Discovery
After the discovery of pulsars in 1967, searches for more pulsars relied on two key characteristics of pulsar pulses in order to distinguish pulsars from noise caused by terrestrial radio signals. The first is the periodic nature of pulsars. By performing periodicity searches through data, "pulsars are detected with much higher signal-to-noise ratios" than when simply looking for individual pulses. The second defining characteristic of pulsar signals is the dispersion in frequency of an individual pulse, due to the frequency dependence of the phase velocity of an electromagnetic wave that travels through an ionized medium. As the interstellar medium features an ionized component, waves traveling from a pulsar to Earth are dispersed, and thus pulsar surveys also focused on searching for dispersed waves. The importance of the combination of the two characteristics is such that in initial data processing from the Parkes Multibeam Pulsar Survey, which is the largest pulsar survey to date, "no search sensitive to single dispersed pulses was included."
After the survey itself had finished, searches began for single dispersed pulses. About a quarter of the pulsars already detected by the survey were found by searching for single dispersed pulses, but there were 17 sources of single dispersed pulses which were not thought to be associated with a pulsar. During follow-up observations, a few of these were found to be pulsars that had been missed in periodicity searches, but 11 sources were characterized by single dispersed pulses, with irregular intervals between pulses lasting from minutes to hours.
Read more about this topic: Rotating Radio Transient
Famous quotes containing the word discovery:
“We are all humiliated by the sudden discovery of a fact which has existed very comfortably and perhaps been staring at us in private while we have been making up our world entirely without it.”
—George Eliot [Mary Ann (or Marian)
“It was one of those evenings when men feel that truth, goodness and beauty are one. In the morning, when they commit their discovery to paper, when others read it written there, it looks wholly ridiculous.”
—Aldous Huxley (1894–1963)
“Your discovery of the contradiction caused me the greatest surprise and, I would almost say, consternation, since it has shaken the basis on which I intended to build my arithmetic.... It is all the more serious since, with the loss of my rule V, not only the foundations of my arithmetic, but also the sole possible foundations of arithmetic seem to vanish.”
—Gottlob Frege (1848–1925)