- ID:
- ivo://CDS.VizieR/J/ApJ/681/1296
- Title:
- Radio evolution of the PN NGC 7027
- Short Name:
- J/ApJ/681/1296
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a 25yr program to monitor the radio flux evolution of the planetary nebula NGC 7027. We find significant evolution of the spectral flux densities. The flux density at 1465MHz, where the nebula is optically thick, is increasing at a rate of 0.251+/-0.015%/yr, caused by the expansion of the ionized nebula. At frequencies where the emission is optically thin, the spectral flux density is changing at a rate of -0.145+/-0.005%/yr, caused by a decrease in the number of ionizing photons coming from the central star. A distance of 980+/-100pc is derived. By fitting interpolated models of post-AGB evolution to the observed changes, we find that over the 25yr monitoring period, the stellar temperature has increased by 3900+/-900K and the stellar bolometric luminosity has decreased by 1.75+/-0.5%. We derive a distance-independent stellar mass of 0.655+/-0.010M_{sun}_ adopting the Blocker stellar evolution models, or about 0.04M_{sun}_ higher when using models of Vassiliadis & Wood. A Cloudy photoionization model is used to fit all epochs at all frequencies simultaneously. The differences between the radio flux density predictions and the observed values show some time-independent residuals of typically 1%. A possible explanation is inaccuracies in the radio flux scale of Baars and coworkers. We propose an adjustment to the flux density scale of the primary radio flux calibrator 3C 286, based on the Cloudy model of NGC 7027. We also calculate precise flux densities for NGC 7027 for all standard continuum bands used at the VLA, as well as for some new 30 GHz experiments.
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- ID:
- ivo://CDS.VizieR/J/A+A/552/A19
- Title:
- Radio-farIR correlation in NGC 6946
- Short Name:
- J/A+A/552/A19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive the distribution of the synchrotron spectral index across NGC 6946 and investigate the correlation between the radio continuum (synchrotron) and far-infrared (FIR) emission using the KINGFISH Herschel PACS and SPIRE data.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A83
- Title:
- Radio flux densities of neutrino associations
- Short Name:
- J/A+A/650/A83
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Identifying the most likely sources for high-energy neutrino emission has been one of the main topics in high-energy astrophysics ever since the first observation of high-energy neutrinos by the IceCube Neutrino Observatory. Active galactic nuclei with relativistic jets, also known as blazars, have been considered to be one of the main candidates because of their ability to accelerate particles to high energies. We study the connection between radio emission and IceCube neutrino events using data from the Owens Valley Radio Observatory (OVRO) and Metsahovi Radio Observatory blazar monitoring programs. We identify sources in our radio monitoring sample that are positionally consistent with IceCube high-energy neutrino events. We estimate their mean flux density and variability amplitudes around the neutrino arrival time, and compare these with values from random samples to establish the significance of our results. We find radio source associations within our samples with 15 high-energy neutrino events detected by IceCube. Nearly half of the associated sources are not detected in the {gamma}-ray energies, but their radio variability properties and Doppler boosting factors are similar to the {gamma}-ray detected objects in our sample, meaning that they could still be potential neutrino emitters. We find that the number of strongly flaring objects in our statistically complete OVRO samples is unlikely to be a random coincidence (at 2{sigma} level). Based on our results, we conclude that although it is clear that not all neutrino events are associated with strong radio flaring blazars, observations of large-amplitude radio flares in a blazar at the same time as a neutrino event are unlikely to be a random coincidence.
- ID:
- ivo://CDS.VizieR/J/MNRAS/477/830
- Title:
- Radio flux density of extremely red quasars
- Short Name:
- J/MNRAS/477/830
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most active galactic nuclei (AGNs) are radio quiet, and the origin of their radio emission is not well understood. One hypothesis is that this radio emission is a byproduct of quasar-driven winds. In this paper, we present the radio properties of 108 extremely red quasars (ERQs) at z=2-4. ERQs are among the most luminous quasars (L_bol_~10^47-48^erg/s^) in the Universe, with signatures of extreme (>>1000km/s) outflows in their [OIII]{lambda}5007{AA} emission, making them the best subjects to seek the connection between radio and outflow activities. All ERQs but one are unresolved in the radio on ~10kpc scales, and the median radio luminosity of ERQs is {nu}L_{nu}_[6GHz]= 10^41.0^erg/s, in the radio-quiet regime, but 1-2 orders of magnitude higher than that of other quasar samples. The radio spectra are steep, with a mean spectral index <{alpha}>=-1.0. In addition, ERQs neatly follow the extrapolation of the low-redshift correlation between radio luminosity and the velocity dispersion of [OIII]-emitting ionized gas. Uncollimated winds, with a power of one per cent of the bolometric luminosity, can account for all these observations. Such winds would interact with and shock the gas around the quasar and in the host galaxy, resulting in acceleration of relativistic particles and the consequent synchrotron emission observed in the radio. Our observations support the picture in which ERQs are signposts of extremely powerful episodes of quasar feedback, and quasar-driven winds as a contributor of the radio emission in the intermediate regime of radio luminosity {nu}L_{nu}_=10^39^-10^42^erg/s.
- ID:
- ivo://CDS.VizieR/J/AJ/151/79
- Title:
- Radio fluxes of 195 ICRF2-Gaia transfer sources
- Short Name:
- J/AJ/151/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The second realization of the International Celestial Reference Frame (ICRF2), which is the current fundamental celestial reference frame adopted by the International Astronomical Union, is based on Very Long Baseline Interferometry (VLBI) data at radio frequencies in X band and S band. The European Space Agency's Gaia mission, launched on 2013 December 19, started routine scientific operations in 2014 July. By scanning the whole sky, it is expected to observe ~500000 Quasi Stellar Objects in the optical domain an average of 70 times each during the five years of the mission. This means that, in the future, two extragalactic celestial reference frames, at two different frequency domains, will coexist. It will thus be important to align them very accurately. In 2012, the Laboratoire d'Astrophysique de Bordeaux (LAB) selected 195 sources from ICRF2 that will be observed by Gaia and should be suitable for aligning the radio and optical frames: they are called ICRF2-Gaia transfer sources. The LAB submitted a proposal to the International VLBI Service (IVS) to regularly observe these ICRF2-Gaia transfer sources at the same rate as Gaia observes them in the optical realm, e.g., roughly once a month. We describe our successful effort to implement such a program and report on the results. Most observations of the ICRF2-Gaia transfer sources now occur automatically as part of the IVS source monitoring program, while a subset of 37 sources requires special attention. Beginning in 2013, we scheduled 25 VLBI sessions devoted in whole or in part to measuring these 37 sources. Of the 195 sources, all but one have been successfully observed in the 12 months prior to 2015 September 01. Of the sources, 87 met their observing target of 12 successful sessions per year. The position uncertainties of all of the ICRF2-Gaia transfer sources have improved since the start of this observing program. For a subset of 24 sources whose positions were very poorly known, the uncertainty has decreased, on average, by a factor of four. This observing program is successful because the two main goals were reached for most of the 195 ICRF2-Gaia transfer sources: observing at the requested target of 12 successful sessions per year and improving the position uncertainties to better than 200{mu}as for both R.A. and decl. However, scheduling some of the transfer sources remains a challenge because of network geometry and the weakness of the sources, and this will be one focus of future sessions used in this ongoing program.
- ID:
- ivo://CDS.VizieR/J/MNRAS/354/485
- Title:
- Radio flux of 15-GHz 9C survey
- Short Name:
- J/MNRAS/354/485
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out extensive radio and optical follow-up of 176 sources from the 15-GHz 9th Cambridge survey. Optical identifications have been found for 155 of the radio sources; optical images are given with radio maps overlaid. The continuum radio spectrum of each source spanning the frequency range 1.4-43GHz is also given.
- ID:
- ivo://CDS.VizieR/J/ApJ/838/139
- Title:
- Radio follow-up on 3FGL unassociated sources
- Short Name:
- J/ApJ/838/139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The third Fermi Large Area Telescope {gamma}-ray source catalog (3FGL) contains over 1000 objects for which there is no known counterpart at other wavelengths. The physical origin of the {gamma}-ray emission from those objects is unknown. Such objects are commonly referred to as unassociated and mostly do not exhibit significant {gamma}-ray flux variability. We performed a survey of all unassociated {gamma}-ray sources found in 3FGL using the Australia Telescope Compact Array and Very Large Array in the range 4.0-10.0 GHz. We found 2097 radio candidates for association with {gamma}-ray sources. The follow-up with very long baseline interferometry for a subset of those candidates yielded 142 new associations with active galactic nuclei that are {gamma}-ray sources, provided alternative associations for seven objects, and improved positions for another 144 known associations to the milliarcsecond level of accuracy. In addition, for 245 unassociated {gamma}-ray sources we did not find a single compact radio source above 2 mJy within 3{sigma} of their {gamma}-ray localization. A significant fraction of these empty fields, 39%, are located away from the Galactic plane. We also found 36 extended radio sources that are candidates for association with a corresponding {gamma}-ray object, 19 of which are most likely supernova remnants or H II regions, whereas 17 could be radio galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/303/420
- Title:
- Radio galaxies and quasars
- Short Name:
- J/A+A/303/420
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The simple unification scheme of powerful radio galaxies and quasars, based entirely on the orientation dependent effects, has been confronted with the observed radio structures for 152 radio galaxies and 173 steep spectrum quasars. Contrary to the scheme's prediction, the cosmological evolution of geometrical parameters describing the large scale structure of these two types of radio sources are different.
- ID:
- ivo://CDS.VizieR/J/ApJ/741/30
- Title:
- Radio/{gamma}-ray correlation in AGN
- Short Name:
- J/ApJ/741/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed statistical analysis of the correlation between radio and gamma-ray emission of the active galactic nuclei (AGNs) detected by Fermi during its first year of operation, with the largest data sets ever used for this purpose. We use both archival interferometric 8.4GHz data (from the Very Large Array and ATCA, for the full sample of 599 sources) and concurrent single-dish 15GHz measurements from the Owens Valley Radio Observatory (OVRO, for a sub sample of 199 objects). Our unprecedentedly large sample permits us to assess with high accuracy the statistical significance of the correlation, using a surrogate data method designed to simultaneously account for common-distance bias and the effect of a limited dynamical range in the observed quantities.
- ID:
- ivo://CDS.VizieR/J/MNRAS/476/158
- Title:
- Radio haloes in nearby galaxies
- Short Name:
- J/MNRAS/476/158
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radio continuum maps of 12 nearby (D<=27Mpc), edge-on (i>=76{deg}), late-type spiral galaxies mostly at 1.4 and 5GHz, observed with the Australia Telescope Compact Array, Very Large Array, Westerbork Synthesis Radio Telescope, Effelsberg 100-m and Parkes 64-m telescopes. All galaxies show clear evidence of radio haloes, including the first detection in the Magellanic-type galaxy NGC 55. In 11 galaxies, we find a thin and a thick disc that can be better fitted by exponential rather than Gaussian functions. We fit our SPINNAKER (SPectral INdex Numerical Analysis of K(c)osmic-ray Electron Radio-emission) 1D cosmic-ray transport models to the vertical model profiles of the non-thermal intensity and to the non-thermal radio spectral index in the halo. We simultaneously fit for the advection speed (or diffusion coefficient) and magnetic field scale height. In the thick disc, the magnetic field scale heights range from 2 to 8kpc with an average across the sample of 3.0+/-1.7kpc; they show no correlation with either star-formation rate (SFR), SFR surface density (Sigma_SFR_) or rotation speed (V_rot_). The advection speeds range from 100 to 700km/s and display correlations of V{prop.to}SFR^0.36+/-0.06^ and V{prop.to}Sigma_SFR_^0.39+/-0.09^; they agree remarkably well with the escape velocities (0.5<=V/V_esc<=2), which can be explained by cosmic-ray driven winds. Radio haloes show the presence of disc winds in galaxies with Sigma_SFR_>10^-3^M_{sun}_/yr/kpc^2^ that extend over several kpc and are driven by processes related to the distributed star formation in the disc.
