<i>NuSTAR</i> observations of wind-fed X-ray pulsar GX 301–2 during unusual spin-up event

Nabizadeh, Armin; Mönkkönen, Juhani; Tsygankov, Sergey S.; Doroshenko, V.; Molkov, S.; Poutanen, Juri

doi:10.1051/0004-6361/201936045

Cited by 28 publications

(20 citation statements)

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“…To study the pulse profile properties over the orbital phase, we calculated the pulse fraction (defined as PF = I max −I min I max +I min ) for all light curves and show the variation of PF versus orbital phase in Figure 5. It is interesting that the mean pulse fraction at the orbital phase 0.85 -0.99 was generally lower than that in other orbital phase for three energy bands, which is also consistent with the results reported by Endo et al (2002) and Nabizadeh et al (2019). The neutron star system approaching the periastron showed the X-ray flares, so that the pulse fraction may depend on the X-ray luminosity.…”

Section: Timing Analysis and Pulse Profilessupporting

confidence: 88%

Timing and spectral variability of high mass X-ray pulsar GX 301--2 over orbital phases observed by Insight-HXMT

Ding,

Wang,

Epili

et al. 2021

Preprint

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We report the orbital X-ray variability of high mass X-ray binary (HMXB) GX 301-2. GX 301-2 undergone a spin up process in 2018-2020 with the period evolving from ∼ 685 s to 670 s. The energy resolved pulse-profiles of the pulsar in 1-60 keV varied from single peaked and sinusoidal shapes to multi-peaked across different orbital phases. Pulse fractions evolving over orbit had negative correlations with the X-ray flux. The broad-band X-ray energy spectrum of the pulsar can be described with a partial covering negative positive cutoff power-law continuum model. Near the periastron passage of the pulsar we found a strong variation in the additional column density (NH 2 ), which correlated with variation of the flux. Curves of growth for both Fe Kα and Fe Kβ lines were plotted to investigate the distribution of matter around neutron star. We have also found the evidence of two cyclotron absorption lines in the phase-averaged spectra in GX 301-2, with one line of 30-42 keV and the other line varying in 48-56 keV. Both two line's centroid energies show the similar relationship with X-ray luminosity: positive correlation in lower luminosity range, and negative relation above a critical luminosity of 10 37 ergs −1 . We estimated the surface magnetic field of the neutron star in GX 301-2 at ∼ (0.5 − 2) × 10 13 G. Two cyclotron line energies have a nearly fixed ratio of ∼ 1.63 while having a low strength ratio (∼ 0.05), suggesting that these two features may actually be one line.

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Section: Timing Analysis and Pulse Profilessupporting

confidence: 88%

Timing and spectral variability of high mass X-ray pulsar GX 301--2 over orbital phases observed by Insight-HXMT

Ding,

Wang,

Epili

et al. 2021

Preprint

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“…The existence of an accretion disk was also reported for other SgXBs, such as OAO 1657-415 (Jenke et al 2012;Taani et al 2019), GX 301-2 (Nabizadeh et al 2019), and Cen X-3 (Tsunemi et al 1996). These results show that disk accretion is happening, although not always, in wind-fed SgXBs.…”

Section: Discussionsupporting

confidence: 76%

Spectral evidence of an accretion disc in wind-fed X-ray pulsar Vela X-1 during an unusual spin-up period

Liao

Liu

Zheng

et al. 2020

Monthly Notices of the Royal Astronomical Society

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In classical supergiant X-ray binaries (SgXBs), the Bondi-Hoyle-Lyttleton wind accretion was usually assumed, and the angular momentum transport to the accretors is inefficient. The observed spin-up/spin-down behavior of the neutron star in SgXBs is not well understood. In this paper, we report an extended low state of Vela X-1 (at orbital phases 0.16-0.2), lasting for at least 30 ks, observed with Chandra during the onset of an unusual spin-up period. During this low state, the continuum fluxes dropped by a factor of 10 compared to the preceding flare period, and the continuum pulsation almost disappeared. Meanwhile, the Fe Kα fluxes of the low state were similar to the preceding flare period, leading to an Fe Kα equivalent width (EW) of 0.6 keV, as high as the Fe Kα EW during the eclipse phase of Vela X-1. Both the pulsation cessation and the high Fe Kα EW indicate an axisymmetric structure with a column density larger than 10 24 cm −2 on a spatial scale of the accretion radius of Vela X-1. These phenomena are consistent with the existence of an accretion disk that leads to the following spin-up of Vela X-1. It indicates that disk accretion, although not always, does occur in classical wind-fed SgXBs.

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“…The flux was transformed to X-ray luminosity using three simultaneous observations by the Nuclear Spectroscopic Telescope Array (NuSTAR). In the full energy band, 3−79 keV, NuSTAR observed absorbed luminosities of (0.24 ± 0.07) × 10 37 , (0.4 ± 0.1) × 10 37 and (1.2 ± 0.3) × 10 37 erg s −1 on MJD 56959, 57299 and 58545 (Nabizadeh et al 2019). The luminosities corrected for absorption in the interstellar medium and in the system are consistently about 20 per cent higher.…”

Section: Data Analysis and Resultsmentioning

confidence: 94%

“…To investigate the orbital dependence of spin frequency changes we used data from Fermi Gamma-Ray Burst Monitor (GBM) Pulsar Project 1 from MJD 54693 to 58575. The chosen GBM spin history shows three distinct spin-up episodes (Finger et al 2010;Nabizadeh et al 2019) which were excluded from our data. GBM measures the spin frequency on ∼ 2 day intervals, and the frequency values of two consecutive points were compared to calculate the frequency derivatives.…”

Section: Data Analysis and Resultsmentioning

confidence: 99%

Discovery of a retrogradely rotating neutron star in the X-ray pulsar GX 301–2

Mönkkönen

Doroshenko

Tsygankov

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We report on the analysis of the spin evolution of a slow X-ray pulsar GX 301−2 along the orbit using long-term monitoring by Fermi/GBM. Based on the observationally confirmed accretion scenario and an analytical model for the accretion of angular momentum we demonstrate that in this system, the neutron star spins retrogradely, that is, in a direction opposite to the orbital motion. This first-of-a-kind discovery of such a system proves the principal possibility of retrograde rotation in accreting systems with suitable accretion torque, and might have profound consequences for our understanding of the spin evolution of X-ray pulsars, estimates of their initial spin periods, and the ultimate result of their evolution.

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NuSTAR observations of wind-fed X-ray pulsar GX 301–2 during unusual spin-up event

Cited by 28 publications

References 50 publications

Timing and spectral variability of high mass X-ray pulsar GX 301--2 over orbital phases observed by Insight-HXMT

Timing and spectral variability of high mass X-ray pulsar GX 301--2 over orbital phases observed by Insight-HXMT

Spectral evidence of an accretion disc in wind-fed X-ray pulsar Vela X-1 during an unusual spin-up period

Discovery of a retrogradely rotating neutron star in the X-ray pulsar GX 301–2

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