Observations detect a new long-period radio transient associated with supernova remnant G22.7-0.2

Using the DAocheng radio telescope (DART), Chinese astronomers have detected a long-lasting transient event. The new transient, which was given the designation DART J1832-0911, has a period of approximately 44 minutes and is associated with a supernova remnant known as G22.7-0.2. The discovery was reported on November 24 on the preprint server. arXiv.

Long-period radio transients (LPTs) are a new class of periodic radio transmitters, with ultra-long rotation periods (ranging from minutes to hours) and strong magnetic fields. Although some studies suggest that LPTs could originate from rotating neutron stars with extremely strong magnetic fields (magnetars) or magnetic white dwarfs, their true nature is still debated.

To date, only eight LPTs have been identified, and now a team of astronomers led by Di Li of Tsinghua University in Beijing, China, reports the detection of the ninth such transient. By performing interferometric imaging with DART, over a frequency range of 149 to 459 MHz, they found an LPT in the projected region of supernova remnant (SNR) G22.7-0.2.

According to the document, DART J1832-0911 has a rotation period of 44.27 minutes and a dispersion measurement of approximately 480 pc/cm.³. The recorded pulses from this LPT showed a maximum flux density estimated between 0.5 and 2 Jy. Subsequently, the transient entered a state of prolonged rest.

Observations revealed that DART J1832-0911 exhibited a range of emission characteristics during its active radio period. It underwent mode changes modulated by variations in pulse width and intensity. These changes revealed its evolution from bright, broad pulses to weaker, narrower pulses.

“In wide pulse mode, pulses are typically strong, with durations of around 200 to 250 seconds, while in narrow pulse mode, pulses are much weaker, with durations of around 40 to 100 seconds,” says the newspaper.

Based on the dispersion measurement, astronomers calculated the distance to DART J1832-0911, estimated to be about 14,700 light years. This is consistent with the distance to G22.7-0.2, indicating that the transient resides in the remaining supernova bubble. This is therefore the first evidence associating LPTs with SNRs.

Additionally, the study revealed that DART J1832-0911 exhibits highly polarized emission. Astronomers explained that it displays either phase-locked circularly polarized emission or nearly 100% linear polarization in the radio bands.

In trying to explain the origin of LPTs, the paper’s authors concluded that the discovery of DART J1832-0911 favors the neutron star scenario. They added that the spatial association between the new LPT and G22.7-0.2 indicates that it is likely the stellar remnants of a supernova, particularly a neutron star, rather than a white dwarf .

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