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

Hu, Chin-Ping; Dage, Kristen C.; Clarkson, William I.; Brumback, McKinley C.; Charles, P. A.; Haggard, Daryl; Hickox, Ryan C.; Mihara, T.; Bahramian, A.; Karam, Rawan; Athukoralalage, Wasundara Ranhari; Altamirano, D.; Neilsen, Joey; Kennea, J. A.

doi:10.1093/mnras/stad384

Cited by 3 publications

(2 citation statements)

References 62 publications

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“…Taking the average of the cycle length found by the up-crossing and down-crossing times, we determined that the superorbital cycles hosting Epochs 1-4 were approximately 46 ± 3 days, 30 ± 3 days, 44 ± 3 days, and 46 ± 3 days, respectively. From these cycle lengths and the excursion measurements of Hu et al (2023), it is clear that SMC X-1 was within a period of superorbital excursion during our observations (see also Dage et al 2019;Hu et al 2019).…”

Section: Nicer Observationssupporting

confidence: 56%

Constraining the Evolution of the Unstable Accretion Disk in SMC X-1 with NICER

Brumback,

Vasilopoulos,

Coley

et al. 2023

ApJ

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Neutron star high-mass X-ray binaries with superorbital modulations in luminosity host warped inner accretion disks that occult the neutron star during precession. In SMC X-1, the instability in the warped disk geometry causes superorbital period “excursions”: times of instability when the superorbital period decreases from its typical value of 55 to ∼40 days. Disk instability makes SMC X-1 an ideal system in which to investigate the effects of variable disk geometry on the inner accretion flow. Using the high-resolution spectral and timing capabilities of the Neutron Star Interior Composition Explorer, we examined the high state of four different superorbital cycles of SMC X-1 to search for changes in spectral shape and connections to the unstable disk geometry. We performed pulse phase-averaged and phase-resolved spectroscopy to closely compare the changes in spectral shape and any cycle-to-cycle variations. While some parameters, including the photon index and absorbing column density, show slight variations with superorbital phase, these changes are most evident during the intermediate state of the superorbital cycle. Few spectral changes are observed within the high state of the superorbital cycle, possibly indicating the disk instability does not significantly change SMC X-1's accretion process.

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Section: Nicer Observationssupporting

confidence: 56%

Constraining the Evolution of the Unstable Accretion Disk in SMC X-1 with NICER

Brumback,

Vasilopoulos,

Coley

et al. 2023

ApJ

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“…The ATCA shows upper limits. There is some evidence of a correlation between spin and superorbital periods (Hu et al 2023). During the week of the campaign it was in the uprise of the superorbital period.…”

Section: Z Sources (8 Sources 5 With Seds)mentioning

confidence: 99%

Spectral Energy Distributions of Southern Binary X-Ray Sources

Dickey,

Vrtilek,

McCollough

et al. 2023

ApJS

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The rapid variability of X-ray binaries (XRBs) produces a wide range of X-ray states that are linked to activity across the electromagnetic spectrum. It is particularly challenging to study a sample of sources large enough to include all types in their various states, and to cover the full range of frequencies that show flux density variations. Simultaneous observations with many telescopes are necessary. In this project, we monitor 48 XRBs with seven telescopes across the electromagnetic spectrum from 5 × 109 to 1019 Hz, including ground-based radio, IR, and optical observatories, and five instruments on two spacecraft over a 1 week period. We construct spectral energy distributions and matching X-ray color–intensity diagrams for 20 sources that have the most extensive detections. Our observations are consistent with several models of expected behavior proposed for the different classes: we detect no significant radio emission from pulsars or atoll sources, but we do detect radio emission from Z sources in the normal or horizontal branch, and from black holes in the high/soft, low/hard, and quiescent states. The survey data provide useful constraints for more detailed models predicting behavior from the different classes of sources.

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Monitoring observations of SMC X-1’s excursions (moose) III. X-ray spectroscopy of a warped, precessing accretion disc

Karam,

Dage,

Tetarenko

et al. 2024

Monthly Notices of the Royal Astronomical Society

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The moose (Monitoring Observations of SMC X-1’s Excursions) program uses the Neutron Star Interior Composition Explorer Mission (NICER) to monitor the high-mass X-ray binary SMC X-1 during its superorbital period excursions. Here, we perform X-ray spectral analyses of 26 NICER observations of SMC X-1, taken at the tail-end of the excursion between 2021-04-01 and 2022-01-05. We use a single spectral model to fit spectra observed in high, intermediate, and low states, using a combination of a partial covering fraction model, a blackbody disc, and a power-law component. We find that the partial covering fraction varies significantly with the superorbital state during superorbital excursion. Our findings suggest that the low/high state in SMC X-1 is caused by a very high obscuration of the accretion disc.

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

Cited by 3 publications

References 62 publications

Constraining the Evolution of the Unstable Accretion Disk in SMC X-1 with NICER

Constraining the Evolution of the Unstable Accretion Disk in SMC X-1 with NICER

Spectral Energy Distributions of Southern Binary X-Ray Sources

Monitoring observations of SMC X-1’s excursions (moose) III. X-ray spectroscopy of a warped, precessing accretion disc

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