Explanipedia

Unveiling the Nature of Superorbital Modulation of SMC X-1 using NinjaSat Open

Chin‐Ping Hu, Naoyuki OTA, Tomoshi Takeda, Teruaki Enoto, Toru Tamagawa , et al. · 2025

We report a long-term, high-cadence timing and spectral observation of the X-ray pulsar SMC X-1 using NinjaSat, a 6U CubeSat in low-Earth orbit, covering nearly a full superorbital cycle. SMC X-1 is a high-mass X-ray binary exhibiting a 0.…

Return of the Clocked Burster: Exceptionally Short Recurrence Time in GS 1826−238 Open

Tomoshi Takeda, Toru Tamagawa, Teruaki Enoto, W. Iwakiri, Akira Dohi , et al. · 2025

We report the discovery of an exceptionally short burst recurrence time in the well-known clocked burster GS 1826−238, observed with the CubeSat X-ray observatory NinjaSat. In 2025 May, GS 1826−238 underwent a soft-to-hard state transition…

Concept of high-z gamma-ray bursts unraveling the dark ages and extreme space-time mission—HiZ-GUNDAM Open

Daisuke Yonetoku, Akihiro Doi, T. Mihara, Hideo Matsuhara, T. Sakamoto , et al. · 2025

Quasiperiodic Variation during a Fast X-Ray Outburst of a High-mass X-Ray Binary MAXI J0709-159/LY CMa Observed by NICER Open

M. Sugizaki, T. Mihara, Kohei Kobayashi, M. Shidatsu, W. Iwakiri , et al. · 2025

We report on a quasiperiodic variation at ∼1 Hz during a fast X-ray outburst of a high-mass X-ray binary MAXI J0709−159/LY CMa observed by the Neutron star Interior Composition ExploreR (NICER). The new X-ray transient MAXI J0709−159 was d…

Quasi-periodic variation during a fast X-ray outburst of a high-mass X-ray binary MAXI J0709-159 / LY CMa observed by NICER Open

M. Sugizaki, T. Mihara, Kohei Kobayashi, M. Shidatsu, W. Iwakiri , et al. · 2025

We report on a quasi-periodic variation at $\sim1$ Hz during a fast X-ray outburst of a high-mass X-ray binary MAXI J0709$-$159 / LY CMa observed by the Neutron-star interior composition explorer (NICER). The new X-ray transient MAXI J0709…

Thermonuclear Superburst of MAXI J1752−457 Observed with NinjaSat and MAXI Open

A Aoyama, Teruaki Enoto, Takuya Takahashi, S. Watanabe, Tomoshi Takeda , et al. · 2025

An uncatalogued bright X-ray transient was detected with MAXI on 2024 November 9, named MAXI J1752−457. The NinjaSat X-ray observatory promptly observed the source from November 10 to 18, while the small angular separation from the Sun ham…

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

Tomoshi Takeda, Toru Tamagawa, Teruaki Enoto, Takao Kitaguchi, Yo Kato , et al. · 2025

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 n…

NinjaSat: Astronomical X-ray CubeSat observatory Open

Toru Tamagawa, Teruaki Enoto, Takao Kitaguchi, W. Iwakiri, Yo Kato , et al. · 2025

NinjaSat is an X-ray CubeSat designed for agile, long-term continuous observations of bright X-ray sources, with the size of 6U ($112.7\times 237.1\times 340.5$ mm3) and a mass of 8 kg. NinjaSat is capable of pointing at X-ray sources with…

Evidence of non-solar elemental composition in the clocked X-ray burster SRGA J144459.2-604207 Open

Akira Dohi, Nobuya Nishimura, Ryosuke Hirai, Tomoshi Takeda, W. Iwakiri , et al. · 2025

In 2024 February and March, a series of many Type I X-ray bursts were observed from the accreting neutron star SRGA J144459.2-604207, which has been identified by multiple X-ray satellites, with the first reports coming from INTEGRAL and N…

GX 301-2 PRE-PERIASTRON AND APASTRON FLARES WITH MAXI Open

Á. Torregrosa, J. J. Rodes‐Roca, J. M. Torrejón, G. Sanjurjo-Ferrín, T. Mihara , et al. · 2025

The bright high-mass X-ray binary GX 301-2 exhibits two periodic flare episodes along its orbit which are produced when the neutron star is close to the apastron and periastron passages. Time-resolved spectra were extracted and several mod…

NinjaSat: Astronomical X-ray CubeSat Observatory Open

Toru Tamagawa, Teruaki Enoto, Takao Kitaguchi, W. Iwakiri, Yo Kato , et al. · 2024

NinjaSat is an X-ray CubeSat designed for agile, long-term continuous observations of bright X-ray sources, with the size of 6U ($100\times200\times300$ mm$^3$) and a mass of 8 kg. NinjaSat is capable of pointing at X-ray sources with an a…

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

Tomoshi Takeda, Toru Tamagawa, Teruaki Enoto, Takao Kitaguchi, Yo Kato , et al. · 2024

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 n…

GX 301-2 pre-periastron and apastron flares with MAXI Open

Á. Torregrosa, J. J. Rodes‐Roca, J. M. Torrejón, G. Sanjurjo-Ferrín, T. Mihara , et al. · 2024

The bright high-mass X-ray binary GX 301-2 exhibits two periodic flare episodes along its orbit which are produced when the neutron star is close to the apastron and periastron passages. Time-resolved spectra were extracted and several mod…

X-ray iron absorption line in Swift J1858.6−0814 Open

Kazumi Asai, T. Mihara, Kento Sakai, Aya Kubota · 2024

We present the spectral analysis of bright steady states in an outburst of the transient neutron star low-mass X-ray binary Swift J1858.6−0814 observed with the Neutron star Interior Composition Explorer (NICER). We detected an ionized iro…

High-speed readout system of X-ray CMOS image sensor for time domain astronomy Open

Naoki Ogino, M. Arimoto, Tatsuya Sawano, Daisuke Yonetoku, Hsien-Chieh Shen , et al. · 2024

We developed an FPGA-based high-speed readout system for a complementary metal-oxide-semiconductor (CMOS) image sensor to observe soft X-ray transients in future satellite missions, such as HiZ-GUNDAM . Our previous research revealed that …

The 2018 X-Ray and Radio Outburst of Magnetar XTE J1810-197 Open

E. V. Gotthelf, J. P. Halpern, Jason Alford, T. Mihara, H. Negoro , et al. · 2024

We present the earliest X-ray observations of the 2018 outburst of XTE. J1810-197, the first outburst since its 2003 discovery as the prototypical transient and radio-emitting anomalous X-ray pulsar (AXP). The Monitor of Allsky X-ray Image…

EXTRAORDINARY LUMINOUS SOFT X-RAY TRANSIENT MAXI J0158–744 AS AN IGNITION OF A NOVA ON A VERY MASSIVE O-Ne WHITE DWARF Open

M. Morii, H. Tomida, Minoru Kimura, F. Suwa, H. Negoro , et al. · 2024

We present the observation of an extraordinary luminous soft X-ray transient, MAXI J0158-744, by the Monitor of All-sky X-ray Image (MAXI) on 2011 November 11. This transient is characterized by a soft X-ray spectrum, a short duration (1.3…

Accretion Spin-up and a Strong Magnetic Field in the Slow-spinning Be X-Ray Binary MAXI J0655-013 Open

Sean N. Pike, M. Sugizaki, J. van den Eijnden, Benjamin M. Coughenour, Amruta Jaodand , et al. · 2023

We present Monitor of All-sky X-ray Image (MAXI) and Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the Be X-ray binary, MAXI J0655−013, in outburst. NuSTAR observed the source once early in the outburst, when spectral anal…

Accretion spin-up and a strong magnetic field in the slow-spinning Be X-ray binary MAXI J0655-013 Open

Sean N. Pike, M. Sugizaki, J. van den Eijnden, Benjamin M. Coughenour, Amruta Jaodand , et al. · 2023

We present MAXI and NuSTAR observations of the Be X-ray binary, MAXI J0655-013, in outburst. NuSTAR observed the source once early in the outburst, when spectral analysis yields a bolometric (0.1--100 keV), unabsorbed source luminosity of …

GRB 221009A: Discovery of an Exceptionally Rare Nearby and Energetic Gamma-Ray Burst Open

Maia A. Williams, J. A. Kennea, S. Dichiara, Kohei Kobayashi, W. Iwakiri , et al. · 2023

We report the discovery of the unusually bright long-duration gamma-ray burst (GRB), GRB 221009A, as observed by the Neil Gehrels Swift Observatory (Swift), Monitor of All-sky X-ray Image, and Neutron Star Interior Composition Explorer Mis…

GRB 221009A: Discovery of an Exceptionally Rare Nearby and Energetic Gamma-Ray Burst Open

Maia A. Williams, J. A. Kennea, S. Dichiara, Kohei Kobayashi, W. Iwakiri , et al. · 2023

We report the discovery of the unusually bright long-duration gamma-ray burst (GRB), GRB 221009A, as observed by the Neil Gehrels Swift Observatory (Swift), Monitor of All-sky X-ray Image (MAXI), and Neutron Star Interior Composition Explo…

Monitoring observations of SMC X-1’s excursions (MOOSE) – II. A new excursion accompanies spin-up acceleration Open

Chin‐Ping Hu, Kristen C. Dage, W. I. Clarkson, McKinley C. Brumback, P. A. Charles , et al. · 2023

SMC X-1 is a high-mass X-ray binary showing superorbital modulation with an unstable period. Previous monitoring shows three excursion events in 1996–1998, 2005–2007, and 2014–2016. The superorbital period drifts from ≳60 to ≲40 d and then…

Monitoring observations of SMC X-1's excursions (MOOSE)-II: A new excursion accompanies spin-up acceleration Open

Chin‐Ping Hu, Kristen C. Dage, W. I. Clarkson, McKinley C. Brumback, P. A. Charles , et al. · 2023

SMC X-1 is a high-mass X-ray binary showing superorbital modulation with an unstable period. Previous monitoring shows three excursion events in 1996--1998, 2005--2007, and 2014--2016. The superorbital period drifts from >60 days to <40 da…

Discovery of a new supergiant fast X-ray transient MAXI J0709−159 associated with the Be star LY Canis Majoris Open

M. Sugizaki, T. Mihara, Kohei Kobayashi, H. Negoro, M. Shidatsu , et al. · 2022

We report on the discovery of a new supergiant fast X-ray transient (SFXT), MAXI J0709−159, and its identification with LY CMa (also known as HD 54786). On 2022 January 25, a new flaring X-ray object, named MAXI J0709−159, was detected by …

Decades' long-term variations in NS-LMXBs observed with MAXI/GSC, RXTE/ASM and Ginga/ASM Open

Keisuke Asai, T. Mihara, M. Matsuoka · 2022

We investigated the decades' long-term X-ray variations in bright low-mass X-ray binaries containing a neutron star (NS-LMXB). The light curves of MAXI/GSC and RXTE/ASM covers $\sim$ 26 yr, and high-quality X-ray light curves are obtained …

MAXI : Monitor of All-sky X-ray Image Open

T. Mihara, H. Tsunemi, H. Negoro · 2022

Monitor of All-sky X-ray Image (MAXI) is a Japanese X-ray all-sky monitor onboard the International Space Station (ISS).

Discovery and Long-term Broadband X-Ray Monitoring of Galactic Black Hole Candidate MAXI J1803–298 Open

M. Shidatsu, Kohei Kobayashi, H. Negoro, W. Iwakiri, S. Nakahira , et al. · 2022

We report the results from the broadband X-ray monitoring of the new Galactic black hole candidate MAXI J1803−298 with MAXI/GSC and Swift/BAT during its outburst. After the discovery on 2021 May 1, the soft X-ray flux below 10 keV rapidly …

MAXI and NuSTAR Observations of the Faint X-Ray Transient MAXI J1848-015 in the GLIMPSE-C01 Cluster Open

Sean N. Pike, H. Negoro, John A. Tomsick, Matteo Bachetti, McKinley C. Brumback , et al. · 2022

We present the results of Monitor of All-sky X-ray Image (MAXI) monitoring and two Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the recently discovered faint X-ray transient MAXI J1848015. Analysis of the MAXI light curve…

A Comprehensive X-Ray Report on AT2019wey Open

Yuhan Yao, S. R. Kulkarni, Keith C. Gendreau, Gaurava K. Jaisawal, Teruaki Enoto , et al. · 2021

Here, we present MAXI, Swift, NICER, NuSTAR, and Chandra observations of the X-ray transient AT2019wey (SRGA J043520.9+552226, SRGE J043523.3+552234). From spectral and timing analyses we classify it as a Galactic low-mass X-ray binary (LM…

Discovery of a strong 6.6 keV emission feature from EXO 1745−248 after the superburst in 2011 October Open

W. Iwakiri, Motoko Serino, T. Mihara, Liyi Gu, Hiroya Yamaguchi , et al. · 2021

We discover an unidentified strong emission feature in the X-ray spectrum of EXO 1745−248 obtained by RXTE at 40 hr after the peak of a superburst. The structure was centered at 6.6 keV and significantly broadened with a large equivalent w…

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