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However, because of the Crab Nebula's variable intensity at different X-ray energies, conversion of the Crab to another units depends on the X-ray energy range of interest. In the photon energy range from 2 to 10 keV , 1 Crab equals 2.4 · 10 −8 erg cm −2 s −1 = 15 keV cm −2 s −1 = 2.4 · 10 −11 W m −2 .
The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus. The common name comes from a drawing that somewhat resembled a crab with arms produced by William Parsons, 3rd Earl of Rosse , in 1842 or 1843 using a 36-inch (91 cm) telescope . [ 6 ]
Thomas Gold has shown that the pulsar's spin-down power is sufficient to power the Crab Nebula. A subsequent study by them, including William D. Brundage, also found that the NP 0532 source is located at the Crab Nebula. [20] A radio source was also reported coincident with the Crab Nebula in late 1968 by L. I. Matveenko in Soviet Astronomy. [21]
The crab is defined as the intensity of X-rays emitted from the Crab Nebula at a given photon energy up to 30 kiloelectronvolts. The Crab Nebula is often used for calibration of X-ray telescopes. For measuring the X-ray intensity of a less energetic source, the milliCrab (mCrab) may be used. One crab is approximately 24 pW/m 2.
The shortest period pulsar, PSR J1748−2446ad, with a period of ~0.0014 seconds or ~1.4 milliseconds (716 times a second). The longest period neutron star pulsar, PSR J0901-4046, with a period of 75.9 seconds. The longest period pulsar, at 118.2 seconds, as well as one of the only known two white dwarf pulsars, AR Scorpii. [68]
The Crab Nebula is a pulsar wind nebula associated with the 1054 supernova.It is located about 6,500 light-years from the Earth. [1]A near-Earth supernova is an explosion resulting from the death of a star that occurs close enough to the Earth (roughly less than 10 to 300 parsecs [30 to 1000 light-years] away [2]) to have noticeable effects on Earth's biosphere.
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The Crab Nebula was identified as the supernova remnant of SN 1054 between 1921 and 1942, at first speculatively (1920s), with some plausibility by 1939, and beyond reasonable doubt by Jan Oort in 1942. In 1921, Carl Otto Lampland was the first to announce that he had seen changes in the structure of the Crab Nebula. [4]