- ID:
- ivo://CDS.VizieR/J/ApJ/744/177
- Title:
- VLBA 5GHz observations of Fermi/LAT AGNs
- Short Name:
- J/ApJ/744/177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA). In total, 232 sources were observed with the VLBA. Ninety sources that were previously observed as part of the VLBA Imaging and Polarimetry Survey (VIPS) have been included in the sample, as well as 142 sources not found in VIPS. This very large, 5GHz flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong {gamma}-ray emission. In particular, we see that {gamma}-ray emission is related to strong, uniform magnetic fields in the cores of the host AGN. Included in this sample are non-blazar AGNs such as 3C84, M82, and NGC 6251. For the blazars, the total VLBA radio flux density at 5GHz correlates strongly with {gamma}-ray flux. The LAT BL Lac objects tend to be similar to the non-LAT BL Lac objects, but the LAT flat-spectrum radio quasars (FSRQs) are significantly different from the non-LAT FSRQs. Strong core polarization is significantly more common among the LAT sources, and core fractional polarization appears to increase during LAT detection.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/450/959
- Title:
- VLBA images of High Frequency Peakers
- Short Name:
- J/A+A/450/959
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We propose a morphological classification based on the parsec scale structure of fifty-one High Frequency Peakers (HFPs) from the "bright" HFP sample. VLBA images at two adjacent frequencies (chosen among 8.4, 15.3, 22.2 and 43.2GHz) have been used to investigate the morphological properties of the HFPs in the optically thin part of their spectrum. We confirm that there is quite a clear distinction between the pc-scale radio structure of galaxies and quasars: the 78% of the galaxies show a "Double/Triple" morphology, typical of Compact Symmetric Objects (CSOs), while the 87% of the quasars are characterised by Core-Jet or unresolved structure. This suggests that most HFP candidates identified with quasars are likely blazar objects in which a flaring self-absorbed component at the jet base was outshining the remainder of the source at the time of the selection based on the spectral shape. Among the sources classified as CSOs or candidates it is possible to find extremely young radio sources with ages of about 100 years or even less.
- ID:
- ivo://CDS.VizieR/J/ApJ/658/203
- Title:
- VLBA imaging and polarimetry survey at 5GHz
- Short Name:
- J/ApJ/658/203
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results of the VLBA Imaging and Polarimetry Survey (VIPS), a 5GHz VLBI survey of 1119 sources with flat radio spectra. Through automated data reduction and imaging routines, we have produced publicly available I, Q, and U images and have detected polarized flux density from 37% of the sources. We have also developed an algorithm to use each source's I image to automatically classify it as a pointlike source, a core jet, a compact symmetric object (CSO) candidate, or a complex source. Using data from the Sloan Digital Sky Survey (SDSS), we have found no significant trend between optical flux and 5 GHz flux density for any of the source categories.
- ID:
- ivo://CDS.VizieR/J/ApJ/741/94
- Title:
- VLBA observations of H20 maser in IRAS 18286-0959
- Short Name:
- J/ApJ/741/94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of multi-epoch Very Long Baseline Array observations of the 22.2GHz H_2_O maser emission associated with the "water fountain" IRAS 18286-0959. We suggest that this object is the second example of a highly collimated bipolar precessing outflow traced by H_2_O maser emission, the other is W 43A. The detected H_2_O emission peaks are distributed over a velocity range from -50km/s to 150km/s. The spatial distribution of over 70% of the identified maser features is found to be highly collimated along a spiral jet (jet 1) extended southeast to northwest; the remaining features appear to trace another spiral jet (jet 2) with a different orientation. The two jets form a "double-helix" pattern which lies across ~200mas. The maser distribution is reasonably fit by a model consisting of two bipolar precessing jets. The three-dimensional velocities of jet 1 and jet 2 are derived to be 138km/s and 99km/s, respectively. The precession period of jet 1 is about 56 years. For jet 2, three possible models are tested and they give different values for the kinematic parameters. We propose that the appearance of two jets is the result of a single driving source with significant proper motion.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/141
- Title:
- VLBA observations of the AGN TXS 0128+554
- Short Name:
- J/ApJ/899/141
- Date:
- 14 Mar 2022 07:07:50
- Publisher:
- CDS
- Description:
- We have carried out a Chandra X-ray and multifrequency radio Very Long Baseline Array study of the active galactic nucleus (AGN) TXS0128+554, which is associated with the Fermi {gamma}-ray source 4FGLJ0131.2+5547. The AGN is unresolved in a target 19.3ks Chandra image, and its spectrum is well fit by a simple absorbed power-law model, with no distinguishable spectral features. Its relatively soft X-ray spectrum compared to other compact symmetric objects (CSOs) may be indicative of a thermal emission component, for which we were able to obtain an upper temperature limit of kT=0.08keV. The compact radio morphology and measured advance speed of 0.32c{+/-}0.07c indicate a kinematic age of only 82yr{+/-}17yr, placing TXS0128+554 among the youngest members of the CSO class. The lack of compact, inverted spectrum hotspots and an emission gap between the bright inner jet and outer radio lobe structure indicate that the jets have undergone episodic activity, and were relaunched a decade ago. The predicted {gamma}-ray emission from the lobes, based on an inverse Compton-emitting cocoon model, is three orders of magnitude below the observed Fermi-LAT flux. A comparison to other Fermi-detected and non-Fermi-detected CSOs with redshift z<0.1 indicates that the {gamma}-ray emission likely originates in the inner jet/core region, and that nearby, recently launched AGN jets are primary candidates for detection by the Fermi-LAT instrument.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A132
- Title:
- VLBA observations of the COSMOS field
- Short Name:
- J/A+A/607/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a project using wide-field Very Long Baseline Interferometry (VLBI) observations at 1.4GHz of 2865 known radio sources in the Cosmic Evolution Survey (COSMOS) field, whose main objective is to determine where Active Galactic Nuclei (AGN) are present. The combination of number of sources, sensitivity, angular resolution and area covered by this project are unprecedented. A catalogue which contains the VLBI detected sources is presented, the main purpose of which is to be used as an AGN catalogue. A catalogue containing complementary multiwavelength information of the VLBI detected sources is also presented.
- ID:
- ivo://CDS.VizieR/J/ApJS/128/17
- Title:
- VLBA obs. of radio reference frame sources. III.
- Short Name:
- J/ApJS/128/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present simultaneous dual-frequency Very Long Baseline Array 2 and 8 GHz observations of 225 of the 560 extragalactic sources for which positions were reported by Johnston and coworkers and which are now part of the International Celestial Reference Frame. These observations represent the third and final in a series of observations intended to obtain single-epoch images of the entire set of sources presented by Johnston and coworkers (1995, Cat. <J/AJ/110/880>) and, together with previously reported observations, bring the total number of sources observed to 389. As with previous papers in this series, we use these data to quantify the magnitude of the expected effect of intrinsic source structure on astrometric bandwidth synthesis Very Long Baseline Interferometry observations and to calculate a source "structure index" for the observed sources. The structure index can be used as an estimate of the astrometric quality of the sources. Based on this indicator, correlations between the observed radio structure and the astrometric position accuracy and stability of the sources have been found. These correlations indicate that the more extended sources have larger position uncertainties and are less positionally stable than the more compact sources.
- ID:
- ivo://CDS.VizieR/J/A+A/538/A136
- Title:
- VLBA SiO maser maps of the star OH 44.8-2.3
- Short Name:
- J/A+A/538/A136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- SiO maser emission occurs in the extended atmosphere of evolved stars and can be studied at high angular resolution. As compact, high-brightness components they can be used as important tracers of the dynamics at distances close to the central star. The masers also serve as probes of the evolutionary path from spherically symmetric AGB stars to aspherical PNe. Very long baseline interferometry (VLBI) observations of Mira variables indicate that SiO masers are significantly linearly polarized with linear polarization fractions up to 100%. However, no information is available at high angular resolution for SiO masers in higher mass loss OH/IR stars. Theory indicates a different SiO pumping mechanism in higher mass loss evolved stars. We extend the VLBI SiO maser studies to OH/IR stars. The observations enable us to understand the SiO pumping mechanisms in higher mass-loss evolved objects and to compare them with Mira variables. Additionally, polarimetric observations of SiO masers help us to understand the magnetic field strength and morphology and to distinguish between conflicting polarization theories.
- ID:
- ivo://CDS.VizieR/J/A+A/638/A17
- Title:
- VLBA SiO masers toward V838 Monocerotis
- Short Name:
- J/A+A/638/A17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present multi-epoch observations with the VLBA of SiO maser emission in the v=1, J=1-0 transition at 43GHz from the remnant of the red nova V838 Mon. We model the positions of maser spots to derive a parallax of 0.166+/-0.060mas. Combining this parallax with other distance information results in a distance of 5.6+/-0.5kpc, which agrees with an independent geometric distance of 6.1+/-0.6kpc from modeling polarimetry images of V838 Mon's light echo. Combining these results, and including a weakly constraining Gaia DR2 parallax, yields a best estimate of distance of 5.9+/-0.4kpc. The maser spots are located close to the peaks of continuum at ~225GHz and SiO J=5-4 thermal emission detected with ALMA. The proper motion of V838 Mon confirms its membership in a small open cluster in the Outer spiral arm of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJ/707/L56
- Title:
- VLBI and bright Fermi/LAT sources
- Short Name:
- J/ApJ/707/L56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A list of 205 {gamma}-ray strong objects was reported recently as a result of a three-month integration with the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope. We attempted identification of these objects, cross-correlating the {gamma}-ray positions with very long baseline interferometry (VLBI) positions of a large all-sky sample of extragalactic radio sources selected on the basis of their parsec-scale flux density. The original associations reported by the Fermi team are confirmed, and six new identifications are suggested. A Monte Carlo analysis shows that the fraction of chance associations in our analysis is less than 5%, and confirms that the vast majority of {gamma}-ray bright extragalactic sources are radio-loud blazars with strong parsec-scale jets. A correlation between the parsec-scale radio and {gamma}-ray flux is supported by our analysis of a complete VLBI flux-density-limited sample of extragalactic jets. The effectiveness of using a VLBI catalog to find associations between {gamma}-ray detections and compact extragalactic radio sources, especially near the Galactic plane, is demonstrated. It is suggested that VLBI catalogs should be used for future identification of Fermi/LAT objects.
