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A Clash of Clusters Provides New Clue to Dark Matter
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Swift Early X-ray Afterglows: 2. the flat decay phase
In this meeting we continue to discuss the early X-ray afterglows observed by Swift, and focus on the early flat decay stage which typically lasts from ~300-500 s, up to ~10^3-10^4 3, where the flux decays as ~t^{-0.5}-t^{-1}. There are many different possible explanations for this flat decay phase, which include continuous energy injection into the afterglow shock (which divides into Type I and Type II energy injection), a viewing angle slightly outside the region of prominent afterglow emission, an initial increase in the efficiency of the afterglow emission, and a two component jet. Each of the different interpretations can have important implications for the efficiency of the prompt gamma-ray emission as well as for the structure and total energy of the relativistic jet, and potentially even for the physics of collisionless relativistic shocks. We will discuss the different interpretations and their possible implications, as well as potential ways for distinguishing between them, and possible complications and problems they face.
- Recommended Reading:
- (Granot & Kumar 2006): Discusses the implications of Type I energy injection (a continuous distribution of ejecta Lorentz factors where slower material0 gradually catches up with the afterglow shock and energizes it).
- (Eichler & Granot 2006): Discusses the interpretation of the flat decay phase as a viewing angle slightly outside the region of prominent afterglow emission, and highlights the implications for the efficiency of the gamma-ray emission.
- (Granot, Konigl & Piran 2006): Discusses various interpretations of the flat decay phase (including the two component jet model, and an initial increase in the afterglow efficiency), as well as the implications for the efficiency of the prompt gamma-ray emission and total energy in the relativistic outflow.
- Additional Reading (not required):
- (Nousek et al. 2006):
Presents the main observational features of Swift early X-ray
afterglows, and discusses their theoretical interpretation and
implications (including Type I versus Type II energy injection).
- (Fan & Piran 2006): Discusses the implications of the flat decay phase for the gamma-ray efficiency, as well as the challenges of the different models in reproducing both the optical and X-ray afterglow light curves.
- (Panaitescu et al. 2006): Presents evidence that in many cases the optical afterglow light curve shows no steepening at the time of the break in the X-ray light curve at the end of the flat decay phase. This challenges the different models for the flat decay phase and calls for additional physical ingredients, or alternatively for a totally new model.
MASS: Lance Simms