Central Neutron Star Research Articles

The Spectral Turnover of the “Filled-Center” Supernova Remnant 3C 58: Implications for When Acceleration Occurs

AbstractIRASobservations the “filled-center” supernova remnant 3C 58 are used to derived upper limits of 0.4, 0.4, 0.8, and 1.5 Jy for its infrared flux density at 12, 25, 60, and 100 μm, respectively. These values imply a break in the spectrum of 3C58 above a few tens of gigahertz—two orders of magnitude below the break in the spectrum of the Crab Nebula—with a change of spectral index across the break for 3C 58 of more than 0.5. This is similar to previous results for another “filled-center” remnant, G74.9+1.2, from radio observations alone. This implies that their emission isnotdominated by a constant injection rate of particles with a power-law distribution. Either the break is due to synchrotron losses in the past, with little particle injection in recent times or it is intrinsic to the acceleration mechanism at work (presumably from a central neutron star).Subject headings: acceleration of particles — ISM: individual (3C 58) — radiation mechanisms: nonthermal — supernova remnants

Upper limits on the infrared flux density of the ‘filled-centre’ supernova remnant 3C58

Upper limits of 0.4, 0.4, 0.8 and 1.5 Jy for the infrared flux density of the ‘filled-centre’ supernova remnant 3C58 are derived from IRAS observations at 12, 25, 60 and 100 μm respectively. These limits are considerably below the infrared flux densities predicted for 3C58 by Reynolds & Chevalier. They are consistent with a break in the spectrum of 3C58 at ≈ 50 GHz, which is two orders of magnitude below the break in the spectrum of the Crab nebula. The change of spectral index across the break for 3C58 is more than 0.5, which implies that the emission from 3C58 is not dominated by a constant injection rate of particles with a power-law distribution. Either the break is intrinsic to the acceleration mechanism at work – presumably from a central neutron star – or it is due to synchrotron losses in the past, with little if any particle injection in recent times.

The structure and evolution of Thorne-Zytkow objects

We construct models of spherically symmetric stars in which a central neutron star core is accreting material from an envelope (Thorne-Zytkow objects or TZOs). Core masses are allowed to grow by accretion from ∼0.5 to 2.0 M ⊙ and envelope masses range from ∼0 to 30 M ⊙ . We find models populating the entire range of both parameters, and a limited range of parameter space in which two distinct types of model can coexist, one where gravitational energy and one where nuclear energy is the dominant source of energy

Binary Sub-Millisecond Pulsar and Rotating Core Collapse Model for SN1987A

The recent discovery of a binary sub-millisecond pulsar in SN1987A strongly suggests that the rotation was important in the core collapse of the progenitor of SN1987A. The observed period of the pulsar 0.5079680 ms is close to the maximum rotation of the neutron star. The periodic modulation of the pulse period with 8 hours suggests the existence of the companion with an almost circular orbit. The mass of the companion is either ~ 1.4 Me (face-on) or ~ 10Me (edge-on) with the semi-major axis of ~2 x lOll cm. In either case, if the companion has existed before the supernova explosion, it is hard to understand why the companion has a circular orbit. The formation of the companion after the bounce of the core is proposed. If the angular momentum of the pre-supernova core is greater than ~ 6 x 10 cgs, the core fragments and a binary proto neutron star is formed. As the separation of two neutron stars decreases in several seconds, the larger mass neutron star begins to accrete the matter of the smaller mass neutron star. The sub-millisecond period of the pulsar is· the consequence of the accretion of matter with the angular momentum ~ 10 cgs. Due to the fidal disruption at the end of the accretion, the system consists of a central neutron star and a rotating thin disk. Similar to the formation of planets in the solar nebula, a Jupiter-like secondary of mass ~ 10Me with a circular orbit ·may be formed within a year at separation of ~ lOll cm. A possible detection of the gravitational radiation from the sub-millisecond pulsar and a possible origin of gamma ray bursters are also demonstrated.

Neutron star disk formation from supernova fall-back and possible observational consequences

We have examined a simple model for gravitational fall-back of supernova ejecta to estimate the effect of delayed fall-back on pulsar activity from the central neutron star. Direct dimensional arguments suggest that a Kepler disk will be created with a mass of the order of 10−5 M⊙ for the probable initial magnetic fields and rotation rates. It has already been argued that such a disk would be required for pulsar action. The disk expected to be formed by fall-back is, at first, too distant to favour pulsar action. We therefore predict a neutron star disk that may be detectable when the nebula around SN1987A clears, although the same model also suggests that the pulsar action might not at first be taking place. Because this disk should be composed of the same sort of shocked and highly processed matter that presently maintains the supernova light curve through radioactive heating, the disk should be hot and luminous, thereby providing a point power-law optical source in the nebula. Thus, observational possibilities include: (1) observation of thermal radiation from the disk, (2) observation of X-rays from a transient episode of accretion on to the neutron star, and (3) a delayed turn-on of the pulsar.

Late Evolution of SN 1987A

AbstractSN 1987A has illuminated a great diversity of astrophysical processes – from neutrino emission during core collapse to the structure of the interstellar medium on a scale of hundreds of parsecs. Here I cover the evolution of SN 1987A from the outside in; the topics are interstellar light echoes, circumstellar light echoes, circumstellar shock waves, late emission and structure of the ejecta, and the effects of a central neutron star.

Model Atmospheres for Cooling Neutron Stars

The failure of Einstein X-ray observations to detect central neutron stars in most young supernova remnants (Helfand and Becker 1984) has provided interesting constraints on cooling theories (cf. review by Tsuruta 1985). The comparison of the measured fluxes with the predicted effective temperatures is sensitive to the nature of the emitted spectrum, commonly assumed to be blackbody. The presence of a substantial absorbing atmosphere can, however, produce significant departures. We have calculated model atmospheres for unmagnetized neutron stars with effective temperatures 105K ≦ Teff ≦ 106.5K using Los Alamos opacities and equations of state (Romani 1986). We consider a range of surface compositions, since the accretion of ∼10−19M⊙ will cover the surface to the X-ray photosphere and subsequent settling in the strong gravitational field can severely deplete the heavy species. In a low Z atmosphere (eg. He) the measured X-ray flux will substantially exceed the blackbody value–the Einstein limits on Teff are correspondingly lowered (eg. by ∼1.6 for SN1006 with a helium surface). For high Z atmospheres, the flux is close to the black body value, but prominent absorption edges are present. Recent calculations of the electron heat transport in magnetized neutron star envelopes (Hernquist 1984, 1985) have shown that, contrary to earlier estimates, magnetic fields will have a small effect on the heat flux (≳ 3 for parallel field geometries and ∼1 for tangled fields). Extension of the atmosphere computations to the magnetic case is important for comparison with X-ray observations of known pulsars.

The influence of nuclear burning on the stability of degenerate and nondegenerate accretion disks

view Abstract Citations (11) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The influence of nuclear burning on the stability of degenerate and nondegenerate accretion disks. Taam, R. E. ; Fryxell, B. A. Abstract The structure and stability of accretion disks composed of hydrogen-rich matter rotating about a central neutron star have been investigated for known sources of viscosity. Two general classes of solutions have been found. For one class the energy generated in the disk is provided by hydrogen burning, whereas for the other class the gravitational binding energy released by viscous dissipation dominates. The former solutions are thermally unstable (stable) whenever hydrogen burns via the normal CNO cycle (pp chain) in a partially or fully degenerate region of the disk. Solutions characterized by nuclear-burning via the Beta-limited CNO cycle or by viscous dissipation only are always stable. On the basis of a local analysis it is shown that modulations of the mass flow in the disk are possible for a range of mass inflow rates into the disk. In such circumstances the disk can undergo a phase transition from a cold, low-viscosity state to a hot, high-viscosity state as a result of the thermonuclear flash instability. Phase transitions from the hot state to the cold state also occur whenever the mass input rate into the disk is less than the equilibrium mass flow rate corresponding to the hot state. It is also shown that for sufficiently high mass flow rates all the hydrogen-rich matter can be processed to helium in the inner regions of the disk before it can be accreted by a neutron star. Publication: The Astrophysical Journal Pub Date: July 1985 DOI: 10.1086/163298 Bibcode: 1985ApJ...294..303T Keywords: Accretion Disks; Mass Flow; Neutron Stars; Nuclear Astrophysics; Nuclear Fusion; Stellar Models; Thermal Stability; Mass Flow Rate; Viscosity; X Ray Sources; Astrophysics full text sources ADS | data products SIMBAD (1)

The Crab Nebula's progenitor

The study of supernovae is hampered by an insufficient knowledge of the initial stellar mass for individual supernova. Because of large uncertainties in estimating both the total mass of a remnant (including the pulsar or black hole) and any mass loss during the pre-supernova stages, the main sequence mass of the progenitor cannot be accurately determined from observations alone. To calculate an initial mass, one must rely on a combination of both theory and observation. Limits on the progenitor's mass range can be estimated by the presence of a compact remnant and comparison of the observed nebular chemical abundances with detailed evolutionary calculations1. The Crab Nebula is an excellent choice for investigation because it contains a unique combination of characteristics: a central neutron star (pulsar) and a bright, well studied nebula having little or no swept-up interstellar material. In fact, several studies1–4 have suggested an initial mass of ∼10M⊙ for the Crab progenitor. Recently, Davidson et al.5, quoting two of us (K.N. and W.M.S.), state that the Crab's progenitor had a mass slightly larger than 8 M⊙. Here we present in detail the reasoning behind this statement and suggest the explosion mechanism.

Supernovae. Part I: the events

Since the heroic era of Baade and Zwicky, our understanding of supernovae has advanced in hops and skips rather than steadily. The most recent jump has been into fairly general agreement that observations of Type I's can be interpreted as the manifestation of the decay of about $1{M}_{\ensuremath{\bigodot}}$ of ${\mathrm{Ni}}^{56}$ and observations of Type II's as the manifestation of \ensuremath{\gtrsim}${10}^{51}$ ergs deposited at the bottom of a supergiant envelope by core bounce as a central neutron star forms. This paper explores the history of these and other ideas of what is going on in supernovae, the presupernova evolution of the parent stars and binary systems, observed properties of the events, and models for them. A later paper (Part II: the aftermath) will address the results of supernovae---their remnants, production of cosmic rays and gamma rays, nucleosynthesis, and galactic evolution---and the future of supernova research.

An X-ray study of two Crablike supernova remnants - 3C 58 and CTB 80

The instruments on the Einstein Observatory have been used to study the X-ray properties of two Crablike SNRs: 3C 58 and CTB 80. Images of the objects are similar, showing an extended plateau of emission surrounding a pronounced central maximum consistent with the presence of a point source. The X-ray spectrum of 3C 58 is consistent with a power law of spectral index 0.5 + 0.5 or -0.2 modified by absorption in a hydrogen column density N sub H of (2 + or - 0.5) x 10 to the 21st/sq cm. These data suggest an analogy with the Crab Nebula, where the extended X-ray emission is nonthermal and the pointlike emission emanates from a central neutron star. Quantitative comparisons of the X-ray and radio properties for six Crablike remnants indicate significant differences which may reflect an evolutionary sequence.

Structure of the Pulsar Magnetosphere

Motivation for the study of the pulsar magnetosphere is multifold. First of all, energy-wise the magnetosphere is the dominant problem, for the energy emitted in the radio pulses is at most one per-cent of the energy loss inferred from the secular increase in the rotation period of the central neutron star. With the possible exception of gamma-ray emission in a few cases, the pulsing observed in all wavelengths can be regarded as a diagnostic of a more basic phenomenon. A successful model should in fact tell us the total rate of energy loss from the star and its distribution between a low-frequency wave, a possible wind, and emission in the radio, optical, X-ray and gamma-ray bands. As a necessary preliminary, the model should predict the strength of the currents leaving and returning to the star, the location of relativistic particles, and the conditions for transition to a quantum magnetosphere via pair production (Sturrock 1971). But even if magnetospheric theory did not offer such hopes of ultimate links with observation, the problem is so well-defined that it is a challenge to the theorist: it is just intolerable that we should not know how a rotating magnetized neutron star comes to terms with its environment.

Is the light cylinder the site of emission in pulsars?

There is no agreement in reports on the oblique-rotator model of pulsars1–9 as to the site of emission within the pulsar magnetosphere. It is generally assumed, however, that the plasma-electromagnetic fields constituting the magnetosphere obey the quasistatic constraint ∂f/∂t = -ω0∂f/∂φ, where ω0 is the angular frequency of rotation of the central neutron star, t the time, and the cylindrical coordinates (r, φ, z) refer to an inertial frame whose z-axis is coincident with the axis of rotation of the star. Accordingly, the pulsar emission is attributed to a source whose distribution has a rigidly rotating pattern; though, of course, none of the charged particles which constitute the source and provide the medium for the propagation of the pattern associated with the source, are themselves constrained to be co-rotating. Here, the spectral distribution of the power emitted by such a rotating pattern is calculated and it is shown that electromagnetic radiation of frequency to ω ≫ ω0, the observed radiation from pulsars, is produced predominantly by the electric currents at the light cylinder r = c/ω0 of the magnetosphere. This is a model-independent result; it is valid irrespective of the type of emission mechanism and applies to all previously proposed models of the magnetosphere which are quasistatic and in which the radial length scale of the plasma distribution is of the order of c/ω0.

Optical Polarization of the Crab Nebula Pulsar. IL Observational Results and FITS by the Relativistic Vector Model

We present three years of observations of the optical polarization of the Crab Nebula pulsar and show that they are fitted quite well by the relativistic rotating vector model. The main pulse is fiited by a rotational velocity of BETA =0.56 and the interpulse by BETA =0.42-0.44. There appear to be secular changes in the angular parameters defining this model and in the overall levels of polarization. However, no changes in the unpolarized pulse shapes have been detected. A free nutation of the central neutron star is proposed to explain these changes. (auth)

The nature of radio emission from pulsars

It is shown that radio emission from pulsars is unlikely to be of coherent synchrotron origin if the surface magnetic field of the central neutron star is greater than 108 G.

Some Models for Pulsed Radio Sources

Already before the discovery of pulsed radio sources, the possibility had been discussed1,2 of rotating neutron stars providing an energy source in supernova remnants. A large number of models have been proposed to explain the pulsed radio sources and some of these invoke a central neutron star, some kind of rotation and some kind of in-homogeneity. In the preceding article Gold has proposed a model in which the neutron star, surrounded only by a tenuous plasma, rotates itself with the inhomogeneity residing merely in the star’s magnetic field. Another model3 considers the possibility that the rotation and inhomogeneity both reside in the orbital motion of a satellite around a neutron star. We discuss here some difficulties associated with models for pulsed radio sources which invoke the orbiting of material satellites around any central object.