The properties of powerful radio sources at 90 GHz

Monthly Notices of the Royal Astronomical Society

Cheung

Feain

et al. 2009

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136

201

The nearby radio galaxy Centaurus A is poorly studied at high frequencies with conventional radio telescopes because of its very large angular size, but is one of a very few extragalactic objects to be detected and resolved by the Wilkinson Microwave Anisotropy Probe (WMAP). We have used the five‐year WMAP data for Cen A to constrain the high‐frequency radio spectra of the 10° giant lobes and to search for spectral changes as a function of position along the lobes. We show that the high‐frequency radio spectra of the northern and southern giant lobes are significantly different: the spectrum of the southern lobe steepens monotonically (and is steeper further from the active nucleus) whereas the spectrum of the northern lobe remains consistent with a power law. The inferred differences in the northern and southern giant lobes may be the result of real differences in their high‐energy particle acceleration histories, perhaps due to the influence of the northern middle lobe, an intermediate‐scale feature which has no detectable southern counterpart. In light of these results, we discuss the prospects for Fermi Gamma‐ray Space Telescope detections of inverse‐Compton emission from the giant lobes and the lobes' possible role in the production of the ultra‐high‐energy cosmic rays (UHECR) detected by the Pierre Auger Observatory. We show that the possibility of a Fermi detection depends sensitively on the physical conditions in the giant lobes, with the northern lobe more likely to be detected, and that any emission observed by Fermi is likely to be dominated by photons at the soft end of the Fermi energy band. On the other hand, we argue that the estimated conditions in the giant lobes imply that UHECRs can be accelerated there, with a potentially detectable γ‐ray signature at TeV energies.

Section: Discussionmentioning

confidence: 99%

High-energy particle acceleration and production of ultra-high-energy cosmic rays in the giant lobes of Centaurus A

Monthly Notices of the Royal Astronomical Society

Cheung

Feain

et al. 2009

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136

201

“…If we define the core prominence as the ratio of core flux density at 1.4 GHz [the exact frequency is unimportant since radio galaxy core spectra are flat up to high frequencies: (e.g. Hardcastle & Looney 2008;Whittam et al 2013)] to total flux density at 150 MHz, then FIRST's 3σ upper limit on core prominence for the faintest objects corresponds to 0.4/80 = 5 × 10 −3 , while we know that the median core prominence for 3CRR objects with detected cores is ∼ 3 × 10 −4 (Mullin et al 2008). 3CRR objects are selected to be the brightest low-frequency sources on the sky and would be expected to have systematically low prominences, so this is an unfair comparison, but clearly it is possible that even moderately faint radio cores are escaping detection in our calculation of the remnant fraction above.…”

Section: Remnant Agnmentioning

confidence: 99%

LOFAR/H-ATLAS: a deep low-frequency survey of theHerschel-ATLAS North Galactic Pole field

Mon. Not. R. Astron. Soc.

Gürkan

Weeren

et al. 2016

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137

119

We present LOFAR High-Band Array (HBA) observations of the Herschel-ATLAS North Galactic Pole survey area. The survey we have carried out, consisting of four pointings covering around 142 square degrees of sky in the frequency range 126-173 MHz, does not provide uniform noise coverage but otherwise is representative of the quality of data to be expected in the planned LOFAR wide-area surveys, and has been reduced using recently developed 'facet calibration' methods at a resolution approaching the full resolution of the datasets (∼ 10 × 6 arcsec) and an rms off-source noise that ranges from 100 µJy beam −1 in the centre of the best fields to around 2 mJy beam −1 at the furthest extent of our imaging. We describe the imaging, cataloguing and source identification processes, and present some initial science results based on a 5-σ source catalogue. These include (i) an initial look at the radio/far-infrared correlation at 150 MHz, showing that many Herschel sources are not yet detected by LOFAR; (ii) number counts at 150 MHz, including, for the first time, observational constraints on the numbers of star-forming galaxies; (iii) the 150-MHz luminosity functions for active and starforming galaxies, which agree well with determinations at higher frequencies at low redshift, and show strong redshift evolution of the star-forming population; and (iv) some discussion of the implications of our observations for studies of radio galaxy life cycles.

“…These diffuse knots can sometimes be faint in the radio but bright in Xrays (see e.g. Hardcastle et al , 2007bHardcastle & Looney 2008;Massaro et al 2010Massaro et al , 2015Mack et al 2009;Werner et al 2012;Goodger et al 2010;Kharb et al 2012;Orienti et al 2012;Hardcastle et al 2016;Worrall et al 2016, and references therein, for examples of different hotspots and knots and their interactions with the environment). It is still not clear what makes some hotspots, knots and jet features X-ray synchrotron sources while others are undetected in the X-rays, and the non-uniform nature of the existing large samples ) makes it hard to draw conclusions from observations.…”

Section: Introductionmentioning

confidence: 99%

An X-ray survey of the 2 Jy sample – II. X-ray emission from extended structures

Mingo

Monthly Notices of the Royal Astronomical Society

Ineson

et al. 2017

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The 2Jy sample is a survey of radio galaxies with flux densities above 2 Jy at 2.7 GHz. As part of our ongoing work on the southern subset of 2Jy sources, in paper I of this series we analysed the X-ray cores of the complete 2Jy sample with redshifts 0.05 < z < 0.7. For this work we focus on the X-ray emission associated with the extended structures (jets, lobes, and environments) of the complete subset of 2Jy sources with 0.05 < z < 0.2, that we have observed with Chandra. We find that hotspots and jet knots are ubiquitous in FRII sources, which also inhabit systematically poorer environments than the FRI sources in our sample. Spectral fits of the hotspots with good X-ray statistics invariably show properties consistent with synchrotron emission, and we show that inverse-Compton mechanisms under-predict the X-ray emission we observe by 1-2 orders of magnitude. Inverse-Compton emission is detected from many of the lobes in our sample, and we find that the lobes of the FRII sources show magnetic fields lower by up to an order of magnitude than expected from equipartition extrapolations. This is consistent with previous results, which show that most FRII sources have electron energy densities higher than minimum energy requirements.cores of the 2Jy sources in the subset of Dicken et al. (2008), using data from Chandra and XMM-Newton, and found our results to be in good agreement with those of Hardcastle et al. (2006Hardcastle et al. ( , 2009 on the 3CRR radio galaxies.In this work we focus on the extended X-ray emission (jets, hotspots, and lobes) and the environments of the 0.05 < z < 0.2 subset of sources that we have observed with Chandra, whose nuclei we studied in paper I. Our knowledge of X-ray jets (see e.g. the review by Worrall 2009) and hotspots (e.g. Hardcastle et al. , 2007bMassaro et al. 2010Massaro et al. , 2015 has certainly improved over the last two decades, as has our understanding of the environment in which radio galaxies live (e.g. Belsole et al. 2007;Croston et al. 2008;Ineson et al. 2013Ineson et al. , 2015, but the samples of radio galaxies with available detailed observations are still relatively small, and more work needs to be done to understand their extended structures and how they co-evolve with the hosts (see also the recent review by Tadhunter 2016). The 2Jy sample is important in that it is not only statistically complete, but uniformly observed, with c 0000 The Authors