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 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 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 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? Standard fireball model is OK? We need some emission mechanism. We need some emission mechanism.

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

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

Luminosity functions Fig1 : typical LFs at 3 diff. freq. Fig1 : typical LFs at 3 diff. freq. L0 : characteristic lum. Sigma & lambda : affect width of func. controling shape – sigma stronger effect L0 : characteristic lum. Sigma & lambda : affect width of func. controling shape – sigma stronger effect 4 tests (to cover all basic effects) 4 tests (to cover all basic effects) 1. Changed upper limit keeping lower limit fixed 2. Changed lower limit keeping upper limit fixed 3. Width changed with a fixed center 4. Center changed with a fixed width

Luminosity functions

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

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