Published in

American Astronomical Society, Astrophysical Journal Letters, 2(935), p. L32, 2022

DOI: 10.3847/2041-8213/ac87f9

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The Discovery of the 528.6 Hz Accreting Millisecond X-Ray Pulsar MAXI J1816–195

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Data provided by SHERPA/RoMEO

Abstract

Abstract We present the discovery of 528.6 Hz pulsations in the new X-ray transient MAXI J1816–195. Using NICER, we observed the first recorded transient outburst from the neutron star low-mass X-ray binary MAXI J1816–195 over a period of 28 days. From a timing analysis of the 528.6 Hz pulsations, we find that the binary system is well described as a circular orbit with an orbital period of 4.8 hr and a projected semimajor axis of 0.26 lt-s for the pulsar, which constrains the mass of the donor star to 0.10–0.55 M . Additionally, we observed 15 thermonuclear X-ray bursts showing a gradual evolution in morphology over time, and a recurrence time as short as 1.4 hr. We did not detect evidence for photospheric radius expansion, placing an upper limit on the source distance of 8.6 kpc.