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Rotating radio transients (RRATs) are sources of short, moderately bright, radio pulses, which were first discovered in 2006. RRATs are thought to be pulsars, i.e. rotating magnetised neutron stars which emit more sporadically and/or with higher pulse-to-pulse variability than the bulk of the known pulsars. The working definition of what a RRAT is, is a pulsar which is more easily discoverable in a search for bright single pulses, as opposed to in Fourier domain searches so that 'RRAT' is little more than a label (of how they are discovered) and does not represent a distinct class of objects from pulsars. over 100 have been reported.〔(RRATALOG table )〕 ==General characteristics== Pulses from RRATs are short in duration, lasting from a few milliseconds. The pulses are comparable to the brightest single pulses observed from pulsars with flux densities of a few Jansky at 1.4 GHz.〔 Andrew Lyne, a radio astronomer involved in the discovery of RRATs, "guesses that there are only a few dozen brighter radio sources in the sky."〔(【引用サイトリンク】 Astronomers Discover Peek-A-Boo Stars )〕 The time intervals between detected bursts range from seconds (one pulse period) to hours. Thus radio emission from RRATs is typically only detectable for less than one second per day.〔 The sporadic emission from RRATs means that they are usually not detectable in standard periodicity searches which use Fourier techniques. Nevertheless, underlying periodicity in RRATs can be determined by finding the greatest common denominator of the intervals between pulses. This yields the maximum period but once many pulse arrival times have been determined the periods which are shorter (by an integer factor) can be deemed statistically unlikely. The periods thus determined for RRATs are on the order of 1 second or longer, implying that the pulses are likely to be coming from rotating neutron stars, and led to the name "Rotating Radio Transient" being given. The periods seen in some RRATs are longer than in most radio pulsars, somewhat expected for sources which are (by definition) discovered in searches for individual pulses. Monitoring of RRATs for the past few years has revealed that they are slowing down. For some of the known RRATs this slow-down rate, while small, is larger than that for typical pulsars, and which is again more in line with that of magnetars. The neutron star nature of RRATs was further confirmed when X-ray observations of the RRAT J1819-1458 were made using the Chandra X-ray telescope. Cooling neutron stars have temperatures of order 1 million Kelvin and so thermally emit at X-ray wavelengths. Measurement of an x-ray spectrum allows the temperature to be determined, assuming it is thermal emission from the surface of a neutron star. The resulting temperature for RRAT J1819-1458 is much cooler than that found on the surface of magnetars, and suggests that despite some shared properties between RRATs and magnetars, they belong to different populations of neutron stars. None of the other pulsars identified as RRATs has yet been detected in X-ray observation. This is in fact the only detection of these sources outside of the radio band. 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「rotating radio transient」の詳細全文を読む スポンサード リンク
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