Hi. As an "I'm bored Saturday afternoon exercise" I have been working out some stuff regarding bending magnets on linacs. This question came to me while thinking about particle energy losses inside the bending magnet. Imagine an electron moving in a synchrotron with constant speed, radius and frequency, in the synchrotron's frame. An observer, in the synchrotron's frame, sees the electron with the aforementioned characteristics. The observer notes the electron is emitting x-rays. In the electron's frame, the synchrotron is rotating. Neglect gravity. Loosely speaking, the observer justifies the x-ray emission by saying the electron is accelerating. In the electron's frame how does the electron justify it's emission of x-rays? I know I must be thinking about something incorrectly. This goes beyond the scope of the GR class I took during undergrad, or at least beyond the scope of what I can remember :).