NinjaSat monitoring of Type-I X-ray bursts from the clocked burster SRGA J144459.2$-$604207
Tomoshi Takeda, Toru Tamagawa, Teruaki Enoto, Takao Kitaguchi, Yo Kato, Tatehiro Mihara, Wataru Iwakiri, Masaki Numazawa, Naoyuki Ota, Sota Watanabe, Arata Jujo, Amira Aoyama, Satoko Iwata, Takuya Takahashi, Kaede Yamasaki, Chin-Ping Hu, Hiromitsu Takahashi, Akira Dohi

TL;DR
This study used the NinjaSat CubeSat to monitor a newly discovered X-ray burster, observing 12 Type-I bursts, analyzing their properties, and demonstrating CubeSat's effectiveness for X-ray astronomy.
Contribution
First long-term observation of SRGA J144459.2$-$604207 with NinjaSat, revealing burst characteristics and their relation to persistent flux, highlighting CubeSat's utility in X-ray monitoring.
Findings
Detected 12 Type-I X-ray bursts with short durations.
Observed changes in burst morphology as persistent flux declined.
Established a relation between burst recurrence time and persistent flux.
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 J144459.2604207 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 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 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…
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Taxonomy
TopicsGamma-ray bursts and supernovae · Astrophysical Phenomena and Observations · Pulsars and Gravitational Waves Research
