NinjaSat monitoring of Type-I X-ray bursts from the clocked burster SRGA J144459.2$-$604207

Abstract

The CubeSat X-ray observatory NinjaSat was launched on 2023 November 11 and has provided opportunities for agile and flexible monitoring of bright X-ray sources. On 2024 February 23, the NinjaSat team started long-term observation of the new X-ray source SRGA J144459.2$-$604207 as the first scientific target, which was discovered on 2024 February 21 and recognized as the sixth clocked X-ray burster. Our 25-day observation covered almost the entire decay of this outburst from two days after the peak at $\sim$100 mCrab on February 23 until March 18 at a few mCrab level. The Gas Multiplier Counter onboard NinjaSat successfully detected 12 Type-I X-ray bursts with a typical burst duration of $\sim$20 s, shorter than other clocked burster systems. As the persistent X-ray emission declined by a factor of five, X-ray bursts showed a notable change in its morphology: the rise time became shorter from 4.4(7) s to 0.3(3) s (1$\sigma$ errors), and the peak amplitude increased by 44%. The burst recurrence time $\Delta t_{\mathrm{rec}}$ also became longer from 2 hr to 10 hr, following the relation of $\Delta t_{\mathrm{rec}}\propto F_{\mathrm{per}}^{-0.84}$, where $F_{\mathrm{per}}$ is the persistent X-ray flux, by applying a Markov chain Monte Carlo method. The short duration of bursts is explained by the He-enhanced composition of accretion matter and the relation between $\Delta t_{\text{rec}}$ and $F_{\mathrm{per}}$ by a massive neutron star. This study demonstrated that CubeSat pointing observations can provide valuable astronomical X-ray data.

7 pages, 5 figures, accepted for publication in PASJ Letter

References in corpus (11)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• The Multi-INstrument Burst ARchive (MINBAR)
• Models of Type I X-ray Bursts from GS 1826-24: A Probe of rp-Process Hydrogen Burning
• Advancement of Photospheric Radius Expansion and Clocked Type-I X-Ray Burst Models with the New ${}^{22}$Mg$(\alpha ,p{)}^{25}$Al Reaction Rate Determined at Gamow Energy
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• Indications for a slow rotator in the Rapid Burster from its thermonuclear bursting behaviour
• Impacts of the direct URCA and Superfluidity inside a Neutron Star on Type-I X-Ray Bursts and X-Ray Superbursts
• SRG/ART-XC discovery of SRGAJ144459.2-604207: a well-tempered bursting accreting millisecond X-ray pulsar
• Discovery of Polarized X-Ray Emission from the Accreting Millisecond Pulsar SRGA J144459.2-604207
• A comprehensive study of type I (thermonuclear) bursts in the new transient SRGA J144459.2$-$604207
• Gas selection for Xe-based LCP-GEM detectors onboard the CubeSat X-ray observatory NinjaSat

Cited by in corpus (8)

• Dense Matter in Neutron Stars with eXTP
• NinjaSat: Astronomical X-ray CubeSat Observatory
• Disk reflection and energetics from the accreting millisecond pulsar SRGA J144459.2-604207
• A simple, flexible method for timing cross-calibration of space missions
• Thermonuclear superburst of MAXI J1752$-$457 observed with NinjaSat and MAXI
• Connecting the m-dots: accretion rates and thermonuclear burst recurrence times on neutron stars and white dwarfs
• Return of the Clocked Burster: Exceptionally Short Recurrence Time in GS 1826-238
• Discovery of burst oscillations in the newly discovered millisecond X-ray pulsar SRGA J144459.2$-$604207