Thirteen new pulsars discovered with MeerKAT

Using the MeerKAT radio telescope, an international team of astronomers has detected 13 new pulsars in the globular cluster NGC 1851. Twelve of them turned out to be millisecond pulsars (MSPs). The discovery was reported March 23 on the arXiv pre-print server.

Pulsars are highly magnetized, rotating neutron stars emitting a beam of electromagnetic radiation. They are usually detected in the form of short bursts of radio emission; however, some of them are also observed via optical, X-ray and gamma-ray telescopes.

The most rapidly rotating pulsars, those with rotation periods below 30 milliseconds, are known as MSPs. Researchers assume that they are formed in binary systems when the initially more massive component turns into a neutron star that is then spun up due to accretion of matter from the secondary star.

Now, astronomers led by Alessandro Ridolfi of the Cagliari Observatory in Italy, report the finding of another 13 new sources that belong to the pulsar family. The new pulsars were detected in the globular cluster NGC 1851, located some 39,000 light years away, as part of the TRansients And PUlsars with MeerKAT (TRAPUM) Large Survey Project.

"Here, we present the results of our search for new pulsars in NGC 1851 using MeerKAT observations made in the context of the TRAPUM GC [globular cluster] pulsar survey, as well as follow-up observations taken within the MeerTime program," the researchers wrote in the paper.

All the 13 newfound pulsars are located in the innermost regions of NGC 1851. Only one of them is a standard pulsar, designated NGC 1851I, as its spin period is 32.65 milliseconds. The other sources are MSPs with spin periods ranging from 2.82 to 6.63 milliseconds. Seven out of the 13 objects turn out to be binaries (including NGC 1851I), while the rest are isolated pulsars.

The researchers noted that two out of 13 pulsars reported in the study have peculiar properties, namely NGC 1851D and NGC 1851E. NGC 1851D is an MSP in a wide orbit with a heavy white dwarf companion (with a mass of around 0.48 solar masses). The system has an eccentricity at a level of 0.86, which makes it the fifth most eccentric binary known to date. NGC 1851E is also an MSP in a very eccentric binary with a neutron star as a companion (with a mass of approximately 1.53 solar masses.

"In all likelihood, both binaries formed in secondary exchange encounters where the original star that recycled the pulsar was replaced by the current, heavier companion," the researchers explained.

Summing up the results, the authors of the paper added that their discovery makes NGC 1851 one of the most pulsar-populated globular clusters known to date. Currently, there are 14 pulsars identified in this GC as the first one, designated PSR J0514−4002A (also known as NGC 1851A), was detected in 2004. The researchers expect further discoveries from the TRAPUM survey, which will significantly increase the known population of pulsars in several other GCs.

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