Introduction Simulations Conclusions

On The Origin Of The Highest 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 Observations & Questions Conclusions Introduction: Observations & Questions

(1) GRB 080913: duration: 8 sec (∼ 1 sec in the restframe) redshift: z = 6.7 (∼ 800 Myr after )

(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 ? Nature: long (collapsar) or short (merger) GRBs? (collapsar: single massive ; merger: NS-NS/BH-NS)

Chris Belczynski Cosmic Explosions Introduction Star. Formation in Early Universe Simulations Single and Binary Evolution Conclusions 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 -5 -4 -3 -2 -1 0 (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: 0 5 10 15 20 25 GRB 080913 & 090423: Pop II stars

Chris Belczynski Cosmic Explosions . Introduction Star Formation in Early Universe Simulations Single and Binary Evolution Conclusions 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 2 4 6 8 10 12 Formation Efficiency: 8 – collapsars: ∼ 2 − 20 per 6 × 10 M 8 – mergers: ∼ 1 − 40 per 6 × 10 M Delay times: (SF -> GRB) – collapsars: ∼ 5 Myr – mergers: ∼ 100 Myr

0 2 4 6 8 10 12 14 Note (1) short delay times (2) similar formation efficiencies

Chris Belczynski Cosmic Explosions Introduction Star Formation in Early. Universe Simulations Single and Binary Evolution Conclusions Collapsars & Mergers in Early Universe Simulations: Collapsars & Mergers in Early Universe

Calculate Intrinsic Rates: – standard cosmology: Ωm = 0.3, ΩΛ = 0.7 POP II ONLY – 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) GRB 080913 (optimistic threshold for short GRB) GRB 090423 Calculate Observed Rates: – collapsars: ∼ 1.0 yr−1 (long GRBs) – mergers: ∼ 0.1 yr−1 (short GRBs)

0 5 10 15 20 It is (10-times) more likely that: GRB 080913 & 090423 are collapsars (long GRBs)

Chris Belczynski Cosmic Explosions Introduction Simulations Caveats & Implications Conclusions Conclusions: Caveats & Implications

Caveats: GRB engine: not yet fully understood (short GRBs) Metallicity evolution: highly uncertain at high 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 Caveats & Implications Conclusions GRBs: Brightness and Detection

Long GRBs: 0.5 – isotropic luminosity: log(Liso) = 50, σ = 1 0.4 – duration: t = 30 s 90 0.3

– total energy: E = Lisot90 erg 0.2 Short GRBs: 0.1 0 – isotropic luminosity: log(Liso) = 50, σ = 1 46 47 48 49 50 51 52 53 54 – 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) GRB 080913 GRB 090423

0 5 10 15 20 SED – fraction of GRBs over detection threshold much larger for long GRBs

Chris Belczynski Cosmic Explosions