A power law with pegged normalization.
where :
par1 = photon index of power law (dimensionless)par2 = lower peg energy range
par3 = upper peg energy range
K = flux (in units of 10
erg/cm
/s) over the energy
range par2-par3 unless par2 = par3, in
which case it is the flux (in micro-Jy) at par2