logpar, zlogpar: log-parabolic blazar model

logpar is a power-law with an index which varies with energy as a log parabola. The zlogpar variant computes a redshifted spectrum. See for instance Massaro et al. (2004).

$$A(E) = K (E/pivotE)^{(-a-b\log{(E/pivotE)})}$$

par1	a, slope at the pivot energy
par2	b, curvature term
par3	pivotE, fixed pivot energy (best near low end of energy range).
norm= K

For zlogpar the formula and corresponding parameters are:

$$A(E) = K ([E(1+z)]/pivotE)^{(-a-b\log{([E(1+z)]/pivotE)})}$$

par1	a, slope at the pivot energy
par2	b, curvature term
par3	pivotE, fixed pivot energy (best near low end of energy range).
par4	z, redshift
norm= K