Letter to the Editor of Reciprocity:
Those of your readers who noted the theoretical basis of my article on Astronomical X-ray Sources, which appeared in your March 1975 issue, should be interested in the additional information concerning the emission from the Crab Nebula pulsar (NP 0532) that was obtained in recent observations that took advantage of occultation of the pulsar by the moon. As reported in the Jan. 10 issue of Science News, the observations show that all of the x-ray emission is coming from the nebula surrounding the pulsar and none from the surface of the pulsar itself. These results came as a distinct surprise to the astronomers and indicate the need for a revision of current ideas as to the physical nature of the pulsars.
On the other hand, the new information is in full agreement with the explanation of the emission that I gave in my article. According to my findings, the x-rays come from matter which has dropped back to speeds below unity (the speed of light) after havina spent some time at higher speeds. As I pointed out in the article, in those cases where there is considerable diffuse low-speed material in the vicinity of the pulsar, as there is in the Crab Nebula, this material “will interact with the adjacent portions of the pulsar, and will reduce the speeds of some of its constituent particles below the unit level, causing the emission of , x-rays.” These low speed particles will, of course, lag behind the matter of the pulsar itself and will form part of the nebula, or halo, around the pulsar, the region from which the new observations show that the x-ravs are emitted.
— D. B. Larson (Reciprocity VI.1, March 1976)