NICER Discovery that SRGA J144459.2-604207 is an Accreting Millisecond X-ray Pulsar

Mason Ng; Paul S. Ray; Andrea Sanna; Tod E. Strohmayer; Alessandro Papitto; Giulia Illiano; Arianna C. Albayati; Diego Altamirano; Tuğba Boztepe; Tolga Güver; Deepto Chakrabarty; Zaven Arzoumanian; D. J. K. Buisson; Elizabeth C. Ferrara; Keith C. Gendreau; Sebastien Guillot; Jeremy Hare; Gaurava K. Jaisawal; Christian Malacaria; Michael T. Wolff

arXiv · 2405.00087

NICER Discovery that SRGA J144459.2-604207 is an Accreting Millisecond X-ray Pulsar

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Abstract

We present the discovery, with the Neutron Star Interior Composition Explorer (NICER), that SRGA J144459.2-604207 is a 447.9 Hz accreting millisecond X-ray pulsar (AMXP), which underwent a four-week long outburst starting on 2024 February 15. The AMXP resides in a 5.22 hr binary, orbiting a low-mass companion donor with $M_d>0.1M_\odot$. We report on the temporal and spectral properties from NICER observations during the early days of the outburst, from 2024 February 21 through 2024 February 23, during which NICER also detected a type-I X-ray burst that exhibited a plateau lasting ~6 s. The spectra of the persistent emission were well described by an absorbed thermal blackbody and power-law model, with blackbody temperature $kT\approx0.9{\rm\,keV}$ and power-law photon index $\Gamma\approx1.9$. Time-resolved burst spectroscopy confirmed the thermonuclear nature of the burst, where an additional blackbody component reached a maximum temperature of nearly $kT\approx3{\rm\,keV}$ at the peak of the burst. We discuss the nature of the companion as well as the type-I X-ray burst.

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Mason Ng, Paul S. Ray, Andrea Sanna, Tod E. Strohmayer, Alessandro Papitto, Giulia Illiano, Arianna C. Albayati, Diego Altamirano, Tuğba Boztepe, Tolga Güver, Deepto Chakrabarty, Zaven Arzoumanian, D. J. K. Buisson, Elizabeth C. Ferrara, Keith C. Gendreau, Sebastien Guillot, Jeremy Hare, Gaurava K. Jaisawal, Christian Malacaria, Michael T. Wolff. 2024-04-30. NICER Discovery that SRGA J144459.2-604207 is an Accreting Millisecond X-ray Pulsar. https://arxiv.org/abs/2405.00087

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