bbodyrad: blackbody spectrum, area normalized

A blackbody spectrum with normalization proportional to the surface area.

$\displaystyle A(E) = {{K \times 1.0344 \times 10^{-3} E^2 dE}\over{\exp(E/kT)-1}}$

where

par1= kT	temperature keV
norm= K	$R_{km}^2/D_{10}^2$ , where $R_{km}$ is the source radius in km and $D_{10}$ is the distance to the source in units of 10 kpc.