Book Reviews

Jaffe, James; Kirby, Dianne; Mason, Keith; O’Malley, Tom; Phillips, Simon; Postles, Dave; Rubinstein, William D.; White, Jonathan

doi:10.2752/147800407x219287

Cited by 3 publications

(5 citation statements)

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“…In order to estimate the flux densities of the total outer doubles, we subtracted the flux densities of the total inner doubles and the cores from the integrated flux densities. The spectral ageing JP model (Jaffe & Perola 1973) has been fitted to the flux densities of the outer doubles. The fitted spectra of inner and outer doubles are shown in Figures 3.…”

Section: Constraining Radio Spectramentioning

confidence: 99%

“…The spectral age is defined as the time elapsed since the radiating particles were last accelerated. In order to determine the spectral age in different parts of the lobes, we apply the Jaffe-Perola model (hereafter JP model, see Jaffe & Perola 1973) which describes the time-evolution of the emission spectrum from particles with an initial power-law energy distribution characterised by injection spectral index (αinj). In applying this model, our assumptions are that (i) the radiating particles after entering the lobes are not re-accelerated, but radiate via the synchrotron process and inverse-Compton scattering against the CMB Table 7.…”

Section: Spectral Ageing Analysismentioning

confidence: 99%

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Episodic radio galaxies J0116−4722 and J1158+2621: can we constrain the quiescent phase of nuclear activity?

Konar

Hardcastle

Jamrozy

et al. 2013

Monthly Notices of the Royal Astronomical Society

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We present multifrequency radio observations of two well known episodic FR II radio galaxies (J0116−4722 and J1158+2621) and a detailed investigation of the life-cycle of episodic radio galaxies from their spectral and radiative properties. Combining our previous work with the present results, we either constrain or place very good limits on the active and quiescent phases of a small sample of episodic FR II radio galaxies. The duration of the quiescent phase can be as small as the hotspot fading time of the previous episode, and as high as a few tens of Myr; however, for none of the sources in our sample is it close to the duration of the active phase of the previous episode. We also find that for many episodic radio galaxies, the nucleus is variable at radio wavelengths. For our small sample of 7 episodic radio galaxies, we find 4 to have strongly variable cores, a much larger proportion than is generally found in samples of normal FR II radio galaxies. Studies with larger samples will be required to establish a statistical association between core variability and episodic radio activity.

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Section: Constraining Radio Spectramentioning

confidence: 99%

Section: Spectral Ageing Analysismentioning

confidence: 99%

Episodic radio galaxies J0116−4722 and J1158+2621: can we constrain the quiescent phase of nuclear activity?

Konar

Hardcastle

Jamrozy

et al. 2013

Monthly Notices of the Royal Astronomical Society

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“…V is the lobe volume. To determine the spectral ages and hence tactiv, we have fitted Jaffe-Perola models (Jaffe & Perola 1973) to the radio spectra of all the sources. We used the formalism of Konar et al (2008) to estimate the minimum energy magnetic field (Bmin), and hence to estimate the total pressure P (= 1 3 (ǫB,min + ǫe,min)) of the lobes, which we take to be cylinders for the purposes of estimating volume.…”

Section: Jet Powermentioning

confidence: 99%

“…The actual observed spectra of large-scale regions of these RGs are more complex, because of the effects of radiative and inverse-Compton losses and adiabatic expansion, which give rise to broken or curved synchrotron spectra (e.g. Heavens & Meisenheimer 1987, Jaffe & Perola 1973 and so in general measurements at several frequencies are needed to determine the injection index.…”

Section: Introductionmentioning

confidence: 99%

Particle acceleration and dynamics of double–double radio galaxies: theory versus observations

Konar¹,

Hardcastle²

2013

Monthly Notices of the Royal Astronomical Society

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In this paper we show that a small sample of radio galaxies with evidence for multiple epochs of jet activity (so-called 'double-double' radio galaxies) have the same electron injection spectral index in the two activity episodes, a result which might be considered surprising given the very different lobe dynamics expected in the first and second episode. We construct models for the dynamics of radio galaxies, with an emphasis on their episodic behaviour, and show that hotspot formation and confinement of lobes for the inner double of double-double radio galaxies are possible even without any thermal matter in the outer cocoon. We argue that (i) the observed similar injection spectral indices are due to similar jet powers in the two episodes, (ii) the 'spectral index-radio power' correlation of a flux limited sample of radio galaxies is the primary one, and not the 'spectral index-redshift correlation', (iii) jets are made of pair plasma and not electron-proton, (iv) and the Lorentz factor of the spine of the jet should be > ∼ 10 to explain the observations. Furthermore, we argue that the observations show that higher power radio galaxies do not have a higher jet bulk Lorentz factors, but instead simply have a higher number density of particles in the jet rest frame. A consequence of our models is that aligned double-double radio galaxies with very old ( > ∼ 10 8 yr) outer doubles, or misaligned double-double radio galaxies, are statistically more likely to have dissimilar injection indices in two different episodes, as they will probably have different jet powers.

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“…We fitted these trends using a JP model (Jaffe & Perola 1974), in which the timescale for continuous isotropization of the electrons is assumed to be much shorter than the radiative timescale. We also assumed that the break frequency ν br ∝ d −2 , where d is the distance from the core.…”

Section: Spectral Analysismentioning

confidence: 99%

A Giant Metrewave Radio Telescope Multifrequency Radio Study of the Isothermal Core of the Poor Galaxy Cluster AWM 4

Giacintucci

Vrtilek

Murgia

et al. 2008

ApJ

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We present a detailed radio morphological study and spectral analysis of the wide-angle-tail radio source 4C +24.36 associated with the dominant galaxy in the relaxed galaxy cluster AWM 4. Our study is based on new high sensitivity GMRT observations at 235 MHz, 327 MHz and 610 MHz, and on literature and archival data at other frequencies. We find that the source major axis is likely oriented at a small angle with respect to the plane of the sky. The wide-angle-tail morphology can be reasonably explained by adopting a simple hydrodynamical model in which both ram pressure (driven by the motion of the host galaxy) and buoyancy forces contribute to bend the radio structure. The spectral index progressively steepens along the source major axis from α ∼0.3 in the region close to the radio nucleus to beyond 1.5 in the lobes. The results of the analysis of the spectral index image allow us to derive an estimate of the radiative age of the source of ∼ 160 Myr. The cluster X-ray emitting gas has a relaxed morphology and short cooling time, but its temperature profile is isothermal out to at least 160 kpc from the centre. Therefore we seek evidence of energy ejection from the central AGN to prevent catastrophic cooling. We find that the energy injected by 4C +24.36 in the form of synchrotron luminosity during its lifetime is far less than the energy required to maintain the high gas temperature in the core. We also find that it is not possible for the central source to eject the requisite energy in the intracluster gas in terms of the enthalpy of buoyant bubbles of relativistic fluid, without creating discernible large cavities in the existing X-ray XMM-Newton observations.

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Book Reviews

Cited by 3 publications

References 0 publications

Episodic radio galaxies J0116−4722 and J1158+2621: can we constrain the quiescent phase of nuclear activity?

Episodic radio galaxies J0116−4722 and J1158+2621: can we constrain the quiescent phase of nuclear activity?

Particle acceleration and dynamics of double–double radio galaxies: theory versus observations

A Giant Metrewave Radio Telescope Multifrequency Radio Study of the Isothermal Core of the Poor Galaxy Cluster AWM 4

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