scholarly journals Pulsar distances, spiral structure and the interstellar medium

1970 ◽  
Vol 38 ◽  
pp. 178-181 ◽  
Author(s):  
B. Y. Mills
Keyword(s):  
Interstellar Medium ◽  
Electron Density ◽  
Supernova Remnants ◽  
Spiral Structure ◽  
Radio Continuum ◽  
Average Electron Density ◽  
Uniform Medium ◽  
The Mean ◽  
Average Electron

The distances of all pulsars are calculated on the assumption that they are immersed in a uniform medium of average electron density 0.06 cm−3. It then appears that the pulsars are concentrated towards the local and Sagittarius spiral features and that their mean height above the plane is consistent with that of known supernova remnants. The mean distances appear to be approximately correct, but individual distances are uncertain by about a factor of two. Evidence from radio continuum results supports this model of the ionized interstellar medium.

scholarly journals Energy balance in the interstellar medium

1979 ◽  
Vol 84 ◽  
pp. 245-252 ◽  
Author(s):  
E. E. Salpeter
Keyword(s):  
Interstellar Medium ◽  
Supernova Remnants ◽  
Stellar Winds ◽  
X Rays ◽  
Phase 2 ◽  
Ob Stars ◽  
Average Electron Density ◽  
Average Electron ◽  
Uv Photons ◽  
Intercloud Medium

A large number (approximately 7) of different components or phases are needed to describe the interstellar medium. The neutral intercloud medium is probably a composite of (a) “lukewarm, substandard” clouds (heated by grain photoeffect and shockwaves), (b) the interfaces between clouds and coronal gas and (c) some “phase 2” gas heated by soft X-rays. Ionizing UV photons are mainly produced by OB-stars and are responsible for most of the average electron density. Bulk kinetic energy for “stirring” the medium and soft X-rays are mainly produced by supernova remnants, less by O-star stellar winds.

scholarly journals X-ray phase determination by the principle of minimum charge

1999 ◽  
Vol 55 (3) ◽  
pp. 489-499 ◽  
Author(s):  
Veit Elser
Keyword(s):  
Electron Density ◽  
Diffraction Data ◽  
Global Minimum ◽  
Unit Cell ◽  
Electronic Charge ◽  
Total Charge ◽  
Phase Determination ◽  
X Ray ◽  
Average Electron Density ◽  
Average Electron

When the electron density in a crystal or a quasicrystal is reconstructed from its Fourier modes, the global minimum value of the density is sensitively dependent on the relative phases of the modes. The set of phases that maximizes the value of the global minimum corresponds, by positivity of the density, to the density having the minimum total charge that is consistent with the measured Fourier amplitudes. Phases that minimize the total electronic charge (i.e. the average electron density) have the additional property that the lowest minima of the electron density become exactly degenerate and proliferate within the unit cell. The large number of degenerate minima have the effect that density maxima are forced to occupy ever smaller regions of the unit cell. Thus, by minimization of the electronic charge, the atomicity of the electron density is enhanced as well. Charge minimization applied to simulated crystalline and quasicrystalline diffraction data successfully reproduces the correct phases starting from random initial phases.

Supernova explosions in stellar wind bubbles

1991 ◽  
Vol 148 ◽  
pp. 331-333
Author(s):  
S. Jane Arthur
Keyword(s):  
Interstellar Medium ◽  
Stellar Wind ◽  
Spherical Symmetry ◽  
Supernova Remnants ◽  
Stellar Winds ◽  
Type Ii ◽  
Uniform Medium ◽  
Nearby Stars ◽  
Supernova Explosions

Type II supernovae play a major role in the dynamics of the interstellar medium. The interstellar medium in which such supernovae evolve is often considerably modified by the strong stellar winds both from the progenitor and other nearby stars. The result is that the appearance and energetics of the remnants can be very different from that of remnants in a uniform medium. In this paper we will consider the evolution of supernova remnants in stellar wind bubbles including the effect of departures from spherical symmetry. The aim is to understand both the appearance of such remnants and their effect on the overall energetics of the interstellar medium.

A radio method of searching for fine structure in H 11 regions

1967 ◽  
Vol 31 ◽  
pp. 237
Author(s):  
O. B. Slee
Keyword(s):  
Fine Structure ◽  
Radio Emission ◽  
Electron Density ◽  
Path Length ◽  
Low Frequency ◽  
Radio Sources ◽  
Average Electron Density ◽  
Scale Size ◽  
Average Electron ◽  
Radio Method

Fine structure with a scale size of about 10-3pc in the galactic ionized hydrogen may scatter the low-frequency radio emission of extragalactic sources with intrinsically small angular diameters, thus making them apparently large. For example, application of the Chandrasekhar scattering formula to a path length of 100 pc through an H 11 region with an average electron density of 0·1 cm-3, and structure of scale size 10-3pc filling 1% of the volume, results in a scattering to half-brightness points of 8″ (arc) at 38 MHz. Radio sources with apparent angular sizes of this amount should be partially resolved by an interferometer with an effective baseline of about 10 000 wavelengths.

scholarly journals Emission Nebulae as Radio Sources

1956 ◽  
Vol 9 (2) ◽  
pp. 218 ◽  
Author(s):  
BY Mills ◽  
AG Little ◽  
KV Sheridan
Keyword(s):  
Electron Temperature ◽  
Electron Density ◽  
Radio Telescope ◽  
Optical Data ◽  
Radio Sources ◽  
Pencil Beam ◽  
Orion Nebula ◽  
Average Electron Density ◽  
Average Electron ◽  
Bright Emission

Attempts have been made to detect 14 bright emission nebulae at a wavelength of 3?5 m using a pencil-beam radio telescope with a beamwidth of 50 min of arc. Of these nebulae, six were probably observed in emission, seven were undetectable, and one, NGC 6357, was observed in absorption; radio isophotes were obtained for NGC 2237 and NGC 3372. Radio and optical data have been combined to estimate electron densities, masses, and sometimes the electron temperature of many of the nebulae. Values range from an electron density of 3 cm?3 and a mass of 3�10. solar masses for the outer regions of the 30 Doradus complex to an average electron density of 500 cm?3 and a mass of 20 solar masses for the Orion Nebula. Temperatures generally appear to be in the neighbourhood of 10,000 �K, except in the case of NGC 6357, for which 6500 �K is estimated.

scholarly journals Multi-wavelength View of the Interstellar Medium in the Large Magellanic Cloud

1998 ◽  
Vol 15 (1) ◽  
pp. 136-140
Author(s):  
You-Hua Chu
Keyword(s):  
Interstellar Medium ◽  
Supernova Remnants ◽  
Optical Emission ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Radio Continuum ◽  
Emission Lines ◽  
X Rays ◽  
Multi Wavelength ◽  
The Relationship

AbstractThe Large Magellanic Cloud (LMC) has been surveyed in optical emission lines, X-rays, radio continuum, HI, and CO lines. These surveys provide views of the interstellar medium (ISM) in the LMC of unprecedented clarity, allowing us to study astrophysical processes and to examine the relationship among the different phases of the ISM. Multi-wavelength images are used to illustrate the physical structures of supernova remnants, superbubbles, and supergiant shells, as well as the global interstellar structure of the LMC.

scholarly journals Unidentified γ-ray emission towards the SNR Kes 41 revisited

2018 ◽  
Vol 619 ◽  
pp. A109
Author(s):  
L. Supan ◽  
G. Castelletti ◽  
A. D. Supanitsky ◽  
M. G. Burton
Keyword(s):  
Interstellar Medium ◽  
Physical Properties ◽  
Supernova Remnants ◽  
Surrounding Medium ◽  
Radio Continuum ◽  
Pion Decay ◽  
Large Area ◽  
Bremsstrahlung Emission ◽  
Γ Ray ◽  
Hadronic Collisions

Kes 41 is one of the Galactic supernova remnants (SNRs) that are proposed to be physically linked to γ-ray emission at GeV energies. The nature of the γ-ray photons has been explained, but inconclusively, as hadronic collisions of particles accelerated at the SNR blast wave with target protons in an adjacent molecular clump. We performed an analysis of Fermi-Large Area Telescope (LAT) data of about nine years to assess the origin of the γ-ray emission. To investigate this matter, we also used spectral modelling constraints from the physical properties of the interstellar medium towards the γ-ray emitting region along with a revised radio continuum spectrum of Kes 41 (α = −0.54 ± 0.10, S ∝ να). We demonstrate that the γ-ray fluxes in the GeV range can be explained through bremsstrahlung emission from electrons interacting with the surrounding medium. We also considered a model in which the emission is produced by pion decay after hadronic collisions, and confirm that this mechanism cannot be excluded.

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