Rome GRB

External Shock/Supranova Model for GRBs : 

External Shock/Supranova Model for GRBs Chuck Dermer (Naval Research Laboratory) Rome 2002 GRB Workshop September 19, 2002 James Chiang (Stanford University) Markus Böttcher (Ohio University) Kurt Mitman (University of Virginia) (Optically thin) external shock model for GRB afterglows External shock model for prompt gamma-ray luminous phase Produces short timescale variability (single explosion) Requires diverse circumburster medium properties Explains Epeak distribution of GRBs Predicts dirty fireballs/X-ray flashes Implications for central engine

External vs. Internal Shocks: Importance: 

External vs. Internal Shocks: Importance Central Engine Physics One-step collapsar model(s): active central engine requires internal shocks Two-step supranova model: collapse of neutron star to black hole consistent with external shock model Other models with prompt explosions (coalescing compact objects; accretion-induced collapse; magnetar; EMBH) Physical Properties Energy Release of Central Engine Density and Distribution of Surrounding Matter (tomography) Information about Progenitors Explain GRB statistics and phenomenology Connection between prompt phase and afterglow

External Shock Model in Afterglow Physics : 

Multiwavelength afterglow modeling Analysis of 4 GRBs (Panaitescu and Kumar 2001): GRB 980703,GRB 990123, GRB 990510, GRB 991216 More consistent with uniform density surroundings than wind Implied low density of surroundings (nISM ~ 10-2 – 10 cm-3) Moderate magnetic field parameter (eB ~ 10-4 – 0.05); 0.01 <~ ee <~ 0.1; q ~ 1o-4o : beaming factor = 13,000/ (q o)2 Constant energy reservoir result (Frail et al. 2001) Key to understanding the nature of GRB progenitors (if true!) External shock model for prompt phase Redshift dependence of GRB sources from GRB statistics ( cosmological star formation rate) GRB emissivity (UHECR and cosmic-ray origin) External Shock Model in Afterglow Physics GRB event rate > 500 x observed rate

Local Spherical Symmetry: 

Local Spherical Symmetry (Fenimore et al. 1996) Colliding shells produce generic pulse profiles Asymmetric profile from kinematics

Internal Shells: Difficulties: 

Internal Shells: Difficulties Daigne and Mochkovitch (1998) Low Efficiencies If Lorentz factor contrast is small High Efficiencies If Lorentz factor contrast is large, but spread in Epeak range of pulse profile widths Kobayashi and Sari (2001)

Predicted Kinematic Relationship: 

Predicted Kinematic Relationship Epeak and Flux vary in a well-defined way Depending only on observable spectral index Soderberg and Fenimore (2001)

External Shock Model?: 

External Shock Model? Radial spreading time scale Angular spreading time scale Note that if 1% of clouds at q 1/10G produce  8-16% of fluence in very narrrow pulses 100x brighter than clouds at q 1/G Beaming factor? Peak pulse flux: Evolution of Epeak similar for identical clouds at different q

Variability Argument against External Shock Model: 

Variability Argument against External Shock Model Sari and Piran (1997) Variability Rapid variability implies low efficiency X X X

Variability from Inhomogeneities: 

Variability from Inhomogeneities Relative timing of different pulses Off-axis clouds produce broadened, low peak-flux pulses observer

Short Timescale Variability due to Inhomogeneities in Surrounding Medium: 

Short Timescale Variability due to Inhomogeneities in Surrounding Medium Clouds with thick columns (>4x1018 cm-2) Total cloud mass still small (>>10-4 Mo) Variability  cloud radii << R/Go, Go = 300 Dermer and Mitman (1999) Requires highly clumpy medium at 1016 – 1017 cm Cloud sizes  1012 –10 13 cm to agree with pulse paradigm (Norris et al. 1996) Criticisms: 1. Pulse width spreading 2. Gaps in light curves 10% partial covering efficiency 100% efficiency r = 3x1013 cm r = 1013 cm r = 3x1012 cm r = 3x1012 cm

Physics of the Blast Wave/Small Cloud Interaction: 

Physics of the Blast Wave/ Small Cloud Interaction Two classes of blast-wave shell Interactions: Forward shock passes through cloud before reverse shock passes through shell: subsequent acceleration Reverse shock passes through shell before forward shock passes through cloud: subsequent deceleration shell cloud

Standard System: 

Standard System Cloud radius is 1013 cm Apparent isotropic energy release = 1053 ergs; G0 = 300 10% partial covering factor 10% efficiency of intercepted energy into radiation (radiated with Band spectrum) Clouds “randomly uniformly” distributed between 1016 and 1017 cm Added Gaussian noise at a level typical of BATSE GRBs

Variation of Cloud Size: 

Variation of Cloud Size Large cloud

Variation of Cloud Radii: 

Variation of Cloud Radii Discrete cloud sizes

Variation of Cloud Radii and Sizes: 

Variation of Cloud Radii and Sizes Equal partial covering factor per logarithmic interval in cloud size between 1012 cm and 3x1013 cm No background noise

Variation of Partial Covering Factor: 

Variation of Partial Covering Factor Cloud radius is 1013 cm

Is the Circumburster Medium of a GRB Structured?: 

Is the Circumburster Medium of a GRB Structured? Supernova remnant simulations of C. Fryer Three-dimensional simulations of 15 Mo star 1 year after SN Rayleigh-Taylor instabilities and clumps of 56Ni on scales of 1o-5o High-velocity bullets of 56Ni

Evidence for circumburster material along line of sight to a GRB: GRB 990705: 

Evidence for circumburster material along line of sight to a GRB: GRB 990705 Observation of absorption edge at ~ 3.8 keV during the prompt phase (Amati et al. 2000) in intervals A and B z = 0.8435 (0.0005) (Andersen et al. 2002)

GRB 990705 : 

GRB 990705 Can be explained with strong Fe enhancements and large amount of Fe within 1 pc; requires strong clumping of ejecta Böttcher, Fryer and Dermer (2002) Size scale of clumps ~< 1013 cm and densities >~ 1010 cm-3 for either resonance scattering (Lazzati et al. 2001) or photoelectric absorption (Böttcher et al. 2002) models Probability of observing absorption in He-merger/collapsar model << 1%

GRB 011211 : 

GRB 011211 Claimed line detection of Ka transitions in Mg XI (or XII), Si XIV, SXVI, Ar XVIII, Ca XX Strongest line at Si XIV   1048 ergs in H-like Ka line Requires very strong clumping of ejecta to make recombination proceed quickly: explained with thermal (coronal) model with r  1012 cm, ne <  1012 cm-3 Long duration (tdur  270 s) GRB at z = 2.140 (0.001)  apparent isotropic energy = 6.31052 ergs zlines= 1.88 (0.06)  emission in outflowing moving with b  0.1 Beaming break or constant energy reservoir result  qj  3-7° Reeves et al. (2002)

Highly Structured SN Remnant Ejecta: 

Highly Structured SN Remnant Ejecta Cas A Supernova Remnant Breaks “uniform random” approximation for cloud distribution

Pulsar Wind Nebulae: 

Pulsar Wind Nebulae Highly inhomogeneous surrounding medium: shells? Crab (plerionic) nebulae

Cartoon: Supranova GRB Model: 

Cartoon: Supranova GRB Model Jet quenching problem (Lazzati et al. 1999; Matzner 2002) ameliorated by pulsar wind and anisotropic SN ejecta MSMNS  2-3 Mo: ~Constant energy reservoir Vietri and Stella (1998)

Variation in G0: 

Variation in G0 No background noise

Variation in G0: 

Variation in G0 Background noise included

Dirty and Clean Fireballs: Uniform Surroundings: 

Dirty and Clean Fireballs: Uniform Surroundings Observed properties most sensitive to initial Lorentz factor of outflow (or baryon loading) Severe instrumental selection biases against detecting fireballs with G0 << 100 and G0 >> 1000 X-Ray Flashes (or X-ray rich GRBs) = Dirty Fireballs (Dermer, Chiang, and Böttcher 1999) GeV Flashes = Clean Fireballs

Most common prompt GRB light curve: 

Most common prompt GRB light curve Reproduces generic temporal behavior of FRED-type profiles Hardness-intensity correlation, hard to soft evolution Near alignment at high energies; lag at lower energies Predictable sequence of energy-dependent temporal indices in rising phase Change in spectral indices between leading and trailing edges of GRB peak follow a well-defined behavior Dermer, Böttcher, and Chiang (2000)

Duration Distribution : 

Duration Distribution Kouveliotou et al. (1993) What sets the characteristic duration of gamma-ray luminous phase? Period of activity in internal shock/collapsar model Deceleration timescale in external shock model

Epk Distribution Explained: 

Epk Distribution Explained

Cosmological Statistics of GRBs in the External Shock Model: 

Cosmological Statistics of GRBs in the External Shock Model Assume that distribution of GRB progenitors follows star formation history of universe Trigger on 1024 ms timescale using BATSE trigger efficiencies (Fishman et al. 1994) Broad distributions of baryon-loading G0 and directional energy releases are required. Assume power laws for these quantities. 10-6 < E54< 1; N(E54)  E54-1.52; G0 < 260; N(G0)  G0 -0.25 Böttcher & Dermer (ApJ, 2000, 529, 635) (Madau et al. 1998) GRB spectral model degenerate in n0G08 Few clean fireballs Beaming Total Energy Prediction for GRB redshift distribution

GRB Statistics: 

GRB Statistics GRB Burst Rate Density (unbeamed) GRB Emissivity Rate per L* galaxy Time-averaged power per L* galaxy GRBs power UHECRs? Vietri (1995), Waxman (1995) GRBs power Cosmic Rays? Dermer (2002) Local density of L* Galaxies: 1/(500 Mpc3) Beaming factor of GRBs: 1/500 (Frail et al. 2002)

GeV Gamma Ray Emission from Secondary Nuclear Production: 

GeV Gamma Ray Emission from Secondary Nuclear Production Secondary nuclear production in dense shell surrounding GRB: explanation for GRB 940217 (Katz 1994) p+p  p0 2g Solution to “Line of Death” Problem (Dermer and Böttcher 2001) Pair production and radiation reprocessing due to reflected photon front backscattered by clouds (Beloborodov 2001) Thomson-thick clouds at radii r~1016 cm from GRB source Produce flash-heated plasma visible with Swift or INTEGRAL from GRBs at z <~0.1

Phenomenology: Qualitative: 

Phenomenology: Qualitative Variability-luminosity correlation (Ramirez-Ruiz and Fenimore 1999; Reichart et al. 2001) Smooth CBM Clumpy CBM Luminosity-lag relation Structured jet (Salmonson 2001) Correlation of Quiescent Period with Subsequent Emission Period (Ramirez-Ruiz and Merloni 2001) Emission at base of jet

Summary: 

Summary External shock model for prompt GRB emission GRB prompt and afterglow phenomenology explained by a single relativistic blast wave interacting with external medium with standard relativistic fireball model Epeak distribution due to blast wave physics and triggering properties of detectors Short timescale variability requires dense clumpy surrounding medium X-ray line observations: GRBs surrounded by dense clumpy medium Source model: Supranova with SNR shell forming circumburster material Predictions: X-ray flash-heated plasmas (Swift or INTEGRAL) X-ray absorption in shells of material correlated with different episodes of GRB gamma-ray emission (Swift) GRB light curves are tomographic images of the distribution of matter surrounding the sources of GRBs