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4th International Meeting on High Energy Gamma-Ray Astronomy, Heidelberg : Allemagne (2008)
MHD and Radiation Modelling of G21.5-0.9
O.C. de Jager1, S.E.S. Ferreira1, A. Djannati-Ataï2

The H.E.S.S. telescopes detected VHE ?-rays from G21.5-0.9, which is most likely the result of IC scattered VHE ?-rays from the central pulsar wind nebula (PWN). The ~1 kyr age constrains the birth period in the range 50 to 55 ms, which also places a tight constraint on the available energetics for IC radiation. The fact that the reverse shock did not yet reach the PWN allows us to model the time dependence of the average PWN magnetic field strength using a MHD approach, where we simulate the evolution of a composite SNR using the birth period and initial spindown power as the starting values for the MHD simulation. The time dependence of the pre-reverse shock average field strength is then used to calculate the current particle spectrum in the PWN. This field evolution then spreads the radiation spectral break between the far infrared and soft X-ray synchrotron frequencies. The present day average field strength is required to be ~25 ?G, which is ~10 times smaller than the equipartition value of ~0.3 mG. This suggests that the magnetic field strength of the PWN of G21.5-0.9 is currenty well below equipartition.
1 :  Unit for Space Physics, North-West University, South-Africa
2 :  APC - UMR 7164 - AstroParticule et Cosmologie
Physique/Astrophysique/Phénomènes cosmiques de haute energie

Planète et Univers/Astrophysique/Phénomènes cosmiques de haute energie
pulsars – magnetohydrodynamics – supernova remnants