Dozen 'dwarf pulses' discovered radiating from a bright pulsar

Scientists discovered a distinct number of "dwarf pulses" emanating from the luminous pulsar dubbed PSR B2111+46. 
Mrigakshi Dixit
Representational image

Observations from the high-tech Five-hundred-meter Aperture Spherical Radio Telescope (FAST) based in China have led to the identification of a new population of dwarf pulsars

Pulsars are a type of neutron stars that rotate at an incredibly high rate and shoot out radiation pulses at regular intervals. 

The team led by the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) discovered a distinct number of "dwarf pulses" emanating from the luminous pulsar dubbed PSR B2111+46. 

According to the official statement, pulsars often emit periodic radio signals. But in some occasions, the older pulsars tend to “quench” for short periods of time, a process known as "pulse nulling." 

In such occasional null episodes, the pulsars usually go silent for a while, with decreased radiation activity. 

The specific cause of the absence of pulsar radiation remains unknown since it is difficult to analyze the physical state of the pulsar's magnetosphere

Analysis of PSR B2111+46 

This pulsar is thought to be rather old, and scientists have long theorized that its emission frequently nulls for extended periods of time. 

Using the FAST, the scientists discovered previously unseen dozens of feeble and narrow pulses during conventional nulling phases. 

The observations were obtained, as part of the Galactic Plane Pulsar Snapshot survey, on August 24, August 26, and September 17, 2020.

The researchers studied this pulsar for two hours again on March 8, 2022, to confirm this new type of emission state. 

"Finally, we picked out 175 such narrow, weak pulses," said Dr. CHEN Xue, the first author of the study, in an official release. 

Dozen 'dwarf pulses' discovered radiating from a bright pulsar
Pulsar radio emission from thunderstorms and raindrops of particles in the magnetosphere of PSR B2111+46 detected by FAST

According to the study's authors, such pulses differ from typical pulses in terms of pulse breadth and energy, and have so been dubbed "dwarf pulses."

"The properties of such dwarf pulses would be hard to be measured by other radio telescopes than FAST. And measurements of such a new population of dwarf pulses reveal that the magnetic field structure for the pulsar radiation remains unchanged even when the radiation is almost ceased," said Prof. HAN. 

"In fact, a smaller number of dwarf pulses have also been detected from a few other pulsars," said YAN Yi, co-author of the study. "Detailed studies of such a dwarf pulse population could uncover some mysteries of unknown pulsar radiation processing and reveal the extreme plasma state in the pulsar magnetosphere."

This study was published in the journal Nature Astronomy.

Study abstract:

Pulsars radiate radio signals when they rotate. However, some old pulsars often stop radiating for some periods. The underlying mechanism remains unknown, as the magnetosphere during nulling phases is hard to probe due to the absence of emission measurements. Here we report the detection and accurate polarization measurements of sporadic, weak, narrow dwarf pulses detected in the ordinary nulling state of pulsar B2111+46 via the Five-Hundred-Meter Aperture Spherical radio Telescope. Further analysis shows that their polarization angles follow the average polarization angle curve of normal pulses, suggesting no change of the magnetic-field structure in the emission region in the two emission states. Whereas radio emission of normal individual pulses is radiated by a ‘thunderstorm’ of particles produced by copious discharges in regularly formed gaps, dwarf pulses are produced by one or a few ‘raindrops’ of particles generated by pair production in a fragile gap of this near-death pulsar.

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