Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/893/68
- Title:
- RadioAstron. III. S5 0716+71 at uarcsec res.
- Short Name:
- J/ApJ/893/68
- Date:
- 03 Dec 2021 00:43:28
- Publisher:
- CDS
- Description:
- We present RadioAstron Space VLBI imaging observations of the BL Lac object S5 0716+71 made on 2015 January 3-4 at a frequency of 22GHz (wavelength {lambda}=1.3cm). The observations were made in the framework of the AGN Polarization Key Science Program. The source was detected on projected space-ground baselines up to 70833km (5.6 Earth diameters) for both parallel-hand and cross-hand interferometric visibilities. We have used these detections to obtain a full-polarimetric image of the blazar at an unprecedented angular resolution of 24{mu}as, the highest for this source to date. This enabled us to estimate the size of the radio core to be <12x5{mu}as and to reveal a complex structure and a significant curvature of the blazar jet in the inner 100{mu}as, which is an indication that the jet viewing angle lies inside the opening angle of the jet conical outflow. Fairly highly (15%) linearly polarized emission is detected in a jet region 19{mu}as in size, located 58{mu}as downstream from the core. The highest brightness temperature in the source frame is estimated to be >2.2x10^13^K for the blazar core. This implies that the inverse-Compton limit must be violated in the rest frame of the source, even for the largest Doppler factor {delta}~25 reported for 0716+714.
- 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/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/A+A/596/A45
- Title:
- Radio light curves of 8 AGN
- Short Name:
- J/A+A/596/A45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To fully exploit the scientific potential of the Fermi mission for the physics of active galactic nuclei (AGN), we initiated the F-GAMMA programme. Between 2007 and 2015 the F-GAMMA was the prime provider of complementary multi-frequency monitoring in the radio regime. Aims. We quantify the radio variability of {gamma}-ray blazars. We investigate its dependence on source class and examine whether the radio variability is related to the {gamma}-ray loudness. Finally, we assess the validity of a putative correlation between the two bands. Methods. The F-GAMMA performed monthly monitoring of a sample of about 60 sources at up to twelve radio frequencies between 2.64 and 228.39GHz. We perform a time series analysis on the first 2.5-yr data set to obtain variability parameters. A maximum likelihood analysis is used to assess the significance of a correlation between radio and {gamma}-ray fluxes. We present light curves and spectra (coherent within ten days) obtained with the Effelsberg 100m and IRAM 30m telescopes. All sources are variable across all frequency bands with amplitudes increasing with frequency up to rest frame frequencies of around 60-80GHz as expected by shock-in-jet models. Compared to flat-spectrum radio quasars (FSRQs), BL Lacertae objects (BL Lacs) show systematically lower variability amplitudes, brightness temperatures, and Doppler factors at lower frequencies, while the difference vanishes towards higher ones. The time scales appear similar for the two classes. The distribution of spectral indices appears flatter or more inverted at higher frequencies for BL Lacs. Evolving synchrotron self-absorbed components can naturally account for the observed spectral variability. We find that the Fermi-detected sources show larger variability amplitudes, brightness temperatures, and Doppler factors than non-detected ones. Flux densities at 86.2 and 142.3GHz correlate with 1GeV fluxes at a significance level better than 3{sigma}, implying that {gamma} rays are produced very close to the mm-band emission region.
- ID:
- ivo://CDS.VizieR/J/PASJ/73/313
- Title:
- Radio loudness and classification for radio source
- Short Name:
- J/PASJ/73/313
- Date:
- 03 Dec 2021 00:54:37
- Publisher:
- CDS
- Description:
- The extragalactic radio sources are divided into two subclasses (radio-loud and radio-quiet sources) in the literature using radio loudness (R), which is defined as the ratio of radio emission to optical emission, but the boundary R-value separating the two classes is different in various sources. In this work, a sample of 2419 objects from the 13th catalog of quasars and active nuclei is used to build a boundary for the two subclasses. To do so, we compiled the radio and optical data, calculated their radio and optical indexes, made K-correction, obtained the radio loudness, and adopted a Bayesian analysis method to the logarithm of radio loudness for classification. We also investigated the correlations of radio loudness with radio/optical luminosities. Our main conclusions are summarized as follows: (1) The distribution of the logarithm of radio loudness (log R) is bimodal, the sources with log R<1.26 are classified as radio-quiet sources, and those with log R>1.26 are classified as radio-loud ones from the Bayesian analysis method. (2) The average radio-optical effective spectral index of radio-quiet sources is <RO>=0.05, while that of radio-loud sources is <{alpha}_RO_>=0.55. (3) There are positive correlations between radio luminosity and radio loudness for both radio-loud sources and radio-quiet sources. (4) A dividing line of separating the distribution of the clusters on the diagram of radio loudness against radio luminosity was obtained statistically to set the boundary between radio-loud sources and radio-quiet sources, with an accuracy of 99.73% based on the classification result from the Bayesian analysis method.
- ID:
- ivo://CDS.VizieR/J/A+AS/109/267
- Title:
- Radio to X-Ray distribution of BL Lac Objects
- Short Name:
- J/A+AS/109/267
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/ApJ/768/40
- Title:
- R-band and polarimetry of the blazar S5 0716+71
- Short Name:
- J/ApJ/768/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of optical (R band) photometric and polarimetric monitoring and Very Long Baseline Array (VLBA) imaging of the blazar S5 0716+714 along with Fermi {gamma}-ray data during a multi-waveband outburst in 2011 October. We analyze total and polarized intensity images of the blazar obtained with the VLBA at 43GHz during and after the outburst. Monotonic rotation of the linear polarization vector at a rate of >~50{deg} per night coincided with a sharp maximum in {gamma}-ray and optical flux. At the same time, within the uncertainties, a new superluminal knot appeared with an apparent speed of 21+/-2c. The general multi-frequency behavior of the outburst can be explained within the framework of a shock wave propagating along a helical path in the blazar's jet.
- ID:
- ivo://CDS.VizieR/J/A+A/596/A78
- Title:
- R-band polarization curves of 48 BL Lacs
- Short Name:
- J/A+A/596/A78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the optical polarization properties of high-energy BL Lac objects using data from the RoboPol blazar monitoring program and the Nordic Optical Telescope. We wish to understand if there are differences between the BL Lac objects that have been detected with the current-generation TeV instruments and those objects that have not yet been detected. We used a maximum-likelihood method to investigate the optical polarization fraction and its variability in these sources. In order to study the polarization position angle variability, we calculated the time derivative of the electric vector position angle (EVPA) change. We also studied the spread in the Stokes Q/I-U/I plane and rotations in the polarization plane.
- ID:
- ivo://CDS.VizieR/J/ApJ/731/118
- Title:
- R-band variability in blazar S5 0716+71
- Short Name:
- J/ApJ/731/118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report rapid optical variability for the blazar S5 0716+71 during 2010 March 8-10 and 19-20 in the CCD observations made from Mt. Abu Infrared Observatory. The light curves are constructed for a duration longer than 3hr each night, with very high temporal resolution (~45s in the R band). During 2010 March 8, the source smoothly decayed by about 0.15mag in 2.88hr, apart from a fast flicker lasting about 30 minutes. S5 0716+71 brightened during March 9 and 10, showing high activity, while it was relatively faint (>14mag in the R band) albeit variable during March 19-20. During March 9 and 10, rapid flickers in the intensity modulated the long-term intra-night (~3hr) variations. The present observations suggest that the blazar S5 0716+71 showed night-to-night and intra-night variability at various timescales with a 100% duty cycle for variation along with microvariability at significant levels. On a night-to-night basis, the source exhibits mild bluer-when-brighter nature. The interaction of shocks with local inhomogeneities in the jet appears to cause intra-night variations, while microvariations could be due to small-scale perturbations intrinsic to the jet.