Optical observations of the 18th magnitude blue star and of the faint red object in the approximate location of the pulsating radio source CP 1919 disclose no pulsations of visible light, in a mode similar to that of the radio pulsations, of more than 0.4 percent or 0.8 percent, respectively, of the total visible output; or, for a sinusoidal modulation with the same period, no more than a 4-percent, or 8-percent, root-mean-square intensity fluctuation.

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http://dx.doi.org/10.1126/science.160.3832.1104DOI Listing

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