Jet brightness asymmetry

An approaching jet can be enhanced and its receding counterpart suppressed by different Doppler factors. A discrete moving emitter with rest-frame power-law spectrum $F_{\nu }\propto {\nu }^{-s}$ has the usual boost ${\delta }_D^{3+s}$, whereas a steady continuous-jet convention changes the exponent. Absorption and environmental asymmetry can also affect the contrast.