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At least 325 records · Page 18
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NASA NTRS1983

JPL pulsar timing observations. II - Geocentric arrival times

Monitoring of the behavior of naturally pulsating galactic radio sources, or pulsars, through regularly spaced measurements of pulse arrival times, has been conducted by several laboratories. A tabular presentation is here made of pulse arrival time measurements from the NASA Deep Space Network between late 1968 and early 1981. By expressing the measurements in ephemeris time, and referring them to the geocenter, usable tables of results have been generated for each pulsar listed in the first of the tables given. The considerations addressed by the tables are: (1) a necessary step in the study of pulsar dynamics is the reduction of topocentric arrival times to the barycenter of the solar system; (2) the tabulated data are accessible to all opinions as to the procedures to be used in interpreting arrival time data; and (3) different observing programs can usually be combined to produce an improvement in the total data set.

Downs, G. S.↗
NASA NTRS1983

Genesis stories for the millisecond pulsar

Theoretical models proposed to explain the origin of the millisecond pulsar (MP) PSR 1937+214 are reviewed, examining their ability to explain its low surface dipole magnetic field (B), its low birth temperature (less than 10 to the 8th K), the absence of a companion or remnant, and its low velocity perpendicular to the Galactic plane. The models discussed are a single isolated explosion forming a rapidly spinning neutron star, spin-up of a dead pulsar by accretion from a companion, collapse of an accreting spinning white dwarf, and fusion of a tight binary composed of two old neutron stars. Although all of the models have difficulties in explaining one or more of the MP characteristics, the second model is found to be most probable in the light of present knowledge. The lack of a companion is explained by its tidal disruption after it had fed the accreting pre-pulsar for 1 Gyr or more and its mass had decreased to about 0.01 solar mass. Neutron stars accreting in this way have been observed in Galactic-bulge X-ray sources.

Ruderman, M. A.↗
NASA NTRS1983

Self-modulational formation of pulsar microstructures

A nonlinear plasma theory for self-modulation of pulsar radio pulses is discussed. A nonlinear Schroedinger equation is derived for strong electromagnetic waves propagating in an electron-positron plasma. The nonlinearities arising from wave-intensity-induced particle-mass variation may excite the modulational instability of circularly and linearly polarized pulsar radiation. The resulting wave envelopes can take the form of periodic wave trains or solitons. These nonlinear stationary waveforms may account for the formation of pulsar microstructures.

Chian, A. C.-L.↗
NASA NTRS1984

Vortex creep and the internal temperature of neutron stars. II - Vela pulsar

The observed complex postglitch behavior of the Vela pulsar is explained as resulting from coupling of the crust to crustal neutron superfluid, specifically that part of the superfluid in which vortex lines are pinned to crustal nuclei. It is shown how the general theory of vortex creep provides an excellent fit to the timing observations of Downs which span the decade 1969-1979 and include four giant glitches. Relaxation times, inertial moments, and limits on superfluid pinning parameters are extracted for three distinct regions of vortex pinning in the star, with results which are consistent with microscopic theories of its internal structure. Relaxation times due to vortex creep are directly proportional to the internal temperature of the star, so that the limits obtained for pinning parameters translate to bounds on this temperature. It is concluded that the internal temperature of the Vela pulsar is about 10-million K and discuss the extent to which improved calculations of vortex pinning as well as soft X-ray observations of other stars will make possible an improved determination of the pulsar temperature.

Alpar, M. A.↗
NASA NTRS1984

Confinement of the Crab pulsar's wind by its supernova remnant

A steady state, spherically symmetric, magnetohydrodynamic model of the Crab nebula is constructed. A highly relativistic positronic pulsar wind is terminated by a strong MHD shock that decelerates the flow and increases its pressure to match boundary conditions imposed by the recently discovered supernova remnant that surrounds the nebula. If the magnetic luminosity of the pulsar wind upstream of the shock is about 0.3 percent of its particle luminosity, the pressure and velocity boundary conditions imposed by the remnant place the shock where it is inferred to be: near the outer boundary of an underluminous region observed to surround the pulsar. It is necessary to include the weak magnetization of the wind to satisfy the boundary conditions and to calculate the regular synchrotron radiation self-consistently.

Kennel, C. F.↗
NASA NTRS1985

The 1000 GeV gamma ray emission from radio pulsars

Radio pulsars have concentrated on long observations of the Crab pulsar and showed that it emits short intense bursts and a persistent weak periodic flux at gamma-ray energies 1000 GeV. It was shown that the light curve of the persistent emission was dominated by a single peak, coincident with the position of the radio and low energy gamma-ray main pulse. The results of a more detailed analysis of the structure of this main pulse are reported following an appraisal of the timing system. It is shown that at energies 1000 GeV the duration of the main pulse is not greater than 0.4 ms, which is less than that seen at all frequencies other than radio. Flux limits for the emission of 1000 GeV gamma-rays by seven other radio pulsars are reported

Chadwick, P. M.↗
NASA NTRS1985

The 1000 GeV gamma rays from ms pulsars

The detection of 1000 GeV gamma-rays with the characteristic 6.1 ms periodicity of the radio pulsar PSR 1953 +29 is reported. This result, significant at the 5.4 beta level, provides the first direct evidence for the association of the 6 ms radio pulsar PSR1953+29 with the gamma-ray source 2CG065+0. Extensive observations of the 1.5 ms pulsar PSR 1937 are also reported.

Chadwick, P. M.↗
NASA NTRS1985

Cosmic rays in the 10(16) to 10(19) eV range from pulsars

The flux is calculated of cosmic rays (CRs) produced by a distribution of pulsars that are: (1) born with rapid rotation rates, (2) slow down as they evolve, and (3) produce energetic nuclei with a characteristic energy proportional to their rotation rates. It is found that, for energy independent escape from the disk of the galaxy, the predicted spectrum will be essentially what is observed between approx 10 to the 16th power to 10 to the 19 power eV if the slow down law as inferred for radio pulsars can be extrapolated to young pulsars with shorter periods.

Wandel, A.↗
NASA NTRS1985

On magnetic pair production above fast pulsar polar caps

Magnetic pair production is one of high-energy electromagnetic conversion processes important to the development of pair-photon cascades in pulsars. On the basis of current polar cap models, the properties of magnetic pair production in fast pulsars are discussed. Suppose there is a roughly dipole magnetic field at the stellar surface, the author estimate the effects on non-zero curvature of magnetic field lines upon curvature radiation from primary particles and pair production rate near the surface of pulsars.

An, S.↗
NASA NTRS1983

Positron production by a hot, young pulsar

The paper considers a way of positron production in pulsars: pair production from electron-photon collisions. It is shown that this process must be the dominant one for a young pulsar when its surface temperature is around 10-million K. This model is applied to the observed positron flux coming from the Galactic Center and it is shown that a pulsar with parameters close to those of the Crab at birth can explain, in principle, the flux.

Brecher, K.↗
NASA NTRS1986

High-sensitivity observations of 28 pulsars

Average 430-MHz pulse profiles and, where possible, modulation indices and pulse-nulling fractions are computed for 28 pulsars. Morphological classifications are determined for most of the pulsars. It is found that core emission components tend to have lower modulation indices than conal components, and that pulsars having only a core component never exhibit pulse pulling. PSR 1612 + 07 is shown to undergo mode changes.

Weisberg, J. M.↗
NASA NTRS1986

Vortex creep and the internal temperature of neutron stars Timing noise in pulsars

Vortex creep theory is used to construct model noise power spectra for three physically distinct types of events which might give rise to pulsar timing noise. These are 'pure' events, in which vortex unpinning is the source of the initial frequency jump; 'mixed' events, in which the initial frequency jump is produced by some physical process other than vortex unpinning but leads to the unpinning of some vortices; and 'external' events, in which the initial frequency jumps responsible for noise do not involve any vortex unpinning. For the first two types of events, it is found that relaxation processes in the region responsible for the noise will give rise to structure in the observed power spectra, while for external events, the resulting noise spectra will not be influenced by vortex creep. The theoretical results are compared with observed power spectra for 25 pulsars. The absence of structure in the observed power spectra of the Crab and Vela pulsars within the range of time scales which characterize their postglitch behavior indicates that the pinning regions which play a role in postglitch behavior do not experience the small unpinning events leading to timing noise.

Alpar, M. Ali↗
NASA NTRS1987

Self-modulational formation of pulsar microstructures

A nonlinear plasma theory for self modulation of pulsar radio pulses is discussed. A nonlinear Schroedinger equation is derived for strong electromagnetic waves propagating in an electron positron plasma. The nonlinearities arising from wave intensity induced particle mass variation may excite the modulational instability of circularly and linearly polarized pulsar radiation. The resulting wave envelopes can take the form of periodic wave trains or solitons. These nonlinear stationary waveforms may account for the formation of pulsar microstructures.

Chian, A. C.-L.↗
NASA NTRS1987

When will a pulsar in supernova 1987a be seen?

The means by which a pulsar might be detected in the remnant of supernova 1987a in the Large Magellanic Cloud is examined. One possibility is that the slower-than-radioactive decay typically seen in the type II light curves is itself the sign of powering by the underlying pulsar, with the decline representing not the spinning down of the pulsar but rather the declining nebular opacity that would allow increasing amounts of the energy to escape as gamma rays. The test of this hypothesis (if the supernova conforms to type II expectations) would be to look for the 'missing' energy in the form of those gamma rays that escape from the remnant instead of powering it.

Michel, F. Curtis↗
NASA NTRS1988

Interaction between high-velocity pulsar in CTB80 and an infrared emission shell

During a survey of infrared emission detected by IRAS from shock-heated dust associated with Galactic SNRs, a roughly 1 deg diameter supernova remnant shell centered 30 arcmin east of SNR CTB80's core was discovered. The pulsar's projected location inside this infrared emission shell, together with similar distance and age estimates, suggest that both the shell and pulsar were produced by the same supernova event. It is proposed that the interaction between the pulsar's energetic particle emission and the shell's compressed interstellar magnetic field can explain CTB80's remarkable radio structure, and the implications of such pulsar/SNR interactions are discussed.

Fesen, Robert A.↗
NASA NTRS1988

Birth of millisecond pulsars in globular clusters

It is argued here that accretion-induced collapse of white dwarfs in binaries can form millisecond pulsars directly without requiring a precursor low-mass X-ray binary stage. Ablation of the precollapse binary companion by the millisecond pulsar's radiation field, a process invoked to explain some of the characteristics of the recently discovered eclipsing millisecond pulsar, can then yield isolated neutron stars witout requiring an additional stellar encounter.

Grindlay, J. E.↗
NASA NTRS1988

A search for optical millisecond pulsars in globular clusters

A search for millisecond optical pulsars in several bright, compact globular clusters was conducted. The sample included M28, and the X-ray clusters 47 Tuc, NGC 6441, NGC 6624, M22, and M15. The globular cluster M28 contains the recently discovered 327 Hz radio pulsar. Upper limits of 4 sigma to pulsed emission of (1-20) solar luminosities were found for the globular clusters tested, and 0.3 solar luminosity for the M28 pulsar for frequencies up to 500 Hz.

Middleditch, J. H.↗
NASA NTRS1989

Submillisecond optical pulsar in supernova 1987A

An optical pulsar with frequency f = 1,968,629 Hz has been detected at the location of supernova 1987A in the LMC. The brightness of the pulsed light increased from magnitude 19 to 18 during a 7-hr observation period starting on 18.1 January 1987 UT. The frequency of the pulsar during this same period varied in a nearly sinusoidal manner, with an amplitude of 1.5 x 10 to the -3rd Hz and a period of 8 hr. If this is interpreted as the result of a binary orbit, it suggests that there may be a Jupiter-size object orbiting the pulsar at a distance of 10 to the 6th km.

Kristian, J.↗