compact binary mergers. Need SN failure & angular momentum –Low metallicity, binary can help Star can explode -> SN if nickel is made. Predicts GRB/SN association. Type Ibc. SN/GRB ratio may depend on angular momentum. “Nickel wind” can explode star -> hypernova –H env. Type II (no GRB), no H Type I + GRB

GRB/GW Long GRBs –not brighter than SN in GW? –very far Gpc –very rare < 1% SN Short GBs –merging ns-bh binaries? –maybe closer than long bursts –short delay between event and GRB? –good for SWIFT/LIGO

Rates SN: 1/s = 100,000 /day GRB: 1/day (BATSE) = 1,000/day GRB rate = 1% of SN rate maybe more collapsars than GRBs => more rapidly rotating SN SN with collapsar engine look for bright Type Ic (w/ broad lines)

SN GW SN1998bw/GRB Mpc maybe dominant GRB rapid rotaters SNAP/ROTSE look for 1998bw 2003dh like SN many light curves -> better t_explode

Implications Probe engine directly collapse duration vs. GRB duration collapse/GRB delay (internal vs. external?) disk properties – low viscosity? big disks?

Issues too much j => no GRB? but bright GW? may need low metallicity for GRB prefer high redshift don’t know nearby rate but may imply rate is high look for weak GRBs like

Principle Results Sustained accretion.1 Msun/s for>10s Jet formation and collimation Sufficient energy for cosmo. GRB Neutrino cooling & photodissociation allows accretion Massive bi-conical outflows develop Time-scale set by He core collapse Fallback -> v. long GRB in WR star or asymmetric SN in SG

With decreasing metallicity, the binding energy of the core and the size of the silicon core both increase, making black hole formation more likely at low metallicity. Woosley, Heger, & Weaver, RMP, (2002) Black hole formation may be unavoidable for low metallicity Solar metallicity Low metallicity

In the absence of mass loss and magnetic fields, there would be abundant progenitors. Unfortunately nature has both. 15 solar mass helium core born rotating rigidly at f times break up The more difficult problem is the angular momentum. This is a problem shared by all current GRB models that invoke massive stars...