radiation.c

/***********************************************************************************
    Copyright 2013 Joshua C. Dolence, Charles F. Gammie, Monika Mo\'scibrodzka,
                   and Po Kin Leung

                        GRMONTY  version 1.0   (released February 1, 2013)

    This file is part of GRMONTY.  GRMONTY v1.0 is a program that calculates the
    emergent spectrum from a model using a Monte Carlo technique.

    This version of GRMONTY is configured to use input files from the HARM code
    available on the same site.   It assumes that the source is a plasma near a
    black hole described by Kerr-Schild coordinates that radiates via thermal 
    synchrotron and inverse compton scattering.
    
    You are morally obligated to cite the following paper in any
    scientific literature that results from use of any part of GRMONTY:

    Dolence, J.C., Gammie, C.F., Mo\'scibrodzka, M., \& Leung, P.-K. 2009,
        Astrophysical Journal Supplement, 184, 387

    Further, we strongly encourage you to obtain the latest version of 
    GRMONTY directly from our distribution website:
    http://rainman.astro.illinois.edu/codelib/

    GRMONTY is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    GRMONTY is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with GRMONTY; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

***********************************************************************************/


/* 

model-independent radiation-related utilities.

*/

#include "decs.h"

double Bnu_inv(double nu, double Thetae)
{

	double x;

	x = HPL * nu / (ME * CL * CL * Thetae);

	if (x < 1.e-3)		/* Taylor expand */
		return ((2. * HPL / (CL * CL)) /
			(x / 24. * (24. + x * (12. + x * (4. + x)))));
	else
		return ((2. * HPL / (CL * CL)) / (exp(x) - 1.));
}

double jnu_inv(double nu, double Thetae, double Ne, double B, double theta)
{
	double j;

	j = jnu_synch(nu, Ne, Thetae, B, theta);

	return (j / (nu * nu));
}

/* return Lorentz invariant scattering opacity */
double alpha_inv_scatt(double nu, double Thetae, double Ne)
{
	double kappa;

	kappa = kappa_es(nu, Thetae);

	return (nu * kappa * Ne * MP);
}

/* return Lorentz invariant absorption opacity */
double alpha_inv_abs(double nu, double Thetae, double Ne, double B,
		     double theta)
{
	double j, bnu;

	j = jnu_inv(nu, Thetae, Ne, B, theta);
	bnu = Bnu_inv(nu, Thetae);

	return (j / (bnu + 1.e-100));
}


/* return electron scattering opacity, in cgs */
double kappa_es(double nu, double Thetae)
{
	double Eg;

	/* assume pure hydrogen gas to 
	   convert cross section to opacity */
	Eg = HPL * nu / (ME * CL * CL);
	return (total_compton_cross_lkup(Eg, Thetae) / MP);
}

/* get frequency in fluid frame, in Hz */
double get_fluid_nu(double X[4], double K[4], double Ucov[NDIM])
{
	double ener, nu;

	/* this is the energy in electron rest-mass units */
	ener = -(K[0] * Ucov[0] +
		 K[1] * Ucov[1] + K[2] * Ucov[2] + K[3] * Ucov[3]);

	nu = ener * ME * CL * CL / HPL;

	if (isnan(ener)) {
		fprintf(stderr, "isnan get_fluid_nu, K: %g %g %g %g\n",
			K[0], K[1], K[2], K[3]);
		fprintf(stderr, "isnan get_fluid_nu, X: %g %g %g %g\n",
			X[0], X[1], X[2], X[3]);
		fprintf(stderr, "isnan get_fluid_nu, U: %g %g %g %g\n",
			Ucov[0], Ucov[1], Ucov[2], Ucov[3]);
	}

	return nu;

}

/* return angle between magnetic field and wavevector */
double get_bk_angle(double X[NDIM], double K[NDIM], double Ucov[NDIM],
		    double Bcov[NDIM], double B)
{

	double k, mu;

	if (B == 0.)
		return (M_PI / 2.);

	k = fabs(K[0] * Ucov[0] + K[1] * Ucov[1] + K[2] * Ucov[2] +
		 K[3] * Ucov[3]);

	/* B is in cgs but Bcov is in code units */
	mu = (K[0] * Bcov[0] + K[1] * Bcov[1] + K[2] * Bcov[2] +
	      K[3] * Bcov[3]) / (k * B / B_unit);

	if (fabs(mu) > 1.)
		mu /= fabs(mu);

	return (acos(mu));
}