Lord of the Rings – Return of the King: Swift-XRT observations of dust scattering rings around V404 Cygni

On 2015 June 15, the black hole X-ray binary V404 Cygni went into outburst, exhibiting extreme X-ray variability which culminated in a final flare on June 26. Over the following days, the Swift-X-ray Telescope detected a series of bright rings, comprising five main components that expanded and faded with time, caused by X-rays scattered from the otherwise unobservable dust layers in the interstellar medium in the direction of the source. Simple geometrical modelling of the rings’ angular evolution reveals that they have a common temporal origin, coincident with the final, brightest flare seen by INTEGRAL's JEM X-1, which reached a 3–10 keV flux of ~25 Crab. The high quality of the data allows the dust properties and density distribution along the line of sight to the source to be estimated. Using the Rayleigh–Gans approximation for the dust scattering cross-section and a power-law distribution of grain sizes a, ∝ a-q, the average dust emission is well modelled by q = 3.90+0.09-0.08 and maximum grain size of a+ = 0.147+0.024-0.004 μm, though significant variations in q are seen between the rings. The recovered dust density distribution shows five peaks associated with the dense sheets responsible for the rings at distances ranging from 1.19 to 2.13 kpc, with thicknesses of ~40 – 80 pc and a maximum density occurring at the location of the nearest sheet. We find a dust column density of Ndust ~ (2.0–2.5) × 1011 cm-2, consistent with the optical extinction to the source. Comparison of the inner rings’ azimuthal X-ray evolution with archival Wide-field Infrared Survey Explorer (WISE) mid-IR data suggests that the second most distant ring follows the general IR emission trend, which increases in brightness towards the Galactic north side of the source

Swift follow-up of the Gravitational Wave source GW150914

The Advanced Laser Interferometer Gravitational-Wave Observatory (ALIGO) observatory recently reported the first direct detection of gravitational waves (GW) which triggered ALIGO on 2015 September 14. We report on observations taken with the Swift satellite two days after the trigger. No new X-ray, optical, UV or hard X-ray sources were detected in our observations, which were focused on nearby galaxies in the GW error region and covered 4.7 deg2 (~2 per cent of the probability in the rapidly available GW error region; 0.3 per cent of the probability from the final GW error region, which was produced several months after the trigger). We describe the rapid Swift response and automated analysis of the X-ray telescope and UV/Optical telescope data, and note the importance to electromagnetic follow-up of early notification of the progenitor details inferred from GW analysis

Histologia hepática e produção em tanques-rede de tilápia-do-nilo masculinizada hormonalmente ou não masculinizada

O objetivo deste trabalho foi avaliar o desempenho e a sanidade da estrutura hepática de tilápia-do-nilo, masculinizada hormonalmente ou não masculinizada, criada em tanques-rede com dois níveis proteicos. Tilápias-do-nilo da linhagem Tailandesa (total de 2.400), com peso médio inicial de 127 g, foram distribuídas em delineamento inteiramente casualizado, com quatro tratamentos, em arranjo fatorial 2×2, correspondente aos grupos de tilápias masculinizadas hormonalmente ou não masculinizadas e ao teor proteico na dieta de 28 ou 32% de proteína bruta, com três repetições. Após 115 dias de alimentação, não houve interação entre os fatores quanto a peso final, ganho de peso, conversão alimentar, comprimento final e sobrevivência. Não houve diferença entre os peixes masculinizados hormonalmente e os não masculinizados, quanto a peso final, ganho de peso e sobrevivência, o que mostra a possibilidade de sua produção em tanques-rede, sem a necessidade de masculinização hormonal. A proteína bruta a 32% na dieta possibita melhor desempenho para ambos os grupos. Alterações histológicas no fígado - como o incremento do volume das células, o desarranjo da disposição cordonal e o aumento de vesículas nos hepatócitos - são encontradas nos peixes masculinizados hormonalmente e são mais acentuadas nos peixes alimentados com 32% de proteína bruta na dieta

The GINGA hard X-ray spectrum of AM Herculis

We present an analysis of the phase-resolved 2-30 keV X-ray spectrum of the prototype magnetic cataclysmic variable AM Herculis obtained with the Ginga satellite. The bremsstrahlung flux varies by more than a factor of 7 as a function of orbital phase, demonstrating that the X-ray orbital intensity variation is due to partial occultation which varies with the viewing angle. The spectrum is hardest when the source is brightest in its orbital cycle, and the phase-resolved spectra are not well fitted by simple models with a narrow line plus continuum. The derived high and variable bremsstrahlung temperature cannot account for the observed line emission, and the residuals to these fits indicate complex behaviour at high and low energies. The latter is shown to be consistent with a complex absorber, and both partial covering and partial ionization give a good description of the soft spectrum. The residuals above 6 keV are well modelled by reflection from the white dwarf surface, where the amount of reflection varies with phase as predicted by the changing inclination of the white dwarf surface. The inclusion of this hard and variable spectral component gives a temperature for the post-shock region of ∼13.5 keV, which is constant with phase. This value is considerably lower than previous estimates, allowing the high equivalent width of the iron line to be explained as a combination of a thermal line blend at 6.8 keV and a 6.4-keV fluorescent component. This new low bremsstrahlung temperature suggests that the hard X-ray luminosities of AM Her systems may have been overestimated, exacerbating the soft X-ray problem. The detailed modelling of the complex low-energy spectrum affects the derived ionization state of the reflector: with partial covering of cold material the reflection spectrum is significantly ionized, but with an ionized absorber the reflecting surface is cold