Achromatic late-time variability in thermonuclear X-ray bursts

Zand, J. J. M. in ’t; Ballantyne, D. R.

doi:10.1051/0004-6361/201015556

Cited by 33 publications

(8 citation statements)

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“…A remarkably similar event was observed by in 't Zand et al (2011) in the accreting neutron star in 2S 0918-549. After an X-ray burst, strong (87% ± 1% peak-to-peak amplitude) achromatic fluctuations were seen as a transient phenomenon.…”

Section: Discussionsupporting

confidence: 81%

“…picture of the evolution in U Sco (see Figure 1 in in 't Zand et al 2011). in't Zand et al (2011 speculated that the fluctuations were due to Thompson scattering by inhomogeneities in a resettling accretion disk that was disrupted by the effects of super-Eddington fluxes, much like in U Sco where the blast wave has destroyed the accretion disk (Drake & Orlando 2010).…”

Section: Discussionmentioning

confidence: 99%

“…The volume of a flared disk rim is of the order of 10 34 cm 3 , e.g., Drake & Orlando (2010). For a mass-loss rate of ∼10 −7 M yr −1 (e.g., Hachisu et al 2000) and a buildup time of ∼5 days, the accretion disk rim density is of order 3 × 10 14 cm −3 . For a path length through the gas of ∼0.1 R , the column density is of order 10 24 cm −2 .…”

Section: Light Curve Modelmentioning

confidence: 99%

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FROM X-RAY DIPS TO ECLIPSE: WITNESSING DISK REFORMATION IN THE RECURRENT NOVA U Sco

Ness

Schaefer

Dobrotka

et al. 2011

ApJ

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The tenth recorded outburst of the recurrent eclipsing nova U Sco was observed simultaneously in X-ray, UV, and optical by XMM-Newton on days 22.9 and 34.9 after the outburst. Two full passages of the companion in front of the nova ejecta were observed, as was the reformation of the accretion disk. On day 22.9, we observed smooth eclipses in UV and optical but deep dips in the X-ray light curve that disappeared by day 34.9, yielding clean eclipses in all bands. X-ray dips can be caused by clumpy absorbing material that intersects the line of sight while moving along highly elliptical trajectories. Cold material from the companion could explain the absence of dips in UV and optical light. The disappearance of X-ray dips before day 34.9 implies significant progress in the formation of the disk. The X-ray spectra contain photospheric continuum emission plus strong emission lines, but no clear absorption lines. Both continuum and emission lines in the X-ray spectra indicate a temperature increase from day 22.9 to day 34.9. We find clear evidence in the spectra and light curves for Thompson scattering of the photospheric emission from the white dwarf. Photospheric absorption lines can be smeared out during scattering in a plasma of fast electrons. We also find spectral signatures of resonant line scattering that lead to the observation of the strong emission lines. Their dominance could be a general phenomenon in high-inclination systems such as Cal 87.

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Section: Discussionsupporting

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Section: Light Curve Modelmentioning

confidence: 99%

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FROM X-RAY DIPS TO ECLIPSE: WITNESSING DISK REFORMATION IN THE RECURRENT NOVA U Sco

Ness

Schaefer

Dobrotka

et al. 2011

ApJ

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“…Perhaps the Eddington limited flux from the neutron star during superexpansion as well as the long period of moderate radius expansion prevent an increase in the accretion rate (e.g., Ballantyne & Everett 2005). Both the occurrence of superexpansion, during which the flux drops below the presuperburst level, and of variability in the tail (achromatic in the PCA band; see Kuulkers 2004;in 't Zand et al 2011) may be indications of mass outflow during the 4U 1820-30 superburst. The 4U 1636-536 superburst lacks both features.…”

Section: Superburst Increases Persistent Emissionmentioning

confidence: 99%

Characterizing the Evolving X-Ray Spectral Features During a Superburst From 4u 1636-536

Keek

Ballantyne

Kuulkers

et al. 2014

ApJ

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Recent studies have shown that runaway thermonuclear burning of material accreted onto neutron stars, i.e., Type I X-ray bursts, may affect the accretion disk. We investigate this by performing a detailed time-resolved spectral analysis of the superburst from 4U 1636-536 observed in 2001 with the Rossi X-Ray Timing Explorer. Superbursts are attributed to the thermonuclear burning of carbon, and are approximately 1000 times more energetic than the regular short Type I bursts. This allows us to study detailed spectra for over 11 ks, compared to, at most, 100 s for regular bursts. A feature is present in the superburst spectra around 6.4 keV that is well fit with an emission line and an absorption edge, suggestive of reflection of the superburst off the accretion disk. The line and edge parameters evolve over time: the edge energy decreases from 9.4 keV at the peak to 8.1 keV in the tail, and both features become weaker in the tail. This is only the second superburst for which this has been detected and shows that this behavior is present even without strong radius expansion. Furthermore, we find the persistent flux more than doubles during the superburst and returns to the pre-superburst value in the tail. The combination of reflection features and increased persistent emission indicates that the superburst had a strong impact on the inner accretion disk and it emphasizes that X-ray bursts provide a unique probe of accretion physics.

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“…Such shells may have already been observed in some X-ray bursts (in't Zand et al 2011). A certain group of bursts indicate radiation-driven ejection of the neutron c 2015 The Authors star gaseous envelope, e.g., Tawara et al (1984); White & Angelini (2001); Wolff et al (2005). Our model is expected to be of particular interest for modelling these so called photospheric radius expansion (PRE) bursts (Lewin et al 1993).…”

Section: Introductionmentioning

confidence: 99%

Levitating atmospheres of Eddington-luminosity neutron stars

Wielgus

Sądowski

Kluźniak

et al. 2016

Mon. Not. R. Astron. Soc.

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We construct models of static, spherically symmetric shells supported by the radiation flux of a luminous neutron star in the Schwarzschild metric. The atmospheres are disconnected from the star and levitate above its surface. Gas pressure and density inversion appear in the inner region of these atmospheres, which is a purely relativistic phenomenon. We account for the scattering opacity dependence on temperature green by using the Klein-Nishina formula. The relativistic M 1 closure scheme for the radiation tensor provides a GR-consistent treatment of the photon flux and radiation tensor anisotropy. In this way we are able to address atmospheres of both large and moderate/low optical depths with the same set of equations. We discuss properties of the levitating atmospheres and find that they may indeed be optically thick, with the distance between star surface and the photosphere expanding as luminosity increases. These results may be relevant for the photosphereric radius expansion X-ray bursts.

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Achromatic late-time variability in thermonuclear X-ray bursts

Cited by 33 publications

References 50 publications

FROM X-RAY DIPS TO ECLIPSE: WITNESSING DISK REFORMATION IN THE RECURRENT NOVA U Sco

FROM X-RAY DIPS TO ECLIPSE: WITNESSING DISK REFORMATION IN THE RECURRENT NOVA U Sco

Characterizing the Evolving X-Ray Spectral Features During a Superburst From 4u 1636-536

Levitating atmospheres of Eddington-luminosity neutron stars

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