RADIO ASTRONOMY / VLBI

Research Highlights

Here we show recent research results from the Radio Astronomy/Very-Long-Baseline Interferometry department.

List of refereed papers from the Radio Astronomy/VLBI department (ADS public library)

Evidence for a toroidal magnetic field in the nucleus of 3C 84

27 May 2024

A study in the current issue of the journal Astronomy & Astrophysics explores the relativistic radio jet of the nearby active galactic nucleus (AGN) 3C 84, using 22 GHz very long baseline interferometry (VLBI) to study its sub-parsec region. By analysing the total intensity and linear polarisation of 3C 84, the researchers tested different relativistic magneto-hydrodynamic (RMHD) simulations, adjusting the jet's bulk Lorentz factor and magnetic field configurations (toroidal, poloidal, helical). The results confirm a limb-brightened jet structure with electric vector position angles (EVPAs) aligned with the jet flow in the centre, but orthogonal near the edges. The observed geometry is consistent with a spine-sheath model with mildly relativistic flow and a toroidal magnetic field, bridging the gap between RMHD simulations and VLBI observations.  These results are led by MPIfR junior researcher Georgios F. Paraschos; more information is available here.

Around the bend in 3C 345's jet

24 April 2024

The current issue of Astronomy & Astrophysics features a study led by PhD student Jan Röder that examines the flat-spectrum radio quasar 3C 345, known for its γ-ray activity since the mid-2000s. The focus is on the 2009 γ-ray burst associated with a relativistic outflow observed with 43 GHz Very Long Baseline Interferometry (VLBI). By analysing data from the VLBA-BU-BLAZAR and BEAM-ME programmes, as well as new observations at 23, 43 and 86 GHz between 2017 and 2019, the research team aimed to study the innermost regions of the ultra-compact jet. Their results reveal a helical geometry in the inner jet, anchored to a stationary feature and evolving over about 8 years. The jet's bends are due to variations in the ejection angle, and the γ-ray emission results from relativistic outflows and interactions within the jet.  More information can be found directly in the publication here.

ERC advanced grant for Prof. Dr. Yuri Kovalev

ERC advanced grant for Prof. Dr. Yuri Kovalev

April 11, 2024
Classical telescopes and neutrino telescopes will allow scientists to understand extreme cosmic super-colliders more

Identifying synergies between ground-based radio and space-based X-ray imaging techniques

04 April 2024

Reconstructing images from noisy, incomplete data is a challenge in many scientific fields, including Very Long Baseline Interferometry (VLBI) and the Spectrometer/Telescope for Imaging X-rays (STIX). A study led by MPIfR junior researcher Hendrik Müller explores the untapped potential of combining imaging techniques from both fields to improve high-resolution, high-fidelity imaging. By organising a semi-blind imaging challenge using typical VLBI and STIX data, the researchers compared seventeen algorithms from six different frameworks. The results showed that methods developed for STIX worked well with VLBI data and vice versa, significantly outperforming the traditional CLEAN algorithm. While entropy-based and Bayesian methods excelled on STIX data, more complex algorithms with multiple regularisation terms proved superior on VLBI data. This synergy suggests a promising future for joint progress, guiding the development of novel imaging algorithms in both fields.   More information can be found in the original paper here.

Understanding AGN jets with the TELAMON programme

28 March 2024

A paper published today shows the results obtained by a team led by Florian Eppel, including scientists from the MPIfR and the University of Würzburg, reporting on the first results from the TELAMON program (PI. M. Kadler).  The TELAMON programme uses the 100 m Effelsberg telescope to monitor radio spectra of active galactic nuclei (AGN), in particular TeV blazars and neutrino-associated AGN. This study focuses on the characterisation of a main sample of TeV-detected blazars. Data from about 2.5 years of observations were analysed, covering frequencies from 14 GHz to 45 GHz. In the pilot phase, 59 TeV-detected blazars in the northern hemisphere were observed. Basic data reduction and calibration procedures were applied to the TELAMON data, and an averaging method was used to compute mean light curves for the sources. The results show that TeV-selected blazars in the sample typically have a flat radio spectrum, with a median spectral index of -0.11. These results are consistent with previous studies of TeV-selected blazars. Compared to the GeV-selected sample, the TELAMON sources have a lower radio flux density, which is consistent with the spectral characteristics of TeV-emitting blazars. The spectral index distribution of the TeV-selected blazar sample is similar to that of the GeV-selected samples. In addition, a strategy for tracking the light curve evolution is presented for future variability and correlation analysis.  More details can be found in the publication, appeared today in Astronomy & Astrophysics, here.

Sagittarius A*

Sagittarius A*

March 27, 2024
Astronomers Unveil Strong Magnetic Fields Spiraling at the Edge of Milky Way’s Central Black Hole more

Selected media echo and parallel press releases (Sgr A* 2017 EHT polarisation image release)

Parallel Press Releases:

English:

Spanish:

German press echo here (VLBI Department Highlights German version)

Magnetic and thermal acceleration in the jet of galaxy NGC 315

22 March 2024

A study led by MPIfR junior researcher Luca Ricci shows how relativistic jets from active galactic nuclei, such as those in NGC 315, reach high velocities on scales of a few to tens of parsecs. Traditionally, the focus has been on magnetic acceleration, while thermal acceleration has been considered negligible beyond compact regions near the central engine. Using a 2D relativistic magnetohydrodynamical code, the researchers studied jet acceleration from sub-parsec to parsec scales, based on observational data from very long baseline interferometry. The results show that when the thermal energy rivals or exceeds the magnetic energy, the thermal acceleration remains significant even at parsec scales, expanding the acceleration range. The study found that expansion drives the acceleration, and that disc-driven winds could be crucial for jet propagation. For NGC 315, models with different magnetic field configurations and shear layer thicknesses successfully replicated the observed acceleration and jet angles, highlighting the potential role of thermal acceleration in jet dynamics.  More information can be found in the original paper in the journal Astronomy & Astrophysics here.

Magnetic launching of black hole jets in Perseus A

Magnetic launching of black hole jets in Perseus A

February 01, 2024
First observations of the radio galaxy Perseus A with the Event Horizon Telescope more

Selected media echo and parallel press releases (Perseus A 2017 EHT image release)

English:

 

New EHT observations of M87 reveal persistent black hole shadow

New EHT observations of M87 reveal persistent black hole shadow

January 18, 2024
Improved observations one year after the discovery image give a better picture more

Selected media echo and parallel press releases (M87 2018 EHT image release)

Here selected parallel press releases and news & views on the A&A publication of the Messier 87* images by the Event Horizon Telescope from observations in 2018.

English:

German:

Spanish:

Unraveling Blazar Mysteries: TANAMI's First-epoch S Band Images

16 January 2024

A team of astronomers led by the MPIfR PhD candidate Petra Benke presents a new publication on southern radio sources. The study focuses on the multi-wavelength emission from blazars, which are celestial objects that emit radiation across the electromagnetic spectrum, from radio to high-energy gamma rays. Recent successes in the study of blazar activity have come from quasi-simultaneous multi-wavelength monitoring programs made possible by the launch of the Fermi Gamma-ray Space Telescope in 2008. The team used VLBI to carry out sensitive, long-term monitoring of a comprehensive sample of gamma-energetic AGN. These observations were made with the Long Baseline Array (LBA) and other radio telescopes in the Southern Hemisphere at 13 cm wavelength (S-band) as part of the TANAMI program. The study presents the first light TANAMI S-band images, highlighting the TeV-detected sub-sample of the full TANAMI sample. The analysis examines the redshift, 0.1-100 GeV photon flux, and S-band core brightness temperature distributions of the TeV-detected objects. In particular, flat-spectrum radio quasars and low-synchrotron-peak sources have on average higher brightness temperatures than high-synchrotron-peak BL Lacs. In addition, sources with bright GeV gamma-ray emission show higher brightness temperatures compared to gamma-low sources. More details of the study can be found in the original paper here (preprint here).
 

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