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The period of 33 milliseconds and location of the Crab Nebula pulsar NP 0532 was discovered by Richard V. E. Lovelace and collaborators on 10 November 1968, at the Arecibo Radio Observatory. [ 18 ] [ 19 ] The discovery of the pulsar with such a short period proved that pulsars are rotating neutron stars (not pulsating white dwarfs, as many ...
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 ]
It spins at a rate of 30 times per second, spewing energy beams and taking on a decidedly pulsating appearance.
The Crab pulsar 33-millisecond pulse period was too short to be consistent with other proposed models for pulsar emission. Moreover, the Crab pulsar is so named because it is located at the center of the Crab Nebula, consistent with the 1933 prediction of Baade and Zwicky. [23]
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.
Pulsed emission gamma-ray radiation from the Crab has recently been observed up to ≥25 GeV, [21] probably due to synchrotron emission by electrons trapped in the strong magnetic field around the pulsar. Polarization in the Crab nebula [22] at energies from 0.1 to 1.0 MeV, illustrates this typical property of synchrotron radiation.
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]