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arXiv · 1805.10065

Millisecond oscillations in the bursting flux of SAX J1810.8-2609

Anna V Bilous·Anna L Watts·Duncan K Galloway·Jean J M in 't Zand
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Abstract

SAX J1810.8-2609 is a faint X-ray transient, mostly known for its abnormally low quiescent thermal luminosity, which disagrees with standard cooling models. It is also one of a small sample of stars whose mass and radius have been estimated using spectral modeling of one of its thermonuclear bursts. Here we report the discovery of millisecond oscillations in a type I thermonuclear X-ray burst from SAX J1810.8-2609 observed by RXTE during the 2007 outburst. A strong signal (Leahy-normalized power of 71.5, 4.5e-9 chance of coincidence with a conservative estimate for the number of trials) was present at 531.8 Hz during the decay of one out of six bursts observed. Oscillations were detected for about 6 seconds, during which their frequency increased from 531.4 to 531.9 Hz in a manner similar to other burst oscillation sources. The millisecond oscillations discovered pinpoint the spin frequency of the neutron star, which is important for the spectral modeling, associated mass-radius inference, and understanding the evolutionary status and cooling behavior of the star. As of April 2018 the source is in outburst again, providing a fleeting opportunity to acquire new material for the burst oscillation searches.

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Anna V Bilous, Anna L Watts, Duncan K Galloway, Jean J M in 't Zand. 2018-05-25. Millisecond oscillations in the bursting flux of SAX J1810.8-2609. https://doi.org/10.3847/2041-8213/aad09c

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