They looked at five events: the discovery of pulsars in 1967, which were not immediately recognized as natural; Ohio astronomer Jerry Ehman's detection of the «Wow!» (washingtonpost.com)
«Measuring the luminosity and spectrum of a large sample of these stars will be crucial for making an accurate census of pulsars in our Galaxy.» (public.nrao.edu)
That motion would, in turn, shorten or stretch the time between pulses from pulsars in different directions, in an effect akin to the Doppler shift. (sciencemag.org)