Marco Nardini Testing an unifying view of Gamma Ray Burst afterglows Gabriele Ghisellini In collaboration with Giancarlo Ghirlanda Annalisa Celotti 44th Rencontres de Moriond La Thuile (Val d'aosta, Italy) February 2nd, 2009
COMPLEX X-RAY LIGHTCURVES BEHAVIOUR
COMPLEX X-RAY LIGHTCURVES BEHAVIOUR Steep
COMPLEX X-RAY LIGHTCURVES BEHAVIOUR Steep Flat
COMPLEX X-RAY LIGHTCURVES BEHAVIOUR Steep Flat Steep
COMPLEX X-RAY LIGHTCURVES BEHAVIOUR X-ray and optical bands go together X-ray and optical bands behave differently Steep Flat Steep
Possible explanations for the flat phase Some examples Modified afterglow: { Reverse shocks (Uhm & Beloborodov 2007 and Genet, Daigne & Mochkovitch 2007) Time dependent micro physical parameters (Ioka et al.2006) Up scattering of forward shock photons (Panaitescu 2008) Energy injection (Zhang et al. 2006) Geometry: { Double jet model (Racusin et al 2008, De Pasquale et al. 2009) Off beam model (Eichler & Granot 2006) Patchy shell model (Toma et al.2006) Two different components: Late prompt model (Ghisellini et al. 2007)
OPTICAL VS X-RAYS SWIFT ERA LUMINOSITY LIGHTCURVES Long GRBs Known redshift Well sampled optical and X- ray lightcurves Known host frame optical extinction
OPTICAL VS X-RAYS SWIFT ERA LUMINOSITY LIGHTCURVES Long GRBs Known redshift Well sampled optical and X- ray lightcurves Known host frame optical extinction 33 GRBs fulfilling all the requests Ghisellini, Nardini, Ghirlanda & Celotti 2009, MNRAS, 393, 253
DIFFERENT OBSERVED BEHAVIOURS
DIFFERENT OBSERVED BEHAVIOURS Optical and X rays go together
DIFFERENT OBSERVED BEHAVIOURS
DIFFERENT OBSERVED BEHAVIOURS Two different power law decays (to be compared with the ones predicted by the standard models)
DIFFERENT OBSERVED BEHAVIOURS
DIFFERENT OBSERVED BEHAVIOURS Presence of chromatic breaks in the X-Rays, in the optical, or in both lightcurves but at different times and with different decay indices
DIFFERENT OBSERVED BEHAVIOURS
OPTICAL TO X-RAYS SEDs Parallel optical and X-rays temporal evolution Log F(ν) Optical X-Rays Log νf(ν) Optical Log ν X-Rays Log t Different optical and X-rays temporal evolution Log νf(ν) Optical X-Rays Optical Log ν Log F(ν) X-Rays Log t Log νf(ν) Optical Log ν X-Rays
A POSSIBLE ALTERNATIVE MODEL Late prompt + standard afterglow emission (Ghisellini et al. 2007) Early prompt γ Ray emission } t 10-100s Late prompt Standard afterglow X Ray emission IR Optical UV emission X Ray emission IR Optical UV emission } 10s<t<10^6s
SOME EXAMPLES Afterglow Late Late Afterglow 071003 z=1.6
JET BREAKS No standard afterglow No jet break Standard afterglow dominated Possible jet break
A FIRST STEP TOWARD A PHYSICAL MODEL F t 5 3 accretion rate of fall back material? Link between early and late prompt emission?
SPECTRAL CHECKS Nardini et al. (2009) in preparation
SED consistency check Possible presence of a break in X-ray late prompt dominated spectra Optical spectral index change when a new component becomes dominant 071003 z=1.6
BREAKS IN X-RAY SPECTRA XRT spectral analysis of the complete sample of 33 GRBs Good fit with a broken powerlaw for 22 events
BREAKS IN X-RAY SPECTRA XRT spectral analysis of the complete sample of 33 GRBs Good fit with a broken powerlaw for 22 events Large N H column densities from single powerlaw fitting. Inconsistent with optical reddening N H estimated from single powerlaw X-ray spectral fitting
BREAKS IN X-RAY SPECTRA XRT spectral analysis of the complete sample of 33 GRBs Good fit with a broken powerlaw for 22 events Large N H column densities from single powerlaw fitting. Inconsistent with optical reddening Broken powerlaw Smaller N H Consistent with A V N H estimated from single powerlaw X-ray spectral fitting
Optical to X rays SEDs t 1000s β 0 =0.97 t 2 10 4 s β 0 =0.48
CONCLUSIONS Optical and X-Rays lightcurves are complex Two components: Late prompt + standard afterglow indication of fallback jet break problem solution Spectral checks broken power law in X-ray: lower N H spectral evolution: confirmation