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Local Rate of SHBs & Life time of SHB progenitors

Local Rate of SHBs & Life time of SHB progenitors. Soomin Jeong (Ewha Womans University) Chang-Hwan Lee (Pusan National University). GRB : The most violent explosion in the Universe. hard X-ray to gamma-ray( first detected in 1967 by US Vela , and first reported in 1973) Last for minutes

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Local Rate of SHBs & Life time of SHB progenitors

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  1. Local Rate of SHBs & Life time of SHB progenitors Soomin Jeong(Ewha Womans University) Chang-Hwan Lee(Pusan National University)

  2. GRB : The most violent explosion in the Universe • hard X-ray to gamma-ray( first detected in 1967 by US Vela , and first reported in 1973) • Last for minutes • Powerful (1049~1054erg ; if isotropic emission) 2007’ October. KPS

  3. Long GRB SHB • Angular distribution- isotropic • Duration distribution-Bimodality(T90 ~2s)- peaked at ~0.3,~20seconds 2007’ October. KPS

  4. The first detected afterglow (GRB 970228) by BeppoSAX - After prompt gamma ray emission, - Slow transient phenomenon, in lower energy bands( X-ray Optical radio emission) • Lasts much longer • Related to GRB progenitor and environments • Accurate positions given • Relatively easy to follow up 2007’ October. KPS

  5. What is Afterglow ? • After prompt gamma ray emission • Slow transient phenomenon, in lower energy bands( X-ray Optical radio emission) • Lasts much longer, • Relatively easy to follow up • Related to GRB progenitor and environments • Accurate positions given 2007’ October. KPS

  6. Long-soft Gamma Ray Burst • The majority of the observed bursts(about ¾), durations longer than~2s, relatively soft spectra, associated with supernovae, red shift (z>1) , known redshift of Long-GRB number- about 100 2007’ October. KPS

  7. Short Hard Gamma Ray Burst • The minority(~1/4), short durations, hard spectra, progenitors- old populations, red shift (z<0.3) • Progenitor candidate- Neutron star mergers or Neutron star black hole mergers Known redshift of SHB 2007’ October. KPS

  8. In 2005, the first detected SHB afterglow by swift • Different progenitor system with long duration gamma ray burst • Using local rate of SHB constrain progenitor’s life time GRB050509B We can constrain GRB progenitors 2007’ October. KPS

  9. Models in numerical calculation • Three star formation rate (per unit comoving volume and comoving time) 2007’ October. KPS

  10. Progenitor model • Various f(τ) (The fraction of SHB progenitors that are born with a lifetime τ) power law – f(τ) = τ –β lognormal distribution- τ*=100Myr~10Gyr σ = 0.3 Power law model is associated with Supernovae 2007’ October. KPS

  11. Universe model • ΛCDM universe- Flat space and accelerating Ωm + ΩΛ = 1, Ωm = 0.3 2007’ October. KPS

  12. Local Rate of SHB • Intrinsic SHB rate per unit comoving volume and comoving time • Observed SHB rate as redshift Ehud Nakar et al, Astrophys.J. 650 (2006) 281-290 2007’ October. KPS

  13. Life time of Short-hard GRBs –Results (1) with power law Power law- no good fit model !! SHB progenitors are not related with supernovae Observed cumulative redshift 2007’ October. KPS

  14. Life time of Short-hard GRBs–Results (2) with lognormal ftn. Lognormal with delay time - good fit model !! • SHB progenitor is consistent with old populations • ≥ 6.5Gyr! 2007’ October. KPS

  15. SHB progenitor’s lifetime as changing matter density Old population with mean timeτ* =6.5Gyr is consistent independent of matter density 2007’ October. KPS

  16. Conclusion 1 • SHB progenitor is surely consistent with old populations ≥ 6.5Gyr! (Nakar et al. 2006) • Not associated with supernovae • Possibly it is associated with NS-NS mergers or NS-BH mergers How about other class?... 2007’ October. KPS

  17. SHB Long GRB ClusterⅢ T90=2S FT=1.6X10-4/T90 ClusterⅠ ClusterⅡ Three Classes of GRB Collapse of massive stars • Recent classification of GRB - ClusterⅠ,Ⅱ,Ⅲ (Chattopadhyay et al. 2007) • Long GRB was divided into two groups – ClusterⅡ,Ⅲ Neutron star systems White dwarf with NS 2007’ October. KPS

  18. Long- soft GRB with Power law(τ –β) β decrease, curve comes up, β increase, curve doesn’t come down any more. Long-soft GRB can not be exactly described by power law model.. So.. something new is needed.. If Long GRB is divided into two groups.. Clusterll & Clusterlll ;Chattopadhyay et. al.2007) 2007’ October. KPS

  19. Clusterll & Clusterlllwith Power law Only Clusterlll data is described well by Power-law model Related with supernovae 2007’ October. KPS

  20. Conclusions • SHB progenitors has little relation with supernovae power-law model • SHB progenitor is consistent with old populations ≥ 6.5Gyr!( Nakar et al.2006) • Using this tools in Long GRB, This might indicate that there exist two subclasses in the long GRB(arXiv:0710.1475) 2007’ October. KPS

  21. Thank you for your attention. S. Jeong 2007’ October. KPS

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