There is a mysterious point-like source in the starburst dwarf galaxy NGC 5408. It is the strongest compact radio source in that galaxy (5-GHz flux density of $\approx$2 mJy, corresponding to a luminosity of $\approx$3 $\times 10^{35}$ erg s$^{-1}$). In the optical, it is too bright and too red ($V \approx 19.5$, $R \approx 18.1$, corresponding to $M_V \approx -9$, $M_R \approx -10.4$) to be...
The X-ray binary SS 433, a Galactic microquasar, has been hypothesized to be an ultraluminous X-ray source (ULX) like those observed in nearby galaxies. It is well known that the compact object emits oppositely directed semi-relativistic jets that carry a much larger kinetic power than observed radiatively in the X-ray band. Much of the radiative power may be obscured from our view, which...
AGN are known to show flux variability over all observable timescales and across the entire electromagnetic spectrum. Over the past decade, a growing number of sources have been observed to show dramatic flux and spectral changes, both in the X-rays and in the optical/UV. Such events, commonly described as “changing-look AGN”, can be divided into two well-defined classes. Changing-obscuration...
The ejection of relativistic outflows is the most spectacular consequence of accretion onto compact objects, powered by the interplay of gravity, particles and magnetic fields. The microquasar SS 433, one of the most exotic binary systems in our Galaxy, shows powerful precessing jets. In these outflows, radio synchrotron emission unveils a complex magnetic field topology, seemingly parallel to...
There has been a large effort in trying to investigate the similarities between supermassive black holes (SMBH) in active galaxies and stellar black holes (SBH) in X-ray binary systems (XRB). Both exhibit changes in accretion states, but on different timescales. Changes in the accretion state of Changing-Look Active Galactic Nuclei (CLAGN) are particularly interesting, as they occur on shorter...
