Séminaire / Seminar GReCO |
| « Gamma-ray burst afterglow plateaus » |
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Hendrick van Eerten |
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Gamma-ray burst (GRBs), lasting seconds to minutes, are the brightest known explosions in the universe. Their extragalactic nature, and association with the formation of a black hole or extremely strongly magnetized neutron star known as a magnetar, were confirmed in the late nineties by the discovery of GRB afterglow radiation. This afterglow fades from X-ray emission on a time scale of days down to radio emission on a time scale of years, allowing for detailed study. The main explanation for the afterglow is that it is produced by synchrotron radiation from a relativistic shell of matter interacting with the medium surrounding the burster. Up until about 2004, the main theoretical issue was how the shells evolved over time from directed outflows to quasi-spherical flow expected at late times. However, with the launch of the Swift satellite, capable of quickly slewing to the source and starting X-ray / optical measurements very early on, a new challenge to the standard model arose: at early times the emission holds more steady than the decline associated with a decelerating shell. Such steady emission requires either long-lasting input from the source or, in the standard black hole model ('collapsar' scenario) a shell embedded in a slower moving ('cocoon') component. In this talk I will discuss these afterglow `plateau' stages in optical and X-ray and how they can be understood from hydrodynamical simulations and self-similar mathematical modelling of outflows from sources with long-lasting luminosity, approaches that can be generalized to any relativistic source. In addition, I will discuss how reported correlations between observables in afterglow light curves (e.g. plateau duration and flux level) rule out the collapsar model, but support the magnetar scenario or a more complicated collapsar model generating ejecta with a range of velocities.
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lundi 31 mars 2014 - 14:00 Salle des séminaires Évry Schatzman Institut d'Astrophysique de Paris |
| Pages web du séminaire / Seminar's webpage |