SRG/ART-XC discovery of SRGAJ144459.2-604207: a well-tempered bursting accreting millisecond X-ray pulsar

Abstract

We report on the discovery of the new accreting millisecond X-ray pulsar SRGAJ144459.2-604207 using the SRG/ART-XC data. The source was observed twice in February 2024 during the declining phase of the outburst. Timing analysis revealed a coherent signal near 447.8~Hz modulated by the Doppler effect due to the orbital motion. The derived parameters for the binary system are consistent with the circular orbit with a period of $\sim 5.2$~h. The pulse profiles of the persistent emission, showing a sine-like part during half a period with a plateau in between, can well be modelled by emission from two circular spots partially eclipsed by the accretion disk. Additionally, during our 133~ks exposure observations, we detected 19 thermonuclear X-ray bursts. All bursts have similar shapes and energetics, and do not show any signs of photospheric radius expansion. The burst rate decreases linearly from one per $\sim$1.6~h at the beginning of observations to one per $\sim$2.2~h at the end and anticorrelates with the persistent flux. Spectral evolution during the bursts is consistent with the models of the neutron star atmospheres heated by accretion and imply a neutron star radius of 11--12~km and the distance to the source of 8--9~kpc. We also detected pulsations during the bursts and showed that the pulse profiles differ substantially from those observed in the persistent emission. However, we could not find a simple physical model explaining the pulse profiles detected during the bursts.

8 pages, 13 figures, 1 table

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Cited by in corpus (10)

• Constraining the Properties of the Thermonuclear Burst Oscillation Source XTE J1814-338 Through Pulse Profile Modelling
• Discovery of Polarized X-Ray Emission from the Accreting Millisecond Pulsar SRGA J144459.2-604207
• Catalog of outbursts of neutron star LMXBs
• NinjaSat monitoring of Type-I X-ray bursts from the clocked burster SRGA J144459.2$-$604207
• A comprehensive study of type I (thermonuclear) bursts in the new transient SRGA J144459.2$-$604207
• Disk reflection and energetics from the accreting millisecond pulsar SRGA J144459.2-604207
• X-ray spectral properties of the accreting millisecond pulsar IGR J17498-2921 during its 2023 outburst
• Modelling polarized X-ray pulses from accreting millisecond pulsars with X-PSI, using different hot spot locations and shapes
• Timing and spectral studies of SRGA J144459.2$-$604207 with NICER, Einstein Probe, IXPE, NuSTAR, Insight-HXMT and INTEGRAL during its 2024 outburst
• Broad-band X-ray spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498$-$2921 during the 2023 outburst