code: def calc_synch_nu_pk(b, ne, delta, sinth, depth, E0=1.):
      
      coldens = ne * depth
      return (3.2e7 * sinth *
              E0**((2 * delta - 2) / (delta + 4)) *
              (8.7e-12 * (delta - 1) * coldens / sinth)**(2./(delta + 4)) *
              b**((delta + 2) / (delta + 4)))
docs: Calculate the frequency of peak synchrotron emission, ν_pk.
  
      This is Dulk (1985) equation 43, which is a fitting function assuming a
      power-law electron population. Arguments are:
  
      b
        Magnetic field strength in Gauss
      ne
        The density of electrons per cubic centimeter with energies greater than 10 keV.
      delta
        The power-law index defining the energy distribution of the electron population,
        with ``n(E) ~ E^(-delta)``. The equation is valid for ``2 <~ delta <~ 5``.
      sinth
        The sine of the angle between the line of sight and the magnetic field direction.
        It's not specified for what range of values the expressions work well.
      depth
        The path length through the emitting medium, in cm.
      E0
        The minimum energy of electrons to consider, in MeV. Defaults to 1 so that
        these functions can be called identically to the gyrosynchrotron functions.
  
      The return value is peak frequency in Hz.
  
      No complaints are raised if you attempt to use the equation outside of its
      range of validity.