- ID:
- ivo://CDS.VizieR/J/A+A/609/A68
- Title:
- Full-Stokes polarimetry of 5 radio sources
- Short Name:
- J/A+A/609/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis pipeline that enables the recovery of reliable information for all four Stokes parameters with high accuracy. Its novelty relies on the effective treatment of the instrumental effects even before the computation of the Stokes parameters, contrary to conventionally used methods such as that based on the Mueller matrix. For instance, instrumental linear polarization is corrected across the whole telescope beam and significant Stokes Q and U can be recovered even when the recorded signals are severely corrupted by instrumental effects. The accuracy we reach in terms of polarization degree is of the order of 0.1-0.2%. The polarization angles are determined with an accuracy of almost 1{def}. The presented methodology was applied to recover the linear and circular polarization of around 150 active galactic nuclei, which were monitored between July 2010 and April 2016 with the Effelsberg 100-m telescope at 4.85GHz and 8.35GHz with a median cadence of 1.2 months. The polarized emission of the Moon was used to calibrate the polarization angle measurements. Our analysis showed a small system-induced rotation of about 1{deg} at both observing frequencies. Over the examined period, five sources have significant and stable linear polarization; three sources remain constantly linearly unpolarized; and a total of 11 sources have stable circular polarization degree m_c_, four of them with non-zero m_c_. We also identify eight sources that maintain a stable polarization angle. All this is provided to the community for future polarization observations reference. We finally show that our analysis method is conceptually different from those traditionally used and performs better than the Mueller matrix method. Although it has been developed for a system equipped with circularly polarized feeds, it can easily be generalized to systems with linearly polarized feeds as well.
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- ID:
- ivo://CDS.VizieR/J/ApJ/731/100
- Title:
- 148GHz ACT extragalactic sources catalog
- Short Name:
- J/ApJ/731/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on extragalactic sources detected in a 455deg^2^ map of the southern sky made with data at a frequency of 148GHz from the Atacama Cosmology Telescope (ACT) 2008 observing season. We provide a catalog of 157 sources with flux densities spanning two orders of magnitude: from 15mJy to 1500mJy. Comparison to other catalogs shows that 98% of the ACT detections correspond to sources detected at lower radio frequencies. Three of the sources appear to be associated with the brightest cluster galaxies of low-redshift X-ray-selected galaxy clusters. Estimates of the radio to millimeter-wave spectral indices and differential counts of the sources further bolster the hypothesis that they are nearly all radio sources, and that their emission is not dominated by re-emission from warm dust. In a bright (>50mJy) 148GHz selected sample with complete cross-identifications from the Australia Telescope 20GHz survey, we observe an average steepening of the spectra between 5, 20, and 148GHz with median spectral indices of {alpha}_5-20_=-0.07+/-0.06, {alpha}_20-148_=-0.39+/-0.04, and {alpha}_5-148_=-0.20+/-0.03. When the measured spectral indices are taken into account, the 148GHz differential source counts are consistent with previous measurements at 30GHz in the context of a source count model dominated by radio sources. Extrapolating with an appropriately rescaled model for the radio source counts, the Poisson contribution to the spatial power spectrum from synchrotron-dominated sources with flux density less than 20mJy is C^Sync^=(2.8+/-0.3)x10^-6^{mu}K^2^.
- ID:
- ivo://CDS.VizieR/J/ApJ/742/27
- Title:
- 15GHz and jet properties of MOJAVE blazars
- Short Name:
- J/ApJ/742/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the Fermi Large Area Telescope {gamma}-ray and 15GHz Very Long Baseline Array radio properties of a joint {gamma}-ray and radio-selected sample of active galactic nuclei (AGNs) obtained during the first 11 months of the Fermi mission (2008 August 4-2009 July 5). Our sample contains the brightest 173 AGNs in these bands above declination -30{deg} during this period, and thus probes the full range of {gamma}-ray loudness ({gamma}-ray to radio band luminosity ratio) in the bright blazar population. The latter quantity spans at least 4 orders of magnitude, reflecting a wide range of spectral energy distribution (SED) parameters in the bright blazar population. The BL Lac objects, however, display a linear correlation of increasing {gamma}-ray loudness with synchrotron SED peak frequency, suggesting a universal SED shape for objects of this class.
- ID:
- ivo://CDS.VizieR/J/A+A/604/A111
- Title:
- 22GHz image of 3C 273
- Short Name:
- J/A+A/604/A111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- RadioAstron is a 10m orbiting radio telescope mounted on the Spektr-R satellite, launched in 2011, performing Space Very Long Baseline Interferometry (SVLBI) observations supported by a global ground array of radio telescopes. With an apogee of ~350000km, it is offering for the first time the possibility to perform as-resolution imaging in the cm-band. The RadioAstron Active Galactic Nuclei (AGN) polarization Key Science Project (KSP) aims at exploiting the unprecedented angular resolution provided by RadioAstron to study jet launching/collimation and magnetic-field configuration in AGN jets. The targets of our KSP are some of the most powerful blazars in the sky. We present observations at 22GHz of 3C 273, performed in 2014, designed to reach a maximum baseline of approximately nine Earth diameters. Reaching an angular resolution of 0.3mas, we study a particularly low-activity state of the source, and estimate the nuclear region brightness temperature, comparing with the extreme one detected one year before during the RadioAstron early science period.We also make use of the VLBA-BU-BLAZAR survey data, at 43GHz, to study the kinematics of the jet in a ~1.5-year time window. We find that the nuclear brightness temperature is two orders of magnitude lower than the exceptionally high value detected in 2013 with RadioAstron at the same frequency (1.4x10^13^K, source-frame), and even one order of magnitude lower than the equipartition value. The kinematics analysis at 43 GHz shows that a new component was ejected ~2 months after the 2013 epoch, visible also in our 22GHz map presented here. Consequently this was located upstream of the core during the brightness temperature peak. Fermi-LAT observations for the period 2010-2014 do not show any gamma-ray flare in conjunction with the passage of the new component by the core at 43GHz. These observations confirm that the previously detected extreme brightness temperature in 3C 273, exceeding the inverse Compton limit, is a short-lived phenomenon caused by a temporary departure from equipartition. Thus, the availability of interferometric baselines capable of providing as angular resolution does not systematically imply measured brightness temperatures over the known physical limits for astrophysical sources.
- ID:
- ivo://CDS.VizieR/J/AJ/137/3718
- Title:
- 15GHz monitoring of AGN jets with VLBA
- Short Name:
- J/AJ/137/3718
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present images from a long-term program (MOJAVE: Monitoring of Jets in active galactic nuclei (AGNs) with VLBA Experiments) to survey the structure and evolution of parsec-scale jet phenomena associated with bright radio-loud active galaxies in the northern sky. The observations consist of 2424 15GHz Very Long Baseline Array (VLBA) images of a complete flux-density-limited sample of 135 AGNs above declination -20{deg}, spanning the period 1994 August to 2007 September. These data were acquired as part of the MOJAVE and 2cm Survey programs, and from the VLBA archive. The sample-selection criteria are based on multi-epoch parsec-scale (VLBA) flux density, and heavily favor highly variable and compact blazars. The sample includes nearly all the most prominent blazars in the northern sky, and is well suited for statistical analysis and comparison with studies at other wavelengths. Our multi-epoch and stacked-epoch images show 94% of the sample to have apparent one-sided jet morphologies, most likely due to the effects of relativistic beaming. Of the remaining sources, five have two-sided parsec-scale jets, and three are effectively unresolved by the VLBA at 15GHz, with essentially all of the flux density contained within a few tenths of a milliarcsecond.
- ID:
- ivo://CDS.VizieR/J/A+A/559/A75
- Title:
- 43GHz observation of the blazar Mrk 421
- Short Name:
- J/A+A/559/A75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results obtained for the AGN Markarian 421 by model-fitting the data in the visibility plane, studing the proper motion of jet components, the light curve, and the spectral index of the jet features. We compare the radio data with optical light curves obtained at the Steward Observatory, considering also the optical polarization information. Mrk 421 has a bright nucleus and a one-sided jet extending towards the north-west for a few parsecs. The model-fits show that brightness distribution is well described using 6-7 circular Gaussian components, four of which are reliably identified at all epochs; all components are effectively stationary except for component D, at ~0.4mas from the core, whose motion is however subluminal. The analysis of the light curve shows two different states, with the source being brighter and more variable in the first half of 2011 than in the second half. The highest flux density is reached in February. A comparison with the optical data reveals an increase of the V magnitude and of the fractional polarization simultaneous with the enhancement of the radio activity.
- ID:
- ivo://CDS.VizieR/J/AJ/133/1947
- Title:
- 37GHz observations of BL Lac objects
- Short Name:
- J/AJ/133/1947
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 37GHz data obtained at Metsahovi Radio Observatory in 2001 December-2005 April for a large sample of BL Lacertae objects. Metsahovi radio telescope is a radome enclosed antenna with a diameter of 13.7 metres. The 37 GHz receiver is a dual horn, Dicke-switched receiver with a HEMT preamplifier, and is operated at room temperature. The observations are ON-ON observations, alternating the source and the sky in each feed horn. A typical integration time to obtain one flux density data point is 1200-1600s, and the detection limit under optimal weather conditions is about 0.2Jy.
- ID:
- ivo://CDS.VizieR/J/other/AstBu/74.348
- Title:
- 164 GHz-peaked spectrum sources
- Short Name:
- J/other/AstBu/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gigahertz-Peaked spectrum (GPS) sources are compact active galactic nuclei, presumably young precursors of bright radio sources. The study of GPS radio properties provides information about the features of synchrotron radiation in extragalactic sources. Also in applied research, GPS sources are useful as compact stationary radio sources in the sky for astrometric purposes. This paper presents the results of a multifrequency GPS study based on quasi-simultaneous measurements with the RATAN-600 radio telescope during the 2006-2017 period. A catalog of GPS spectral flux densities at six frequencies - 1.1, 2.3, 4.8, 7.7/8.2, 11.2, and 21.7GHz - is obtained. In addition, for the analysis of radio spectra, data from low-frequency surveysGLEAM(GaLactic and Extragalactic AllskyMurchisonwidefield array survey) and TGSS (Tata institute for fundamental research GMRT Sky Survey) and high-frequency measurements from Planck survey are used. A total number of 164 GPS and candidates have been identified (17 of them are new discoveries), which makes up a small fraction of GPS in the initial sample of bright AGNs - about 2%. The physical properties and formation conditions of synchrotron radiation is found to be quite different in GPS of different AGNs types. The deficit of distant GPS (z>2) with low maximum frequencies (less than 1GHz) has been confirmed. The existing "size-peak frequency" anticorrelation is continuous. The continuum radio spectra are found to become statistically steeper with increasing redshift.
- ID:
- ivo://CDS.VizieR/J/ApJ/704/1433
- Title:
- 31GHz survey of low-frequency radio sources
- Short Name:
- J/ApJ/704/1433
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 100m Robert C. Byrd Green Bank Telescope and the 40m Owens Valley Radio Observatory telescope have been used to conduct a 31GHz survey of 3165 known extragalactic radio sources over 143deg^2^ of the sky. Target sources were selected from the NRAO VLA Sky Survey in fields observed by the Cosmic Background Imager (CBI); most are extragalactic active galactic nuclei (AGNs) with 1.4GHz flux densities of 3-10mJy. The resulting 31GHz catalogs are presented in full online. Using a maximum-likelihood analysis to obtain an unbiased estimate of the distribution of the 1.4-31GHz spectral indices of these sources, we find a mean 31-1.4GHz flux ratio of 0.110+/-0.003 corresponding to a spectral index of {alpha}=-0.71+/-0.01 (S_{nu}_{prop.to}{nu}^{alpha}^); 9.0%+/-0.8% of sources have {alpha}>-0.5 and 1.2%+/-0.2% have {alpha}>0. By combining this spectral-index distribution with 1.4GHz source counts, we predict 31GHz source counts in the range 1mJy<S_31_<4mJy, N(>S_31_)=(16.7+/-1.7)deg^-2^(S_31_/1mJy)^-0.80+/-0.07^.
- ID:
- ivo://CDS.VizieR/J/MNRAS/502/4779
- Title:
- 28-40GHz variability and polarimetry
- Short Name:
- J/MNRAS/502/4779
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observed 51 sources in the Q-U-I JOint TEnerife (QUIJOTE) cosmological fields which were brighter than 1Jy at 30GHz in the Planck Point Source Catalogue (version 1), with the Very Large Array at 28-40GHz, in order to characterise their high-radio-frequency variability and polarization properties. We find a roughly log-normal distribution of polarization fractions with a median of 2%, in agreement with previous studies, and a median rotation measure (RM) of ~1110rad/m^2^ with one outlier up to ~64000rad/m^2^ which is among the highest RMs measured in quasar cores. We find hints of a correlation between the total intensity flux density and median polarization fraction. We find 59% of sources are variable in total intensity, and 100% in polarization at 3{sigma} level, with no apparent correlation between total intensity variability and polarization variability. This indicates that it will be difficult to model these sources without simultaneous polarimetric monitoring observations and they will need to be masked for cosmological analysis.