C+
C NAME:
C	ThomsonElectron
C PURPOSE:
C	Determines the intensity scattered from single coronal electron
C	by Thomson scattering
C CALLING SEQUENCE:
	function ThomsonElectron(ElSun,SinChi,U, P)
C INPUTS:
C	ElSun	real	distance Sun-Electron (in solar radii)
C	SinChi	real	sine of angle Sun-Electron-Observer
C	U	real	limb darkening coefficient
C OUTPUTS:
C	ThomsonElectron
C		real	scattered intensity; units: 10^-26 times the
C			flux from the solar disk -incident- on the electron
C	P	real	polarization	(-1<=P<=1)
C CALLS:
C	ThomsonBase
C INCLUDE:
	include		'phys.h'
C PROCEDURE:
C >	See Chapt. 6, Sect. B of Billings' "A guide to the solar corona" (p.150)
C	Sigma	= Thomson cross section=7.96x10^-26 cm^2/sterad
C	Omega	= angular size of Sun from electron
C	Chi	= angle Sun-Electron-Observer
C	I0	= intensity at disk center
C	RSun	= solar radius = 7x10^10 cm
C
C	Billings specifies the scattered intensity in the form
C		I=0.5*Pi*Sigma*I0*Func(Omega,Chi) (erg/s/sterad)
C	The average intensity coming from the solar disk is
C		i=(Pi*RSun^2)*I0*(1-U/3) (erg/s/sterad)
C	The flux incident on the electron is F=i/ElSun^2 (erg/s/cm^2)
C	The ratio
C		I/F = 0.5*Sigma*Func(Omega,Chi)/( (RSun/ElSun)^2*(1-U/3) )
C	is returned here, except for a factor 10^-26 (from Sigma).
C
C >	For purposes of integration along a line of sight
C		B = Int[0,Inf]{ n(s) I(s) ds}
C	I(s) (the scattered intensity per election) should be in units
C	of the flux received from the solar disk by the observer at ScSun
C	(rather than the electron). This is
C		I(s) =(I/Fobs) = (I/F)*(ScSun/ElSun)^2
C		     = 0.5*Sigma*Func(Omega,Chi)/( (RSun/ScSun)^2*(1-U/3) )
C	Note that the s-dependence is restricted to Func(Omega,Chi)
C
C >	The scattered flux from the electron incident on the observer is
C	I/ScEl^2  (erg/s/cm^2).
C >	The ratio (I/F)*(ScSun/(ElSun*ScEl))^2 gives the flux received from
C	the electron in units of the flux received from the solar disk by
C	the observer.
C MODIFICATION HISTORY:
C	JUL-1996, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
C-
	    real	ElSun
	    real	SinChi
	    real	U
	    real	P

	ThomsonElectron = ElSun*ElSun/(1-U/3)*0.5*PHYS__THOMSON*ThomsonBase(ElSun,SinChi,U,P,Y,Z)

	return
	end