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

BULT, PETER; ALTAMIRANO, DIEGO; ARZOUMANIAN, ZAVEN; CHAKRABARTY, DEEPTO; CHENEVEZ, JÉRÔME; FERRARA, ELIZABETH C.; GENDREAU, KEITH C.; GUILLOT, SEBASTIEN; GÜVER, TOLGA; IWAKIRI, WATARU; JAISAWAL, GAURAVA K.; MANCUSO, GIULIO C.; MALACARIA, CHRISTIAN; NG, MASON; SANNA, ANDREA; STROHMAYER, TOD E.; WADIASINGH, ZORAWAR; WOLFF, MICHAEL T.

The Astrophysical Journal Letters

IOP PUBLISHING LTD

Año: 2022 vol. 935

2041-8205

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.