Interstellar Broadening of Compact Low Galactic Latitude Radio Sources

Dennison, B.; Thomas, M.; Broderick, J. J.; Booth, R. S.; Brown, Robert L.; Condon, J. J.

doi:10.1007/978-94-010-9938-7_83

Cited by 10 publications

(14 citation statements)

References 7 publications

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“…Results for 1980 January to 1984 December have been reported in Mitchell et al (1994, hereafter Paper I), and discussions of selected sources can be found in Altschuler et al (1984), Dennison et al (1984), andOÏDell et al (1988). Here we present the data observed subsequent to 1984.…”

Section: Introductionmentioning

confidence: 54%

“…26) shows our results for this source for over 10 yr of monitoring at 318 and 430 MHz. Between about 1985.75 and1987.75, the 430 MHz Ñux density suddenly decreased from a relatively steady value of 3.3 Jy (a value also measured in 1981 October by Dennison et al 1984) to a steady value of 2.25 Jy, returning to approximately 3.3 Jy after this period. We note that this behavior is not at all reÑected in the 318 MHz monitoring data, where the Ñux density remained at a level of approximately 3 Jy over the whole period.…”

Section: B2050]364mentioning

confidence: 86%

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14‐year Program Monitoring the Flux Densities of 33 Radio Sources at Low Frequencies

Salgado¹,

Altschuler²,

Ghosh³

et al. 1999

ASTROPHYS J SUPPL S

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We present the results of a low-frequency Ñux density monitoring program of 33 extragalactic radio sources. The light curves at 318 and 430 MHz over a 14 yr period are presented. The measurements were made with the NAIC Arecibo 305 m radio telescope at approximately bimonthly intervals between 1980 January and 1989 February and at less regular intervals between 1989 October and 1993 October, for a total of 64 observing sessions. In addition, we provide a Ðrst discussion of the results, pointing out several source properties and interesting objects.

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Section: Introductionmentioning

confidence: 54%

Section: B2050]364mentioning

confidence: 86%

14‐year Program Monitoring the Flux Densities of 33 Radio Sources at Low Frequencies

Salgado¹,

Altschuler²,

Ghosh³

et al. 1999

ASTROPHYS J SUPPL S

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“…The normalization coefficient is a slowly varying C N 2 function of position and variations on angular scales as small as a few degrees have been reported (Fey, Spangler, & Mutel 1989 ;Dennison et al 1984). Observations indicate that the power spectral index b is close to 11/3.…”

Section: Turbulence and Interstellar Scatteringmentioning

confidence: 80%

“…In equations (1) and (2), the coefficient may vary slowly both transversely and along C N 2 the line of sight. The angular size reÑects the integral of C N 2 along the line of sight and has been reported to vary between di †erent, sometimes quite closely spaced, lines of sight (Dennison et al 1984 ;Fey et al 1989 ;Desai et al 1994 ;Frail et al 1994). As discussed by Rickett (1977), an interferometer samples spatial scales in the medium corresponding to the projected baselines of the interferometer transverse to the line of sight and averaged over a multipath scale.…”

Section: Turbulence and Interstellar Scatteringmentioning

confidence: 99%

Anisotropic Interstellar Scattering toward the Cygnus Region

Desai¹,

Fey²

2001

ASTROPHYS J SUPPL S

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We were unable to reliably determine scattering disk parameters for 2021]317 at frequencies from 8.5 GHz down to 1.67 GHz because of its complex intrinsic source structure. The scattering disks are elliptical with axial ratios of about 0.75 : 1 with little measurable variation between these sources. We interpret our measurements as due to the e †ects of anisotropic interstellar turbulence. The anisotropy parameters, axial ratio and position angle, for those sources for which we have data at multiple frequencies appear to be frequency-independent making refractive distortions of isotropic turbulence an unlikely explanation. Our estimates of b, the power-law index of the power spectrum of electron density Ñuctuations, based upon direct model Ðts to the data on a source-by-source and frequency-by-frequency basis, are consistent with b \ 4 for most of the data but are strongly a †ected by our estimate of the intrinsic structure of the sources. Two of these sources, 2005]403 and 2021]317, exhibit signiÐcant intrinsic source structure at frequencies as low as 1.67 GHz, while the other two, 2008]332 and 2048]312, lack discernible source structure at frequencies lower then 2.3 GHz. The frequency scalings of the scattered angular sizes are also consistent with b \ 4. We discuss the implications of our measurements for the inner and outer scales of the turbulence.

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“…At most frequencies, the formal uncertainties are comparable to the size of the points. The datum at 0.25 GHz is from P. Rao (2001, private communication) and that at 0.408 from Dennison et al (1984). For reference, three curves are also plotted, one showing a À2 dependence for the diameter (dotted line), one showing a À2:2 dependence (dashed line), and one showing a À1:4 dependence (dot-dashed line) that would be expected if the angular broadening for B1849+005 is anomalous in a manner similar to that for PSR B1849+00 (x 4.2).…”

Section: The Electron Density Spectrummentioning

confidence: 99%

On the Enhanced Interstellar Scattering toward B1849+005

Lazio

2004

ApJ

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This paper reports new Very Large Array ( VLA) and Very Long Baseline Array ( VLBA) observations of the extragalactic source B1849+005 (Galactic coordinates ' ¼ 33N44, b ¼ þ0N21) at frequencies between 0.33 and 15 GHz and the reanalysis of archival VLA observations at 0.33, 1.5, and 4.9 GHz. The structure of this source is complex, confirming previous suggestions, but interstellar scattering dominates the structure of the central component at least to 15 GHz. An analysis of the phase structure functions of the interferometric visibilities shows the density fluctuations along this line of sight to be anisotropic (axial ratio = 1.3) with a frequency-independent position angle and having an inner scale of roughly a few hundred kilometers. The anisotropies occur on length scales of order 10 15 cm (D/5 kpc), which within the context of certain magnetohydrodynamic turbulence theories indicates the length scale on which the kinetic and magnetic energy densities are comparable. A conservative upper limit on the velocity of the scattering material is 1800 km s À1 , based on the lack of changes in the shapes of the 0.33 GHz images. In the 0.33 GHz field of view, there are a number of other sources that might also be heavily scattered, which would suggest that there are large changes in the scattering strength on lines of sight separated by a degree or less. Both B1849+005 and PSR B1849+00 are highly scattered, and they are separated by only 13 0 . If the lines of sight are affected by the same ''clump'' of scattering material, it must be at least 2.3 kpc distant. However, a detailed attempt to account for the scattering observables toward these sources (angular broadening of the extragalactic source, pulse broadening of the pulsar, and upper limits on the angular broadening of the pulsar) does not produce a self-consistent set of parameters for a clump that can reproduce all three measured scattering observables. A clump of H emission, possibly associated with the H ii region G33.418À0.004, lies between these two lines of sight, but it seems unable to account for all of the required excess scattering.

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Interstellar Broadening of Compact Low Galactic Latitude Radio Sources

Cited by 10 publications

References 7 publications

14‐year Program Monitoring the Flux Densities of 33 Radio Sources at Low Frequencies

14‐year Program Monitoring the Flux Densities of 33 Radio Sources at Low Frequencies

Anisotropic Interstellar Scattering toward the Cygnus Region

On the Enhanced Interstellar Scattering toward B1849+005

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