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Galactic Astronomy - Paper

Galactic Astronomy - Paper. Luminosity Functions of GRB Afterglows. Dong-hyun Lee 2007/09/18. LF of GRB Afterglow : summary. Using standard fireball model => create virtual population of GRB afterglow => study LFs

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Galactic Astronomy - Paper

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  1. Galactic Astronomy- Paper Luminosity Functions of GRB Afterglows Dong-hyun Lee 2007/09/18

  2. LF of GRB Afterglow : summary • Using standard fireball model => create virtual population of GRB afterglow => study LFs • Numerical sim. Varying parameters of fireball model randomly => create virtual population => compare 1day observational data => check the consistency of model • LFs are described by a func. sim. to log normal dist. with exponential cutoff & func. parameters are dep. on model parameters => comparison : difficult to explain simultaneously X-ray & optical data • Standard fireball model is OK? • We need some emission mechanism.

  3. Intro. • Standard fireball model since 1997 • Used to explain GRB afterglow • Observed data from Swift satellite(rapid burst) & its XRT(detected afterglow ~200) • LFs can be described to a high accuracy by anal. func.

  4. Virtual population of afterglow • Numerical calculation : Johannessen et al.(2006) • Based on standard fireball jet model – E is injected instaneously into a narrow jet • Model parameter : varying logarithmic (except p) • Fix z=1 (to concentrate on intrinsic properties)

  5. Luminosity functions • Fig1 : typical LFs at 3 diff. freq. • L0 : characteristic lum. Sigma & lambda : affect width of func. controling shape – sigma stronger effect • 4 tests (to cover all basic effects) • Changed upper limit keeping lower limit fixed • Changed lower limit keeping upper limit fixed • Width changed with a fixed center • Center changed with a fixed width

  6. Luminosity functions

  7. Luminosity functions

  8. Comparison with Observations • Data : normalized to an observer’s time of 1 day & z=1 • Difference b/w optical & X-ray lum. func. • bimodality • Model needs to be refined • Observed optical LF may be incomplete

  9. Discussion & Conclusions • LF : simple log normal dist. with exponential cutoff • Shape of LF is not sensitive to shape of model parameter dist. • Sigma & lambda are somewhat dep. on model parameter dist. => but not significant correlations • Generally, good agreement with observations • Incompatibility b/w optical & X-ray : bimodality in optical but not in X-ray • More detailed model or entirely different one is required

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