MAXI J1816-195: new accreting millisecond X-ray pulsars are found

Reference : The discovery of the 528.6 Hz accreting millisecond X-ray pulsar MAXI J1816-195, by Bult et al. 2022, arXiv:2208.04721

A new accreting millisecond X-ray pulsar has been found by a team of astronomers using the Neutron Star Interior Composition Explorer (NICER). The rotation period of the newly discovered pulsar, known as MAXI J1816-195, is around 1.89 milliseconds. The discovery is detailed in a publication posted on the arXiv pre-print on August 9, 2022.

Strictly periodic changes in X-ray intensity, which can last as short as a fraction of a second, are present in X-ray pulsars. Short spin periods of accreting millisecond X-ray pulsars (AMXPs), a rare subclass of X-ray pulsars, are brought on by protracted material transfer from a low-mass partner star via an accretion disc onto a slowly spinning neutron star. AMXPs are viewed by astronomers as astrophysical research facilities that may be essential in furthering our understanding of thermonuclear burst events.

AMXPs are somewhat uncommon; so far only a small number of these objects have been identified. The scientific community is still actively looking for these sources with space observatories like NICER deployed on the International Space Station (ISS) in order to increase the list of these peculiar objects.

A new AMXP with NICER has been discovered, according to a team of astronomers led by Astronomer Peter Bult of the University of Maryland, USA. They discovered that the previously identified MAXI J1816-195 X-ray transient displays 528.6 Hz pulsations. On June 7, 2022, the ISS’s Monitor of All-sky X-ray Image (MAXI) discovered MAXI J1816-195 for the first time. Additional observations of this source using NICER proved that it was an AMXP.

Location of NICER observatory on International Space Station (ISS)

In this article, they report finding “528.6 Hz pulsations in the newly discovered X-ray transient MAXI J1816-195. Over the course of 28 days, we used NICER to observe the first transient outburst from the neutron star low-mass X-ray binary MAXI J1816-195”

The investigation found that MAXI J1816-195 has an orbital period of around 4.8 hours and a spin period of 1.89 milliseconds. It was determined that the donor star had a mass of between 0.1 and 0.55 solar masses. The maximum distance to this pulsar was determined to be 28,000 light years based on the findings.

15 thermonuclear X-ray bursts from MAXI J1816-195 were discovered through measurements to have gradually changed in form over time. These bursts had an average recurrence time of 1.4 hours, according to the measurements. MAXI J1816-195 turned out to be a typical burster with a recurrence time that increases throughout the outburst.

The investigation also discovered that all detected X-ray bursts had a fairly similar progression in terms of both their spectra and light curve. The burst durations indicate hydrogen-rich surroundings ignition, which implies that the donor star and the accreted material both must be hydrogen-rich. The researchers also said that there was no proof of burst oscillations in the gathered data.

Last Updated on August 19, 2022 by Sonkamble Satish