%%%%%%%%%%Regarding parity-even parity odd nature of E and B.

%unchanged whereas $B$ changes sign, analogous to electric and magnetic fields.
%AB: My initial thinking was misled, because I thought about helicity
%AB: when talking about *sign*. To explain this, I've changed it such
%AB: that we talk about *directionality* instead.

%AB: I doubt that the full E vector for the electric field is parity even.
%AB: Or have you read this? In the time-dependent case, E can have a curl,
%AB: and E.curlE would be finite, right?
%AP: "$E$ remains unchanged whereas $B$ changes sign, analogous
%AP: to electric and magnetic fields." I found a similar statement in
%AP: \cite{Zaldarriaga} below equation (6).
%AB: ok, see my changes above.


%AB: could you clarify the sentence above? Yes, Faraday depends
%AB: on frequency, but also on electron density and line-of-sight
%AB: magnetic field. When you talk about the line core, isn't
%AB: it perhaps the electron density and that is different?
%AB: And isn't it less in the line core?
%AP: The terms in the propagation matrix $K$ of eq.\ref{rte}
%AP: responsible for Faraday rotation, have a Faraday-Voigt profile wrt
%AP: wavelength with peaks (a maxima and minima) near the core of the line
%AP: Hence I meant that the effects of Faraday rotation are strongest
%AP: near the core than in the wing or the continuum.
%AB: See my changes above!


%\textcolor{red}{As Nishant has rightly pointed out, such a magnetic field does not obey $\nabla \cdot \vec{b} = 0$, should address this somehow.}
%AB: added this to address this; in my spin-2 paper, I give such an
%AB: example in terms of superpotentials, but there is probably no
%AB: need to go further into this here.



%wavelength positions; this can be attributed to differing strengths of
%AB: inserted "perhaps", or how sure are you here?
%AP: Not absolutely certain, I agree with the perhaps

%field. However, Faraday rotation is frequency dependent, and is
%AB: talking here about frequency dependence misled me, but I
%AB: think it can (or should) be omitted. When you talk about
%AB: a line core, it is clear that you talk about different
%AB: frequency, whereas Faraday rotation as such is really
%AB: just K*n*B*lambda^2*z, so you might think it is strongest
%AB: at long wavelengths ...
%AP: Agreed, best to omit it and phrase it like you have!



%AB: it is also surprising that cA reaches + and -1.
%MJK This is the most puzzling thing, and I wonder whether Axel could try to
%MJK reproduce this spectrum; perhaps something still goes wrong at our end here.
%AB: I think there could be an odd/even issue. You better plot only even
%AB: or only odd ones, and maybe don't normalise either, i.e., just EB.
%AP: Changed the previous figure and the related text, and replaced it with one where I just plot EB and not the normalised C_A