A 78 Day X-Ray Period Detected From NGC 5907 Ulx1 by Swift

Walton, D. J.; Fürst, Felix; Bachetti, Matteo; Barret, D.; Brightman, Murray; Fabian, A. C.; Gehrels, N.; Harrison, Fiona A.; Heida, Marianne; Middleton, M.; Rana, V.; Roberts, T. P.; Stern, Daniel; Tao, Lian; Webb, N.

doi:10.3847/2041-8205/827/1/l13

Cited by 84 publications

(88 citation statements)

References 47 publications

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“…Similar variability has also recently been found in ultraluminous X-ray pulsars (e.g. NGC 5907 ULX1; NGC 7793 P13; M82 X-2, Walton et al 2016;Fürst et al 2018;Brightman et al 2019). However, the mechanism responsible for the long timescale modulation in wind-fed SGXBs remains poorly understood.…”

Section: Introductionsupporting

confidence: 82%

A Study of the 20 day Superorbital Modulation in the High-mass X-Ray Binary IGR J16493-4348

Coley

Corbet

Fürst

et al. 2019

ApJ

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We report on Nuclear Spectroscopic Telescope Array (NuSTAR), Neil Gehrels Swift Observatory (Swift) X-ray Telescope (XRT) and Swift Burst Alert Telescope (BAT) observations of IGR J16493-4348, a wind-fed Supergiant X-ray Binary (SGXB) showing significant superorbital variability. From a discrete Fourier transform of the BAT light curve, we refine its superorbital period to be 20.058 ± 0.007 days. The BAT dynamic power spectrum and a fractional root mean square analysis both show strong variations in the amplitude of the superorbital modulation, but no observed changes in the period were found. The superorbital modulation is significantly weaker between MJD 55,700 and MJD 56,300. The joint NuSTAR and XRT observations, which were performed near the minimum and maximum of one cycle of the 20 day superorbital modulation, show that the flux increases by more than a factor of two between superorbital minimum and maximum. We find no significant changes in the 3-50 keV pulse profiles between superorbital minimum and maximum, which suggests a similar accretion regime. Modeling the pulse-phase averaged spectra we find a possible Fe Kα emission line at 6.4 keV at superorbital maximum. The feature is not significant at superorbital minimum. While we do not observe any significant differences between the pulse-phase averaged spectral continua apart from the overall flux change, we find that the hardness ratio near the broad main peak of the pulse profile increases from superorbital minimum to maximum. This suggests the spectral shape hardens with increasing luminosity. We discuss different mechanisms that might drive the observed superorbital modulation.

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Section: Introductionsupporting

confidence: 82%

A Study of the 20 day Superorbital Modulation in the High-mass X-Ray Binary IGR J16493-4348

Coley

Corbet

Fürst

et al. 2019

ApJ

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“…Most of these monitoring programs are dedicated for the study of long-term variability of ULXs including the search of periodic or quasi-periodic signals (e.g., Kaaret & Feng 2009;Strohmayer 2009;Grisé et al 2013;Lin et al 2015;Walton et al 2016a;Hu et al 2017). For a single observation, the typical exposure time is 1-3 ks, and the typical recurrent time between observations is 2-6 days.…”

Section: Data and Resultsmentioning

confidence: 99%

Evidence for Precession due to Supercritical Accretion in Ultraluminous X-Ray Sources

Weng

Feng

2018

ApJ

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Most ultraluminous X-ray sources (ULXs) are thought to be supercritical accreting compact objects, where massive outflows are inevitable. Using the long-term monitoring data with the Swift X-ray Telescope, we identified a common feature in bright, hard ULXs: they display a quasi-periodic modulation in their hard X-ray band but not in their soft band. As a result, some sources show a bimodal distribution on the hardness intensity map. We argue that these model-independent results can be well interpreted in a picture that involves supercritical accretion with precession, where the hard X-ray emission from the central funnel is more or less beamed, while the soft X-rays may arise from the photosphere of the massive outflow and be nearly isotropic. It implies that precession may be ubiquitous in supercritical systems, such as the Galactic microquasar SS 433. How the hard X-rays are modulated can be used to constrain the angular distribution of the hard X-ray emission and the geometry of the accretion flow. We also find that two ULX pulsars (NGC 5907 ULX-1 and NGC 7793 P13) show similar behaviors but no bimodal distribution, which may imply that they have a different beaming shape or mechanism.

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“…Furthermore, the majority of the variability is seen at intermediate energies/temperatures in terms of the broadband spectra obtained (∼1-10 keV); if the inner regions of the flow were being blocked from our view at times, and exposed at other times, one would likely again expect to see the highest energies respond similarly. Indeed, in the case of NGC 5907 ULX1, where 78 day super-orbital 15 variations that may well be related to precession of the accretion flow are observed (Walton et al 2016a), there is evidence that high-energy flux does vary along with the lower-energy emission (Fürst et al 2017; although observations are still sparse).…”

Section: Discussionmentioning

confidence: 99%

The Broadband Spectral Variability of Holmberg IX X-1

Walton

Fürst

Harrison

et al. 2017

ApJ

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We present results from four new broadband X-ray observations of the extreme ultraluminous X-ray source Holmberg IX X-1 ( > L 10 X 40 erg s −1 ), performed by Suzaku and NuSTAR in coordination. Combined with the archival data, we now have broadband observations of this remarkable source from six separate epochs. Two of these new observations probe lower fluxes than seen previously, allowing us to extend our knowledge of the broadband spectral variability exhibited. The spectra are well fit by two thermal blackbody components thatdominate the emission below 10 keV, as well as a steep (G~3.5) power-law tail thatdominates above ∼15 keV. Remarkably, while the 0.3-10.0 keV flux varies by a factor of ∼3 between all these epochs, the 15-40 keV flux varies by only ∼20%. Although the spectral variability is strongest in the ∼1-10 keV band, both of the thermal components are required to vary when all epochs are considered. We also revisit the search for iron absorption features byleveraging the high-energy NuSTAR data to improve our sensitivity to extreme velocity outflows in light of the ultra-fast outflow recently detected in NGC 1313 X-1. Iron absorption from a similar outflow along our line of sight can be ruled out in this case. We discuss these results in the context of superEddington accretion models that invoke a funnel-like geometry for the inner flow, and propose a scenario in which we have an almost face-on view of a funnel that expands to larger radii with increasing flux, resulting in an increasing degree of geometrical collimation for the emission from intermediate-temperature regions.

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A 78 Day X-Ray Period Detected From NGC 5907 Ulx1 by Swift

Abstract: We report the detection of a 78.1 ± 0.5 day period in the X-ray light curve of the extreme ultraluminous X-ray source NGC 5907 ULX1 ( L X,peak ∼ 5 × … Show more

Cited by 84 publications

References 47 publications

A Study of the 20 day Superorbital Modulation in the High-mass X-Ray Binary IGR J16493-4348

A Study of the 20 day Superorbital Modulation in the High-mass X-Ray Binary IGR J16493-4348

Evidence for Precession due to Supercritical Accretion in Ultraluminous X-Ray Sources

The Broadband Spectral Variability of Holmberg IX X-1

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