Вращающиеся Радио-Переходные Источники: Новое в Радиоастрономии

Phenomenon in radio astronomy
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. as of March 2015 over 100 have been reported.

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. 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 neutron star nature of RRATs was further confirmed when X ray observations of the RRAT J1819 1458 were made using the space based Chandra X ray Observatory. Cooling neutron stars have temperatures of order 1 million kelvins 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.

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." the RRATs with known periods and period derivatives do not lie near canonical death regions. Since most RRATs have large dispersion measures that indicate larger distances, combining with the similar emission properties, some RRATs could be due to the telescope detection threshold. Nevertheless, the possibility that RRATs share the similar emission mechanism with those pulsars with so called "giant pulses" can neither be excluded. To fully understand the emission mechanisms of RRATs would require directly observing the debris surrounding a neutron star, which is not possible now, but may be possible in the future with the Square Kilometer Array. Nevertheless, as more RRATs are detected by observatories such as Arecibo, the Green Bank Telescope, and the Parkes Observatory at which RRATs were first discovered, some of the characteristics of RRATs may become clearer.