New binary pulsar discovered with CHIME

Astronomers using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) have discovered a new radio pulsar in a binary star system with a massive, nondegenerate companion star. The discovery of the pulsar, which was given the designation PSR J2108+4516, was detailed in an article published on September 14 on the arXiv preprint server.

Pulsars are highly magnetized, spinning neutron stars that emit a beam of electromagnetic radiation. They are usually detected in the form of short radio bursts; However, some of them are also observed with optical, X-ray and gamma-ray telescopes.

Now, an international team of astronomers led by Bridget C. Andersen of McGill University in Montréal, Canada, reports the discovery of a new rare type of binary pulsar hosting a massive companion. Detection was performed with CHIME, a radio telescope with a very wide field of view, large collection area and high sensitivity in the 400–800 MHz range.

“We discovered and initially monitored PSR J2108+4516 with the CHIME telescope, using the CHIME/FRB and CHIME/Pulsar backends to collect different types of data,” the researchers wrote in the paper.

All in all, the team has conducted near-daily CHIME/Pulsar observations of PSR J2108+4516 for almost three years, spanning from October 20, 2018 to September 3, 2021. Profile drifts during the pulse phase indicated that the pulsar experienced significant acceleration from orbit with a massive binary companion.

Observations of PSR J2108+4516 revealed that it has a spin period of about 0.58 seconds and an orbital period of 269 days. The orbital eccentricity was about 0.09 and the characteristic age of the pulsar was estimated to be about 2.1 million years. The surface magnetic field of PSR J2108+4516 has been measured to be around 1.2 trillion gauss.

As for the companion object, the results suggest that its mass should be between 11.7 and 113 solar masses. The study revealed that the companion is a bright OBe star known as EM* UHA 138, located about 10,600 light-years away. The researchers estimate that the mass of this star is most likely between 17 and 23 solar masses.

Summarizing the results, the astronomers emphasized that PSR J2108+4516 is the sixth young pulsar with a massive nondegenerate companion discovered so far.

“We presented the CHIME/FRB discovery and 2.8-year CHIME/pulsar timing of a new radiopulsar/massive star binary, PSR J2108+4516, only the 6th such binary pulsar known,” they closed.

The paper’s authors added that PSR J2108+4516 could serve as a rare laboratory for studying massive stellar winds and circumstellar disks. They propose future optical spectroscopic observations of this pulsar to determine the companion type and whether it has a disk, as well as X-ray and gamma-ray studies to study disk-wind interactions.

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