Enter 500 under Resolution (it doesn't say "DPI" but I think that's what it means)
Uncheck Try bounding box (since the bounding box cuts off the edge, unfortunately. You can try with the bounding box first.)
Enter large values for Width and Height
Check Color
Check Strong anti-aliasing for both graphics and text
Crop off extra whitespace (Shift+C if you can't find it in the toolbox)
Possibly need to rotate it: Click Image → Transform → Rotate 90 degrees clockwise
Filters → Blur → Gaussian blur at 2.0 px (No need to blur if you use strong anti-aliasing during conversion. I see no significant difference between end results.)
Image → Scale Image...
Width and Height at 25%
Cubic interpolation
You can view at normal size if you want by pressing 1, Ctrl+E
Save as Exponentialchirp.png
(There were some artifacts of the lines being "painted with a pointy brush" in the high frequency section, so I just clipped off the tops with the GIMP brush.)
(In short, this means that you can copy and modify the image freely as long as you provide attribution; preferably in the form of a link back to this page.)