Thermonuclear (Type I) X-Ray Bursts Observed by the Rossi X-Ray Timing Explorer
01 Dec 2008-Astrophysical Journal Supplement Series (American Astronomical Society)-Vol. 179, Iss: 2, pp 360-422
TL;DR: In this article, a sample of 1187 thermonuclear (type I) X-ray bursts from observations of 48 accreting neutron stars was assembled, spanning more than 10 years.
Abstract: We have assembled a sample of 1187 thermonuclear (type I) X-ray bursts from observations of 48 accreting neutron stars by the Rossi X-ray Timing Explorer, spanning more than 10 years. The sample contains examples of two of the three theoretical ignition regimes (confirmed via comparisons with numerical models) and likely examples of the third. We present a detailed analysis of the variation of the burst profiles, energetics, recurrence times, presence of photospheric radius expansion, and presence of burst oscillations, as a function of accretion rate. We estimated the distance for 35 sources exhibiting radius-expansion bursts, and found that the peak flux of such bursts varies typically by 13%. We classified sources into two main groups based on the burst properties: (1) both long and short bursts (indicating mixed H/He accretion), and (2) consistently short bursts (primarily He accretion), and we calculated the mean burst rate as a function of accretion rate for the two groups. The decrease in burst rate observed at > 0.06dot MEdd (~2 × 10^37 ergs s^−1) is associated with a transition in the persistent spectral state and (as has been suggested previously) may be related to the increasing role of steady He burning. We found many examples of bursts with recurrence times <30 minutes, including burst triplets and even quadruplets. We describe the oscillation amplitudes for 13 of the 16 burst oscillation sources, as well as the stages and properties of the bursts in which the oscillations are detected. The burst properties are correlated with the burst oscillation frequency; sources spinning at <400 Hz generally have consistently short bursts, while the more rapidly spinning systems have both long and short bursts. This correlation suggests either that shear-mediated mixing dominates the burst properties, or alternatively that the nature of the mass donor (and hence the evolutionary history) has an influence on the long-term spin evolution.
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Kavli Institute for Theoretical Physics1, University of Bonn2, University of California, Berkeley3, University of California, Santa Barbara4, University of Nice Sophia Antipolis5, Arizona State University6, Netherlands Institute for Space Research7, University of Wisconsin-Madison8, University of Alabama9
TL;DR: Modules for Experiments in Stellar Astrophysics (MESA) as discussed by the authors can now simultaneously evolve an interacting pair of differentially rotating stars undergoing transfer and loss of mass and angular momentum, greatly enhancing the prior ability to model binary evolution.
Abstract: We substantially update the capabilities of the open-source software instrument Modules for Experiments in Stellar Astrophysics (MESA). MESA can now simultaneously evolve an interacting pair of differentially rotating stars undergoing transfer and loss of mass and angular momentum, greatly enhancing the prior ability to model binary evolution. New MESA capabilities in fully coupled calculation of nuclear networks with hundreds of isotopes now allow MESA to accurately simulate advanced burning stages needed to construct supernova progenitor models. Implicit hydrodynamics with shocks can now be treated with MESA, enabling modeling of the entire massive star lifecycle, from pre-main sequence evolution to the onset of core collapse and nucleosynthesis from the resulting explosion. Coupling of the GYRE non-adiabatic pulsation instrument with MESA allows for new explorations of the instability strips for massive stars while also accelerating the astrophysical use of asteroseismology data. We improve treatment of mass accretion, giving more accurate and robust near-surface profiles. A new MESA capability to calculate weak reaction rates "on-the-fly" from input nuclear data allows better simulation of accretion induced collapse of massive white dwarfs and the fate of some massive stars. We discuss the ongoing challenge of chemical diffusion in the strongly coupled plasma regime, and exhibit improvements in MESA that now allow for the simulation of radiative levitation of heavy elements in hot stars. We close by noting that the MESA software infrastructure provides bit-for-bit consistency for all results across all the supported platforms, a profound enabling capability for accelerating MESA's development.
2,166 citations
Cites background or methods from "Thermonuclear (Type I) X-Ray Bursts..."
...Time resolved spectra were binned during the bursts’ rise time and decay (Galloway et al. 2008; Zamfir et al. 2012)....
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...…et al. 2006), the spatial distribution of burning on the surface of the NS (Bildsten 1995), the type of burning that occurs between bursts (Galloway et al. 2008) as well as possibly other conditions, for instance “superbursts” where carbon, rather than H/He, burns (Cumming & Bildsten…...
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...GS 1826-24 has been studied by the Rossi X-Ray Timing Explorer (RXTE) over several years (Galloway et al. 2004, 2008)....
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Kavli Institute for Theoretical Physics1, University of Bonn2, University of California, Berkeley3, University of California, Santa Barbara4, University of Nice Sophia Antipolis5, Arizona State University6, Netherlands Institute for Space Research7, University of Wisconsin-Madison8, University of Alabama9
TL;DR: Modules for Experiments in Stellar Astrophysics (MESA) as discussed by the authors can now simultaneously evolve an interacting pair of differentially rotating stars undergoing transfer and loss of mass and angular momentum, greatly enhancing the prior ability to model binary evolution.
Abstract: We substantially update the capabilities of the open-source software instrument Modules for Experiments in Stellar Astrophysics (MESA). MESA can now simultaneously evolve an interacting pair of differentially rotating stars undergoing transfer and loss of mass and angular momentum, greatly enhancing the prior ability to model binary evolution. New MESA capabilities in fully coupled calculation of nuclear networks with hundreds of isotopes now allow MESA to accurately simulate advanced burning stages needed to construct supernova progenitor models. Implicit hydrodynamics with shocks can now be treated with MESA, enabling modeling of the entire massive star lifecycle, from pre-main sequence evolution to the onset of core collapse and nucleosynthesis from the resulting explosion. Coupling of the GYRE non-adiabatic pulsation instrument with MESA allows for new explorations of the instability strips for massive stars while also accelerating the astrophysical use of asteroseismology data. We improve treatment of mass accretion, giving more accurate and robust near-surface profiles. A new MESA capability to calculate weak reaction rates "on-the-fly" from input nuclear data allows better simulation of accretion induced collapse of massive white dwarfs and the fate of some massive stars. We discuss the ongoing challenge of chemical diffusion in the strongly coupled plasma regime, and exhibit improvements in MESA that now allow for the simulation of radiative levitation of heavy elements in hot stars. We close by noting that the MESA software infrastructure provides bit-for-bit consistency for all results across all the supported platforms, a profound enabling capability for accelerating MESA's development.
1,401 citations
TL;DR: In this paper, the authors summarize the current knowledge of neutron-star masses and radii and show that the distribution of neutron star masses is much wider than previously thought, with three known pulsars now firmly in the 1.9-2.0-M⊙ mass range.
Abstract: We summarize our current knowledge of neutron-star masses and radii. Recent instrumentation and computational advances have resulted in a rapid increase in the discovery rate and precise timing of radio pulsars in binaries in the past few years, leading to a large number of mass measurements. These discoveries show that the neutron-star mass distribution is much wider than previously thought, with three known pulsars now firmly in the 1.9–2.0-M⊙ mass range. For radii, large, high-quality data sets from X-ray satellites as well as significant progress in theoretical modeling led to considerable progress in the measurements, placing them in the 10–11.5-km range and shrinking their uncertainties, owing to a better understanding of the sources of systematic errors. The combination of the massive-neutron-star discoveries, the tighter radius measurements, and improved laboratory constraints of the properties of dense matter has already made a substantial impact on our understanding of the composition and bulk p...
1,082 citations
TL;DR: In this paper, the authors summarize the current knowledge of neutron star masses and radii and show that the neutron star mass distribution is much wider than previously thought, with 3 known pulsars now firmly in the 1.9-2.0 Msun mass range.
Abstract: We summarize our current knowledge of neutron star masses and radii. Recent instrumentation and computational advances have resulted in a rapid increase in the discovery rate and precise timing of radio pulsars in binaries in the last few years, leading to a large number of mass measurements. These discoveries show that the neutron star mass distribution is much wider than previously thought, with 3 known pulsars now firmly in the 1.9-2.0 Msun mass range. For radii, large, high quality datasets from X-ray satellites as well as significant progress in theoretical modeling led to considerable progress in the measurements, placing them in the 9.9-11.2 km range and shrinking their uncertainties due to a better understanding of the sources of systematic errors. The combination of the massive neutron star discoveries, the tighter radius measurements, and improved laboratory constraints of the properties of dense matter has already made a substantial impact on our understanding of the composition and bulk properties of cold nuclear matter at densities higher than that of the atomic nucleus, a major unsolved problem in modern physics.
906 citations
TL;DR: In this paper, an empirical dense matter equation of state (EOS) from a heterogeneous data set of six neutron stars was derived from a Markov chain Monte Carlo algorithm within a Bayesian framework to determine nuclear parameters such as the incompressibility and density dependence of the bulk symmetry energy.
Abstract: We determine an empirical dense matter equation of state (EOS) from a heterogeneous data set of six neutron stars: three Type-I X-ray bursters with photospheric radius expansion, studied by ?zel et?al., and three transient low-mass X-ray binaries. We critically assess the mass and radius determinations from the X-ray burst sources and show explicitly how systematic uncertainties, such as the photospheric radius at touchdown, affect the most probable masses and radii. We introduce a parameterized EOS and use a Markov chain Monte Carlo algorithm within a Bayesian framework to determine nuclear parameters such as the incompressibility and the density dependence of the bulk symmetry energy. Using this framework we show, for the first time, that these parameters, predicted solely on the basis of astrophysical observations, all lie in ranges expected from nuclear systematics and laboratory experiments. We find significant constraints on the mass-radius relation for neutron stars, and hence on the pressure-density relation of dense matter. The predicted symmetry energy and the EOS near the saturation density are soft, resulting in relatively small neutron star radii around 11-12?km for M = 1.4 M ?. The predicted EOS stiffens at higher densities, however, and our preferred model for X-ray bursts suggests that the neutron star maximum mass is relatively large, 1.9-2.2 M ?. Our results imply that several commonly used equations of state are inconsistent with observations.
832 citations
Cites background from "Thermonuclear (Type I) X-Ray Bursts..."
...Hydrogen mass fraction:Galloway et al. (2008) noted that EXO 1745–248 has exhibitedlong Type I bursts with estimated values of ∫ dt Fpersistent/ ∫ dt Fburst ≈ GM/R/Enuc ≈ 20–46....
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...Hydrogen mass fraction: The bursts in 4U 1608–522 suggest an accretion rate in of 3%-5% ṀEdd, which suggests H ignition (Galloway et al. 2008); the brighter bursts from this system are of short duration, however, so it is likely that much of the hydrogen is consumedvia the HCNO cycle prior to He…...
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...Galloway et al. (2008) examined a large sample of PRE bursts....
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...About 20% of X-ray bursts show evidence for photospheric radius expansion (hereafter PRE; Galloway et al. 2008)....
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...We fitted each burst spectrum with a blackbody model multiplied by a low-energy cutoff, representing interstellar absorption using the cross-sections of Morrison & McCammon (1983) and solar abundances from Anders & Ebihara (1982)....
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01 Jan 1961
TL;DR: The major Reformation of the 16th century is represented in the Netherlands most clearly by Cassander, Coornhert and Lipsius as mentioned in this paper, who follow one another chronologically in this order and they show in that order an increasing subjection to the influence of the Classics and a reduced need of supernatural salvation in the christian sense.
Abstract: What I have called the major Reformation of the 16th century is represented in the Netherlands most clearly by Cassander, Coornhert and Lipsius. They follow one another chronologically in this order and they show in that order an increasing subjection to the influence of the Classics and a reduced need of supernatural salvation in the christian sense. The first of these men is a Christian carrying out humanistic studies, while the third is a humanistic philosopher who is a faithful Christian as well.
1,812 citations
TL;DR: In this article, Buchdahl and Tolman showed that the moment of inertia and the binding energy of a neutron star are nearly universal functions of the star's compactness, which can be understood by considering two analytic, yet realistic, solutions of Einstein's equations.
Abstract: The structure of neutron stars is considered from theoretical and observational perspectives We demonstrate an important aspect of neutron star structure: the neutron star radius is primarily determined by the behavior of the pressure of matter in the vicinity of nuclear matter equilibrium density In the event that extreme softening does not occur at these densities, the radius is virtually independent of the mass and is determined by the magnitude of the pressure For equations of state with extreme softening or those that are self-bound, the radius is more sensitive to the mass Our results show that in the absence of extreme softening, a measurement of the radius of a neutron star more accurate than about 1 km will usefully constrain the equation of state We also show that the pressure near nuclear matter density is primarily a function of the density dependence of the nuclear symmetry energy, while the nuclear incompressibility and skewness parameters play secondary roles In addition, we show that the moment of inertia and the binding energy of neutron stars, for a large class of equations of state, are nearly universal functions of the star's compactness These features can be understood by considering two analytic, yet realistic, solutions of Einstein's equations, by, respectively, Buchdahl and Tolman We deduce useful approximations for the fraction of the moment of inertia residing in the crust, which is a function of the stellar compactness and, in addition, the pressure at the core-crust interface
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