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I'm quite certain it's a trail from the brightest star, the only star of that brightness in the FOV hence one trail. The camera would have been moved (or perhaps sagged on the tripod) and it moved at such a rate that only the trail of the brightest star was recorded. I see the same often when a tripod head slips or I kick the tripod or the trakcing stops, or I step on the nearby decking which moves the tripod enough to show a trail or whatever. I would say there's a reasonable chance the second brightest star in the image has a similar trail if the levels were pushed extreme enough, but not necessarily, as it depends on the exposure details.
it's certainly not a cosmic ray, they look very different to that in my experience.
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