From a2b61f982ed52465a9c76fd17a8f288c3d1253a7 Mon Sep 17 00:00:00 2001
From: Aaron LI <aly@aaronly.me>
Date: Sat, 29 Jul 2017 23:52:29 +0800
Subject: clusters/halo.py: Add method "calc_emissivity()"

This method invokes ``SynchrotronEmission`` to calculate the synchrotron
emissivity at specified frequencies for the derived electron spectrum.

Signed-off-by: Aaron LI <aly@aaronly.me>
---
 fg21sim/extragalactic/clusters/halo.py | 43 +++++++++++++++++++++++++++++-----
 1 file changed, 37 insertions(+), 6 deletions(-)

diff --git a/fg21sim/extragalactic/clusters/halo.py b/fg21sim/extragalactic/clusters/halo.py
index d7b3ec4..2cc391f 100644
--- a/fg21sim/extragalactic/clusters/halo.py
+++ b/fg21sim/extragalactic/clusters/halo.py
@@ -44,11 +44,11 @@ import numpy as np
 
 from . import helper
 from .solver import FokkerPlanckSolver
+from .emission import SynchrotronEmission
 from ...configs import CONFIGS
 from ...utils import COSMO
 from ...utils.units import (Units as AU,
-                            UnitConversions as AUC,
-                            Constants as AC)
+                            UnitConversions as AUC)
 
 
 logger = logging.getLogger(__name__)
@@ -72,10 +72,6 @@ class RadioHalo:
     4. Determine the initial electron density
     TODO...
 
-    after that, calculate the electron acceleration and time evolution
-    by solving the Fokker-Planck equation; and finally derive the radio
-    emission from the electron spectra.
-
     Parameters
     ----------
     M_obs : float
@@ -223,6 +219,41 @@ class RadioHalo:
                                                  tstop=tstop)
         return self.electron_spec
 
+    def calc_emissivity(self, frequencies, n_e=None, gamma=None):
+        """
+        Calculate the synchrotron emissivity for the derived electron
+        spectrum.
+
+        Parameters
+        ----------
+        frequencies : float, or 1D `~numpy.ndarray`
+            The frequencies where to calculate the synchrotron emissivity.
+            Unit: [MHz]
+        n_e : 1D `~numpy.ndarray`, optional
+            The electron spectrum (w.r.t. Lorentz factors γ).
+            If not provided, then used the cached ``self.electron_spec``
+            solved above.
+            Unit: [cm^-3]
+        gamma : 1D `~numpy.ndarray`, optional
+            The Lorentz factors γ of the electron spectrum.
+            If not provided, then used ``self.gamma``.
+
+        Returns
+        -------
+        emissivity : float, or 1D `~numpy.ndarray`
+            The calculated synchrotron emissivity at each specified
+            frequency.
+            Unit: [erg/s/cm^3/Hz]
+        """
+        if n_e is None:
+            n_e = self.electron_spec
+        if gamma is None:
+            gamma = self.gamma
+        syncem = SynchrotronEmission(gamma=gamma, n_e=n_e,
+                                     B=self.magnetic_field)
+        emissivity = syncem.emissivity(frequencies)
+        return emissivity
+
     def fp_injection(self, gamma, t=None):
         """
         Electron injection (rate) term for the Fokker-Planck equation.
-- 
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