On The Origin Of The Highest Redshift GRBs: GRB 080913 and GRB - - PowerPoint PPT Presentation

Introduction Simulations Conclusions

On The Origin Of The Highest Redshift GRBs: GRB 080913 and GRB 090423

Chris Belczynski1,2

1Los Alamos National Laboratory 2Astronomical Observatory, Warsaw University

and Daniel Holz, Chris Fryer, Edo Berger, Dieter Hartmann, Brian O’Shea The Ancient Universe with GRBs, Kyoto, Apr 19, 2010

Chris Belczynski Cosmic Explosions

Introduction Simulations Conclusions Observations & Questions

Introduction: Observations & Questions

(1) GRB 080913: duration: 8 sec (∼ 1 sec in the restframe) redshift: z = 6.7 (∼ 800 Myr after Big Bang) (2) GRB 090423: duration: 9 sec (∼ 1 sec in the restframe) redshift: z = 8.1 (∼ 600 Myr after Big Bang) (3) Questions: Origin: Pop III or Pop II stars? Nature: long (collapsar) or short (merger) GRBs? (collapsar: single massive star; merger: NS-NS/BH-NS)

Chris Belczynski Cosmic Explosions

Introduction Simulations Conclusions Star Formation in Early Universe Single and Binary Evolution Collapsars & Mergers in Early Universe

Simulations: Star Formation in Early Universe

Star Formation History: Strolger et al. – fast rise: low z – maximum: z ∼ 1 − 2 – decline: high z (uncertain: extinction) Metallicity Evolution: – slow model: Pei et al. 1999 (UV, optical and IR) – fast model: Young & Fryer 2007 (SDSS, Galex, Spitzer, Kamiokande) POP III – POP II transition: – our models: z ∼ 10 − 20 (slow-fast) – detailed calc: z ∼ 15 (Mackey et al.) Despite some recent claims: GRB 080913 & 090423: Pop II stars

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Chris Belczynski Cosmic Explosions

Introduction Simulations Conclusions Star Formation in Early Universe Single and Binary Evolution Collapsars & Mergers in Early Universe

Simulations: Single and Binary Evolution

Evolve Pop II Stars: pop. synthesis – long GRB: He/CO star + direct BH 1 − 10%: high rotation required (Podsiadlowski et al.; Yoon et al.) – short GRB: NS-NS or BH-NS merger 1 − 40% of BH-NS, 100% of NS-NS and factor of ∼ 6 – pop. synthesis Formation Efficiency: – collapsars: ∼ 2 − 20 per 6 × 108M⊙ – mergers: ∼ 1 − 40 per 6 × 108M⊙ Delay times: (SF -> GRB) – collapsars: ∼ 5 Myr – mergers: ∼ 100 Myr Note (1) short delay times (2) similar formation efficiencies

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Chris Belczynski Cosmic Explosions

Introduction Simulations Conclusions Star Formation in Early Universe Single and Binary Evolution Collapsars & Mergers in Early Universe

Simulations: Collapsars & Mergers in Early Universe

Calculate Intrinsic Rates: – standard cosmology: Ωm = 0.3, ΩΛ = 0.7 – cosmic SFR: Pop II stars only – propagate: collapsars and mergers Swift Detection: total energy – duration: 30 sec (long), 0.3 sec (short) – isotropic luminosity: same (long/short) – threshold: 3 × 1050 (long), 1050 erg (short) (optimistic threshold for short GRB) Calculate Observed Rates: – collapsars: ∼ 1.0 yr−1 (long GRBs) – mergers: ∼ 0.1 yr−1 (short GRBs) It is (10-times) more likely that: GRB 080913 & 090423 are collapsars (long GRBs)

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5 10 15 20 GRB 090423 GRB 080913 POP II ONLY

Chris Belczynski Cosmic Explosions

Introduction Simulations Conclusions Caveats & Implications

Conclusions: Caveats & Implications

Caveats: GRB engine: not yet fully understood (short GRBs) Metallicity evolution: highly uncertain at high redshifts Monte Carlo study: does not exclude other options Implications: GRB 080913 & 090423 most likely: originate from Pop II stars GRB 080913 & 090423 most likely: are collapsars (long GRBs) (Belczynski et al. 2010, ApJ 708, 117)

Chris Belczynski Cosmic Explosions

Introduction Simulations Conclusions Caveats & Implications

GRBs: Brightness and Detection

Long GRBs: – isotropic luminosity: log(Liso) = 50, σ = 1 – duration: t90 = 30 s – total energy: E = Lisot90 erg Short GRBs: – isotropic luminosity: log(Liso) = 50, σ = 1 – duration: t90 = 0.3 s – total energy: E = Lisot90 erg Swift Detection: total energy threshold – long GRB: 3 × 1050 (z = 1) – long GRB: 1 × 1050 (z = 1) (optimistic threshold for short GRB) ǫSED – fraction of GRBs over detection threshold much larger for long GRBs

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5 10 15 20 GRB 080913 GRB 090423 46 47 48 49 50 51 52 53 54 0.1 0.2 0.3 0.4 0.5 5 10 15 20 GRB 080913 GRB 090423 46 47 48 49 50 51 52 53 54 0.1 0.2 0.3 0.4 0.5

Chris Belczynski Cosmic Explosions