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- ID:
- ivo://CDS.VizieR/J/ApJS/197/24
- Title:
- Chandra large-scale extragalactic jets. I.
- Short Name:
- J/ApJS/197/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we report the first stages of an investigation into the X-ray properties of extragalactic jets (XJET project). Our approach is to subject all sources for which X-ray emission has been detected by Chandra to uniform reduction procedures. Using Chandra archival data for 106 such sources, we measure X-ray fluxes in three bands and compare these to radio fluxes. We discuss the sample, the reduction methods, and present first results for the ratio of X-ray to radio flux for jet knots and hotspots. In particular, we apply statistical tests to various distributions of key observational parameters to evaluate differences between the different classes of sources.
- ID:
- ivo://CDS.VizieR/J/AJ/131/1262
- Title:
- Circular polarization images at 15GHz of AGN jets
- Short Name:
- J/AJ/131/1262
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report first-epoch circular polarization results for 133 active galactic nuclei in the MOJAVE (Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments) program to monitor the structure and polarization of a flux-limited sample of extragalactic radio jets with the VLBA at 15GHz. We found strong circular polarization (0.3%) in approximately 15% of our sample. The circular polarization was usually associated with jet cores; however, we did find a few strong jet components to be circularly polarized.
- ID:
- ivo://CDS.VizieR/J/ApJ/887/134
- Title:
- Classification of Fermi blazar cand. from the 4FGL
- Short Name:
- J/ApJ/887/134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The recently published fourth Fermi Large Area Telescope source catalog (4FGL) reports 5065 gamma-ray sources in terms of direct observational gamma-ray properties. Among the sources, the largest population is the active galactic nuclei (AGNs), which consists of 3137 blazars, 42 radio galaxies, and 28 other AGNs. The blazar sample comprises 694 flat-spectrum radio quasars (FSRQs), 1131 BL Lac-type objects (BL Lacs), and 1312 blazar candidates of an unknown type (BCUs). The classification of blazars is difficult using optical spectroscopy given the limited knowledge with respect to their intrinsic properties, and the limited availability of astronomical observations. To overcome these challenges, machine-learning algorithms are being investigated as alternative approaches. Using the 4FGL catalog, a sample of 3137 Fermi blazars with 23 parameters is systematically selected. Three established supervised machine-learning algorithms (random forests (RFs), support vector machines (SVMs), artificial neural networks (ANNs)) are employed to general predictive models to classify the BCUs. We analyze the results for all of the different combinations of parameters. Interestingly, a previously reported trend the use of more parameters leading to higher accuracy is not found. Considering the least number of parameters used, combinations of eight, 12 or 10 parameters in the SVM, ANN, or RF generated models achieve the highest accuracy (Accuracy ~91.8%, or ~92.9%). Using the combined classification results from the optimal combinations of parameters, 724 BL Lac type candidates and 332 FSRQ type candidates are predicted; however, 256 remain without a clear prediction.
- ID:
- ivo://CDS.VizieR/J/MNRAS/470/1291
- Title:
- Classifying 3FGL with ANN
- Short Name:
- J/MNRAS/470/1291
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In its first four years of operation, the Fermi-Large Area Telescope (LAT) detected 3033 {gamma}-ray emitting sources. In the Fermi-LAT Third Source Catalogue (3FGL) about 50 per cent of the sources have no clear association with a likely {gamma}-ray emitter. We use an artificial neural network algorithm aimed at distinguishing BL Lacs from FSRQs to investigate the source subclass of 559 3FGL unassociated sources characterized by {gamma}-ray properties very similar to those of active galactic nuclei. Based on our method, we can classify 271 objects as BL Lac candidates, 185 as FSRQ candidates, leaving only 103 without a clear classification. We suggest a new zoo for {gamma}-ray objects, where the percentage of sources of uncertain type drops from 52 per cent to less than 10 per cent. The result of this study opens up new considerations on the population of the {gamma}-ray sky, and it will facilitate the planning of significant samples for rigorous analyses and multiwavelength observational campaigns.
- ID:
- ivo://CDS.VizieR/J/other/PASA/30.4
- Title:
- Corrections to the VV13 Catalogue
- Short Name:
- J/other/PASA/30.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Fixes are presented to be applied to the Veron-Cetty and Veron (VCV) Quasar Catalogue, 13th edition (Cat. VII/258). These are comprised of 39 deduplicati ons, 380 astrometric moves of 8+ arcseconds of which 31 are over 10 arcminutes, and 30 indicated delistings.
- ID:
- ivo://CDS.VizieR/J/AJ/115/1253
- Title:
- Deep X-Ray Radio Blazar Survey (DXRBS). I.
- Short Name:
- J/AJ/115/1253
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have undertaken a survey, the Deep X-Ray Radio Blazar Survey (DXRBS), of archived, pointed ROSAT Position Sensitive Proportional Counter data for blazars by correlating the ROSAT WGACAT database with several publicly available radio catalogs, restricting our candidate list to serendipitous flat radio spectrum sources ({alpha}_r_<=0.70, where S_{nu}_{prop}{nu}^-{alpha}_r_^). We discuss our survey methods, identification procedure, and first results. Our survey is found to be 95% efficient at finding flat-spectrum radio-loud quasars (FSRQs; 59 of our first 85 identifications) and BL Lacertae objects (22 of our first 85 identifications), a figure that is comparable to or greater than that achieved by other radio and X-ray survey techniques. The identifications presented here show that all previous samples of blazars (even when taken together) did not representatively survey the blazar population, missing critical regions of (LX, LR) parameter space within which large fractions of the blazar population lie. Particularly important is the identification of a large population of FSRQs (>=25% of DXRBS FSRQs) with ratios of X-ray to radio luminosity >=10^-6^({alpha}_rx_<=0.78). In addition, as a result of our greater sensitivity, the DXRBS has already more than doubled the number of FSRQs in complete samples with 5GHz (radio) luminosities between 10^31.5^ and 10^33.5^ergs/s/Hz, and fills in the region of parameter space between X-ray-selected and radio-selected samples of BL Lac objects. The DXRBS is the very first sample to contain statistically significant numbers of blazars at low luminosities, approaching what should be the lower end of the FSRQ luminosity function.
- ID:
- ivo://CDS.VizieR/J/MNRAS/323/757
- Title:
- Deep X-Ray Radio Blazar Survey (DXRBS). II.
- Short Name:
- J/MNRAS/323/757
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have searched the archived, pointed ROSAT Position Sensitive Proportional Counter data for blazars by correlating the WGACAT X-ray data base with several publicly available radio catalogues, restricting our candidate list to serendipitous X-ray sources with a flat radio spectrum ({alpha}_r_<=0.70, where S_{nu}_~{nu}^-{alpha}^). his makes up the Deep X-ray Radio Blazar Survey (DXRBS). Here we present new identifications and spectra for 106 sources, including 86 radio-loud quasars, 11 BL Lacertae objects, and nine narrow-line radio galaxies. Together with our previously published objects and already-known sources, our sample now contains 298 identified objects: 234 radio-loud quasars [181 flat-spectrum quasars: FSRQ ({alpha}_r_<=0.50) and 53 steep-spectrum quasars: SSRQ], 36 BL Lacs and 28 narrow-line radio galaxies. Redshift information is available for 96 per cent of these. Thus our selection technique is ~90 per cent efficient at finding radio-loud quasars and BL Lacs. Reaching 5-GHz radio fluxes ~50mJy and 0.1-2.0keV X-ray fluxes a few W10-14erg/cm^2^/s, DXRBS is the faintest and largest flat-spectrum radio sample with nearly complete (~85 per cent) identification.
- ID:
- ivo://CDS.VizieR/J/other/RAA/14.1135
- Title:
- Doppler factor for a Fermi blazar sample
- Short Name:
- J/other/RAA/14.1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We selected 457 blazars (193 flat spectrum radio quasars, 61 low-synchrotron peaked blazars, 69 intermediate-synchrotron peaked blazars and 134 high-synchrotron peaked blazars) from the second Fermi-LAT catalog (2FGL) of {gamma}-ray sources, which have X-ray observations. We calculated the lower limits for their Doppler factors, {delta}_{gamma}_, and compared the lower limits with the available Doppler factors and the apparent superluminal velocities in the literature.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A130
- Title:
- Dynamic SEDs of southern blazars - DSSB
- Short Name:
- J/A+A/591/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Simultaneous broadband spectral and temporal studies of blazars are an important tool for investigating active galactic nuclei (AGN) jet physics. We study the spectral evolution between quiescent and flaring periods of 22 radio-loud AGN through multiepoch, quasi-simultaneous broadband spectra. For many of these sources these are the first broadband studies. We use a Bayesian block analysis of Fermi/LAT light curves to determine time ranges of constant flux for constructing quasi-simultaneous spectral energy distributions (SEDs). The shapes of the resulting 81 SEDs are described by two logarithmic parabolas and a blackbody spectrum where needed.