Nuclear reactions on accreting neutron star surface

1985 ◽  
Vol 116 (1) ◽  
pp. 97-106
Author(s):  
K. Duorah ◽  
H. L. Duorah
Keyword(s):  
Neutron Star ◽  
Nuclear Reactions ◽  
Star Surface

scholarly journals Discovery of accretion-driven pulsations in the prolonged low X-ray luminosity state of the Be/X-ray transient GX 304–1

2018 ◽  
Vol 620 ◽  
pp. L13 ◽  
Author(s):  
A. Rouco Escorial ◽  
J. van den Eijnden ◽  
R. Wijnands
Keyword(s):  
Neutron Star ◽  
Stable State ◽  
Type I ◽  
X Ray ◽  
Monitoring Campaign ◽  
Spin Period ◽  
One Year ◽  
The Many ◽  
Low X ◽  
Star Surface

We present our Swift monitoring campaign of the slowly rotating neutron star Be/X-ray transient GX 304–1 (spin period of ∼275 s) when the source was not in outburst. We found that between its type I outbursts, the source recurrently exhibits a slowly decaying low-luminosity state (with luminosities of 1034 − 35 erg s−1). This behaviour is very similar to what has been observed for another slowly rotating system, GRO J1008–57. For that source, this low-luminosity state has been explained in terms of accretion from a non-ionised (“cold”) accretion disc. Because of the many similarities between the two systems, we suggest that GX 304–1 enters a similar accretion regime between its outbursts. The outburst activity of GX 304–1 ceased in 2016. Our continued monitoring campaign shows that the source is in a quasi-stable low-luminosity state (with luminosities a few factors lower than previously seen) for at least one year now. Using our NuSTAR observation in this state, we found pulsations at the spin period, demonstrating that the X-ray emission is due to accretion of matter onto the neutron star surface. If the accretion geometry during this quasi-stable state is the same as during the cold-disc state, then matter indeed reaches the surface (as predicted) during this later state. We discuss our results in the context of the cold-disc accretion model.

scholarly journals Thermal evolution and quiescent emission of transiently accreting neutron stars

2019 ◽  
Vol 629 ◽  
pp. A88 ◽  
Author(s):  
A. Y. Potekhin ◽  
A. I. Chugunov ◽  
G. Chabrier
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Nuclear Reactions ◽  
Thermal Evolution ◽  
Theoretical Models ◽  
Equilibrium Temperature ◽  
Theoretical Interpretation ◽  
Quasi Equilibrium ◽  
Accretion Rates

Aims. We study the long-term thermal evolution of neutron stars in soft X-ray transients (SXTs), taking the deep crustal heating into account consistently with the changes of the composition of the crust. We collect observational estimates of average accretion rates and thermal luminosities of such neutron stars and compare the theory with observations. Methods. We performed simulations of thermal evolution of accreting neutron stars, considering the gradual replacement of the original nonaccreted crust by the reprocessed accreted matter, the neutrino and photon energy losses, and the deep crustal heating due to nuclear reactions in the accreted crust. We also tested and compared results for different modern theoretical models. We updated a compilation of the observational estimates of the thermal luminosities in quiescence and average accretion rates in the SXTs and compared the observational estimates with the theoretical results. Results. The long-term thermal evolution of transiently accreting neutron stars is nonmonotonic. The quasi-equilibrium temperature in quiescence reaches a minimum and then increases toward the final steady state. The quasi-equilibrium thermal luminosity of a neutron star in an SXT can be substantially lower at the minimum than in the final state. This enlarges the range of possibilities for theoretical interpretation of observations of such neutron stars. The updates of the theory and observations leave the previous conclusions unchanged, namely that the direct Urca process operates in relatively cold neutron stars and that an accreted heat-blanketing envelope is likely present in relatively hot neutron stars in the SXTs in quiescence. The results of the comparison of theory with observations favor suppression of the triplet pairing type of nucleon superfluidity in the neutron-star matter.

scholarly journals A model of an ion-proton radio pulsar polar cap

2019 ◽  
Author(s):  
P B Jones
Keyword(s):  
Neutron Star ◽  
Surface Temperature ◽  
Emission Mechanism ◽  
Polar Cap ◽  
Ion Proton ◽  
S Period ◽  
Basic Equations ◽  
Radio Transients ◽  
Star Surface ◽  
Rotating Radio Transients

Abstract A number of previous papers have developed an ion-proton theory of the pulsar polar cap. The basic equations summarizing this are given here with the results of sets of model step-to-step calculations of pulse-precursor profiles. The nature of step-to-step profile variations is described by calculated phase-resolved modulation indices. The conditions under which nulls are present in step sequences are analysed. The change of mean null length with neutron-star surface temperature shows a pathway ending in emission similar to the Rotating Radio Transients. The model accommodates exceptional pulsars, the millisecond pulsars (in principle), and the 8.5 s period PSR J2144-3933. These are considered separately and their emission mechanism discussed in some detail.

scholarly journals Neutron Star Cooling: Effects of Envelope Physics

1983 ◽  
Vol 101 ◽  
pp. 513-516
Author(s):  
Kenneth A. Van Riper
Keyword(s):  
Neutron Star ◽  
Surface Temperature ◽  
Supernova Remnants ◽  
Temperature Drop ◽  
Magnetic Star ◽  
Pion Condensate ◽  
Neutron Star Cooling ◽  
Cooling Mechanism ◽  
Cooling Effects ◽  
Star Surface

Neutron star cooling calculations are reported which employ improved physics in the calculation of the temperature drop through the atmosphere. The atmosphere microphysics is discussed briefly. The predicted neutron star surface temperatures, in the interesting interval 300 ≤ t (yr) ≤ 105, do not differ appreciably from the earlier results of Van Riper and Lamb (1981) for a non-magnetic star; for a magnetic star, the surface temperature is lower than in the previous work. Comparison with observational limits show that an exotic cooling mechanism such as neutrino emission from a pion-condensate or in the presence of percolating quarks, is not required, unless the existence of a neutron star in the Tycho or SN1006 supernova remnants is established.

scholarly journals Einstein Observatory Limits on Neutron Star Surface Temperatures

1987 ◽  
Vol 125 ◽  
pp. 457-457
Author(s):  
F.R. Harnden
Keyword(s):  
Star Formation ◽  
Neutron Star ◽  
Neutron Stars ◽  
Supernova Remnants ◽  
Theoretical Models ◽  
X Ray ◽  
Star Models ◽  
Formation And Evolution ◽  
Star Surface ◽  
Einstein Observatory

For years the theoretical models of neutron star formation and evolution had remained largely unconstrained by observation. Following the Einstein X-ray Observatory surveys of supernova remnants and pulsars, however, strict temperature limits were placed on many putative neutron stars. The Einstein search for additional objects in the class of supernova remnants with embedded pulsars has increased the number of such objects by two. For the four objects in this class, the surface temperature limits (see Table 1) provide meaningful logically sound constraints on the neutron star models. For the future, however, still better X-ray observations are needed, both to increase the number of objects available for study and to refine the spatial and spectral capabilities of the X-ray measurements.

scholarly journals Radiation Beaming in Pulsars

1971 ◽  
Vol 46 ◽  
pp. 455-456
Author(s):  
V. Canuto
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Coming Out ◽  
Critical Magnetic Field ◽  
Zero Field ◽  
Ordinary Wave ◽  
Magnetic Field Axis ◽  
Field Lines ◽  
Star Surface ◽  
The Magnetic Field

It is usually considered that the beaming of the radiation coming out of a pulsar has to be strictly connected with the mechanism producing the radiation itself. We want to show that even when the emitting mechanism gives rise to an isotropically distributed radiation, the presence of a strong magnetic field will automatically beam the radiation preferentially along the magnetic field line rather than in any other direction. We have computed the Compton scattering and from that the opacity KH (K0 is the opacity for zero field). In Figure 1 the ratio KH/K0 is given vs. θ, the angle between the propagation vector and the magnetic field axis. Hq is a critical magnetic field numerically equal to 4.41 × 1013 G; Ne is the electron density. For the ordinary wave the opacity is reduced at θ = 0, while it is unaffected at θ = π/2 where KH → K0. Even at θ = π/4 the ratio KH/K0 is still ≃ 10−2, and a good beaming is still present. The values of the parameters are proper for a neutron star surface. It is to be noticed that the ratio KH/K0 is of the order of (ω/ωH)2 or [(kT/mc2)/(H/Hq]2. One therefore can conclude that the presence of a magnetic field itself assures the beaming of radiation along the field lines.

scholarly journals The optical/UV excess of X-ray-dim isolated neutron star II. Nonuniformity of plasma on a strangeon star surface

2018 ◽  
Vol 18 (7) ◽  
pp. 082
Author(s):  
Wei-Yang Wang ◽  
Yi Feng ◽  
Xiao-Yu Lai ◽  
Yun-Yang Li ◽  
Ji-Guang Lu ◽  
...  
Keyword(s):  
Neutron Star ◽  
X Ray ◽  
Uv Excess ◽  
Star Surface
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