Crab Nebula Pulsar Research Articles

Measurement of circular polarisation in the Crab Nebula at 1,415 MHz

RECENTLY Rees and Gunn1 suggested that the 30-Hz wave power probably emerging from the Crab Nebula Pulsar NP0532 does not propagate further than a small region around the pulsar with a radius of about 10% of the nebular radius. Beyond this, in the main body of the nebula, the magnetic field is built up in toroidal form to equipartition strength so that the continuum emission from the bulk of the nebula is entirely synchrotron radiation. The axis of this toroid is aligned with the rotational axis of the pulsar which is assumed to be lying in the plane of the sky along the major axis of the nebula (NW/SE). A test of this proposal is the measurement of a characteristic sign change in the distribution of Faraday rotation or circular polarisation over the nebula. If the nebula is divided into quadrants along its major and minor axes, then adjacent quadrants should have the opposite sign and opposite quadrants the same sign. Since any measured Faraday rotation does not necessarily arise within the body of the nebula, the critical test becomes a detection of the characteristic sign distribution in the small amount of circular polarisation (∼0.1 %) expected at radio frequencies from ordinary synchrotron radiation2. The theoretical frequency dependence of ν−1/2 for the fraction of circular polarisation would then explain the null result of Landstreet and Angel3 (see also ref. 4) at optical frequencies. Here I report a measurement of the distribution of circular polarisation (Stokes parameter V) in the Crab Nebula at 1,415 MHz obtained during a series of high accuracy full polarisation measurements with the Westerbork Synthesis Radio Telescope in November 1971.

Color-difference photometry of the Crab Nebula pulsar and the rotating relativistic vector model

view Abstract Citations (13) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Color-difference photometry of the Crab nebula pulsar and the rotating relativistic vector model. Cocke, W. J. ; Ferguson, D. C. Abstract Light curves of the Crab Nebula pulsar in U and V are given, as are normalized difference curves for the main and secondary pulses. The ratios of total intensity for main to secondary are: 1.866 for U, and 1.916 for V. The intensity difference curve for the secondary pulse is fitted by the rotating relativistic vector model. Timing errors prevent a fit for the main pulse. Publication: The Astrophysical Journal Pub Date: December 1974 DOI: 10.1086/153294 Bibcode: 1974ApJ...194..725C Keywords: Astronomical Models; Crab Nebula; Light Curve; Pulsars; Relativistic Theory; Luminous Intensity; Mathematical Models; Tables (Data); Ubv Spectra; Vector Analysis; Astrophysics full text sources ADS |

High Speed Photometry at Mt Stromlo Observatory

Important observations of X-ray sources and searches for the optical counterparts of X-ray and radio pulsars require a capability of detecting and analysing light variations with a time scale of milliseconds. X-ray sources in binary star systems are expected to be collapsed objects – neutron stars or black holes (Peterson 1973) – and are expected to produce light variations. In the case of a neutron star, pulses with the same period as the rotation period of the neutron star would be produced, and such have been observed from Cen X-3 (schreier et al. 1972) in the X-ray, and from Her X-1 (Middleditch and Nelson 1973) and the Crab Nebula pulsar (Cocke et al. 1969) in the X-ray optical.

Period Irregularities in Pulsars

view Abstract Citations (43) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Period Irregularities in Pulsars Manchester, R. N. ; Taylor, J. H. Abstract Period irregularities have been detected in pulsars with periods longer than 0.1 5. A discontinuous decrease in the period of PSR 1508+55 occurred near the end of 1972 in which the fractional change of rotation frequency was 2 X 1010. Subsequent to the event, the period derivative apparently relaxed to a new value approximately 0.5 percent less than the original value. Random changes in period, apparently similar to those observed in the Crab Nebula pulsar, have been observed in PSR 1642-03 and PSR 0329+54, but not in PSR 1919+21. Subject headings: neutron stars - pulsars Publication: The Astrophysical Journal Pub Date: July 1974 DOI: 10.1086/181549 Bibcode: 1974ApJ...191L..63M full text sources ADS |

Optical polarization of the Crab nebula pulsar. 3. New observations, predictions, and the possibility of variability.

Optical polarization of the Crab nebula pulsar. 3. New observations, predictions, and the possibility of variability.

The Optical Polarization of the Crab Nebula Pulsar. I. a Relativistic Vector Model

view Abstract Citations (26) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Optical Polarization of the Crab Nebula Pulsar. I. a Relativistic Vector Model Ferguson, Dale C. Abstract A model is proposed to explain the optical polarization behavior of the Crab pulsar, NP 0532. The emission comes from regions orbiting the neutron star at relativistic velocities, and the plane and amount of polarization are dependent upon the direction and length of the apparent projection of the local magnetic field lines on the plane of the sky. Subject headings: neutron stars - polarization - pulsars - relativity - rotation, stellar Publication: The Astrophysical Journal Pub Date: August 1973 DOI: 10.1086/152284 Bibcode: 1973ApJ...183..977F full text sources ADS |

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)

VLBI Observations of the Crab Nebula Pulsar

Observations of the Crab Nebula pulsar at meter wavelengths using VLBi techniques have been made. At 196.5 MHz we observe no resolution of the pulsar, all the puise shapes observed with the interferometers are similar to single-dish profiles, and all the power puisates. At 111.5 MHz besides the puising power there is always a steady component, presumably due to multipath propagation effects. The puisar is slightly resolved at 111.5 MHz with an apparent angular diameter of 0"07 t 0'.'01. We observe 50 percent linear polarization of the time-averaged power at 196.5 MHz; at 111.5 MHz, 20 percent of the total time-averaged power is polarized, 35 percent of the pulsing power is polarized. The steady component is unpolarized. The total flux of the steady plus pulsating component appears to remain constant while the distribution of power betw&n these components varies. Subject headings:pulsars - Crab Nebula

Lorentz Transformation Properties of the Stokes Parameters

FERGUSON (ref. 1 and unpublished work) and Cocke, Ferguson and Muncaster (in preparation) have interpreted the optical polarization of the Crab Nebula pulsar by means of a rotating relativistic vector model. It was assumed in this work that the percentage linear polarization of a collimated beam of light is the same when measured by different observers in relative motion with respect to each other. This assumption led us to investigate the general Lorentz transformation characteristics of partially elliptically polarized radiation and in this paper we study the transformation properties of the Stokes parameters. This problem has astrophysical interest, not only for the Crab Nebula pulsar, but also for other cosmic sources emitting elliptically polarized radiation, such as the synchrotron sources studied by Pacholczyk and Swihart2.

Detection of 10–100 MeV γ-Rays from the Crab Nebula Pulsar NP 0532

Pulsed γ-ray emission from NP 0532 has been detected up to 100 MeV. For the main pulse from 10 to 30 MeV the signal to noise is (5–6σ). The energy spectrum of the main pulse from 1 keV to 100 MeV can be fitted by a single power law of index (−0.9).

γ-Ray Absorption for a Beam Model of NP0532

THE possibility of γ-ray absorption near the Crab Nebula pulsar NP0532 was pointed out by McBreen1. Recently Pollack et al.2 have shown that the critical energy Ec above which absorption is observed to take place can in principle be used to determine the size of the emitting region in γ-ray sources such as pulsars, quasars and supernovae explosions. Neither of these authors, however, attempted to take account of beaming in pulsars such as NP0532 which has the effect of significantly raising the value of Ec. Without taking account of beaming, there would seem to be a conflict between surface emission models such as that of Chiu et al.3 and recent reports of the detection of pulsed γ-ray emission from the Crab Nebula4–6. These observations seem to rule out any model involving emission from the surface of the pulsar according to he calculations of Pollack et al. because those calculations indicate that γ-radiation with energy greater than 1 MeV originating at the surface of the pulsar would be strongly attenuated.

Crab Nebula Pulsar Radio Pulse Arrival Times at Arecibo Observatory

view Abstract Citations (18) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Crab Nebula Pulsar Radio Pulse Arrival Times at Arecibo Observatory Rankin, J. M. ; Counselman, C. C., III ; Richards, D. W. Abstract U. T. C. times of reception at Arecibo Observatory of 430-MHz radio pulses from the Crab Nebula pulsar are tabulated at approximately 3-day intervals from 10 May 1969 to 6 April 1971. Some arrival times re- corded at various frequencies prior to May 1969 are also given. Publication: The Astronomical Journal Pub Date: October 1971 DOI: 10.1086/111185 Bibcode: 1971AJ.....76..686R full text sources ADS | Related Materials (1) Erratum: 1971AJ.....76.1154R

Time Variations in High Energy Cosmic Rays

SEVERAL authors have proposed models in which pulsars are strong sources of cosmic rays1,2. Grewing and Heintzmann3 have proposed a detailed model for the Crab Nebula pulsar in which they predict a cosmic ray injection rate of 1036 particles s−1 with energies of 1014 eV per particle. They suggest that this periodic flux might be detectable if the magnetic field configuration along the line of sight to the pulsar were favourable. In this communication, I shall consider the conditions under which this would be possible; it seems that a detailed study of the times of arrival of high energy cosmic rays is warranted.

On the Mechanism of the Glitches in the Crab Nebula Pulsar

New observations of the wisps in the Crab Nebula show further examples of activity connected with sudden changes in the rotation rate of the pulsar. The evidence leads to a model of the “glitches” in which plasma is released explosively from the closed magneto-sphere of the neutron star.

Observation of the Crab Nebula at 30–100 keV

ON October 17, 1970, a measurement of the pulsed emission of hard X-rays from the Crab Nebula pulsar NP 0532 was made with a balloon-borne X-ray telescope launched from Palestine, Texas. The detectors consisted of three proportional counters filled with xenon at 2.5 atm and sensitive in the 30–100 keV X-ray region. Each counter was equipped with a 20×5 inch beryllium window and the depth of the gas volume was 5 inches. The efficiency was 80 % at 60 keV and the total effective area was 480 cm2. A multigrid collimator provided a field of view 3° FWHM in elevation and 12° FWHM in azimuth. Charged particle rejection was accomplished by surrounding the detector with an anticoincidence shield of argon-filled proportional counters.

Production of γ-rays in the crab nebula pulsar

The γ-ray flux at energies above 50 MeV from NP 0532 is evaluated for a pulsar model in which the optical and X radiations are produced by the synchrotron effect. Synchrotron radiation and inverse Compton scattering are considered as production mechanisms of the γ-rays. The theoretical estimates are compared with the experimental values.

Rotation Axis and Magnetic Field Axis of the Crab Nebula Pulsar PSR 0532 + 22

The pulse shape and the polarization data for the pulsar PSR 0532+22, at optical and radio wavelengths, together show that the magnetic axis is inclined at an angle approximately 45° to the rotation axis

Timing Observations of the Crab Nebula Pulsar at the Arecibo Observatory

Timing Observations of the Crab Nebula Pulsar at the Arecibo Observatory

Magnetic Field Structure around the Crab Nebula Pulsar

Forman and Visvanathan1 recently reported observations of the linear polarization in the central regions of the Crab Nebula. Their interpretations of the data in terms of magnetic fields must be substantially modified because the observations refer to an integration along the line of sight over the entire depth of the nebula, (This difficulty, of course, is common to all such observations, as is the fact that only the projection of the polarization onto the plane of the sky can be observed.) I would like to discuss the necessary modifications and also present some rather old but previously unpublished data on the polarization of the wisps.

On the empirical foundations of special relativity

It is known that the Lorentz transformation can be derived from purely topological and kinematical axioms, without reference to the velocity of light or to electrodynamics. The major consequences of this approach are discussed, and some deeply ingrained ideas are found wanting. The value of the kinematical limiting velocity c0 must be determined empirically; the usual assumption, here called the « signal postulate », identifies it with the light velocityc, but the evidence is fragmentary. The weakest link is the « second postulate » stating the independence ofc from the state of motion of the source; further work is desirable under circumstances where nonelectrodynamical forces, radiative reactions and changes of source acceleration play prominent roles. The signal postulate holds if and only ifc does not depend on frequency. Eecent observations on the Crab Nebula pulsar, an effectively stationary flash source, have established a constancy ofc in the visible region which can plausibly be interpreted as implying a photon rest mass of less than 2 MHz. However, a smaller limit may be surmised from the consistency of quantum electrodynamics as known at present; thus the pulsar work should be extended. It is also possible to determine c0 directly; the best way seems to be a calculation from combined nuclear transmutation energies and accuratem/e values. The kinematical approach also calls for sharper verifications of the direct consequences of the Lorentz transformation, such as Doppler effect, time dilatation and Einstein addition law; any observed violation would mean a failure of the underlying assumptions about the topological nature of space and time.