Invisible Plasma Content in Blazars? The Case of Markarian 421

Abstract

Invisible plasma content in blazar jets such as protons and/or thermal electron-positron ($e^{\pm }$) pairs is explored through combined arguments of dynamical and radiative processes. By comparing physical quantities required by the internal shock model with those obtained through the observed radio-to-gamma-ray spectra for Mrk 421, we find the existence of a copious amount of invisible plasma in the jet. We speculate that the blazar sequence could arise from variations of total amount and/or blending ratio of $e^{\pm }$ pair and electron-proton plasma.

4 pages, 2 figure for the proceedings of 'Approaching Micro-Arcsecond Resolution with VSOP-2: Astrophysics and Technology' (3-7 December 2007, ISAS/JAXA, Sagamihara, Japan)