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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Crab (unit) ： ウィキペディア英語版 Crab (unit) A Crab is a standard astrophotometrical unit for measurement of the intensity of Astrophysical X-ray sources. One Crab is defined as the intensity of the Crab Nebula at the corresponding X-ray photon energy. The Crab Nebula, and the Crab Pulsar within it, is an intense space X-ray source. It is used as a standard candle in the calibration procedure of X-ray instruments in space. 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. For energies greater than ~30 keV, the Crab Nebula becomes unsuitable for calibration purposes, as its flux can no longer be characterized by a single coherent model.〔 The unit ''mCrab'', or ''milliCrab'', is sometimes used instead of the Crab. == References == 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Crab (unit)」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.