What is the difference between $E_\gamma$ and $E_{\gamma,iso}$ in gamma ray bursts?
I will answer with what I now believe to be the correct answer. We see some gamma-ray burst emission hit our satellite which carries an amount of energy $E_{obs}$. If we say the burst was emitted equally in all directions (isotropic) then we derive a quantity $E_{iso}$. If we say that the burst was actually emitted in a tight beam then we derive $E_\theta$ where $\theta$ is the opening angle of the burst and we will find $E_{iso} &gt; E_{\theta}$. $E_{iso}$ is used to compare burst energies in the literature without needing to find the opening angle.