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: Others : Example of Analysis Session : Spectrum Distribution   目次

Interpretation of Data

図 5: Chart for interpretation of emission mechanism from the spectrum distribution
\begin{figure}
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The interpretation is done by using the chart in Figure 5. Physical information can be obtained when the emission is by "optically-thin gyrosynchrotron" or by "optically-thin free-free". We can derive the variable using the Dulk's (1985) models.

In case "optically-thin gyrosynchrotron" emission, we obtain power-law index of the non-thermal electrons. Here we assume the distribution function of electrons to be

\begin{displaymath}
{{d NV(E)} \over {d E}} = K \left({{E}\over{E_{0}}}\right)^{-\delta}.
\end{displaymath}

where $E$ is electron energy (keV), $NV(E)$ is number of electrons (particles) that has larger energy than $E$. This distribution is described with parameters $\delta$, $E_{0}$, and $K$. But it is usual to use $NV(E_0)=K/(\delta -1)/E_0^{\delta-1}$ instead of $K$. And we fix $E_{0} = 10\ {\rm keV}$ after Dulk (1985). If we find the emission to be "optically-thin gyrosynchrotron", we will obtain $\delta$ from $\alpha$ by

\begin{displaymath}
\delta=-1.1 (\alpha - 1.2).
\end{displaymath}

In case "optically-thin free-free" emission, we obtain line-of-sight component of coronal magnetic field. From the circular polarization degree $r_{c}$,

\begin{displaymath}
B \approx 30 {\rm G} \left({r_{c}\over 1\%}\right).
\end{displaymath}

For example, figure 4 can be interpreted as follows: First, the strong polarized source at $(x,y)=(180,-520)$ is by gyroresonance. It may be confirmed by comparing the image with optical magnetogram to see if there is a sunspot. Next, the area inside the contour line of $T_{b}^{\rm 17GHz}=1{\rm MK}$ is emitting by optically-thin gyrosynchrotron. Non-thermal power-law index $\delta$ is obtained from $\alpha$ immediately and we see that the emission from two-sides of the loop structure is 'softer' than that of the top. Next is for the area where $T_{b}^{\rm 17GHz}<1{\rm MK}$. Around $(x,y)=(270,-500)$, it is hard to judge if it is 'optically-thin gyrosynchrotron' or "optically-thin free-free" because $\alpha \approx 0$. If it is bright in soft X-ray it may be free-free emission. In this case, line-of-sight component of coronal magnetic field is obtained. Since the other area has $\alpha>0$, it is optically thick and no information can be obtained.


next up previous contents
: Others : Example of Analysis Session : Spectrum Distribution   目次
Takaaki YOKOYAMA 平成12年10月25日