Magnetic Burial and the Harmonic Content of Millisecond Oscillations in Thermonuclear X‐Ray Bursts

Payne, D. J. B.; Melatos, A.

doi:10.1086/507589

Cited by 19 publications

(49 citation statements)

References 30 publications

(53 reference statements)

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“…belt) on the neutron star surfaces (e.g. Payne & Melatos 2006), higher local temperature (sufficient for ignition) near the magnetic poles, while ignition condition is not reached at rest of the stellar surface (Watts et al 2008), or something else. Whatever be the reason, the indication of burning in confined regions reported in this paper may have significant impact in understanding the accreting pulsars, burst oscillations, burst ignition conditions, surface magnetic field structure and its interaction with flame spreading, etc.…”

Section: Discussionmentioning

confidence: 99%

Thermonuclear X-ray bursts from the 401-Hz accreting pulsar IGR J17498−2921: indication of burning in confined regions

Chakraborty¹,

Bhattacharyya²

2012

Monthly Notices of the Royal Astronomical Society

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We use the 2011 Rossi X‐ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of the 401‐Hz accreting pulsar and burster IGR J17498−2921 to perform timing analysis and time‐resolved spectroscopy of 12 thermonuclear X‐ray bursts. We confirm previously reported burst oscillations from this source with a much higher significance (8.8σ). We note that the bursts can be divided into three groups: big photospheric radius expansion (PRE) bursts are about 10 times more luminous than medium bursts, while the latter are about 10 times more luminous than small bursts. The PCA field of view of these observations contains several known bursters, and hence some of the observed bursts might not be from IGR J17498−2921. The oscillations during big bursts at the known pulsar frequency show that these bursts were definitely from IGR J17498−2921. We find that at least several of the other bursts were also likely originated from IGR J17498−2921. Spectral analysis reveals that the luminosity differences among various bursts are primarily due to differences in normalizations, and not temperatures, even when we consider the effects of colour factor. This shows burning on a fraction of the stellar surface for those small and medium bursts, which originated from IGR J17498−2921. The low values of the upper limits of burst oscillation amplitude for these bursts suggest a small angle between the spin axis and the magnetic axis. We find indications of the PRE nature of a medium burst, which likely originated from IGR J17498−2921. If true, then, to the best of our knowledge, this is the first time that two PRE bursts with a peak count rate ratio of as high as ≈12 have been detected from the same source.

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Section: Discussionmentioning

confidence: 99%

Thermonuclear X-ray bursts from the 401-Hz accreting pulsar IGR J17498−2921: indication of burning in confined regions

Chakraborty¹,

Bhattacharyya²

2012

Monthly Notices of the Royal Astronomical Society

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“…Thus, it is plausible that we have observed a similar phenomenon. Following the theoretical work of and Payne & Melatos (2006), Galloway et al (2007a) suggest that the reason why the pulsations in HETE J1900.1Ϫ2455 sometimes "switch off" is because the magnetic field is buried by accreted material, and thus it cannot channel the flow which gives rise to the pulsations in the first place. In contrast with HETE J1900.1Ϫ245, these pulsations were not present at the beginning of the outburst but well into it.…”

Section: Discussionmentioning

confidence: 99%

Discovery of 442 Hz Pulsations from an X-Ray Source in the Globular Cluster NGC 6440

Gavriil

Strohmayer

Swank

et al. 2007

ApJ

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We report on the serendipitous discovery of a 442 Hz pulsar during a Rossi X-Ray Timing Explorer (RXTE) observation of the globular cluster NGC 6440. The oscillation is detected following a burstlike event which was decaying at the beginning of the observation. The timescale of the decay suggests we may have seen the tail end of a long-duration burst. Low-mass X-ray binaries (LMXBs) are known to emit thermonuclear X-ray bursts that are sometimes modulated by the spin frequency of the star, the so-called burst oscillations. The pulsations reported here are peculiar if interpreted as canonical burst oscillations. In particular, the pulse train lasted for ∼500 s, much longer than in standard burst oscillations. The signal was highly coherent and drifted down by ∼2 # 10 Ϫ3 Hz, much smaller than the ∼Hz drifts typically observed during normal bursts, but consistent with orbital motion of the neutron star. The pulsations are reminiscent of those observed during the much more energetic "superbursts"; however, the temporal profile and the energetics of the burst suggest that it was not the tail end nor the precursor feature of a superburst. Rather, it is likely that we caught a portion of an outburst from a new "intermittent" accreting millisecond pulsar, a phenomenon which until now had only been seen in HETE J1900.1Ϫ2455.

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“…Several mechanisms have been explored in the literature. Payne & Melatos (2006) suggested that magnetic field evolution on an accreting neutron star might result in the development of strong magnetic belts around the equator that would then impede north-south heat transport. On rapidly rotating stars, a reduction in Coriolis-mediated confinement as the flame front tries to cross the equator might result in stalling (Spitkovsky, Levin & Ushomirsky 2002, Zingale et al 2003).…”

Section: Spin Axismentioning

confidence: 99%

Thermonuclear Burst Oscillations

Watts

2012

Annu. Rev. Astron. Astrophys.

188

234

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Burst oscillations, a phenomenon observed in a significant fraction of Type I (thermonuclear) X-ray bursts, involve the development of highly asymmetric brightness patches in the burning surface layers of accreting neutron stars.Intrinsically interesting as nuclear phenomena, they are also important as probes of dense matter physics and the strong gravity, high magnetic field environment of the neutron star surface. Burst oscillation frequency is also used to measure stellar spin, and doubles the sample of rapidly rotating (above 10 Hz) accreting neutron stars with known spins. Although the mechanism remains mysterious, burst oscillation models must take into account thermonuclear flame spread, nuclear processes, rapid rotation, and the dynamical role of the magnetic field. This review provides a comprehensive summary of the observational properties of burst oscillations, an assessment of the status of the theoretical models that are being developed to explain them, and an overview of how they can be used to constrain neutron star properties such as spin, mass and radius.

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Magnetic Burial and the Harmonic Content of Millisecond Oscillations in Thermonuclear X‐Ray Bursts

Cited by 19 publications

References 30 publications

Thermonuclear X-ray bursts from the 401-Hz accreting pulsar IGR J17498−2921: indication of burning in confined regions

Thermonuclear X-ray bursts from the 401-Hz accreting pulsar IGR J17498−2921: indication of burning in confined regions

Discovery of 442 Hz Pulsations from an X-Ray Source in the Globular Cluster NGC 6440

Thermonuclear Burst Oscillations

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