673 research outputs found
Is Radiation of Quantized Black Holes Observable?
If primordial black holes (PBH) saturate the present upper limit on the dark
matter density in our Solar system and if their radiation spectrum is discrete,
the sensitivity of modern detectors is close to that necessary for detecting
this radiation. This conclusion is not in conflict with the upper limits on the
PBH evaporation rate.Comment: 6 pages, 1 figure (reproduced properly in pdf file
Air hydrodynamics of the ultrafast laser-triggered spark gap
We present space and time resolved measurements of the air hydrodynamics
induced by ultrafast laser pulse excitation of the air gap between two
electrodes at high potential difference. We explore both plasma-based and
plasma-free gap excitation. The former uses the plasma left in the wake of
femtosecond filamentation, while the latter exploits air heating by
multiple-pulse resonant excitation of quantum molecular wavepackets. We find
that the cumulative electrode-driven air density depression channel initiated
by the laser plays the dominant role in the gap evolution leading to breakdown
South-West extension of the hard X-ray emission from the Coma cluster
We explore the morphology of hard (18-30 keV) X-ray emission from the Coma
cluster of galaxies. We analyze a deep (1.1 Ms) observation of the Coma cluster
with the ISGRI imager on board the \emph{INTEGRAL} satellite. We show that the
source extension in the North-East to South-West (SW) direction ()
significantly exceeds the size of the point spread function of ISGRI, and that
the centroid of the image of the source in the 18-30 keV band is displaced in
the SW direction compared to the centroid in the 1-10 keV band. To test the
nature of the SW extension we fit the data assuming different models of source
morphology. The best fit is achieved with a diffuse source of elliptical shape,
although an acceptable fit can be achieved assuming an additional point source
SW of the cluster core. In the case of an elliptical source, the direction of
extension of the source coincides with the direction toward the subcluster
falling onto the Coma cluster. If the SW excess is due to the presence of a
point source with a hard spectrum, we show that there is no obvious X-ray
counterpart for this additional source, and that the closest X-ray source is
the quasar EXO 1256+281, which is located from the centroid of the
excess. The observed morphology of the hard X-ray emission clarifies the nature
of the hard X-ray "excess" emission from the Coma cluster, which is due to the
presence of an extended hard X-ray source SW of the cluster core.Comment: 7pages, 10 figure
AUTOMATED RECONSTRUCTION OF 3D BUILDINGS IN HISTORIC CITY CENTERS FROM LIDAR DATA AND 2D BUILDING FOOTPRINTS
This paper describes a process for the automated generation of 3D buildings using 2D building footprints derived from cadastral maps and LIDAR point cloud data. In our approach we extract relevant geometric information from 2D building footprints in order to classify point cloud data. One key concept is the fact that roofs in most cases are aligned to the angles of the walls of a building. This concept is utilized to create contiguous surfaces and to extract ridges. In a field study involving two historic city centers in Switzerland we evaluate the results of our approach
Discovery of the INTEGRAL X/Gamma-ray transient IGR J00291+5934: a Comptonised accreting ms pulsar ?
We report the discovery of a high-energy transient with the IBIS/ISGRI
detector on board the INTEGRAL observatory. The source, namely IGR J00291+5934,
was first detected on 2nd December 2004 in the routine monitoring of the
IBIS/ISGRI 20--60 keV images. The observations were conducted during Galactic
Plane Scans, which are a key part of the INTEGRAL Core Programme observations.
After verifying the basic source behaviour, the discovery was announced on 3rd
December. The transient shows a hard Comptonised spectrum, with peak energy
release at about 20 keV and a total luminosity of ~ 0.9E36 erg/s in the 5--100
keV range, assuming a distance of 3 kpc. Following the INTEGRAL announcement of
the discovery of IGR J00291+5934, a number of observations were made by other
instruments. We summarise the results of those observations and, together with
the INTEGRAL data, identifiy IGR J00291+5934 as the 6th member of a class of
accreting X-ray millisecond pulsars.Comment: Accepted for publication as an A&A Letter 24/01/2005. 5 pages, 2
figure
INTEGRAL discovery of non-thermal hard X-ray emission from the Ophiuchus cluster
We present the results of deep observations of the Ophiuchus cluster of
galaxies with INTEGRAL in the 3-80 keV band. We analyse 3 Ms of INTEGRAL data
on the Ophiuchus cluster with the IBIS/ISGRI hard X-ray imager and the JEM-X
X-ray monitor. In the X-ray band using JEM-X, we show that the source is
extended, and that the morphology is compatible with the results found by
previous missions. Above 20 keV, we show that the size of the source is
slightly larger than the PSF of the instrument, and is consistent with the soft
X-ray morphology found with JEM-X and ASCA. Thanks to the constraints on the
temperature provided by JEM-X, we show that the spectrum of the cluster is not
well fitted by a single-temperature thermal Bremsstrahlung model, and that
another spectral component is needed to explain the high energy data. We detect
the high energy tail with a higher detection significance (6.4 sigma) than the
BeppoSAX claim (2 sigma). Because of the imaging capabilities of JEM-X and
ISGRI, we are able to exclude the possibility that the excess emission comes
from very hot regions or absorbed AGN, which proves that the excess emission is
indeed of non-thermal origin. Using the available radio data together with the
non-thermal hard X-ray flux, we estimate a magnetic field B ~ 0.1-0.2 mu G.Comment: 8 pages, 9 figures, accepted by A&
Scientific Performance of the ISDC Quick Look Analysis
The INTEGRAL Science Data Centre (ISDC) routinely monitors the Near Real Time
data (NRT) from the INTEGRAL satellite. A first scientific analysis is made in
order to check for the detection of new, transient or highly variable sources
in the data. Of primary importance for this work is the Interactive Quick Look
Analysis (IQLA), which produces JEM-X and ISGRI images and monitors them for
interesting astrophysical eventsComment: 4 pages, 3 figures. Proceedings of 5th INTEGRAL Workshop: The
INTEGRAL Universe, Munich, 16-20 February 2004. Accepted for publication in
European Space Agency Special Publication 552. See paper for institute
affiliation
INTEGRAL hard X-ray spectra of the cosmic X-ray background and Galactic ridge emission
We derive the spectra of the cosmic X-ray background (CXB) and of the
Galactic ridge X-ray emission (GRXE) in the ~20-200 keV range from the data of
the IBIS instrument aboard the INTEGRAL satellite obtained during the four
dedicated Earth-occultation observations of early 2006. We analyse the
modulation of the IBIS/ISGRI detector counts induced by the passage of the
Earth through the field of view of the instrument. Unlike previous studies, we
do not fix the spectral shape of the various contributions, but model instead
their spatial distribution and derive for each of them the expected modulation
of the detector counts. The spectra of the diffuse emission components are
obtained by fitting the normalizations of the model lightcurves to the observed
modulation in different energy bins. The obtained CXB spectrum is consistent
with the historic HEAO-1 results and falls slightly below the spectrum derived
with Swift/BAT. A 10% higher normalization of the CXB cannot be completely
excluded, but it would imply an unrealistically high albedo of the Earth. The
derived spectrum of the GRXE confirms the presence of a minimum around 80 keV
with improved statistics and yields an estimate of ~0.6 M_Sun for the average
mass of white dwarfs in the Galaxy. The analysis also provides updated
normalizations for the spectra of the Earth's albedo and the cosmic-ray induced
atmospheric emission.Comment: 13 pages, 13 figures, minor changes to text, A&A in pres
RXTE observations of the first transient Z source XTE J1701-462: shedding new light on mass accretion in luminous neutron star LMXBs
(Abridged) We report on ten weeks of RXTE observations of the X-ray transient
XTE J1701-462. Comparisons with other sources suggest it had all the
characteristics of the neutron star Z sources (the brightest persistent neutron
star LMXBs). These include Z tracks in X-ray color diagrams and typical
variability components detected in the power spectra. XTE J1701-462 is the
first transient Z source and provides unique insights into mass accretion rate
(Mdot) and luminosity dependencies in neutron star LMXBs. As its overall
luminosity decreased, we observed a switch between two types of Z-source
behavior, with most of the branches of the Z-track changing their shape and/or
orientation. We interpret this switch as an extreme case of the longterm
changes seen in the persistent Z sources and suggest that these result from
changes in Mdot. We also suggest that the Cyg-like Z sources (Cyg X-2, GX 5-1,
and GX 340+0) might be more luminous (> 50%) than the Sco-like Z sources (Sco
X-1, GX 17+2, and GX 349+2). Adopting a possible explanation for the behavior
of kHz QPOs, which involves a prompt as well as a filtered response to changes
in Mdot, we propose that changes in Mdot can explain both movement along the Z
track and changes in the shape of the Z track. We discuss some consequences of
this and consider the possibility that the branches of the Z will evolve into
the branches observed in the X-ray color diagrams of the less luminous atoll
sources, but not in a way that was previously suggested.Comment: Accepted for publication in ApJ, 11 page
- âŠ