Chinese astronomers, using the DAocheng Radio Telescope (DART), have recently detected a new long-period transient (LPT), named DART J1832-0911, which marks a significant advancement in the study of these rare and mysterious celestial phenomena. The detection was made in the region of the supernova remnant (SNR) G22.7-0.2, and the finding was reported on November 24 on the preprint server arXiv. This discovery is the ninth LPT identified, shedding light on a new class of periodic radio emitters with ultralong rotation periods.
Long-period radio transients are a newly recognized class of astronomical objects, distinguished by their extremely long rotational periods, which can range from minutes to hours, and their strong magnetic fields. These objects produce periodic bursts of radio emissions, and their exact origin remains a topic of significant debate within the astrophysical community. While some researchers have speculated that LPTs may be related to magnetars—neutron stars with exceptionally strong magnetic fields—or even magnetic white dwarfs, the true nature of these transients is still unclear.
Prior to this discovery, only eight LPTs had been detected, making each new identification crucial in helping to understand their characteristics and origins. The latest detection, DART J1832-0911, was made by a team of astronomers led by Di Li from Tsinghua University in Beijing, China. They used the DART, which performed interferometric imaging across a frequency range of 149–459 MHz, to detect the LPT within the projected region of SNR G22.7-0.2.
DART J1832-0911 exhibits a spin period of 44.27 minutes, which places it firmly in the category of long-period transients. The transient’s dispersion measure, which provides an estimate of the amount of ionized material along the line of sight, was calculated to be about 480 parsecs per cubic centimeter (pc/cm³). The LPT exhibited strong radio emissions with peak flux densities ranging from 0.5 to 2 Jansky (Jy). However, after its active phase, the transient entered a quiescent state, characteristic of many LPTs, which remain inactive for long periods between emission bursts.
One of the remarkable features of DART J1832-0911 is its variability in emission characteristics. During its active phase, the transient exhibited mode changes, with the pulse width and intensity fluctuating over time. These changes manifested as the object shifting from wide-pulse mode, where the pulses were strong and broad (200–250 microseconds in width), to narrow-pulse mode, where the pulses became weaker and much narrower (40–100 microseconds). This variation in pulse structure provides key insights into the physical processes at work in LPTs and suggests complex, evolving mechanisms governing their emission patterns.
The team also used the dispersion measure to calculate the distance to DART J1832-0911, estimating it to be about 14,700 light-years from Earth. This distance is in line with the location of the supernova remnant G22.7-0.2, reinforcing the idea that DART J1832-0911 resides within the supernova remnant’s “bubble.” The association of LPTs with SNRs is an important step in understanding these enigmatic objects, as it marks the first evidence suggesting that LPTs could be linked to the remnants of stellar explosions, specifically the remnants of neutron stars rather than white dwarfs.
Another intriguing aspect of DART J1832-0911 is its high level of polarization in the emitted radio waves. The transient showed either phase-locked circularly polarized emission or nearly 100% linear polarization in its radio emissions. This strong polarization is a distinctive feature of some neutron stars, which are known for their highly magnetized and organized emission processes. The high polarization observed in this LPT strengthens the hypothesis that neutron stars might be responsible for this type of radio transient.
Given the spatial proximity between DART J1832-0911 and the supernova remnant G22.7-0.2, the team suggests that the most plausible origin for this LPT is a neutron star. This conclusion is supported by the fact that neutron stars are the expected stellar remnants of supernovae, particularly those that have undergone a core collapse. Neutron stars are known to possess strong magnetic fields and rapid rotation rates, both of which are consistent with the properties of LPTs.
The findings from this study make an important contribution to the ongoing investigation of long-period radio transients. The discovery of DART J1832-0911 adds to a growing body of evidence linking LPTs to neutron stars, while also opening up new avenues for further research into the relationship between these enigmatic objects and their surrounding environments, such as supernova remnants. The detection of polarization, periodicity, and mode switching in LPTs suggests that there may be much more to learn about their magnetic properties, emission mechanisms, and evolutionary stages.
Looking forward, further studies of LPTs like DART J1832-0911 could yield valuable insights into the nature of neutron stars, magnetars, and the fundamental physics of extreme magnetic fields and high-energy processes in the universe. As astronomers continue to refine their observational techniques and technologies, it is likely that more LPTs will be discovered, each offering unique clues to unraveling the mysteries of these extraordinary cosmic phenomena. The continued development of radio telescopes, such as DART, will play a pivotal role in advancing our understanding of the universe’s most exotic and mysterious objects.