scholarly journals The Absorption by the Interstellar Medium of 80 MHz Radio Emission from Galactic Supernova Remnants

1972 ◽  
Vol 25 (4) ◽  
pp. 429 ◽  
Author(s):  
GA Dulk ◽  
OB Slee
Keyword(s):  
High Resolution ◽  
Radio Emission ◽  
Interstellar Medium ◽  
Flux Density ◽  
Electron Density ◽  
Supernova Remnants ◽  
Line Of Sight ◽  
The Galaxy

High resolution 80 MHz observations of 20 galactic supernova remnants have been made with the Culgoora radioheliograph. More than half of the sources have an unexpectedly low flux density at 80 MHz, probably as a result of free?free absorption taking place in the inner arms of the Galaxy. The observations imply an r.m.s. electron density of about 0�1?0�5 cm?3 along the line of sight. This large value for the electron density seems to require a greater ionizing flux than that which occurs in the solar vicinity.

scholarly journals High-Precision NBPP Timing Measurements at Nançay

2000 ◽  
Vol 177 ◽  
pp. 55-56
Author(s):  
I. Cognard ◽  
J.-F. Lestrade ◽  
D.C. Backer ◽  
P.S. Ray ◽  
R.S. Foster ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Real Time ◽  
Flux Density ◽  
Electron Density ◽  
San Francisco ◽  
High Precision ◽  
Line Of Sight ◽  
Radio Sources ◽  
Search Data ◽  
Scattering Events

The Nançay radiotelescope in France is a large collecting area (7000m2) with receivers around 1.4, 1.7 and 3.5GHz. At this observatory, we are conducting frequent high-precision timing observations of 5 millisecond pulsars (PSR B1937+21, B1821-24 since 1988; J1643-1224, J1713+0747 and B1620-26 since 1996) with a swept frequency oscilllator based on a DDS as a dedisperser.The most interesting result from these dense series of observations is the detection of several Extreme Scattering Events in direction of B1937+21 and possibly in direction of B1821-24 (Cognard, 1993,Nature,366, 320; Cognard & Lestrade, 1996, in ASP Conf. Ser. Vol 105, Pulsars: Problems and Progress (San Francisco: ASP), 469; Lestrade, Rickett & Cognard 1998, A&A,334, 1068). The flux density variations and TOA fluctuations observed have been used to estimate the size (several AU) and electron density (a few hundreds electrons cm−3) of the discrete ionised clouds localized in the interstellar medium that are thought to be responsible for this phenomena. The number of events recorded at Nançay in direction of B1937+21 yields the space density 105– 106pc−3for these clouds. This density is very large and is about 100 times higher than the density estimated from Extreme Scattering Events observed in direction of extragalactic radio sources (Fiedler et al., 1994,ApJ,430, 581). This might mean that the line of sight to B1937+21 is peculiar. This is being investigated with additional observations of a larger array of pulsars at Nançay with the Navy-Berkeley-Pulsar Processor (Figure 1) This processor NBPP (Foster et al., in ASP Conf. Ser. Vol 105, Pulsars: Problems and Progress (San Francisco: ASP), 25) has been used to acquire pulsar search data for 2 years at Nancay and we are now using its real-time folding capability.

Pulsars and Interstellar Scintillations

2000 ◽  
Vol 177 ◽  
pp. 539-544
Author(s):  
Y. Gupta
Keyword(s):  
Interstellar Medium ◽  
Electron Density ◽  
Density Fluctuations ◽  
Current Understanding ◽  
Pulsar Emission ◽  
The Galaxy ◽  
Electron Density Fluctuations

AbstractIn this paper, I review our current understanding of interstellar scintillations (ISS) of pulsars. The emphasis is on new results that have appeared during the last five years. The topics covered include (i) review of the understanding of refractive ISS (ii) the shape of the spectrum of electron density fluctuations in the interstellar medium (iii) the distribution of scattering plasma in the Galaxy (iv) resolving pulsar emission regions using ISS and (v) ISS and pulsar velocities.

scholarly journals High Resolution X-ray Images of Puppis a and IC 443

1983 ◽  
Vol 101 ◽  
pp. 289-293
Author(s):  
R. Petre ◽  
C. R. Canizares ◽  
P. F. Winkler ◽  
F. D. Seward ◽  
R. Willingale ◽  
...  
Keyword(s):  
High Resolution ◽  
Interstellar Medium ◽  
Molecular Cloud ◽  
Supernova Remnants ◽  
Surface Brightness ◽  
Middle Aged ◽  
X Ray ◽  
Giant Molecular Cloud

We present soft X-ray photomosaic images of two supernova remnants, Puppis A and IC 443, constructed from a series of exposures by the Einstein imaging instruments. The complex morphologies displayed in these images reflect the interaction between “middle-aged” supernova remnants and various components of the interstellar medium. Surface brightness variations across Puppis A suggest that inhomogeneities on scales from 0.2 to 30 pc are present in the interstellar medium, while the structure of IC 443 is apparently dominated by the interaction between the remnant and a giant molecular cloud.

scholarly journals Radio Emission from Supernova Remnants

1996 ◽  
Vol 145 ◽  
pp. 333-340
Author(s):  
Richard G. Strom
Keyword(s):  
Cosmic Rays ◽  
Radio Emission ◽  
Supernova Remnants ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Energy Content ◽  
Particle Energy ◽  
The Galaxy ◽  
Radio Frequencies ◽  
Shock Fronts

Most of the supernova remnants known in the Galaxy have only been detected at radio frequencies. The reason for this is absorption in the Galactic plane at both optical and X-ray wavelengths. All available evidence suggests that the shock fronts which accompany supernova remnants accelerate enough cosmic rays to GeV energies to produce readily detectable radio emission. This is fortunate, for it enables us to study remnants throughout the Galactic disk, although existing catalogues may be anywhere from 50 to 90 % incomplete. Cosmic rays and the magnetic fields in which they gyrate are the essential ingredients for producing the synchrotron radiation which is observed at radio frequencies. Various methods for estimating magnetic field strengths can be applied to a small number of remnants, and produce values not far from those based upon equipartition between the energy contents of particles and fields. From this, the particle energy content is derived for a number of objects.

scholarly journals Is there a Depolarization Horizon?

2018 ◽  
Author(s):  
A. S. Hill
Keyword(s):  
Interstellar Medium ◽  
Density Distribution ◽  
Electron Density ◽  
High Frequency ◽  
Electron Density Distribution ◽  
Low Frequency ◽  
Line Of Sight ◽  
Low Frequencies ◽  
Ionic Medium ◽  
Spiral Arm

Modern radio spectrometers make measurement of polarized intensity as a function of Faraday depth possible. I investigate the effect of depolarization along a model line of sight. I model sightlines with two components informed by observations: a diffuse interstellar medium with a lognormal electron density distribution and a narrow, denser component simulating a spiral arm or H~{\sc ii} region, all with synchrotron-emitting gas mixed in. I then calculate the polarized intensity from 300-1800 MHz and calculate the resulting Faraday depth spectrum. The idealized synthetic observations show far more Faraday complexity than is observed in Global Magneto-Ionic Medium Survey observations. In a model with a very nearby H~{\sc ii} region observed at low frequencies, most of the effects of a ``depolarization wall'' are evident: the H~{\sc ii} region depolarizes background emission and less (but not zero) information from beyond the H~{\sc ii} region reaches the observer. In other cases, the effects are not so clear, as significant amounts of information reach the observer even through significant depolarization, and it is not clear that low-frequency observations sample largely different volumes of the interstellar medium than high-frequency observations. The observed Faraday depth can be randomized such that it does not always have any correlation with the true Faraday depth.

scholarly journals Radio Emission from the Supernova Remnant Vela-X

1968 ◽  
Vol 21 (2) ◽  
pp. 201 ◽  
Author(s):  
DK Milne
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Radio Emission ◽  
Spectral Index ◽  
Supernova Remnants ◽  
Supernova Remnant ◽  
Magnetic Field Direction ◽  
Radio Observations ◽  
Optical Identification ◽  
Polarization Measurements

Radio observations are presented of the fairly large galactic complex Vela-X, Y, and Z. These sources are believed to be the remnant of a supernova having an optical identification with the filamentary nebula Stromlo 16. The brightness distributions, obtained at four frequencies, indicate an open annular structure reminiscent of other supernova remnants. The variation of spectral index over the region is investigated and shows that the radiation is substantially nontherm81, the integrated fluxes yielding a spectral index of -0,3. A high resolution distribution of magnetic field direction is deduced from polarization measurements made at three frequencies; a circumferential magnetic field is a possible interpretation of the field orientations.

scholarly journals Radio Emission from the Seyfert Galaxy NGC 5548

1982 ◽  
Vol 97 ◽  
pp. 191-192
Author(s):  
J. S. Ulvestad ◽  
A. S. Wilson ◽  
D. G. Wentzel
Keyword(s):  
High Resolution ◽  
Radio Emission ◽  
Radio Source ◽  
Seyfert Galaxy ◽  
Central Component ◽  
The Galaxy ◽  
Ngc 5548

Weak radio emission from the type 1.5 Seyfert galaxy NGC 5548 has been mapped with high resolution at the VLA at both 1465 and 4885 MHz. The galaxy contains the largest (5.9 kpc) triple radio source known in a Seyfert galaxy. The central component of that triple is unresolved (<0.39×0.15 kpc) and has a flatter spectrum than the well-resolved outer lobes. In addition, the field surrounding NGC 5548 and two of the sources in that field have been mapped at 1465 MHz; the field sources are unlikely to be physically associated with NGC 5548.

Goddard high-resolution spectrograph observations of the local interstellar medium and the deuterium/hydrogen ratio along the line of sight toward Capella

1993 ◽  
Vol 402 ◽  
pp. 694 ◽  
Author(s):  
Jeffrey L. Linsky ◽  
Alexander Brown ◽  
Ken Gayley ◽  
Athanassios Diplas ◽  
Blair D. Savage ◽  
...  
Keyword(s):  
High Resolution ◽  
Interstellar Medium ◽  
Line Of Sight ◽  
Local Interstellar Medium

scholarly journals MHD Simulation of Supernova Remnants

2017 ◽  
Vol 12 (S331) ◽  
pp. 174-177
Author(s):  
D. Wu ◽  
M. F. Zhang ◽  
S. S. Shan ◽  
W. W. Tian
Keyword(s):  
Radio Emission ◽  
Interstellar Medium ◽  
Density Distribution ◽  
Supernova Remnants ◽  
Stellar Winds ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Formation And Evolution ◽  
Progenitor Stars

AbstractWe present some Magnetohydrodynamic (MHD) simulations for supernova remnants (SNRs), which hints the thicknesses of SNRs’ shells are likely related to the density and density distribution of surrounding interstellar medium (ISM). The simulations show clear formation and evolution of reverse shocks. In addition, we find that stellar winds can blow a bubble around the progenitor stars then lead to weaker radio emission at the center of SNRs.

Supernova Remnants: A Generalized Theoretical Approach to the Radio Evolution

1979 ◽  
Vol 3 (5) ◽  
pp. 343-347 ◽  
Author(s):  
J. L. Caswell ◽  
I. Lerche
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Interstellar Medium ◽  
Theoretical Approach ◽  
Supernova Remnants ◽  
Theoretical Work ◽  
Relativistic Particles

Theoretical work on the radio emission from supernova remnants (SNRs) has not developed much since the pioneering work of Shklovsky (1960) and van der Laa (1962a, b). Despite agreement that the emission results from the synchrotron process, the origin of the relativistic particles and magnetic field is not clear. There are three reasonable alternatives: (i) particles and field originate within the ejected material (e.g. Shklovsky 1960);(ii) both field and particles originate in the compressed interstellar medium (e.g. van der Laan 1962a);(iii) the field is interstellar but the particles are from the ejecta (as outlined by van der Laan 1962b).

Sign in / Sign up

Export Citation Format

Share Document