How can I add a glowing effect (like a halo) around a region in WinForms?

Below is my code, where being given two ellipses (a bigger one and a smaller one), I extract their difference.
 I would like to add a glowing effect around this new region. I would appreciate any help.
Graphics gb =Graphics.FromImage(bm);var edgeBrush =newLinearGradientBrush(...)GraphicsPath circle =newGraphicsPath();
circle.AddEllipse(rcBm2.X, rcBm2.Y, rcBm2.Width, rcBm2.Height);GraphicsPath circleBig =newGraphicsPath();
circleBig.AddEllipse(rcBm.X, rcBm.Y, rcBm.Width, rcBm.Height);Region region =newRegion(rcBm);

region.Intersect(circleBig);
region.Exclude(circle);

gb.SmoothingMode=SmoothingMode.AntiAlias;
gb.FillRegion(edgeBrush, region);
Note: rcBm and rcBm2 are two rectangles previously defined.