Accueil > Séminaires d’Astrophysique > Automne 2006 > The brightness temperature problem and the spectral implications of a low energy electron cut-off

 

The brightness temperature problem and the spectral implications of a low energy electron cut-off

Olivia Tsang (Max Planck Institute for Nuclear Physics, Heidelberg, Allemagne)

Par Stephane Charpinet - 8/01/2007

 

Séminaires d’Astrophysique

de l’Observatoire Midi-Pyrénées


Séminaire de

Olivia TSANG

 (Max Planck Institute for Nuclear Physics, Heidelberg, Allemagne)


Jeudi 14 Septembre 2006 à 11h

CESR


The brightness temperature problem and the spectral implications of a low energy electron cut-off


According to the standard synchrotron-self-Compton (SSC) model, where the underlying electron spectrum is assumed to be in the form of a power-law, a synchrotron source cannot exceed a brightness temperature of 10¹² K. Above this temperature, the energy density of each succession of inverse Compton scattered photons exceeds the previous one, resulting in the so-called "Compton catastrophe", where electrons are cooled extremely rapidly through scattering. However, studies of the variability in AGN’s have found numerous rapidly varying radio sources, termed "intra-day variables" (IDV). Causality arguments suggested that these sources have brightness temperature well above 10¹² K, and in some extreme cases, up to 10²¹ K. The cause of the variability in most of these extreme cases are found to be external effects such as interstellar scintillation, which implies that the brightness temperature at the source is in fact considerably lower. Despite that, many of these sources still show a temperature of >10¹² K. In this talk, I will show that this problem may be solved by assuming a low energy cut-off in the electron population, and discussed the spectral properties of the resulting SSC emission.

 

 

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