The Spectra of Radio Sources in the Revised 3c Catalogue

Kellermann, K. I.; Pauliny-Toth, I. I. K.; Williams, P. J. S.

doi:10.1086/150046

Cited by 273 publications

(127 citation statements)

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“…However, at frequencies 300 MHz, the RBC scale is in agreement with the KPW scale (Kellermann et al 1969), for which we have conversion factors from the Baars scale (Baars et al 1977 , Table 7). Therefore, we used those factors to rescale the maps at 1.4, 1.6, and 10.55 GHz from the Baars scale to the RBC scale.…”

Section: Absolute Flux Densitysupporting

confidence: 69%

“…To do that, we collected the total flux measurements available in the literature in the frequency range from 10 to 1400 MHz (Braude et al 1969;Bridle & Purton 1968;Roger et al 1969;Viner & Erickson 1975;Kellermann et al 1969;Wright & Otrupcek 1990). Each data-point was corrected to match the Roger et al (1973;RBC) flux scale with correction factors from Laing & Peacock (1980) and Scaife & Heald (2012).…”

Section: Absolute Flux Densitymentioning

confidence: 99%

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M 87 at metre wavelengths: the LOFAR picture

Gasperin

Orrù

Murgia

et al. 2012

A&A

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Context. M 87 is a giant elliptical galaxy located in the centre of the Virgo cluster, which harbours a supermassive black hole of mass 6.4 × 10 9 M , whose activity is responsible for the extended (80 kpc) radio lobes that surround the galaxy. The energy generated by matter falling onto the central black hole is ejected and transferred to the intra-cluster medium via a relativistic jet and morphologically complex systems of buoyant bubbles, which rise towards the edges of the extended halo. Aims. To place constraints on past activity cycles of the active nucleus, images of M 87 were produced at low radio frequencies never explored before at these high spatial resolution and dynamic range. To disentangle different synchrotron models and place constraints on source magnetic field, age and energetics, we also performed a detailed spectral analysis of M 87 extended radio-halo. Methods. We present the first observations made with the new Low-Frequency Array (LOFAR) of M 87 at frequencies down to 20 MHz. Three observations were conducted, at 15−30 MHz, 30−77 MHz and 116−162 MHz. We used these observations together with archival data to produce a low-frequency spectral index map and to perform a spectral analysis in the wide frequency range 30 MHz-10 GHz. Results. We do not find any sign of new extended emissions; on the contrary the source appears well confined by the high pressure of the intracluster medium. A continuous injection of relativistic electrons is the model that best fits our data, and provides a scenario in which the lobes are still supplied by fresh relativistic particles from the active galactic nuclei. We suggest that the discrepancy between the low-frequency radiospectral slope in the core and in the halo implies a strong adiabatic expansion of the plasma as soon as it leaves the core area. The extended halo has an equipartition magnetic field strength of 10 μG, which increases to 13 μG in the zones where the particle flows are more active. The continuous injection model for synchrotron ageing provides an age for the halo of 40 Myr, which in turn provides a jet kinetic power of 6−10 × 10 44 erg s −1 .

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Section: Absolute Flux Densitysupporting

confidence: 69%

Section: Absolute Flux Densitymentioning

confidence: 99%

M 87 at metre wavelengths: the LOFAR picture

Gasperin

Orrù

Murgia

et al. 2012

A&A

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“…As we have used the RBC flux scale for scaling our LOFAR data, measurements at other frequencies must be rescaled. Fortunately, at frequencies 300 MHz, the RBC scale is in agreement with KPW scale (Kellermann et al 1969) and therefore we can use the conversion factors from the Baars scale (Table 7 in Baars et al 1977).…”

Section: Integrated Radio Continuum Spectrummentioning

confidence: 97%

The nature of the low-frequency emission of M 51

Mulcahy

Horneffer²,

Beck³

et al. 2014

A&A

113

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Context. Low-frequency radio continuum observations (<300 MHz) can provide valuable information on the propagation of low-energy cosmic ray electrons (CRE). Nearby spiral galaxies have hardly been studied in this frequency range because of the technical challenges of low-frequency radio interferometry. This is now changing with the start of operations of LOFAR. Aims. We aim to study the propagation of low-energy CRE in the interarm regions and the extended disk of the nearly face-on spiral galaxy Messier 51. We also search for polarisation in M 51 and other extragalactic sources in the field. Methods. The grand-design spiral galaxy M 51 was observed with the LOFAR High Frequency Antennas (HBA) and imaged in total intensity and polarisation. This observation covered the frequencies between 115 MHz and 175 MHz with 244 subbands of 8 channels each, resulting in 1952 channels. This allowed us to use RM synthesis to search for polarisation. Results. We produced an image of total emission of M 51 at the mean frequency of 151 MHz with 20 resolution and 0.3 mJy rms noise, which is the most sensitive image of a galaxy at frequencies below 300 MHz so far. The integrated spectrum of total radio emission is described well by a power law, while flat spectral indices in the central region indicate thermal absorption. We observe that the disk extends out to 16 kpc and see a break in the radial profile near the optical radius of the disk. The radial scale lengths in the inner and outer disks are greater at 151 MHz, and the break is smoother at 151 MHz than those observed at 1.4 GHz. The arm-interarm contrast is lower at 151 MHz than at 1400 MHz, indicating propagation of CRE from spiral arms into interarm regions. The correlations between the images of radio emission at 151 MHz and 1400 MHz and the FIR emission at 70 μm reveal breaks on scales of 1.4 and 0.7 kpc, respectively. The total (equipartition) magnetic field strength decreases from about 28 μG in the central region to about 10 μG at 10 kpc radius. No significant polarisation was detected from M 51, owing to severe Faraday depolarisation. Six extragalactic sources are detected in polarisation in the M 51 field of 4.1 • × 4.1 • size. Two sources show complex structures in Faraday space. Conclusions. Our main results, the scale lengths of the inner and outer disks at 151 MHz and 1.4 GHz, arm-interarm contrast, and the break scales of the radio-FIR correlations, can be explained consistently by CRE diffusion, leading to a longer propagation length of CRE of lower energy. The distribution of CRE sources drops sharply at about 10 kpc radius, where the star formation rate also decreases sharply. We find evidence that thermal absorption is primarily caused by H ii regions. The non-detection of polarisation from M 51 at 151 MHz is consistent with the estimates of Faraday depolarisation. Future searches for polarised emission in this frequency range should concentrate on regions with low star formation rates.Key words. polarization -cosmic rays -galaxies: ISM -galaxies: ...

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“…Baars et al (1965) refined the spectrum of these four calibration sources by using only the most accurate determinations of absolute flux density and paying careful attention to corrections due to receiver nonlinearity, angular resolution, and the secular decrease in flux density of Cas A. Kellermann et al (1969) extended this technique to establish a set of small angular size secondary calibrators to determine the spectra of 3CR sources between 38 MHz and 5 GHz and made further readjustments to the flux density scales. Later Baars & Hartsuijker (1972) reported evidence that the rate of flux density decrease of Cas A might be frequency dependent and reported new determinations of the absolute spectra of Cas A, Cyg A, and Taurus A.…”

Section: The Paper By Baars Et Al On "The Absolute Spectrum Of Cas Amentioning

confidence: 99%