A kinetic theory boundary value problem in a flowing plasma - The impedance of a grid pair

Kinetic theory boundary value problem in flowing plasma - impedance of grid pai

The ruff of equatorial emission around the SS433 jets: its spectral index and origin

We present unique radio observations of SS433, using MERLIN, the VLBA, and the VLA, which allow us to, for the first time, properly image and derive a meaningful spectral index for the `ruff' of equatorial emission which surrounds SS433's jet. We interpret this smooth ruff as a wind-like outflow from the binary.Comment: 4 pages, 4 figures, to appear in Proceedings of the 4th Microquasar Workshop, eds. Ph Durouchoux, Y. Fuchs and J. Rodrigue

The analysis of the impact of small retention on water resources in the catchment

The aim of this study was to analyse the impact of selected small water retention measures on surface and groundwater level in river basins. The study was limited to the analysis of measures like small water reservoirs, restoration of bogs and reconstruction of drainage systems in the river valleys. A few study cases were described. Dutch SIMGRO numerical model describing the regional surface water and groundwater flow has been used for simulation modelling of different cases. The result of the study has shown that small retention measures are a good and effective method to increase the ability to retain water in the small river basins. Construction of small water reservoirs and weirs on ditches and creeks and restoration of drained bogs can limit the fast outflow of precipitation and melting water from the catchment. The study has proved that the small water retention measures can be helpful for flood protection and in decreasing of drought threats in small river basins.</p

Simulated Radio Images and Light Curves of Young Supernovae

We present calculations of the radio emission from supernovae based on high-resolution simulations of the hydrodynamics and radiation transfer, using simple energy density relations which link the properties of the radiating electrons and the magnetic field to the hydrodynamics. As a specific example we model the emission from SN1993J, which cannot be adequately fitted with the often-used analytic mini-shell model, and present a good fit to the radio evolution at a single frequency. Both free-free absorption and syncrotron self- absorption are needed to fit the light curve at early times and a circumstellar density profile of rho~r^-1.7 provides the best fit to the later data. We show that the interaction of density structures in the ejecta with the reverse supernova shock may produce features in the radio light curves such as have been observed. We discuss the use of high-resolution radio images of supernovae to distinguish between different absorption mechanisms and determine the origin of specific light curve features. Comparisons of VLBI images of SN1993J with synthetic model images suggest that internal free-free absorption completely obscures emission at 8.4 GHz passing through the center of the supernova for the first few tens of years after explosion. We predict that at 8.4 GHz the internal free-free absorption is currently declining, and that over the next 40 years the surface brightness of the center of the source should increase relative to the bright ring of emission seen in VLBI images. Similar absorption in a nearby supernova would make the detection of a radio pulsar at 1 GHz impossible for ~150 years after explosion.Comment: 17 pages, 9 figures, accepted for publication in Ap

The 2011 Outburst of Recurrent Nova T Pyx: X-ray Observations Expose the White Dwarf Mass and Ejection Dynamics

The recurrent nova T Pyx underwent its sixth historical outburst in 2011, and became the subject of an intensive multi-wavelength observational campaign. We analyze data from the Swift and Suzaku satellites to produce a detailed X-ray light curve augmented by epochs of spectral information. X-ray observations yield mostly non-detections in the first four months of outburst, but both a super-soft and hard X-ray component rise rapidly after Day 115. The super-soft X-ray component, attributable to the photosphere of the nuclear-burning white dwarf, is relatively cool (~45 eV) and implies that the white dwarf in T Pyx is significantly below the Chandrasekhar mass (~1 M_sun). The late turn-on time of the super-soft component yields a large nova ejecta mass (>~10^-5 M_sun), consistent with estimates at other wavelengths. The hard X-ray component is well fit by a ~1 keV thermal plasma, and is attributed to shocks internal to the 2011 nova ejecta. The presence of a strong oxygen line in this thermal plasma on Day 194 requires a significantly super-solar abundance of oxygen and implies that the ejecta are polluted by white dwarf material. The X-ray light curve can be explained by a dual-phase ejection, with a significant delay between the first and second ejection phases, and the second ejection finally released two months after outburst. A delayed ejection is consistent with optical and radio observations of T Pyx, but the physical mechanism producing such a delay remains a mystery.Comment: Re-submitted to ApJ after revision

Direct Photons at RHIC

The PHENIX experiment has measured direct photons in $\sqrt{s_{NN}} = 200$ GeV Au+Au collisions and p+p collisions. The fraction of photons due to direct production in Au+Au collisions is shown as a function of $p_T$ and centrality. This measurement is compared with expectation from pQCD calculations. Other possible sources of direct photons are discussed.Comment: 7 pages, 5 figures, presented at Hot Quarks 2004, Taos, N

The Radio Light Curve of the Gamma-Ray Nova in V407 Cyg: Thermal Emission from the Ionized Symbiotic Envelope, Devoured from Within by the Nova Blast

We present multi-frequency radio observations of the 2010 nova event in the symbiotic binary V407 Cygni, obtained with the Karl G. Jansky Very Large Array and spanning 1-45 GHz and 17-770 days following discovery. This nova---the first ever detected in gamma rays---shows a radio light curve dominated by the wind of the Mira giant companion, rather than the nova ejecta themselves. The radio luminosity grew as the wind became increasingly ionized by the nova outburst, and faded as the wind was violently heated from within by the nova shock. This study marks the first time that this physical mechanism has been shown to dominate the radio light curve of an astrophysical transient. We do not observe a thermal signature from the nova ejecta or synchrotron emission from the shock, due to the fact that these components were hidden behind the absorbing screen of the Mira wind. We estimate a mass loss rate for the Mira wind of Mdot_w ~ 10^-6 M_sun/yr. We also present the only radio detection of V407 Cyg before the 2010 nova, gleaned from unpublished 1993 archival VLA data, which shows that the radio luminosity of the Mira wind varies by a factor of >~20 even in quiescence. Although V407 Cyg likely hosts a massive accreting white dwarf, making it a candidate progenitor system for a Type Ia supernova, the dense and radially continuous circumbinary material surrounding V407 Cyg is inconsistent with observational constraints on the environments of most Type Ia supernovae.Comment: Resubmitted to ApJ after incorporating referee's comment