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We present high-quality, wide spectral coverage long-slit optical spectra for 12 powerful radio sources at low and intermediate redshifts (z < 0.7) that show evidence for a substantial ultraviolet (UV) excess. These data were taken using the William Herschel Telescope and the ESO Very Large Telescope with the aim of determining the detailed properties of the young stellar populations (YSPs) in the host galaxies as part of a larger project to investigate evolutionary scenarios for the active galactic nucleus (AGN) host galaxies. The results of our spectral synthesis model fits to the spectra highlight the importance of taking into account AGN-related components (emission lines, nebular continuum, scattered light) and reddening of the stellar populations in studies of this type. It is also clear that careful examination of the fits to the spectra, as well consideration of auxiliary polarimetric and imaging data, are required to avoid degeneracies in the model solutions. In three out of the 12 sources in our sample we find evidence for broad permitted line components, and a combination of AGN-related continuum components and an old (12.5 Gyr) stellar population provides an adequate fit to the data. However, for the remaining nine sources we find strong evidence for YSPs. In contrast to some recent studies that suggest relatively old post-starburst ages for the YSPs in radio galaxies (0.3-2.5 Gyr), we deduce a wide range of ages for the YSPs in our sample objects (0.02-1.5 Gyr), with ∼50 per cent of the sample showing evidence for young YSP ages ( 0.1 Gyr) in their nuclear regions. The nuclear YSPs are often significantly reddened [0.2 < E(B − V) < 1.4] and make up a substantial fraction (∼1-35 per cent) of the total stellar mass in the regions sampled by the spectroscopic slits. Moreover, in all the cases in which we have sufficient spatial resolution we find that the UV excess is extended across the full measurable extent of the galaxy (typically 5-30 kpc), suggesting galaxy-wide starbursts. The implications for photometric and spectroscopic studies of active galaxies are discussed.

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Low Mass X-ray Binaries (LMXB s) with either a black hole or a neutron star show power spectra characterised by Quasi Periodic Oscillations (QPOs). Twin peak high frequency QPOs are characterised by frequencies that are typical for matter orbiting within 10 fg from the compact object. We consider clumps of material orbiting a Schwarzschild black hole, that are deformed by tidal interaction. We present some preliminary calculations of corresponding light curves and power spectra. We were able to fit the simulated power spectra with the high frequency part of the power spectra observed in the LMXB XTE J1550-564 containing ablackhole. Ournumerical simulations reproduce the twin high frequency QPOs and the power-law. The lower peak corresponds to the Keplerian frequency, the upper one to the sum of the Keplerian and the radial frequency.

On the ground of the large number of gamma-ray bursts (GRBs) detected with cosmological redshift, we have introduced a new classification of GRBs in seven subclasses, all with binary progenitors originating gravitational waves (GWs). Each binary is composed by a different combination of carbonoxygen cores (CO core ), neutron stars (NSs), black holes (BHs) and white dwarfs (WDs). This opens an ample new scenario for the role of GWs both as detectable sources and as a determining factor in the coalescence process of the GRB binary progenitors. The long bursts, traditionally assumed to originate from a single BH with an ultra-relativistic jetted emission, not expected to emit GWs, have instead been subclassified as (I) X-ray flashes (XRFs), (II) binary-driven hypernovae (BdHNe), and (III) BH-supernovae (BH-SNe). They are framed within the induced gravitational collapse (IGC) paradigm with progenitor a tight binary composed of a CO core and a NS or BH companion. The supernova (SN) explosion of the CO core triggers a hypercritical accretion process onto the companion NS or BH. If the accretion is not sufficient for the NS to reach its critical mass, an XRF occurs, while when the BH is already present or formed by the hypercritical accretion, a BdHN occurs. In the case these binaries are not disrupted by the mass-loss process, XRFs lead to NS-NS binaries and BdHNe lead to NS-BH ones. The short bursts, originating in NS-NS mergers, are subclassified as (IV) short gamma-ray flashes (S-GRFs) and (V) short GRBs (S-GRBs), the latter when a BH is formed. Two additional families are (VI) ultra-short GRBs (U-GRBs) and (VII) gamma-ray flashes (GRFs), respectively formed in NS-BH and NS-WD mergers. We use the estimated occurrence rate of the above subclasses and their GW emission to assess their detectability by Advanced LIGO and Virgo, eLISA, and resonant bars. We also discuss the consequences of our results in view of the recent announcement of the LIGO-Virgo Collaboration of the source GW 170817 as being originated by a NS-NS merger.