Radio and γ-ray activity in the jet of the blazar S5 0716+714

We explore the connection between the γ-ray and radio emission in the jet of the blazar 0716+714 by using 15, 37, and 230 GHz radio and 0.1–200 GeV γ-ray light curves spanning 10.5 yr (2008–2019). We find significant positive and negative correlations between radio and γ-ray fluxes in different time ranges. The time delays between radio and γ-ray emission suggest that the observed γ-ray flares originated from multiple regions upstream of the radio core, within a few parsecs from the central engine. Using time-resolved 43 GHz Very Long Baseline Array maps we identified 14 jet components moving downstream along the jet. Their apparent speeds range from 6c to 26c, and they show notable variations in their position angles upstream from the stationary component (∼0.53 mas from the core). The brightness temperature declines as a function of distance from the core according to a power law that becomes shallower at the location of the stationary component. We also find that the periods at which significant correlations between radio and γ-ray emission occur overlap with the times when the jet was oriented to the north. Our results indicate that the passage of a propagating disturbance (or shock) through the radio core and the orientation of the jet might be responsible for the observed correlation between the radio and γ-ray variability. We present a scenario that connects the positive correlation and the unusual anticorrelation by combining the production of a flare and a dip at γ-rays by a strong moving shock at different distances from the jet apex.https://iopscience.iop.org/article/10.3847/1538-4357/ac31b4/pdfPublished versio

The core shift effect in the blazar 3C 454.3

Peer reviewe

Continuum source catalog for the first APERTIF data release

The first data release from Apertif survey contains 3074 radio continuum images, covering a thousand square degrees of the sky. The observations were performed between August 2019 and July 2020. The continuum images were produced at a central frequency 1355 MHz, with a bandwidth of ~150 MHz and angular resolution of up to 10âà  ³. In this work, we introduce and apply a new method to obtain a primary beam model based on a machine-learning approach, namely, Gaussian process regression. The primary beam models obtained with this method have been published, along with the data products for the first Apertif data release. We applied the method to the continuum images, carried out a mosaicking process on their basis, and extracted the source catalog. The catalog contains 249672 radio sources, many of which have been detected for the first time at these frequencies. We cross-matched the coordinates with the NVSS, LOFAR/DR1/value-Added, and LOFAR/DR2 catalogs a resulting in 44523, 22825, and 152824 common sources, respectively. The first sample provides a unique opportunity for detecting long-Term transient sources, which have significantly changed their flux density over the past 25 yr. A combination of the second and the third samples provides valuable information on the spectral properties of the sources in addition to redshift estimates

Continuum source catalog for the first APERTIF data release

The first data release from Apertif survey contains 3074 radio continuum images, covering a thousand square degrees of the sky. The observations were performed between August 2019 and July 2020. The continuum images were produced at a central frequency 1355 MHz, with a bandwidth of ~150 MHz and angular resolution of up to 10âà  ³. In this work, we introduce and apply a new method to obtain a primary beam model based on a machine-learning approach, namely, Gaussian process regression. The primary beam models obtained with this method have been published, along with the data products for the first Apertif data release. We applied the method to the continuum images, carried out a mosaicking process on their basis, and extracted the source catalog. The catalog contains 249672 radio sources, many of which have been detected for the first time at these frequencies. We cross-matched the coordinates with the NVSS, LOFAR/DR1/value-Added, and LOFAR/DR2 catalogs a resulting in 44523, 22825, and 152824 common sources, respectively. The first sample provides a unique opportunity for detecting long-Term transient sources, which have significantly changed their flux density over the past 25 yr. A combination of the second and the third samples provides valuable information on the spectral properties of the sources in addition to redshift estimates

Probing the gravitational redshift with an Earth-orbiting satellite

International audienceWe present an approach to testing the gravitational redshift effect using the RadioAstron satellite. The experiment is based on a modification of the Gravity Probe A scheme of nonrelativistic Doppler compensation and benefits from the highly eccentric orbit and ultra-stable atomic hydrogen maser frequency standard of the RadioAstron satellite. Using the presented techniques we expect to reach an accuracy of the gravitational redshift test of order 10−5 , a magnitude better than that of Gravity Probe A. Data processing is ongoing, our preliminary results agree with the validity of the Einstein Equivalence Principle

Detection statistics of the RadioAstron AGN survey

The largest Key Science Program of the RadioAstron space VLBI mission is a survey of active galactic nuclei (AGN). The main goal of the survey is to measure and study the brightness of AGN cores in order to better understand the physics of their emission while taking interstellar scattering into consideration. In this paper we present detection statistics for observations on ground-space baselines of a complete sample of radio-strong AGN at the wavelengths of 18, 6, and 1.3 cm. Two-thirds of them are indeed detected by RadioAstron and are found to contain extremely compact, tens to hundreds of μas structures within their cores.Peer reviewe

Lockman Hole Apertif map at 1.4GHz

VizieR online Data Catalogue associated with article published in journal Astronomy & Astrophysics with title 'The best of both worlds: combining LOFAR and Apertif to derive resolved radio spectral index images.' (bibcode: 2021A&A...648A...9M

Lockman Hole Apertif map at 1.4GHz

VizieR online Data Catalogue associated with article published in journal Astronomy & Astrophysics with title 'The best of both worlds: combining LOFAR and Apertif to derive resolved radio spectral index images.' (bibcode: 2021A&A...648A...9M