China’s Tianyan discovers “dwarf pulse group”

On August 18, Nature Astronomy published the new results of the Wang Shouqian Sky Survey Commando Team led by researcher Han Jinlin of the National Astronomical Observatory of the Chinese Academy of Sciences, which used the Chinese Sky Eye FAST to successfully detect and analyze a batch of pulsar B2111+46 magnetosphere sporadic raindrop-like weak dwarf pulse radiation, which is a new form of pulsar radiation that is difficult to observe by other radio telescopes in the world, revealing the physical fact that the magnetospheric structure of pulsar radiation is basically unchanged when it is on the verge of extinction.

China’s sky eye discovers a new form of pulsar radiation – dwarf pulse population (Photo courtesy of National Astronomical Observatory, Chinese Academy of Sciences)

Pulsars typically emit radio signals periodically as they rotate. However , some pulsars often have radiation completely extinguished during certain periods , a phenomenon known as ” pulse zeroing ” . Possible physical causes of pulse zeroing include changes in magnetosphere structure and radiation region, insufficient pulsar induced potential resulting in the failure of the cascade of discharge sparks and positron and negative electron pairs, or plasma in some regions of the other magnetosphere that floods the pulsar’s induced electric field. Since there is no radiation at all after the pulsar radiation is extinguished, the magnetospheric structure and physical characteristics are difficult to detect, so the physical mechanism of “pulse zeroing” has been difficult to determine.

In the latest published paper, researchers carefully processed the data during the pulsar search using FAST and found that a known pulsar B2111+46 still has sporadic faint and narrow pulses in the originally thought “pulse zero” state, such pulses are named “dwarf pulses”.

After that, they conducted 2 hours of verification observations of the star, acquiring more than 100 dwarf pulses, which were clearly separated from normal pulses in the distribution of pulse intensity and width, forming an independent radiation population. Because of the ultra-high sensitivity of FAST, the accurate polarization measurement results of the short pulse show that the magnetostructure of the short pulse radiation region is basically unchanged compared with the normal pulse, but the flow rate in the high frequency band is easier to become strong in the short pulse. Inverted radiation spectra for fine measurements of single-particle droplet radiation have been quite rare in previous astronomical observations.

According to researchers, pulsar B2111+46 is relatively old and already located in the “death valley” of pulsars, so “pulse zeroing” is likely to be due to the radiation instability caused by insufficient induced potential and particle acceleration energy of old pulsars. The normal pulsar pulse is radiated by steadily accelerating a large number of charged particles and producing a large number of “thunderstorm” particle droplets, while the dwarf pulse is produced by one or a few particle droplets formed by the dying pulsar in a fragile and unstable state.

The dwarf pulse of pulsar B2111+46 is clearly separated from normal pulses in terms of pulse width and radiation energy, becoming a new form of pulsar radiation (Photo courtesy of the research team)

The team also detected a small number of dwarf pulses in the “pulse zeroing” state of several other pulsars, a new state of extremely weak radiation patterns that can only be detected with extremely sensitive telescopes like FAST.

Industry experts believe that the discovery of the dwarf pulse population has opened a new window for the study of pulsar radiation problems, and has important scientific significance for revealing the physics of pulsar magnetosphere and its extreme plasma environment. (Source: China Science News Gan Xiao)

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