D. A. Graham

Superluminal non-ballistic jet swing in the quasar NRAO 150 revealed by mm-VLBI

Context. NRAO 150, a compact and bright radio to mm source showing core/jet structure, has been recently identified as a quasar at redshift

Sub-Milliarcsecond Imaging of Sgr A* and M 87

z = 1.52

Giant pulses with nanosecond time resolution detected from the Crab pulsar at 8.5 and 15.1 GHz

through a near-IR spectral observation. Aims. To study the jet kinematics on the smallest accessible scales and to compute the first estimates of its basic physical properties. Methods. We have analysed the ultra-high-resolution images from a new monitoring program at 86 GHz and 43 GHz with the Global mm VLBI Array and the VLBA, respectively. An additional archival calibration VLBA data set, covering the period from 1997 to 2007, has been used. Results. Our data show an extreme projected counter-clockwise jet position angle swing at an angular rate of up to ≈ 11° yr within the inner

First 230? GHz VLBI fringes on 3C 279 using the APEX Telescope (Research Note)

approx

147 GHz VLBI observations: Detection of 3C 273 and 3C 279 on the 3100 km baseline Metsähovi – Pico Veleta

3 pc of the jet, which is associated with a non-ballistic superluminal motion of the jet within this region. Conclusions. The results suggest that the magnetic field could play an important role in the dynamics of the jet in NRAO 150, which is supported by the large values of the magnetic field strength obtained from our first estimates. The extreme characteristics of the jet swing make NRAO 150 a prime source to study the jet wobbling phenomenon.

The Innermost Regions of AGN with Future mm-VLBI

We present and discuss new result from mm-VLBI observations of M 87 and Sgr A*. The imaging of these sources with a spatial resolutions of a few to a few ten Schwarzschild radii offers new possibilities to study the immediate environment of super-massive black holes.

First Detection of SGR A* with VLBI at 7 mm and 3 mm Wavelength

Aims. We present a study of shapes, spectra, and polarization properties of giant pulses (GPs) from the Crab pulsar at the very high frequencies of 8.5 and 15.1 GHz. Studies at 15.1 GHz are performed for the first time. We probe GP emission at high frequencies and examine its intrinsic spectral and polarization properties with high time and spectral resolution. The use of high radio frequencies also alleviates the effects of pulse broadening caused by interstellar scattering, which masks the intrinsic properties of GPs at low frequencies. Methods. Observations were conducted with the 100-m radio telescope in Effelsberg in Oct.‐Nov. 2007 at the frequencies of 8.5 and 15.1 GHz as part of an extensive campaign of multi-station multi-frequency observations of the Crab pulsar. A selection of the strongest pulses was recorded with a new data acquisition system, based on a fast digital oscilloscope, providing nanosecond time resolution in two polarizations with a bandwidth of about 500 MHz. In total, 29 and 85 GPs at longitudes of the main pulse and interpulse were recorded at 8.5 and 15.1 GHz during 10 and 17 h of observing time respectively. We analyzed the pulse shapes, polarisation and dynamic spectra of GPs as well as the cross-correlations between their LHC and RHC signals. Results. No events were detected outside the main pulse and interpulse windows. The GP properties were found to be very different for GPs emitted at longitudes of the main pulse and the interpulse. Cross-correlations of the LHC and RHC signals show regular patterns in the frequency domain for the main pulse, which are missing for the interpulse GPs. We consider the consequences of applying the rotating vector model to explain the apparent smooth variation in the position angle of linear polarization for main pulse GPs. We also introduce a new scenario of GP generation as a direct consequence of the polar cap discharge. Conclusions. We find further evidence of strong nano-shot discharges in the magnetosphere of the Crab pulsar. The repetitive frequency spectrum seen in GPs at the main pulse phase is interpreted as a diffraction pattern of regular structures in the emission region. The interpulse GPs however have a spectrum that resembles that of amplitude modulated noise. Propagation effects may be the cause of the differences.

Towards the Event Horizon: High Resolution VLBI Imaging of Nuclei of Active Galaxies

Aims. We report about a 230 GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO). Methods. We installed VLBI equipment and measured the APEX station position to 1 cm accuracy (1σ). We then observed 3C 279 on 2012 May 7 in a 5 h 230 GHz VLBI track with baseline lengths of 2800 Mλ to 7200 Mλ and a finest fringe spacing of 28.6 μas. Results. Fringes were detected on all baselines with signal-to-noise ratios of 12 to 55 in 420 s. The correlated flux density on the longest baseline was ∼0.3 Jy beam−1, out of a total flux density of 19.8 Jy. Visibility data suggest an emission region .38 μas in size, and at least two components, possibly polarized. We find a lower limit of the brightness temperature of the inner jet region of about 1010 K. Lastly, we find an upper limit of 20% on the linear polarization fraction at a fringe spacing of ∼38 μas. Conclusions. With APEX the angular resolution of 230 GHz VLBI improves to 28.6 μas. This allows one to resolve the last-photon ring around the Galactic Center black hole event horizon, expected to be 40 μas in diameter, and probe radio jet launching at unprecedented resolution, down to a few gravitational radii in galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in detail, follow-up observations with APEX and five other mm-VLBI stations have been conducted (March 2013) and are being analyzed.

Probing the sub-parsec scale structures in extragalactic radio jets: VLBI at 43 GHz

We report a successful VLBI observation at 147u2009GHz (2.1u2009mm) on the 3u2009100 km long baseline between the telescopes at Metsahovi (Finland) and Pico Veleta (Spain). The sources 3Cu2009273B and 3Cu2009279 were detected with a SNR of . For these sources we estimate that 25–30% of the total flux is detectable as correlated flux on the 3u2009100u2009km baseline, which gives at 147u2009GHz a lower limit of the brightness temperature of the inner VLBI jet region of ~1

The structure of the quasar 3C345 at lambda 49cm and its relation to low-frequency variability

times