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Studies of gamma-ray bursts (GRBs) and their multi-wavelength afterglows have led to insights in electron acceleration and emission properties from relativistic, high-energy astrophysical sources. Broadband modeling across the…
The Gaia optical astrometric mission has measured the precise positions of millions of objects in the sky, including extragalactic sources also observed by Very Long Baseline Interferometry (VLBI). In the recent Gaia EDR3 release, an effect…
Context: Phase referencing is a standard calibration technique in radio interferometry, particularly suited for the detection of weak sources close to the sensitivity limits of the interferometers. However, effects from a changing…
We present a series of sixteen Very Long Baseline Array (VLBA) high angular resolution observations of a cluster of suspected low-mass young stars in the Monoceros R2 region. Four compact and highly variable radio sources are detected;…
I present an overview of important results obtained using high-resolution very long baseline interferometry (VLBI) observations of X-ray binary systems. These results derive from both astrometric observations and resolved imaging of…
The observational validation of General Relativity (GR) has been propelled in recent years by recent breakthroughs in Very Long Baseline Interferometry (VLBI) augmented by ALMA. We explore ALMA2040 opportunities to transform these studies…
Strong gravitational lensing effect is a powerful tool to probe cosmological models and gravity theories. Recently, the time-delay cosmography from strong lensing and the stellar kinematics of the deflector, which encode the Hubble constant…
Many important techniques for investigating the properties of extragalactic radio sources, such as spectral-index and rotation-measure mapping, involve the comparison of images at two or more frequencies. In the case of radio…
The presence of a gravitational wave background (GWB) can be established not only via exquisitely precise pulsar timing array (PTA) measurements, but also via astrometric observations. Indeed, the very same background responsible for the…
We use the correlation relation between the energy emitted by the GRBs in their prompt phases and the X-ray afterglow fluxes, in an effort to constrain cosmological parameters and aiming to construct a Hubble diagram at high redshifts, i.e.…
Gravitational-wave observations provide a unique opportunity to test general relativity (GR) in the strong-field and highly dynamical regime of the theory. Parametrized tests of GR are one well-known approach for quantifying violations of…
We present simulated images of Supernova 1993J at 8.4 GHz using Very Long Baseline Interferometry (VLBI) techniques. A spherically symmetric source model is convolved with realistic uv-plane distributions, together with standard imaging…
We propose an alternative method to detect the secular aberration drift induced by the solar system acceleration due to the attraction to the Galaxy centre. This method is free of the individual radio source proper motion caused by…
Positions and proper motions of Gaia sources are expressed in a reference frame that ideally should be non-rotating relative to distant extragalactic objects, coincident with the International Celestial Reference System (ICRS), and…
Astrometry at centimeter wavelengths using Very Long Baseline Interferometry is approaching accuracies of ~1 uas for the angle between a target and a calibrator source separated by <1 degree on the sky. The BeSSeL Survey and the Japanese…
A global network of laser interferometric gravitational wave detectors is projected to be in operation by around the turn of the century. Here, the noisy output of a single instrument is examined. A gravitational wave is assumed to have…
From 43GHz VLBA observations of the pair of radio sources 1928+738 and 2007+777 we have demonstrated the feasibility of precision phase-delay differential astrometric techniques at millimeter wavelengths. For a pair of sources with 5…
Since its observation in 2019, the first image of a super-massive black hole using Very Long Baseline Interferometry (VLBI) with an Earth-scale baseline has generated much scientific and public interest, including the possible extension of…
We present Very Long Baseline Interferometry (VLBI) observations 217 days after the gamma-ray burst of 2003 March 29. These observations provide further measurements of the size and position of GRB 030329 that are used to constrain the…
We have studied Very Long Baseline Array (VLBA) polarimetric observations of 8 sources including quasars and BL Lacs at 12, 15, 22, 24 and 43 GHz and high frequency rotation measure ($RM$) maps are presented. We find typical values for the…