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Séminaire MHD (SEMHD)

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Theory of pulsar magnetosphere: From radio to high-energy pulsed emission
Jérôme Pétri (Strasbourg I)

20 octobre 2008

Although discovered 40 years ago, pulsars remain astrophysical objects of enigmatic behavior. We can summarize our current theoretical knowledge by saying that they are strongly-magnetized rotating neutron stars (Michel, 1991). To date, indeed, no self-consistent model is able to either predict their observed emission spectrum or explain the acceleration and radiation (from radio to high-energy gamma-ray) mechanism of particles. Nevertheless, an important effort towards modeling the pulsar magnetosphere seems to provide a satisfactory picture of what a pulsar is.
To begin with, I will briefly review the main observational facts about pulsar emission properties. I will then expose the different existing models able to describe pulsed radiation from radio frequencies up to high-energy gamma-rays. Finally, I will discuss in detail an alternative scenario accounting for the production of high-energy pulsed emission, which is related to a peculiar structure called striped wind, whose geometrical configuration is very similar to the solar wind (Coroniti, 1990; Michel, 1994; Bogovalov, 1999). I will show that the polarization of the synchrotron emission emanating from such a geometry is in agreement with recent optical observations from the Crab pulsar (Pétri & Kirk, 2005).
Extrapolating to the highest energies through inverse Compton scattering, I compute and reproduce the light curves and phase-resolved spectral variability of some gamma-ray pulsars. Indeed, with the help of the striped wind model, I can fit observations above 10 MeV for the Vela and Geminga pulsars (Fierro et al. 1998). The recent launch of the GLAST satellite, working between 20 MeV and 300 GeV, will allow a detailed study of the gamma-ray radiation and therefore of the acceleration process in a pulsar magnetosphere. Eventually, a discrimination between the proposed models will be possible.
Bibliographie :
– Bogovalov S.V., Astron. Astrophys., 349 (1999), 1017.
– Coroniti F.V., Astrophys. J., 349 (1990), 538.
– Fierro J.M., Michelson P.F., Nolan P.L., Thompson D.J., Astrophys. J., 494 (1998), 734.
– Michel F.C., Theory of Neutron-Star Magnetospheres (Chicago, Chicago University Press, 1991).
– Michel F.C., Astrophys. J., 431 (1994), 397.
– Pétri J. & Kirk J.G., Astrophys. J., 627 (2005), L37.

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Jérôme Pétri Jérôme Pétri (Strasbourg I)
Maître de conférences à l’université Strasbourg I, Jérôme Pétri travaille au sein de l’équipe "Hautes énergies" de l’observatoire astronomique de Strasbourg.