Search results for " Basel"
showing 10 items of 66 documents
Wisps in the Galactic center: Near-infrared triggered observations of the radio source Sgr A* at 43 GHz
2016
Context. The compact radio and near-infrared (NIR) source Sagittarius A* (Sgr A*) associated with the supermassive black hole in the Galactic center was observed at 7 mm in the context of a NIR triggered global Very Long Baseline Array (VLBA) campaign. Aims. Sgr A* shows variable flux densities ranging from radio through X-rays. These variations sometimes appear in spontaneous outbursts that are referred to as flares. Multi-frequency observations of Sgr A* provide access to easily observable parameters that can test the currently accepted models that try to explain these intensity outbursts. Methods. On May 16-18, 2012 Sgr A* has been observed with the VLBA at 7 mm (43 GHz) for 6 hours each…
VLBI imaging of M81* at 43GHz
2011
The nearby spiral galaxy M81 harbors in its core a Low-Luminosity AGN (LLAGN), and appears closely related to the more distant and powerful AGNs seen in quasars and radio galaxies. The intrinsic size of this object is unknown due to scattering, and it has shown a core-jet morphology with weak extended emission rotating with wavelength. The proximity of M\,81 (D=3.63 Mpc) allows a detailed investigation of its nucleus to be made. The nucleus is four orders of magnitude more luminous than the Galactic centre, and is therefore considered a link between SgrA* and the more powerful nuclei of radio galaxies and quasars. Our main goal was to determine the size of M81* at a shorter wavelength thus …
Radio-optical scrutiny of compact AGN: Correlations between properties of pc-scale jets and optical nuclear emission
2010
We study the correlations between the Very Long Baseline Array radio emission at 15 GHz, extended emission at 151 MHz, and optical nuclear emission at 5100 AA for a complete sample of 135 compact jets. We use the partial Kendall's tau correlation analysis to check the link between radio properties of parsec-scale jets and optical luminosities of host AGN. We find a significant positive correlation for 99 quasars between optical nuclear luminosities and total radio (VLBA) luminosities of unresolved cores at 15 GHz originated at milliarcseconds scales. For 18 BL Lacs, the optical continuum emission correlates with the radio emission of the jet at 15 GHz. We suggest that the radio and optical …
23 GHz VLBI Observations of SN 2008ax
2009
We report on phase-referenced 23 GHz Very-Long-Baseline-Interferometry (VLBI) observations of the type IIb supernova SN 2008ax, made with the Very Long Baseline Array (VLBA) on 2 April 2008 (33 days after explosion). These observations resulted in a marginal detection of the supernova. The total flux density recovered from our VLBI image is 0.8$\pm$0.3 mJy (one standard deviation). As it appears, the structure may be interpreted as either a core-jet or a double source. However, the supernova structure could be somewhat confused with a possible close by noise peak. In such a case, the recovered flux density would decrease to 0.48$\pm$0.12 mJy, compatible with the flux densities measured with…
Absolute kinematics of radio source components in the complete S5 polar cap sample I. First and second epoch maps at 8.4 GHz
2001
We observed the thirteen extragalactic radio sources of the S5 polar cap sample at 8.4 GHz with the Very Long Baseline Array, on 1997.93 and 1999.41. We present the maps from those two epochs and briefly discuss the morphological changes experimented by some of the radio sources in the 1.4 yr elapsed. These results correspond to the first two epochs at 8.4 GHz of a program directed to study the absolute kinematics of the radio source components of the members of the sample by means of phase delay astrometry at 8.4, 15 and 43 GHz.
Subparsec Polarimetric Radio Observations of 3C 120: A Close‐up Look at Superluminal Motion
1998
We present two-epoch polarimetric images of the radio galaxy 3C 120 obtained with the Very Long Baseline Array at 22 and 43 GHz. Because of the proximity of 3C 120 (z = 0.033), the 43 GHz observations allow us to observe superluminal motions with the highest resolution achieved to date, 0.07 h-1 pc. Up to ten different superluminal components, with velocities between 2.3 and 5.4 h-1c, can be observed in this active source, with approximately monthly ejections of new components. Polarization is observed in several components and at both frequencies, with peaks in the linearly polarized flux not always coincident with the peaks in total intensity. The orientation of the magnetic field is obse…
Absolute kinematics of radio source components in the complete S5 polar cap sample
2004
We observed the thirteen extragalactic radio sources of the complete S5 polar cap sample at 15.4 GHz with the Very Long Baseline Array, on 27 July 1999 (1999.57) and 15 June 2000 (2000.46). We present the maps from those two epochs, along with maps obtained from observations of the 2 cm VLBA survey for some of the sources of the sample, making a total of 40 maps. We discuss the apparent morphological changes displayed by the radio sources between the observing epochs. Our VLBA observations correspond to the first two epochs at 15.4 GHz of a program to study the absolute kinematics of the radio source components of the members of the sample, by means of phase delay astrometry at 8.4 GHz, 15.…
Changes in the trajectory of the radio jet in 0735+178?
2001
We present multi-epoch 8.4 and 43 GHz Very Long Baseline Array images of the BL Lac object 0735+178. The images confirm the presence of a twisted jet with two sharp apparent bends of 90$^{\circ}$ within two milliarcseconds of the core, resembling a helix in projection. The observed twisted geometry could be the result of precession of the jet inlet, but is more likely produced by pressure gradients in the external medium through which the jet propagates. Quasi-stationary components are observed at the locations of the 90$^{\circ}$ bends, possibly produced by differential Doppler boosting. Identification of components across epochs, since the earliest VLBI observations of this source in 1979…
THE ACCELERATING JET OF 3C 279
2012
Analysis of the proper motions of the subparsec scale jet of the quasar 3C 279 at 15 GHz with the Very Long Baseline Array shows significant accelerations in four of nine superluminal features. Analysis of these motions is combined with the analysis of flux density light curves to constrain values of Lorentz factor and viewing angle (and their derivatives) for each component. The data for each of these components are consistent with significant changes to the Lorentz factor, viewing angle, and azimuthal angle, suggesting jet bending with changes in speed. We see that for these observed components Lorentz factors are in the range Γ = 10-41, viewing angles are in the range = 0.°1-5.°0, and in…
Millimeter VLBI of NGC 1052: Dynamics
2016
The LINER galaxy NGC 1052 is an ideal target to study the innermost regions of active galactic nuclei (AGN), given its close distance of about 20 Mpc. The source was observed at 29 epochs from 2005 to 2009 with the Very Long Baseline Array (VLBA) at 43 GHz. Here, we present a kinematic study of its twin-jet system from a subset of 9 epochs at 43 GHz carried out in 2005 and 2006, finding a bright central feature as the dynamic center. The resulting mean velocities of β = v / c = 0 . 46 ± 0 . 08 and β = 0 . 69 ± 0 . 02 for the western and eastern jet, respectively, give hints towards higher velocities in the eastern jet.