35 research outputs found
Intensive monitoring of the strongly variable BL Lac S5 0716+714
The BL Lac object S5 0716+714 was monitored during a multifrequency campaign
in 1996. Preliminary analysis of the optical, ROSAT and RXTE data are
presented. Strong variability on short time scales was observed. The data
suggest an interpretation within a multi-component model.Comment: To appear in The Active X-ray Sky: Results from BeppoSAX and
Rossi-XTE, Rome, Italy, 21-24 October, 1997. Eds.: L. Scarsi, Bradt, P.
Giommi and F. Fiore. PS-file avialable at
http://www.lsw.uni-heidelberg.de/projects/extragalactic/bl_lac.htm
Single coronary artery from the right sinus of Valsalva
We describe a case of a single coronary artery originating from the right coronary sinus and bifurcating into the left coronary artery (LCA) and right coronary artery (RCA) in a 74-year old woman, with a non-ST elevation acute myocardial infarction (NSTEMI). Diagnosis was made by coronary angiography which ruled out stenosis, and showed normal LCA and RCA branching. The connection path of LCA, with the opposite cusp, was defined retroaortic by multislice computed tomography (CT). The variants of this coronary anomaly, together with their clinical implications and pathophysiology of acute myocardial infarction (AMI) are discussed. Multislice CT is fundamental for clinical decision making
Numerical Solutions of ideal two-fluid equations very closed to the event horizon of Schwarzschild black hole
The 3+1 formalism of Thorne, Price and Macdonald has been used to derive the
linear two-fluid equations describing transverse and longitudinal waves
propagating in the two-fluid ideal collisionless plasmas surrounding a
Schwarzschild black hole. The plasma is assumed to be falling in radial
direction toward the event horizon. The relativistic two-fluid equations have
been reformulate, in analogy with the special relativistic formulation as
explained in an earlier paper, to take account of relativistic effects due to
the event horizon. Here a WKB approximation is used to derive the local
dispersion relation for these waves and solved numerically for the wave number
k.Comment: 16 pages, 15 figures. arXiv admin note: text overlap with
arXiv:0902.3766, arXiv:0807.459
Star Formation and Dynamics in the Galactic Centre
The centre of our Galaxy is one of the most studied and yet enigmatic places
in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre
(GC) is the ideal environment to study the extreme processes that take place in
the vicinity of a supermassive black hole (SMBH). Despite the hostile
environment, several tens of early-type stars populate the central parsec of
our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and
inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the
SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The
formation of such early-type stars has been a puzzle for a long time: molecular
clouds should be tidally disrupted by the SMBH before they can fragment into
stars. We review the main scenarios proposed to explain the formation and the
dynamical evolution of the early-type stars in the GC. In particular, we
discuss the most popular in situ scenarios (accretion disc fragmentation and
molecular cloud disruption) and migration scenarios (star cluster inspiral and
Hills mechanism). We focus on the most pressing challenges that must be faced
to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in
expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A.,
'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201
Active Galactic Nuclei at the Crossroads of Astrophysics
Over the last five decades, AGN studies have produced a number of spectacular
examples of synergies and multifaceted approaches in astrophysics. The field of
AGN research now spans the entire spectral range and covers more than twelve
orders of magnitude in the spatial and temporal domains. The next generation of
astrophysical facilities will open up new possibilities for AGN studies,
especially in the areas of high-resolution and high-fidelity imaging and
spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These
studies will address in detail a number of critical issues in AGN research such
as processes in the immediate vicinity of supermassive black holes, physical
conditions of broad-line and narrow-line regions, formation and evolution of
accretion disks and relativistic outflows, and the connection between nuclear
activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic
Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical
Symposia Serie
Observations of the Sun at Vacuum-Ultraviolet Wavelengths from Space. Part II: Results and Interpretations
XUV EMISSION FEATURES FROM THE LIVERMORE SOFT X-RAY LASER EXPERIMENTS
The measured wavelengths i n the soft x-ray region for 3p to 3s and 3d to 3p transitions in neon-, sodium-, and magnesium-like selenium are presented. The experimental results for the neon-like ions are compared to theoretical wavelength values and with values extrapolated along the isoelectronic sequence. The ions were contained in a plasma heated in a line-focus of a Nd-glass laser. The measurements were made with a time-gated microchannel-plate-intensified grazing incidence spectrograph