- ID:
- ivo://CDS.VizieR/J/A+A/610/A1
- Title:
- TANAMI II. Additional sources
- Short Name:
- J/A+A/610/A1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- TANAMI is a multiwavelength program monitoring active galactic nuclei (AGN) south of -30{deg} declination including high-resolution Very Long Baseline Interferometry (VLBI) imaging, radio, optical/UV, X-ray and {gamma}-ray studies. We have previously published first-epoch 8.4GHz VLBI images of the parsec-scale structure of the initial sample. In this paper, we present images of 39 additional sources. The full sample comprises most of the radio- and {gamma}-ray brightest AGN in the southern quarter of the sky, overlapping with the region from which high-energy (>100TeV) neutrino events have been found. We characterize the parsec-scale radio properties of the jets and compare with the quasi-simultaneous Fermi/LAT {gamma}-ray data. Furthermore, we study the jet properties of sources which are in positional coincidence with high-energy neutrino events as compared to the full sample. We test the positional agreement of high-energy neutrino events with various AGN samples. TANAMI VLBI observations at 8.4GHz are made with Southern-Hemisphere radio telescopes located in Australia, Antarctica, Chile, New Zealand, and South Africa. Our observations yield the first images of many jets below -30{deg} declination at milliarcsecond resolution. We find that {gamma}-ray loud TANAMI sources tend to be more compact on parsec-scales and have higher core brightness temperatures than {gamma}-ray faint jets, indicating higher Doppler factors. No significant structural difference is found between sources in positional coincidence with high-energy neutrino events and other TANAMI jets. The 22 {gamma}-ray brightest AGN in the TANAMI sky show only a weak positional agreement with high-energy neutrinos demonstrating that the >100TeV IceCube signal is not simply dominated by a small number of the {gamma}-ray brightest blazars. Instead, a larger number of sources have to contribute to the signal with each individual source having only a small Poisson probability for producing an event in multi-year integrations of current neutrino detectors.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/569/A115
- Title:
- TANAMI monitoring of Centaurus A.
- Short Name:
- J/A+A/569/A115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Centaurus A (Cen A) is the closest radio-loud active galactic nucleus. Very Long Baseline Interferometry (VLBI) enables us to study the spectral and kinematic behavior of the radio jet-counterjet system on milliarcsecond scales, providing essential information for jet emission and propagation models. In the framework of the TANAMI monitoring, we investigate the kinematics and complex structure of Cen A on subparsec scales. We have been studying the evolution of the central parsec jet structure of Cen A for over 3.5-years. The proper motion analysis of individual jet components allows us to constrain jet formation and propagation and to test the proposed correlation of increased high-energy flux with jet ejection events. Cen A is an exceptional laboratory for such a detailed study because its proximity translates to unrivaled linear resolution, where one milliarcsecond corresponds to 0.018pc. As a target of the southern-hemisphere VLBI monitoring program TANAMI, observations of Cen A are done approximately every six months at 8.4GHz with the Australian Long Baseline Array (LBA) and associated telescopes in Antarctica, Chile, New Zealand, and South Africa, complemented by quasi-simultaneous 22.3GHz observations. The first seven epochs of high-resolution TANAMI VLBI observations at 8.4GHz of Cen A are presented, resolving the jet on (sub-)milliarcsecond scales. They show a differential motion of the subparsec scale jet with significantly higher component speeds farther downstream where the jet becomes optically thin. We determined apparent component speeds within a range of 0.1c to 0.3c and identified long-term stable features. In combination with the jet-to-counterjet ratio, we can constrain the angle to the line of sight to {theta}~12{deg}-45{deg}. The high-resolution kinematics are best explained by a spine-sheath structure supported by the downstream acceleration occurring where the jet becomes optically thin. On top of the underlying, continuous flow, TANAMI observations clearly resolve individual jet features. The flow appears to be interrupted by an obstacle causing a local decrease in surface brightness and circumfluent jet behavior. We propose a jet-star interaction scenario to explain this appearance. The comparison of jet ejection times to high X-ray flux phases yields a partial overlap of the onset of the X-ray emission and increasing jet activity, but the limited data do not support a robust correlation.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A148
- Title:
- TANAMI radio galaxies I
- Short Name:
- J/A+A/627/A148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the framework of the TANAMI multi-wavelength and VLBI monitoring, we study the evolution of the parsec-scale radio emission in radio galaxies in the southern hemisphere and their relationship to the gamma-ray properties of the sources. Our study investigates systematically, for the first time, the relationship between the two energy regimes in radio galaxies. In this first paper, we focus on Fermi-LAT-detected sources. The TANAMI program monitors a large sample of radio-loud AGN at 8.4GHz and 22.3GHz with the Australian Long Baseline Array(LBA) and associated telescopes in Antarctica, Chile, New Zealand and South Africa. We perform a kinematic analysis for five gamma-ray detected radio galaxies using multi-epoch 8.4 GHz VLBI images, deriving limits on intrinsic jet parameters such as speed and viewing angle. We analyzed103 months of Fermi-LAT data in order to study possible connections between the gamma-ray properties and the pc-scale jets of Fermi-LAT-detected radio galaxies, both in terms of variability and average properties. We discuss the individual source results and draw preliminary conclusions on sample properties including published VLBI results from the MOJAVE survey, with a total of fifteen sources. We find that the first gamma-ray detection of Pictor A might be associated with the passage of a new VLBI component through the radio core, which appears to be a defining feature of high-energy emitting Fanaroff-Riley type II radio galaxies. For the peculiar AGN PKS 0521-36, we detect subluminal parsec-scale jet motions, and we confirm the presence of fast gamma-ray variability in the source down to timescales of 6 hours, which is not accompanied by variations in the VLBI jet. We robustly confirm the presence of significant superluminal motion, up to {beta}_app_~3, in the jet of the TeV radio galaxy PKS 0625-35. Our VLBI results constrain the jet viewing angle to be {theta}<53{deg}, allowing for the possibility of a closely aligned jet. Finally, by analyzing the first pc-scale multi-epoch images of the prototypical Compact Symmetric Object (CSO) PKS 1718-649, we place an upper limit on the separation speed between the two mini-lobes, which in turn allows us to derive a lower limit on the age of the source.Conclusions.We can draw some preliminary conclusions on the relationship between pc-scale jets and gamma-ray emission in radio galaxies, basedonFermi-LAT-detected sources with available multi-epoch VLBI measurements. We find that the VLBI core flux density correlates with the gamma-ray flux, as seen in blazars. On the other hand, the gamma-ray luminosity does not show any dependence on the core brightness temperature and core dominance, two common indicators of jet Doppler boosting. This seems to indicate that gamma-ray emission in radio galaxies is not driven by orientation-dependent effects, as in blazars, which is consistent with the unified model of jetted AGN.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A152
- Title:
- TANAMI radio galaxies II
- Short Name:
- J/A+A/641/A152
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second paper in our series studying the evolution of parsec-scale radio emission in radio galaxies in the southern hemisphere. Following our study of the radio and high-energy properties of gamma-ray-emitting sources, here we investigate the kinematic and spectral properties of the parsec-scale jets of radio galaxies that have not yet been detected by the Fermi Large Area Telescope (Fermi-LAT) instrument on board NASA's Fermi Gamma-ray Space Telescope. For many sources, these results represent the first milliarcsecond resolution information in the literature. These studies were conducted within the framework of the Tracking Active Nuclei with Austral Milliarcsecond Interferometry (TANAMI) monitoring program and in the context of high-energy gamma-ray observations from Fermi-LAT. We take advantage of the regular 8.4GHz and 22.3GHz Very Long Baseline Interferometry (VLBI) observations provided by the TANAMI monitoring program, and explore the kinematic properties of six gamma-ray-faint radio galaxies. We complement this with ~8.5 years of Fermi-LAT data, deriving updated upper limits on the gamma-ray emission from this subsample of TANAMI radio galaxies. We include publicly available VLBI kinematics of gamma-ray-quiet radio galaxies monitored by the MOJAVE program and perform a consistent Fermi-LAT analysis. We combine these results with those from our previous paper to construct the largest sample of radio galaxies with combined VLBI and gamma-ray measurements to date. The connection between parsec-scale jet emission and high-energy properties in the misaligned jets of radio galaxies is explored. We report for the first time evidence of superluminal motion up to beta_app_=3.6 in the jet of the gamma-ray-faint radio galaxy PKS 2153-69. We find a clear trend of higher apparent speed as a function of distance from the jet core, which indicates that the jet is still being accelerated on scales of tens of parsecs, or ~10^5^R_{sun}_, corresponding to the end of the collimation and acceleration zone in nearby radio galaxies. We find evidence of subluminal apparent motion in the jets of PKS 1258-321 and IC 4296, and no measurable apparent motion for PKS 1549-79, PKS 1733-565 and PKS 2027-308. For all these sources, TANAMI provides the first multi-epoch kinematic analysis on parsec scales. We then compare the VLBI properties of gamma-ray-detected and undetected radio galaxies, and find that the two populations show a significantly different distribution of median core flux density, and, possibly, of median core brightness temperature. In terms of correlation between VLBI and gamma-ray properties, we find a significant correlation between median core flux density and gamma-ray flux, but no correlation with typical Doppler boosting indicators such as median core brightness temperature and core dominance. Our study suggests that high-energy emission from radio galaxies is related to parsec-scale radio emission from the inner jet, but is not driven by Doppler boosting effects, in contrast to the situation in their blazar counterparts. This implies that gamma-ray loudness does not necessarily reflect a higher prevalence of boosting effects.
55. The epoch ICRF
- ID:
- ivo://CDS.VizieR/J/MNRAS/430/2633
- Title:
- The epoch ICRF
- Short Name:
- J/MNRAS/430/2633
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The epoch International Celestial Reference Frame (epoch ICRF) is proposed as a new concept in order to consider the effect of apparent proper motion of the position of a radio source due to acceleration of the spatial origin of the ICRF, the centre of mass of the Solar system. This apparent proper motion has a magnitude of approximately 5.8-microarcsec ({mu}as) per year, and for the 30-year very long baseline interferometry (VLBI) observational history these position variations will exceed 100{mu}as. We show that the dipole structure of the apparent proper motions leads to global rotation in the ICRF2 and the main term, the shift of direction of the origin of right ascension, reaches 25{mu}as per century. The 'epoch ICRF' is constructed using epoch positions at J2000.0 and apparent proper motions of radio sources, which are reported here for 295 ICRF2-defining sources.
- ID:
- ivo://CDS.VizieR/J/MNRAS/419/1097
- Title:
- The EVN Galactic Plane Survey - EGaPS
- Short Name:
- J/MNRAS/419/1097
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I present a catalogue of positions and correlated flux densities of 109 compact extragalactic radio sources in the Galactic plane determined from analysis of a 48 hour VLBI experiment at 22GHz with the European VLBI Network. The median position uncertainty is 9mas. The correlated flux densities of detected sources are in the range of 20 to 300mJy. In addition to target sources, nine water masers have been detected, two of them new. I derived position of masers with accuracies 30 to 200mas and determined velocities of maser components and their correlated flux densities.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A146
- Title:
- The gNLS1 galaxy PKS 2004-447. VLBI images
- Short Name:
- J/A+A/588/A146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gamma-ray-detected radio-loud narrow-line Seyfert 1 (g-NLS1) galaxies constitute a small but interesting sample of the g-ray-loud AGN. The radio-loudest g-NLS1 known, PKS 2004-447, is located in the southern hemisphere and is monitored in the radio regime by the multiwavelength monitoring programme TANAMI. We aim for the first detailed study of the radio morphology and long-term radio spectral evolution of PKS 2004-447, which are essential for understanding the diversity of the radio properties of g-NLS1s. The TANAMI VLBI monitoring program uses the Australian Long Baseline Array (LBA) and telescopes in Antarctica, Chile, New Zealand, and South Africa to monitor the jets of radio-loud active galaxies in the southern hemisphere. Lower resolution radio flux density measurements at multiple radio frequencies over four years of observations were obtained with the Australia Telescope Compact Array (ATCA). The TANAMI VLBI image at 8.4GHz shows an extended one-sided jet with a dominant compact VLBI core. Its brightness temperature is consistent with equipartition, but it is an order of magnitude below other g-NLS1s with the sample value varying over two orders of magnitude. We find a compact morphology with a projected large-scale size <11kpc and a persistent steep radio spectrum with moderate flux-density variability. PKS 2004-447 appears to be a unique member of the g-NLS1 sample. It exhibits blazar-like features, such as a flat featureless X-ray spectrum and a core-dominated, one-sided parsec-scale jet with indications for relativistic beaming. However, the data also reveal properties atypical for blazars, such as a radio spectrum and large-scale size consistent with compact-steep-spectrum (CSS) objects, which are usually associated with young radio sources. These characteristics are unique among all g-NLS1s and extremely rare among g-ray-loud AGN.
- ID:
- ivo://CDS.VizieR/J/A+A/617/A38
- Title:
- The hydrogen gas outflow in 3C236
- Short Name:
- J/A+A/617/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The energetic feedback that is generated by radio jets in active galactic nuclei (AGNs) has been suggested to be able to produce fast outflows of atomic hydrogen (HI) gas which can be studied in absorption at high spatial resolution. We have used the Very Large Array (VLA) and a global very-long-baseline-interferometry (VLBI) array to locate and study in detail the HI outflow discovered with the Westerbork Synthesis Radio Telescope (WSRT) in the restarted radio galaxy 3C 236. Based on the VLA data, the presence of a blue-shifted wing of the HI with a width of ~1000km/s. This HI outflow is partially recovered by the VLBI observation. In particular, we detect four clouds with masses of 0.28-1.5x10^4^M_{sun}_ with VLBI that do not follow the regular rotation of most of the HI. Three of these clouds are located, in projection, against the nuclear region on scales of <~40pc, while the fourth is cospatial to the southeast lobe at a projected distance of ~270pc. Their velocities are between 150 and 640km/s blueshifted with respect to the velocity of the disk-related HI. These findings suggest that the outflow is at least partly formed by clouds, as predicted by some numerical simulations, and that it originates already in the inner (few tens of pc) region of the radio galaxy. Our results indicate that the entire outflow might consist of many clouds, possibly with comparable properties as those clearly detected, but also distributed at larger radii from the nucleus where the lower brightness of the lobe does not allow us to detect them. However, we cannot rule out a diffuse component of the outflow. Because 3C 236 is a low excitation radio galaxy, it is less likely that the optical AGN is able to produce strong radiative winds. This leaves the radio jet as the main driver for the HI outflow.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A159
- Title:
- The third realization of the ICRF, ICRF3
- Short Name:
- J/A+A/644/A159
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new realization of the International Celestial Reference Frame (ICRF) is presented based on the work achieved by a working group of the International Astronomical Union (IAU) mandated for this purpose. This new realization follows the initial realization of theICRF completed in 1997 and its successor, ICRF2, adopted as a replacement in 2009. The new frame, referred to as ICRF3, is based on nearly 40 years of data acquired by very long baseline interferometry at the standard geodetic and astrometric radio frequencies (8.4 and 2.3GHz), supplemented with data collected at higher radio frequencies (24GHz and dual-frequency 32 and 8.4GHz) over the past 15 years. State-of-the-art astronomical and geophysical modeling has been used to analyze these data and derive source positions. The modeling integrates, for the first time, the effect of the galactocentric acceleration of the solar system (directly estimated from the data) which, if not considered, induces significant deformation of the frame due to the data span. The new frame includes positions at 8.4GHz for 4536 extragalactic sources. Of these, 303 sources, uniformly distributed on the sky, are identified as "defining sources" and as such serve to define the axes of the frame. Positions at 8.4GHz are supplemented with positions at 24GHz for 824 sources and at 32GHz for 678 sources. In all, ICRF3 comprises 4588 sources, with three-frequency positions available for 600 of these. Source positions have been determined independently at each of the frequencies in order to preserve the underlying astrophysical content behind such positions. They are reported for epoch 2015.0 and must be propagated for observations at other epochs for the most accurate needs, accounting for the acceleration toward the Galactic center, which results in a dipolar proper motion field of amplitude 0.0058 milliarcsecond/yr (mas/yr). The frame is aligned onto the International Celestial Reference System to within the accuracy of ICRF2 and shows a median positional uncertainty of about 0.1mas in right ascension and 0.2 mas in declination, with a noise floor of 0.03mas in the individual source coordinates. A subset of 500 sources is found to have extremely accurate positions, in the range of 0.03 to 0.06mas, at the traditional 8.4GHz frequency. Comparing ICRF3 with the recently released Gaia Celestial Reference Frame 2 in the optical domain, there is no evidence for deformations larger than 0.03 mas between the two frames, in agreement with the ICRF3 noise level. Significant positional offsets between the three ICRF3 frequencies are detected for about 5% of the sources.Moreover, a notable fraction (22%) of the sources shows optical and radio positions that are significantly offset. There are indications that these positional offsets may be the manifestation of extended source structures. This third realization of the ICRF was adopted by the IAU at its 30th General Assembly in August 2018 and replaced the previous realization, ICRF2, on January 1, 2019.
- ID:
- ivo://CDS.VizieR/J/AJ/142/35
- Title:
- The VLBA Galactic Plane Survey (VGaPS)
- Short Name:
- J/AJ/142/35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We presents accurate absolute positions from a 24 GHz Very Long Baseline Array (VLBA) search for compact extragalactic sources in an area where the density of known calibrators with precise coordinates is low. The goals were to identify additional sources suitable for use as phase calibrators for galactic sources, determine their precise positions, and produce radio images. In order to achieve these goals, we developed a new software package, PIMA, for determining group delays from wide-band data with much lower detection limit. With the use of PIMA we have detected 327 sources out of 487 targets observed in three 24 hour VLBA experiments. Among the 327 detected objects, 176 are within 10 degrees of the Galactic plane. This VGaPS catalogue of source positions, plots of correlated flux density versus projected baseline length, contour plots, as well as weighted CLEAN images and calibrated visibility data in FITS format, are available on the Web at http://astrogeo.org/vgaps. Approximately one half of objects from the 24GHz catalogue were observed at dual band 8.6GHz and 2.3GHz experiments. Position differences at 24GHz versus 8.6/2.3GHz for all but two objects on average are strictly within reported uncertainties. We found that for two objects with complex structure positions at different frequencies correspond to different components of a source.
