Astronomers discover rare accreting X-ray pulsar

(ORDO NEWS) — Using the Neutron Star Interior Composition Explorer (NICER), an international team of astronomers has discovered a new accreting millisecond X-ray pulsar, MAXI J1816-195. This is reported in an article published August 9 on arXiv.org.

Accreting millisecond X-ray pulsars (AMXP) are a special type of X-ray pulsars whose short-period pulsations are caused by mass transfer from a low-mass companion star through an accretion disk to a slowly rotating neutron star. AMXPs are relatively rare, with only a few dozen pulsars of this type having been found to date.

A team of astronomers led by Peter Bult of the University of Maryland announced the discovery of a new AMHR.

A newly discovered X-ray transient, named MAXI J1816-195, exhibits pulsations at a frequency of 528.6 Hz. MAXI J1816-195 was first identified on June 7, 2022 using the Monitor of All-sky X-ray Image (MAXI) aboard the ISS. Follow-up observations with NICER confirmed that this is AMXP.

According to the study, MAXI J1816-195 has a rotation period of 1.89 milliseconds and an orbital period of about 4.8 hours.

The mass of the donor star is between 0.1 and 0.55 solar masses. It was found that the upper limit of the distance to this pulsar is 28,000 light years.

The observations revealed 15 X-ray fusion bursts from MAXI J1816-195. The average recurrence time for these outbreaks is estimated to be approximately 1.4 hours.

In addition, the study showed that all observed X-ray bursts showed a very similar evolution both in the light curve and in their spectroscopy.

The duration of the flares indicates that a hydrogen-rich medium is burning, suggesting that the accreted material, and therefore the donor star, must be rich in hydrogen. The researchers added that no waveform data was found in the collected data.

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