Activity and radio spectral index variations near the center of the Crab nebula

1992 ◽  
Vol 393 ◽  
pp. 206 ◽  
Author(s):  
M. F. Bietenholz ◽  
P. P. Kronberg
Keyword(s):  
Spectral Index ◽  
Crab Nebula ◽  
The Crab Nebula

scholarly journals Diffusion and advection model for particle transport in young pulsar wind nebulae

2012 ◽  
Vol 8 (S291) ◽  
pp. 265-268
Author(s):  
Xiaping Tang ◽  
Roger A. Chevalier
Keyword(s):  
Spectral Index ◽  
Particle Transport ◽  
Crab Nebula ◽  
Outer Boundary ◽  
Outer Part ◽  
Pulsar Wind Nebulae ◽  
Pure Diffusion ◽  
Pulsar Wind ◽  
Kink Instability ◽  
The Crab Nebula

AbstractThe magnetohydrodynamic (MHD) model for young pulsar wind nebulae (PWN) has been successful in reproducing many features of the nebulae. The model is characterized by a termination shock (TS) between the PWN and unshocked pulsar wind. Relativistic particles are injected at the TS and follow an advective flow to the outer boundary. However, toroidal structure of well studied young PWN like the Crab Nebula, 3C 58 and G21.5-0.9 is only present in the region close to the TS. In the outer parts of the nebulae, filamentary and loop-like structure is observed. Also, the radial variation of spectral index due to synchrotron losses is smoother than expected in the MHD flow model. We find that a pure diffusion model with energy independent diffusion and a transmitting boundary can reproduce the basic data on nebular size and spectral index variation for the Crab, 3C 58, and G21.5-0.9. Energy dependent diffusion is also discussed. Power law variations of the coefficient with energy are degenerate with variation in the input particle energy distribution index in the steady state case. Monte Carlo simulations of particle transport with both diffusion and advection for the Crab nebula and 3C 58 suggest a picture in which advection dominates the inner part of the PWN where toroidal structure is clearly present. Diffusion dominates the outer part of the PWN where filamentary and loop-like structure is observed. The source of the chaotic field is uncertain, but may be related to Rayleigh-Taylor instability at the outer boundary of young nebulae and/or the kink instability of the toroidal magnetic field.

scholarly journals The Radio Spectral Index of the Crab Nebula

1997 ◽  
Vol 490 (1) ◽  
pp. 291-301 ◽  
Author(s):  
M. F. Bietenholz ◽  
N. Kassim ◽  
D. A. Frail ◽  
R. A. Perley ◽  
W. C. Erickson ◽  
...  
Keyword(s):  
Spectral Index ◽  
Crab Nebula ◽  
The Crab Nebula

scholarly journals The dust content of the Crab Nebula

2019 ◽  
Vol 488 (1) ◽  
pp. 164-182 ◽  
Author(s):  
I De Looze ◽  
M J Barlow ◽  
R Bandiera ◽  
A Bevan ◽  
M F Bietenholz ◽  
...  
Keyword(s):  
Spectral Index ◽  
Near Infrared ◽  
Crab Nebula ◽  
Dust Emission ◽  
Infrared Emission ◽  
Small Contribution ◽  
Dust Extinction ◽  
Dust Mass ◽  
The Crab Nebula ◽  
Dust Condensation

ABSTRACT We have modelled the near-infrared to radio images of the Crab Nebula with a Bayesian SED model to simultaneously fit its synchrotron, interstellar (IS), and supernova dust emission. We infer an IS dust extinction map with an average AV = 1.08 ± 0.38 mag, consistent with a small contribution (${\lesssim }22{{\ \rm per\ cent}}$) to the Crab’s overall infrared emission. The Crab’s supernova dust mass is estimated to be between 0.032 and 0.049 M⊙ (for amorphous carbon grains) with an average dust temperature Tdust = 41 ± 3 K, corresponding to a dust condensation efficiency of 8–12 ${{\ \rm per\ cent}}$. This revised dust mass is up to an order of magnitude lower than some previous estimates, which can be attributed to our different IS dust corrections, lower SPIRE flux densities, and higher dust temperatures than were used in previous studies. The dust within the Crab is predominantly found in dense filaments south of the pulsar, with an average V-band dust extinction of AV = 0.20–0.39 mag, consistent with recent optical dust extinction studies. The modelled synchrotron power-law spectrum is consistent with a radio spectral index αradio = 0.297 ± 0.009 and an infrared spectral index αIR = 0.429 ± 0.021. We have identified a millimetre excess emission in the Crab’s central regions, and argue that it most likely results from two distinct populations of synchrotron emitting particles. We conclude that the Crab’s efficient dust condensation (8–12 ${{\ \rm per\ cent}}$) provides further evidence for a scenario where supernovae can provide substantial contributions to the IS dust budgets in galaxies.

scholarly journals A Newly-Recognised Galactic Supernova Remnant with Shell-Type and Filled-Centre Features

1988 ◽  
Vol 101 ◽  
pp. 347-350
Author(s):  
Peter J. Barnes ◽  
A.J. Turtle
Keyword(s):  
Spectral Index ◽  
Supernova Remnants ◽  
Supernova Remnant ◽  
Crab Nebula ◽  
Dual Nature ◽  
Valuable Addition ◽  
Shell Type ◽  
The Crab Nebula ◽  
Galactic Object

While the number of galactic supernova remnants (SNRs) now known is fairly large (>150), the subset among these that are known to resemble the Crab Nebula is still distressingly small, about 15 or so (Green, 1984). Thus any object that can be unambiguously included in this exclusive club forms a valuable addition to our knowledge of this class. We report here observations of a newly recognised nonthermal galactic object, G18.94-l.06, having all the hallmarks of the classical shell-type SNRs, while also appearing to have a filled-centre component located inside the shell. Among the known Crab-like remnants, about one third show this dual nature (Green, 1984). This diagnosis of G18.94-1.06 is supported mainly by the variations in spectral index α (Sν∝ να) across the source, as seen between the two observation frequencies, 408 MHz and 5.0 GHz.

scholarly journals The Electromagnetic Spectrum of the Crab Nebula

1971 ◽  
Vol 46 ◽  
pp. 22-31 ◽  
Author(s):  
J. E. Baldwin
Keyword(s):  
Flux Density ◽  
Spectral Index ◽  
Crab Nebula ◽  
Electromagnetic Spectrum ◽  
Optical Range ◽  
X Ray ◽  
Radio Data ◽  
A Value ◽  
The Crab Nebula

I shall discuss observations of the spectrum of the integrated emission from the Crab Nebula. The radio data with accurate calibrations lead to a flux density spectral index of −0.26. Discrepancies in the published fluxes at millimetre wavelengths can be resolved if appropriate angular dimensions are used. In the optical range the spectral index has increased to a value of −0.9 if 1m.0 of absorption is used. At X-ray wavelengths the spectral index has increased further to −1.2.

scholarly journals THE RADIO-2 mm SPECTRAL INDEX OF THE CRAB NEBULA MEASURED WITH GISMO

2011 ◽  
Vol 734 (1) ◽  
pp. 54 ◽  
Author(s):  
R. G. Arendt ◽  
J. V. George ◽  
J. G. Staguhn ◽  
D. J. Benford ◽  
M. J. Devlin ◽  
...  
Keyword(s):  
Spectral Index ◽  
Crab Nebula ◽  
The Crab Nebula

scholarly journals The Lunar Occultation Of The Crab Nebula Observed At Parkes On June 21, 1963

1966 ◽  
Vol 19 (3) ◽  
pp. 409 ◽  
Keyword(s):  
Spectral Index ◽  
Linear Polarization ◽  
Radio Occultation ◽  
Crab Nebula ◽  
Frequency Range ◽  
Lunar Occultation ◽  
Central Regions ◽  
Optical Continuum ◽  
Optical Brightness ◽  
The Crab Nebula

Measurements of the intensity and percentage linear polarization of the Crab nebula radiation at 404 and 1420 Mc/s were made during the partial occultation of .June 21, 1963. The radio occultation curves are similar in shape to that calculated from the isophotes of the optical continuum and show the same principal features. However, the ratio of radio to optical brightness varies in a systematic way across the source, the ratio being greater at the edges than in the central regions. This steepening of the spectral index towards the outer edges continues in the radio frequency range from 1420 to 404 Mc/s. The 1420 Mc/s linear polarization is stronger in the inner areas (2,5%) than in the outer areas (< 1%) of the source.

scholarly journals Infrared Observations of the Crab Nebula

2000 ◽  
Vol 177 ◽  
pp. 503-504
Author(s):  
Yves A. Gallant ◽  
Richard J. Tuffs
Keyword(s):  
Spectral Index ◽  
Narrow Band ◽  
Crab Nebula ◽  
Infrared Observations ◽  
The Crab Nebula ◽  
Index Maps

AbstractWe obtained narrow-band continuum images of the Crab Nebula at 16, 6.4 and 2.2µm. From these we derive spectral index maps, extending the optical work of Véron-Cetty &amp; Woltjer (1993). In the central parts of the Nebula the IR spectral index is close to the radio one, indicating the region where the radio-emitting electrons are accelerated.

The X-Ray Pulsed Fraction of NP0532 and Interstellar Grains

1975 ◽  
Vol 2 (6) ◽  
pp. 325-327
Author(s):  
R.M. Thomas
Keyword(s):  
Spectral Index ◽  
Interstellar Dust ◽  
Crab Nebula ◽  
X Rays ◽  
Dust Grains ◽  
X Ray ◽  
Interstellar Dust Grains ◽  
Low Energies ◽  
Pulse Structure ◽  
The Crab Nebula

In this paper we report that the available data on the measured pulsed fraction of X-rays from the Crab Nebula between the energies 0.7 and 300 keV indicate that it is no longer necessary to postulate an intrinsic change in the pulsar spectral index near 30 keV. Furthermore the spectral flattening which is evident at low energies can be entirely attributed, within the precision of the available statistics to the destruction of time coherence of the pulse structure by the scattering action of interstellar dust grains.

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