Photodisintegration-triggered Nuclear Energy Release in Superbursts

Schatz, H.; Bildsten, Lars; Cumming, Andrew

doi:10.1086/368107

Cited by 76 publications

(86 citation statements)

References 23 publications

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“…However, there are problems with this scenario: (1) producing enough C during H/He burning (e.g., Schatz et al 2003;Woosley et al 2004), (2) heating the neutron star ocean strongly enough to reach ignition temperature (e.g., Cumming et al 2006;Keek et al 2008), and (3) accreting rapidly enough for the C to survive to the ignition depth (Cumming & Bildsten 2001;Cumming et al 2006).…”

Section: The Superburstmentioning

confidence: 99%

What ignites on the neutron star of 4U 0614+091?

Kuulkers¹,

Zand

Atteia

et al. 2010

A&A

103

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The low-mass X-ray binary 4U 0614+091 is a source of sporadic thermonuclear (type I) X-ray bursts. We find bursts with a wide variety of characteristics in serendipitous wide-field X-ray observations by the WATCH on EURECA, the ASM on RXTE, the WFCs on BeppoSAX, the FREGATE on HETE-2, the IBIS/ISGRI on INTEGRAL, and the BAT on Swift, as well as pointed observations with the PCA and HEXTE on RXTE. Most of the bursts are bright, i.e., they reach a peak flux of about 15 Crab, but a few are weak and only reach a peak flux below a Crab. One of the bursts shows a very strong photospheric radius-expansion phase. This allows us to evaluate the distance to the source, which we estimate to be 3.2 kpc. The burst durations vary generally from about 10 s to 5 min. However, after one of the intermediate-duration bursts, a faint tail is seen to at least about 2.4 h after the start of the burst. One very long burst was observed, which lasted for several hours. This superburst candidate was followed by a normal type-I burst only 19 days later. This is, to our knowledge, the shortest burst-quench time among the superbursters. The observation of a superburst in this system is difficult to reconcile if the system is accreting at about 1% of the Eddington limit. We describe the burst properties in relation to the persistent emission. No strong correlations are apparent, except that the intermediate-duration bursts occurred when 4U 0614+091's persistent emission was lowest and calm, and when bursts were infrequent (on average roughly one every month to 3 months). The average burst rate increased significantly after this period. The maximum average burst recurrence rate is about once every week to 2 weeks. The burst behaviour may be partly understood if there is at least an appreciable amount of helium present in the accreted material from the donor star. If the system is an ultra-compact X-ray binary with a CO white-dwarf donor, as has been suggested, this is unexpected. If the bursts are powered by helium, we find that the energy production per accumulated mass is about 2.5 times less than expected for pure helium matter.

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Section: The Superburstmentioning

confidence: 99%

What ignites on the neutron star of 4U 0614+091?

Kuulkers¹,

Zand

Atteia

et al. 2010

A&A

103

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“…[1][2][3][4]) as well as deep crustal heating of neutron stars in X-ray transients (e.g., Refs. [4][5][6][7]).…”

Section: Introductionmentioning

confidence: 99%

Neutron degeneracy and plasma physics effects on radiative neutron captures in neutron star crust

et al. 2012

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We consider the astrophysical reaction rates for radiative neutron capture reactions (n, γ) in the crust of a neutron star. The presence of degenerate neutrons at high densities (mainly in the inner crust) can drastically affect the reaction rates. Standard rates assuming a Maxwell-Boltzmann distribution for neutrons can underestimate the rates by several orders of magnitude. We derive simple analytical expressions for reaction rates at a variety of conditions with account for neutron degeneracy. We also discuss the plasma effects on the outgoing radiative transition channel in neutron radiative capture reactions and show that these effects can also increase the reaction rates by a few orders of magnitude. In addition, using detailed balance, we analyze the effects of neutron degeneracy and plasma physics on reverse (γ, n) photodisintegration. We discuss the dependence of the reaction rates on temperature and neutron chemical potential and outline the efficiency of these reactions in the neutron star crust.

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“…Accretion drives various nuclear burning processes near the neutron star surface that depend on the accretion rate and the composition of accreted material (Keek et al 2014). Nuclear burning regimes include stable hydrogen burning (Schatz et al 1999), unstable hydrogen burning in Type I X-ray bursts (Schatz et al 1998;Woosley et al 2004;Parikh et al 2013), unstable carbon burning in superbursts (Strohmayer & Brown 2002;Schatz et al 2003;Keek & Heger 2011), and each burning regime produces a characteristic nuclear abundance "ash" distribution. Further accretion compresses nuclear burning ashes deeper in the neutron star and drives further nuclear reaction sequences (Sato 1979) that replace the neutron star crust with processed ashes.…”

mentioning

confidence: 99%

Constraints on Bygone Nucleosynthesis of Accreting Neutron Stars

Meisel

Deibel

2017

ApJ

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Nuclear burning near the surface of an accreting neutron star produces ashes that, when compressed deeper by further accretion, alter the star's thermal and compositional structure. Bygone nucleosynthesis can be constrained by the impact of compressed ashes on the thermal relaxation of quiescent neutron star transients. In particular, Urca cooling nuclei pairs in nuclear burning ashes, which cool the neutron star crust via neutrino emission from e − -capture/β − -decay cycles, provide signatures of prior nuclear burning over the ∼century timescales it takes to accrete to the e − -capture depth of the strongest cooling pairs. Using crust cooling models of the accreting neutron star transient MAXI J0556-332, we show that this source likely lacked Type I X-ray bursts and superbursts 120 years ago. Reduced nuclear physics uncertainties in rp-process reaction rates and e − -capture weak-transition strengths for low-lying transitions will improve nucleosynthesis constraints using this technique.

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Photodisintegration-triggered Nuclear Energy Release in Superbursts

Cited by 76 publications

References 23 publications

What ignites on the neutron star of 4U 0614+091?

What ignites on the neutron star of 4U 0614+091?

Neutron degeneracy and plasma physics effects on radiative neutron captures in neutron star crust

Constraints on Bygone Nucleosynthesis of Accreting Neutron Stars

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