1,871 research outputs found
Statistics of gamma-ray point sources below the Fermi detection limit
An analytic relation between the statistics of photons in pixels and the
number counts of multi-photon point sources is used to constrain the
distribution of gamma-ray point sources below the Fermi detection limit at
energies above 1 GeV and at latitudes below and above 30 degrees. The derived
source-count distribution is consistent with the distribution found by the
Fermi collaboration based on the first Fermi point source catalogue. In
particular, we find that the contribution of resolved and unresolved active
galactic nuclei (AGN) to the total gamma-ray flux is below 20% - 25%. In the
best fit model, the AGN-like point source fraction is 17% +- 2%. Using the fact
that the Galactic emission varies across the sky while the extra-galactic
diffuse emission is isotropic, we put a lower limit of 51% on Galactic diffuse
emission and an upper limit of 32% on the contribution from extra-galactic weak
sources, such as star-forming galaxies. Possible systematic uncertainties are
discussed.Comment: 26 pages, 10 figures, 1 table; v2: clarifications and references
added, v3: more detailed presentation of the metho
Surface morphology of DyxOy films grown on Si
The crystalline structure and surface morphology of DyxOy dielectric films grown on Si substrates were studied by grazing incidence diffraction and absorption with use of synchrotron radiation and by atomic force microscopy. The crystalline structure and the roughness of DyxOy films were found to be strongly dependent on the deposition rate. The dielectric-silicon interface depends on the type of gas used in the annealing process. Moreover. results from the near edge X-ray absorption studies, have revealed that none of the examined films has a stoichiometry close to the Dy2O3. The level of stoichiometry is determined by the technological conditions. Nevertheless, MOS structures with Dy(x)Q(y) films (EOT similar to 23 angstrom) have shown a rather good DyxOy-Si interface properties, which can be further improve by thermal annealing, and introducing of several additives, therefore DyxOy films can be considered as suitable candidates for gate dielectric in MOS devices. (c) 2006 Elsevier B.V. All rights reserved
A high-sensitivity 6.7 GHz methanol maser survey toward H2O sources
We present the results of a high sensitivity survey for 6.7 GHz methanol
masers towards 22 GHz water maser using the 100 m Efflesberg telescope. A total
of 89 sources were observed and 10 new methanol masers were detected. The new
detections are relatively faint with peak flux densities between 0.5 and 4.0
Jy. A nil detection rate from low-mass star forming regions enhances the
conclusion that the masers are only associated with massive star formation.
Even the faintest methanol maser in our survey, with a luminosity of 1.1
is associated with massive stars as inferred from its
infrared luminosity.Comment: Accepted for publication in A&
An approximate analysis of a bernoulli alternating service model
We consider a discrete-time queueing system with one server
and two types of customers, say type-1 and type-2 customers. The server
serves customers of either type alternately according to a Bernoulli pro-
cess. The service times of the customers are deterministically equal to
1 time slot. For this queueing system, we derive a functional equation
for the joint probability generating function of the number of type-1 and
type-2 customers. The functional equation contains two unknown partial
generating functions which complicates the analysis. We investigate the
dominant singularity of these two unknown functions and propose an
approximation for the coefficients of the Maclaurin series expansion of
these functions. This approximation provides a fast method to compute
approximations of various performance measures of interest
Absolute positions of 6.7-GHz methanol masers
The ATCA, MERLIN and VLA interferometers were used to measure the absolute
positions of 35 6.7 GHz methanol masers to subarcsecond or higher accuracy. Our
measurements represent essential preparatory data for Very Long Baseline
Interferometry, which can provide accurate parallax and proper motion
determinations of the star-forming regions harboring the masers. Our data also
allow associations to be established with infrared sources at different
wavelengths. Our findings support the view that the 6.7 GHz masers are
associated with the earliest phases of high-mass star formation.Comment: A&A accepted 29 pages, 6 figures, 5 table
Multi-wavelength observations of the binary system PSR B1259−63/LS 2883 around the 2014 periastron passage
We report on the results of the extensive multi-wavelength campaign from optical to GeV γ-rays of the 2014 periastron passage of PSR B1259−63, which is a unique high-mass γ-ray emitting binary system with a young pulsar companion. Observations demonstrate the stable nature of the post-periastron GeV flare and prove the coincidence of the flare with the start of rapid decay of the Hα equivalent width, usually interpreted as a disruption of the Be stellar disc. Intensive X-ray observations reveal changes in the X-ray spectral behaviour happening at the moment of the GeV flare. We demonstrate that these changes can be naturally explained as a result of synchrotron cooling of monoenergetic relativistic electrons injected into the system during the GeV flare
The Formation of Crystal Defects in a Fe-Mn-Si Alloy Under Cyclic Martensitic Transformations
Construction of a Full Scale Superconducting Undulator Module for the International Linear Collider Positron Source
Search for Early Gamma-ray Production in Supernovae Located in a Dense Circumstellar Medium with the Fermi LAT
Supernovae (SNe) exploding in a dense circumstellar medium (CSM) are
hypothesized to accelerate cosmic rays in collisionless shocks and emit GeV
gamma rays and TeV neutrinos on a time scale of several months. We perform the
first systematic search for gamma-ray emission in Fermi LAT data in the energy
range from 100 MeV to 300 GeV from the ensemble of 147 SNe Type IIn exploding
in dense CSM. We search for a gamma-ray excess at each SNe location in a one
year time window. In order to enhance a possible weak signal, we simultaneously
study the closest and optically brightest sources of our sample in a
joint-likelihood analysis in three different time windows (1 year, 6 months and
3 months). For the most promising source of the sample, SN 2010jl (PTF10aaxf),
we repeat the analysis with an extended time window lasting 4.5 years. We do
not find a significant excess in gamma rays for any individual source nor for
the combined sources and provide model-independent flux upper limits for both
cases. In addition, we derive limits on the gamma-ray luminosity and the ratio
of gamma-ray-to-optical luminosity ratio as a function of the index of the
proton injection spectrum assuming a generic gamma-ray production model.
Furthermore, we present detailed flux predictions based on multi-wavelength
observations and the corresponding flux upper limit at 95% confidence level
(CL) for the source SN 2010jl (PTF10aaxf).Comment: Accepted for publication in ApJ. Corresponding author: A. Franckowiak
([email protected]), updated author list and acknowledgement
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