Rapid X-ray variability properties during the unusual very hard state in neutron-star low-mass X-ray binaries

Wijnands, Rudy; Parikh, A. S.; Altamirano, D.; Homan, J.; Degenaar, N.

doi:10.1093/mnras/stx2006

Cited by 19 publications

(34 citation statements)

References 57 publications

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“…They find N H = 0.24 × 10 22 cm −2 which is also consistent. This supports the notion that the emission in our XRT data is not due to the burst and likely an expression of the strong variability inferred by Wijnands et al (2017). We, therefore, refrain from further discussing this event.…”

Section: Burst From Igr J18245-2452supporting

confidence: 87%

Searching for the most powerful thermonuclear X-ray bursts with the Neil Gehrels Swift Observatory

Zand¹,

Kries²,

Palmer

et al. 2019

A&A

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We searched for thermonuclear X-ray bursts from Galactic neutron stars in all event mode data of the Neil Gehrels Swift Observatory collected until March 31, 2018. In particular, we are interested in the intermediate-duration bursts (shell flashes fueled by thick helium piles) with the ill-understood phenomenon of strong flux fluctuations. Nine such bursts have been discussed in the literature to date. Swift is particularly suitable for finding additional examples. We find and list a total of 134 X-ray bursts; 44 are detected with BAT only, 41 with XRT only, and 49 with both. Twenty-eight bursts involve automatic slews. We find 12 intermediate-duration bursts, all detected in observations involving automatic slews. Five show remarkably long Eddington-limited phases in excess of 200 s. Five show fluctuations during the decay phase; four of which are first discussed in the present study. We discuss the general properties of the fluctuations, considering also 7 additional literature cases. In general two types of fluctuations are observed: fast ones, with a typical timescale of 1 s and up and downward fluctuations of up to 70%, and slow ones, with a typical timescale of 1 min and only downward fluctuations of up to 90%. The latter look like partial eclipses because the burst decay remains visible in the residual emission. We revisit the interpretation of this phenomenon in the context of the new data set and find that it has not changed fundamentally despite the expanded data set. It is thought to be due to a disturbance of the accretion disk by outflowing matter and photons, causing obscuration and reflection due to Thompson scattering in an orbiting highly ionized cloud or structure above or below the disk. We discuss in detail the most pronounced burster SAX J1712.6-3739. One of the bursts from this source is unusual in that it lasts longer than 5600 s, but does not appear to be a superburst.

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Section: Burst From Igr J18245-2452supporting

confidence: 87%

Searching for the most powerful thermonuclear X-ray bursts with the Neil Gehrels Swift Observatory

Zand¹,

Kries²,

Palmer

et al. 2019

A&A

Self Cite

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“…Ten neutron stars have been monitored after accretion outbursts with the aim to study how their accretion-heated crusts cool in quiescence (see Wijnands et al 2017, for a review). The high temperatures observed within the first few hundred days of quiescence require an additional source of energy to heat the crust (e.g.…”

mentioning

confidence: 99%

Crust cooling of the neutron star in Aql X-1: different depth and magnitude of shallow heating during similar accretion outbursts

Degenaar

Ootes

Page

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The structure and composition of the crust of neutron stars plays an important role in their thermal and magnetic evolution, hence in setting their observational properties. One way to study the properties of the crust of a neutron star, is to measure how it cools after it has been heated during an accretion outburst in a low-mass X-ray binary (LMXB). Such studies have shown that there is a tantalizing source of heat, of currently unknown origin, that is located in the outer layers of the crust and has a strength that varies between different sources and different outbursts. With the aim of understanding the mechanism behind this "shallow heating", we present Chandra and Swift observations of the neutron star LMXB Aql X-1, obtained after its bright 2016 outburst. We find that the neutron star temperature was initially much lower, and started to decrease at much later time, than observed after the 2013 outburst of the source, despite the fact that the properties of the two outbursts were very similar. Comparing our data to thermal evolution simulations, we infer that the depth and magnitude of shallow heating must have been much larger during the 2016 outburst than during the 2013 one. This implies that basic neutron star parameters that remain unchanged between outbursts, do not play a strong role in shallow heating. Furthermore, it suggests that outbursts with a similar accretion morphology can give rise to very different shallow heating. We also discuss alternative explanations for the observed difference in quiescent evolution after the 2016 outburst.

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“…This work reports on all three spectral states in a broad energy range (0.8-200.0 keV) and, in particular, the only data set that has high-quality broadband X-ray data available in the peculiar spectral/timing state, i.e., the so-called very hard state by Parikh et al (2017) and Wijnands et al (2017). Both the persistent and X-ray burst emission have been analyzed in this work.…”

Section: Resultsmentioning

confidence: 99%

“…The mechanism for producing such a hard spectrum remained unclear. Wijnands et al (2017) used two XMM-Newton observations to study the rapid variability properties of 1RXSJ180408.9−342058: one obtained early during the outburst in March 6 (see also Ludlam et al 2016) and one just before the transition to the soft state on April 1. These authors reported the source exhibited an unusually strong noise component, particularly during the first XMM-Newton observation.…”

Section: Introductionmentioning

confidence: 99%

Quasi-simultaneous INTEGRAL, SWIFT, and NuSTAR Observations of the New X-Ray Clocked Burster 1RXS J180408.9-342058

Fiocchi

Bazzano

Bruni

et al. 2019

ApJ

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We report the quasi-simultaneous INTEGRAL, SWIFT, and NuSTAR observations showing spectral state transitions in the neutron star low-mass X-ray binary 1RXSJ180408.9−342058 during its 2015 outburst. We present results of the analysis of high-quality broad energy band (0.8-200 keV) data in three different spectral states: high/soft, low/very-hard, and transitional state. The broadband spectra can be described in general as the sum of thermal Comptonization and reflection due to illumination of an optically thick accretion disk. During the high/soft state, blackbody emission is generated from the accretion disk and the surface of the neutron star. This emission, measured at a temperature of kT bb ∼1.2 keV, is then Comptonized by a thick corona with an electron temperature of ∼2.5keV. For the transitional and low/very-hard state, the spectra are successfully explained with emission from a double Comptonizing corona. The first component is described by thermal Comptonization of seed disk/ neutron star photons (kT bb ∼1.2 keV) by a cold corona cloud with kT e ∼8-10 keV, while the second one originates from lower temperature blackbody photons (kT bb 0.1 keV) Comptonized by a hot corona (kT e ∼ 35 keV). Finally, from NuSTAR observations, there is evidence that the source is a new clocked burster. The average time between two successive X-ray bursts corresponds to ∼7.9 and ∼4.0 ks when the persistent emission decreases by a factor of ∼2, moving from a very hard to transitional state. The accretion rate (☉´-M 4 10 yr 9 1) and the decay time of the X-ray bursts longer than ∼30 s suggest that the thermonuclear emission is due to mixed H/He burning triggered by thermally unstable He ignition. Unified Astronomy Thesaurus concepts: Binary stars (154); Low-mass X-ray binary stars (939); X-ray astronomy (1810); Gamma-ray bursters (1878); Gamma-ray astronomy (628)

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Rapid X-ray variability properties during the unusual very hard state in neutron-star low-mass X-ray binaries

Cited by 19 publications

References 57 publications

Searching for the most powerful thermonuclear X-ray bursts with the Neil Gehrels Swift Observatory

Searching for the most powerful thermonuclear X-ray bursts with the Neil Gehrels Swift Observatory

Crust cooling of the neutron star in Aql X-1: different depth and magnitude of shallow heating during similar accretion outbursts

Quasi-simultaneous INTEGRAL, SWIFT, and NuSTAR Observations of the New X-Ray Clocked Burster 1RXS J180408.9-342058

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