Seminar

The study of astrophysical transients (whose flux and spectra evolve over hours to months) provides an opportune discovery space and enables the understanding of underlying physical mechanisms. They include energetic and cataclysmic phenomena (e.g. active galaxies, stellar mergers and explosions, tidal disruptions) that entail extreme conditions and hence, multi-messenger observational signatures (electromagnetic radiation from radio to gamma-rays, particles: cosmic rays and neutrinos, gravitational waves). They point to the presence/formation of a central engine powered by accretion onto a compact object (neutron star or stellar-mass/supermassive black hole) and associated jet/outflow activity.

I will discuss recent/upcoming studies on a subset of sources (active galaxies, slow transients), their observational characteristics (variability, and morphological, astrometric, and spectral evolution), and the unravelling of their physical nature (central engine: accretion - jet activity and environmental properties). Enabling these studies are high resolution (milli-arcsecond) very long baseline interferometry (VLBI; typically, in the 1.4 GHz - 43 GHz radio frequencies) observations for imaging and astrometric monitoring (localization, proper motion), and the varying/evolving flux densities (VLBI and single dish radio, and X-rays) in the time domain monitoring. An effective interface between observations and the modelling of transients can help design optimal strategies for the utilization of existing/upcoming observational facilities. I will then discuss their applicability, and briefly cover analysis techniques to handle large data volumes and undesirable properties including radio frequency interference, and investigations on novel observation concepts and their context.