Low-frequency Spectrum of the Crab Nebula

Nature ◽  
1970 ◽  
Vol 225 (5237) ◽  
pp. 1035-1037 ◽  
Author(s):  
A. H. BRIDLE
Keyword(s):  
Frequency Spectrum ◽  
Crab Nebula ◽  
Low Frequency ◽  
The Crab Nebula

Preferential acceleration of heavy ions from thermal velocities

1968 ◽  
Vol 46 (10) ◽  
pp. S638-S641 ◽  
Author(s):  
D. B. Melrose
Keyword(s):  
Frequency Spectrum ◽  
High Frequency ◽  
Heavy Ions ◽  
Crab Nebula ◽  
Low Frequency ◽  
High Frequency Waves ◽  
Hydromagnetic Waves ◽  
The Crab Nebula ◽  
Low Frequency Waves

The acceleration of ions from thermal velocities is analyzed to determine conditions under which heavy ions can be preferentially accelerated. Two accelerating mechanisms involving high-and low-frequency hydromagnetic waves respectively are considered. Preferential acceleration of heavy ions occurs for high-frequency waves if the frequency spectrum falls off faster than (frequency)−1. For the low-frequency waves heavy ions are less effectively accelerated than lighter ions. However, very heavy ions can be preferentially accelerated, the abundances of the very heavy ions being enhanced by a factor Ai over the thermal abundances. Acceleration of ions in the envelope of the Crab nebula is considered as an example.

scholarly journals Strong Waves from Pulsars and Morphologies in SNRs

1983 ◽  
Vol 101 ◽  
pp. 499-501
Author(s):  
Gregory Benford ◽  
Attilio Ferrari ◽  
Silvano Massaglia
Keyword(s):  
Large Amplitude ◽  
Crab Nebula ◽  
Surrounding Medium ◽  
Low Frequency ◽  
Optical Emission ◽  
Amplitude Wave ◽  
Surface Magnetic Field ◽  
Plasma Absorption ◽  
The Crab Nebula ◽  
Large Amplitude Wave

Canonical models for pulsars predict the emission of low–frequency waves of large amplitudes, produced by the rotation of a neutron star possessing a strong surface magnetic field. Pacini (1968) proposed this as the basic drain which yields to the pulsar slowing–down rate. The main relevance of the large amplitude wave (LAW) is the energetic link it provides between the pulsar and the surrounding medium. This role has been differently emphasized (Rees and Gunn, 1974; Ferrari, 1974), referring to absorption effects by relativistic particle acceleration and thermal heating, either close to the pulsar magnetosphere or in the nebula. It has been analyzed in the special case of the Crab Nebula, where observations are especially rich (Rees, 1971). As the Crab Nebula displays a cavity around the pulsar of dimension ∼1017cm, the function of the wave in sweeping dense gas away from the circumpulsar region is widely accepted. Absorption probably occurs at the inner edges of the nebula; i.e., where the wave pressure and the nebular pressure come into balance. Ferrari (1974) interpreted the wisps of the Crab Nebula as the region where plasma absorption occurs, damping the large amplitude wave and driving “parametric” plasma turbulence, thus trasferring energy to optical radiation powering the nebula. The mechanism has been extended to interpret the specific features of the “wisps” emission (Benford et al., 1978). Possibly the wave fills the nebula completely, permeating the space outside filaments with electromagnetic energy, continuously accelerating electrons for the extended radio and optical emission (Rees, 1971).

scholarly journals Reconnection in Pulsar Winds

2001 ◽  
Vol 18 (4) ◽  
pp. 415-420 ◽  
Author(s):  
J. G. Kirk ◽  
Y. Lyubarsky
Keyword(s):  
Magnetic Field ◽  
Energy Transport ◽  
Crab Nebula ◽  
Low Frequency ◽  
Frequency Wave ◽  
Poynting Flux ◽  
High Particle ◽  
The Crab Nebula ◽  
Pulsar Winds ◽  
The Magnetic Field

AbstractThe spin-down power of a pulsar is thought to be carried away in an MHD wind in which, at least close to the star, the energy transport is dominated by Poynting flux. The pulsar drives a low frequency wave in this wind, consisting of stripes of toroidal magnetic field of alternating polarity, propagating in a region around the equatorial plane. The current implied by this configuration falls off more slowly with radius than the number of charged particles available to carry it, so that the MHD picture must, at some point, fail. Recently, magnetic reconnection in such a structure has been shown to accelerate the wind significantly. This reduces the magnetic field in the comoving frame and, consequently, the required current, enabling the solution to extend to much larger radius. This scenario is discussed and, for the Crab Nebula, the range of validity of the MHD solution is compared with the radius at which the flow appears to terminate. For sufficiently high particle densities, it is shown that a low frequency entropy wave can propagate out to the termination point. In this case, the ‘termination shock’ itself must be responsible for dissipating the wave.This paper is dedicated to Don Melrose on his 60th birthday.

The Fortieth Anniversary of Extragalactic Radio Astronomy: Radiophysics in Exile

1990 ◽  
Vol 8 (04) ◽  
pp. 381-383 ◽  
Author(s):  
J. G. Bolton
Keyword(s):  
Radio Astronomy ◽  
Crab Nebula ◽  
Low Frequency ◽  
Early Years ◽  
Owens Valley ◽  
Detection Range ◽  
Staff Members ◽  
Cygnus A ◽  
The Galaxy ◽  
The Crab Nebula

In 1931 Karl Jansky established that radio noise was associated with our own galaxy–the Milky Way. For a decade and a half there was little follow-up; those of us who were associated with low frequency radar during the war regarded it as a nuisance which could limit the detection range of enemy aircraft. Grote Reber was the first to make a detailed but fairly low resolution map of the radiation from the galaxy showing, for the first time, some detailed structure. The event which we celebrate today occurred when Gordon Stanley, Bruce Slee and I showed that three of the discrete sources that we had discovered could be identified with visual objects. One was with the Crab Nebula, a supernova remnant within our own galaxy and the other two with galaxies, far beyond our own system, in the constellations of Virgo and Centaurus. Thus began extragalactic radio astronomy. In 1982 at the Noosa meeting of the ASA, I gave an account of those early years, later to be published in the ASA Proceedings. As I don’t wish to repeat myself, I propose to speak on my involvement in a later development which was to extend the observable scale of the universe to look-back times as great as the age of the oldest stars in our own system. The first important step was Graham Smith’s identification of Cygnus A with a galaxy that was much fainter than our two. The spectrum by Minkowski revealed an instrinsically highly-luminous galaxy with strong emission lines and opened up the possibility of discovering similar objects at significantly greater distance. This was achieved nine years later with the building of the Owens Valley Observatory and my title of ‘Radiophysics in Exile’ comes from the fact the observatory owed its existence and early successes very largely to past and future staff members of Radiophysics. They were, in order of appearance, J. G. Bolton, G. J. Stanley, K. C. Westfold, J. A. Roberts, V. Radhakrishnan, D. Morris and K. I. Kellermann. Some still bear . the scars–Westfold left the tip of one index finger in the Owens Valley!

Position of the Low Frequency Radio Source in the Crab Nebula

Nature ◽  
1967 ◽  
Vol 213 (5082) ◽  
pp. 1213-1214 ◽  
Author(s):  
J. F. R. GOWER
Keyword(s):  
Radio Source ◽  
Crab Nebula ◽  
Low Frequency ◽  
The Crab Nebula

Observation of Polarization for the Crab Nebula with PHENEX Polarimeter

2010 ◽  
Vol 8 (ists27) ◽  
pp. Tm_35-Tm_40 ◽  
Author(s):  
Yuji KISHIMOTO ◽  
Shuichi GUNJI ◽  
Yushi ISHIKAWA ◽  
Makoto TAKADA ◽  
Tatehiro MIHARA ◽  
...  
Keyword(s):  
Crab Nebula ◽  
The Crab Nebula

A Model for the Moving “Wisps” in the Crab Nebula

1999 ◽  
Vol 512 (2) ◽  
pp. 755-760 ◽  
Author(s):  
Mitchell C. Begelman
Keyword(s):  
Crab Nebula ◽  
The Crab Nebula

scholarly journals The Crab nebula variability at short time-scales with the Cherenkov telescope array

2020 ◽  
Vol 501 (1) ◽  
pp. 337-346
Author(s):  
E Mestre ◽  
E de Oña Wilhelmi ◽  
D Khangulyan ◽  
R Zanin ◽  
F Acero ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Crab Nebula ◽  
Spectral Energy Distribution ◽  
Spectral Energy ◽  
Telescope Array ◽  
Cherenkov Telescopes ◽  
Cherenkov Telescope ◽  
Emission Models ◽  
Short Time ◽  
The Crab Nebula

ABSTRACT Since 2009, several rapid and bright flares have been observed at high energies (>100 MeV) from the direction of the Crab nebula. Several hypotheses have been put forward to explain this phenomenon, but the origin is still unclear. The detection of counterparts at higher energies with the next generation of Cherenkov telescopes will be determinant to constrain the underlying emission mechanisms. We aim at studying the capability of the Cherenkov Telescope Array (CTA) to explore the physics behind the flares, by performing simulations of the Crab nebula spectral energy distribution, both in flaring and steady state, for different parameters related to the physical conditions in the nebula. In particular, we explore the data recorded by Fermi during two particular flares that occurred in 2011 and 2013. The expected GeV and TeV gamma-ray emission is derived using different radiation models. The resulting emission is convoluted with the CTA response and tested for detection, obtaining an exclusion region for the space of parameters that rule the different flare emission models. Our simulations show different scenarios that may be favourable for achieving the detection of the flares in Crab with CTA, in different regimes of energy. In particular, we find that observations with low sub-100 GeV energy threshold telescopes could provide the most model-constraining results.

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