The distribution of old neutron stars in the galaxy (original) (raw)
Related papers
Modeling the Spatial Distribution of Neutron Stars in the Galaxy
2016
In this paper we investigate the space and velocity distributions of old neutron stars (aged 10 9 to 10 10 yr) in our Galaxy. Galactic old Neutron Stars (NSs) population fills a torus-like area extending to a few tens kiloparsecs above the galactic plane. The initial velocity distribution of NSs is not well known, in this work we adopt a three component initial distribution, as given by the contribution of kick velocities, circular velocities and Maxwellian velocities. For the spatial initial distribution we use a Γ function. We then use Monte Carlo simulations to follow the evolution of the NSs under the influence of the Paczyński Galactic gravitational potential. Our calculations show that NS orbits have a very large Galactic radial expansion and that their radial distribution peak is quite close to their progenitors' one. We also study the NS vertical distribution and find that it can well be described by a double exponential low. Finally, we investigate the correlation of the vertical and radial distribution and study the radial dependence of scale-heights.
The evolution of the \vec{z} distribution of normal neutron stars in the Galaxy
Astronomische Nachrichten, 2010
Under the two initial 1-D one parameter velocity distribution forms (one is normal, the other is exponential), the z direction scale height evolution of normal neutron stars in the Galaxy is studied by numerical simulation. We do statistics for the cases at different time segments, also do statistics for the cumulative cases made of each time segment. The results show in the cumulative cases the evolution curves of the scale heights are smoother than in the each time segment, i.e., the cumulation improve the signal-to-noise ratio. Certainly the evolution cases are different at different Galactic disk locations, which also have very large difference from the average cases in the whole disk. In the initial stages of z evolution of normal neutron stars, after the beginning transient states, the cumulative scale heights increase linearly with time, and the cumulative scale height increasing rates have linear relationship with the initial velocity distribution parameters, which have larger fluctuation in the vicinity of the Sun than in the whole disk. We utilize the linear relationship of the cumulative scale height increasing rates vs. the initial velocity distribution parameters in the vicinity of the Sun to make comparison with the observation near the Sun. The results show if there is no magnetic decay, then the deserved initial velocity parameters are obvious lower than the present well known results from some authors; whereas if introducing magnetic decay, for the 1-D normal case we can make consistence among concerning results using magnetic decay time values which are supported by some authors, while for the 1-D exponential case the results show the lackness of young pulsar samples in the larger z in the vicinity of the Sun.
The evolution of the z distribution of normal neutron stars in the Galaxy
Astronomische Nachrichten, 2010
Under the two initial 1‐D one parameter velocity distribution forms (one is normal, the other is exponential), the z direction scale height evolution of normal neutron stars in the Galaxy is studied by numerical simulation. We do statistics for the cases at different time segments, also do statistics for the cumulative cases made of each time segment. The results show in the cumulative cases the evolution curves of the scale heights are smoother than in the each time segment, i.e., the cumulation improve the signal‐to‐noise ratio. Certainly the evolution cases are different at different Galactic disk locations, which also have very large difference from the average cases in the whole disk. In the initial stages of z evolution of normal neutron stars, after the beginning transient states, the cumulative scale heights increase linearly with time, and the cumulative scale height increasing rates have linear relationship with the initial velocity distribution parameters, which have larg...
The Astrophysical Journal, 1995
Evolution of the coalescence rate of double neutron stars (NS) and neutron star { black hole (BH) binaries are computed for model galaxies with di erent star formation rates. Assuming gamma-ray bursts (GRB) to originate from NS+NS or NS+BH merging in distant galaxies, theoretical log N{log S distributions for gamma-ray bursts (GRB) are calculated for the rst time taking the computed merging rates into account. We use a at cosmological model ( = 1) with di erent values of the cosmological constant and under various assumptions about the star formation history in galaxies. The calculated source evolution predicts a 5-10 times increase of the source statistics at count rates 3-10 times lower than the exising BATSE sensitivity limit. The most important parameter in tting the 2nd BATSE catalogue is the initial redshift of star formation, which is found to be z = 2 5 depending on a poorly determined average spectral index of GRB.
Population synthesis of young neutron stars
We investigate the fortune of young neutron stars (NS) in the whole volume of the Milky Way with new code for population synthesis. We start our modeling from the birth of massive OB stars and follow their motion in the Galaxy up to the Supernova explosion. Next we integrate the equations of motion of NS in the averaged gravitational potential of the Galaxy. We estimate the mean kick velocities from a comparison the model Z and R-distributions of radio emitting NS with that for galactic NS accordingly ATNF pulsar catalog. We follow the history of the rotational velocity and the surface magnetic field of NS taking into account the significant magnetic field decay during the first million year of a neutron star's life. The derived value for the mean time of ohmic decay is 2.3 • 10 5 years. We model the subsample of galactic radio pulsars which can be detected with available radio telescopes, using a radio beaming model with inhomogeneous distribution of the radio emission in the cone. The distributions functions of the pulsar periods P, period derivativesṖ and surface magnetic fields B appear to be in a close agreement with those obtained from an ensemble of neutron stars in the ATNF catalogue.
The Astrophysical Journal, 2000
The paucity of old isolated accreting neutron stars in ROSAT observations is used to derive a lower limit on the mean velocity of neutron stars at birth. The secular evolution of the population is simulated following the paths of a statistical sample of stars for different values of the initial kick velocity, drawn from an isotropic Gaussian distribution with mean velocity 0 ≤ V ≤ 550 km s −1. The spin-down, induced by dipole losses and the interaction with the ambient medium, is tracked together with the dynamical evolution in the Galactic potential, allowing for the determination of the fraction of stars which are, at present, in each of the four possible stages: Ejector, Propeller, Accretor, and Georotator. Taking from the ROSAT All Sky Survey an upper limit of ∼ 10 accreting neutron stars within ∼ 140 pc from the Sun, we infer a lower bound for the mean kick velocity, V ∼ > 200 − 300 km s −1 , corresponding to a velocity dispersion σ V ∼ > 125−190 km s −1. The same conclusion is reached for both a constant magnetic field (B ∼ 10 12 G) and a magnetic field decaying exponentially with a timescale ∼ 10 9 yr. Such high velocities are consistent with those derived from radio pulsar observations. Present results, moreover, constrain the fraction of low velocity stars, which could have escaped pulsar statistics, to less than 1%.
Gamma-ray bursts from galactic neutron stars?
Nuclear Physics B - Proceedings Supplements, 1989
The q-ray burst distap.ce scale is not known and quiescent counterparts of q-ray bursts have no'~ been unambiguously identified in any wavelength band. It is generally assumed that 7-ray bursts originate on or near neutron stars in the general vicinity of our galaxy. Statistical tools for determining the ?-ray burst spatial distribution are their brightness distribution ("log N-log S" and V/Vmax) and their angular distribution on the celestial sphere. We discuss in detail the dipole-and quadrupole moments and the angular autocovariance function w(0) of the positional data. The observations suggest zero angular correlation and small multipole moments which places severe constraints on the spatial distribution of ?-ray bursts. We discuss a Monte Carlo simulation of the population of galactic neutron stars which can be used to test the hypothesis that 7-ray bursts originate on galactic neutron stars.
Neutron Star Populations at the Millenium
International Astronomical Union Colloquium, 2000
Identified neutron star (NS) classes evidently are determined by several intertwined features: kinematics of NS at their formation (spin and translational); magnetic field strength; and binary membership. I discuss the well-known classes of isolated and accreting NS while keeping in mind recent discoveries of magnetars, anomalous X-ray pulsars, and long-period radio pulsars. I summarize the results of several likelihood analyses on radio pulsars, which yield information on the velocity distribution, luminosity function, and birth rate of high-field radio pulsars. I review the evidence for the occurrence of momentum kicks at the time of NS birth. Discerning the relationship of the classic radio pulsars to the more exotic classes probably requires careful comparison of magnetic fields, kinematics and birthrates, a program for the next millenium. Exciting discoveries of classic pulsars will also be made: sub-millisecond pulsars, massive binaries in fast orbits and truly hyper-velocity ...