120 research outputs found
Systematic and quantitative approach for the identification of high energy gamma-ray source populations
A large fraction of the detections to be made by the Gamma-ray Large Area
Space Telescope (GLAST) will initially be unidentified. We argue that
traditional methodological approaches to identify individuals and/or
populations of -ray sources will encounter procedural limitations.
These limitations will hamper our ability to classify source populations lying
in the anticipated dataset with the required degree of confidence, particularly
those for which no member has yet been convincingly detected in the predecessor
experiment EGRET. Here we suggest a new paradigm for achieving the
classification of -ray source populations based on the implementation
of an a priori protocol to search for theoretically-motivated candidate
sources. In order to protect the discovery potential of the sample, it is
essential that such paradigm will be defined before the data is unblinded. Key
to the new procedure is a statistical assessment by which the discovery of a
new population can be claimed. Although we explicitly refer here to the case of
GLAST, the scheme we present may be adapted to other experiments confronted
with a similar problematic.Comment: In press in The Astrophysical Journal Letters. Accepted on July 12,
200
A New Determination Of The Diffuse Galactic and Extragalactic Gamma-Ray Emission
The GALPROP model for cosmic-ray propagation is able to make explicit
predictions for the distribution of galactic diffuse gamma-rays. We compare
different propagation models with gamma-ray spectra measured by EGRET for
various regions of the sky. This allows sensitive tests of alternative
explanations for the apparent excess emission observed at GeV gamma-rays. We
find that a population of hard-spectrum gamma-ray sources cannot be solely
responsible for the excess since it also appears at high latitudes; on the
other hand a hard cosmic-ray electron spectrum cannot explain the gamma-ray
excess in the inner Galaxy. By normalizing the cosmic ray spectra within
reasonable bounds under preservation of their shape we are able to obtain our
best prediction of the Galactic component of diffuse gamma rays, and show that
away from the Galactic plane it gives an accurate prediction of the observed
gamma-ray intensities. On this basis we reevaluate the extragalactic gamma-ray
background. We find that for some energies previous work underestimated the
Galactic contribution and hence overestimated the background. The new EGRB
spectrum shows a positive curvature similar to that expected for models of the
extragalactic gamma-ray emission based on contributions from unresolved
blazars.Comment: 6 pages, 3 figures, 1 tabl
Propagation in 3D spiral-arm cosmic-ray source distribution models and secondary particle production using PICARD
We study the impact of possible spiral-arm distributions of Galactic
cosmic-ray sources on the flux of various cosmic-ray nuclei throughout our
Galaxy. We investigate model cosmic-ray spectra at the nominal position of the
sun and at different positions within the Galaxy. The modelling is performed
using the recently introduced numerical cosmic ray propagation code
\textsc{Picard}. Assuming non-axisymmetric cosmic ray source distributions
yields new insights on the behaviour of primary versus secondary nuclei.
We find that primary cosmic rays are more strongly confined to the vicinity
of the sources, while the distribution of secondary cosmic rays is much more
homogeneous compared to the primaries. This leads to stronger spatial variation
in secondary to primary ratios when compared to axisymmetric source
distribution models. A good fit to the cosmic-ray data at Earth can be
accomplished in different spiral-arm models, although leading to decisively
different spatial distributions of the cosmic-ray flux. This results in very
different cosmic ray anisotropies, where even a good fit to the data becomes
possible. Consequently, we advocate directions to seek best fit propagation
parameters that take into account the higher complexity introduced by the
spiral-arm structure on the cosmic-ray distribution. We specifically
investigate whether the flux at Earth is representative for a large fraction of
the Galaxy. The variance among possible spiral-arm models allows us to quantify
the spatial variation of the cosmic-ray flux within the Galaxy in presence of
non-axisymmetric source distributions.Comment: 38 pages, 16 figures, accepted for publication in Astroparticle
Physic
EGRET upper limits and stacking searches of gamma-ray observations of luminous and ultra-luminous infrared galaxies
We present a stacking analysis of EGRET -ray observations at the
positions of luminous and ultraluminous infrared galaxies. The latter were
selected from the recently presented HCN survey, which is thought to contain
the most active star forming regions of the universe. Different sorting
criteria are used and, whereas no positive collective detection of -ray
emission from these objects we determined both collective and individual upper
limits. The upper most excess we find appears in the case of ULIRGs ordered by
redshift, at a value of 1.8.Comment: Accepted for publication in the Astrophysical Journa
Suzaku observation of the unidentified VHE gamma-ray source HESS J1702-420
A deep X-ray observation of the unidentified very high energy (VHE) gamma-ray
source HESS J1702-420, for the first time, was carried out by Suzaku. No bright
sources were detected in the XIS field of view (FOV) except for two faint
point-like sources. The two sources, however, are considered not to be related
to HESS J1702-420, because their fluxes in the 2-10 keV band (~ 10^-14 erg s^-1
cm^-2) are ~ 3 orders of magnitude smaller than the VHE gamma-ray flux in the
1-10 TeV band (F_{TeV} = 3.1 x 10^-11 erg s^-1 cm^-2). We compared the energy
spectrum of diffuse emission, extracted from the entire XIS FOV with those from
nearby observations. If we consider the systematic error of background
subtraction, no significant diffuse emission was detected with an upper limit
of F_X <2.7 x 10^-12 erg s^-1 cm^-2 in the 2-10 keV band for an assumed
power-law spectrum of \Gamma=2.1 and a source size same as that in the VHE
band. The upper limit of the X-ray flux is twelve times as small as the VHE
gamma-ray flux. The large flux ratio (F_{TeV}/F_X) indicates that HESS
J1702-420 is another example of a "dark" particle accelerator. If we use a
simple one-zone leptonic model, in which VHE gamma-rays are produced through
inverse Compton scattering of the cosmic microwave background and interstellar
far-infrared emission, and the X-rays via the synchrotron mechanism, an upper
limit of the magnetic field (1.7 \mu G) is obtained from the flux ratio.
Because the magnetic field is weaker than the typical value in the Galactic
plane (3-10 \mu G), the simple one-zone model may not work for HESS J1702-420
and a significant fraction of the VHE gamma-rays may originate from protons.Comment: 7 pages, accepted for publication in PASJ (Suzaku and MAXI special
issue
Identification of high energy gamma-ray sources and source populations in the era of deep all-sky coverage
A large fraction of the anticipated source detections by the Gamma-ray Large
Area Space Telescope (GLAST-LAT) will initially be unidentified. We argue that
traditional approaches to identify individuals and/or populations of gamma ray
sources will encounter procedural limitations. Those limitations are discussed
on the background of source identifications from EGRET observations. Generally,
our ability to classify (faint) source populations in the anticipated GLAST
dataset with the required degree of statistical confidence will be hampered by
sheer source wealth. A new paradigm for achieving the classification of gamma
ray source populations is discussed.Comment: Comments: 6 pages, 2 figures, Accepted for publication in
Astrophysics and Space Science, Proc. of "The Multi-Messenger Approach to
High-Energy Gamma-ray Sources (Third Workshop on the Nature of Unidentified
High-Energy Sources)", Barcelona, July 4-7, 200
On the cross correlation between the arrival direction of ultra-high energy cosmic rays, BL Lacertae, and EGRET detections: A new way to identify EGRET sources?
With the aim of testing recent claims for a particularly strong correlation
between ultra-high energy cosmic rays (UHECRs), observed with the AGASA and the
Yakutsk experiments, and a sample of BL Lacertae (BL Lacs), we here conduct a
blind statistical assessment. We search for associations between the same set
of BL Lac objects and the arrival directions of 33 relevant UHECRs observed
with the Haverah Park and the Volcano Ranch experiments. Within the accuracy of
angle determination, there are no positional coincidences. The probability that
this null result arises as a statistical fluctuation from the strongly
correlated case is less than 5%. This implies that the possible correlation
between the arrival directions of UHECRs and BL Lacs is not statistically
sustained. We discuss the impact of our findings on the propose additional
connection among UHECRs, BL Lacs, and EGRET gamma-ray blazars. Recently, such
an association was used as classification technique for EGRET sources. Here we
show that its main underlying hypothesis, i.e., the EGRET angular uncertainty
is twice that quoted in the Third EGRET Catalog, underestimates the goodness of
existing gamma-ray data.Comment: References added. Accepted for publication in Astrophys. J. Let
Structural Barriers In The Context Of Opiate Substitution Treatment In Germany - A Survey Among Physicians In Primary Care
Background
Opiate substitution treatment (OST) is the most widely used treatment for opioid dependence in Germany with substantial long-term benefits for the patient and for society. Due to lessened restrictive admission criteria, the number of registered OST patients in Germany has increased continuously in the recent years, whereas the number of physicians providing OST has remained constant. Previous data already indicated a deteriorating situation in the availability or quality of OST delivered and that structural barriers impede physicians in actively providing OST. The present survey among a sample of primary care physicians in Germany aimed to identify and assess potential structural barriers for the provision of health care in the context of OST.
Methods
An anonymous written questionnaire was sent out to a sample of 2,332 physicians across Germany providing OST. Physicians contacted were identified through databases of the Federal State Chambers of Physicians and/or of the Federal Associations of Statutory Health Insurance Physicians. Data obtained were analysed descriptively.
Results
The response rate was 25,5% and the majority of 596 physicians sampled viewed substantial problems in terms of the regulatory framework of OST care in the German context. Furthermore, financial remuneration, insufficient qualification, as well as inadequate interdisciplinary cooperation in the treatment of comorbidities of opiate substituted patients were regarded as problematic. The number of physicians providing OST in Germany is expected to substantially decrease in the near future.
Conclusion
Despite less restrictive admission criteria for OST in Germany, the legal regulation framework for OST is still a limiting factor through raising concerns on the provider and consumer side to be unable to adhere to the strict rules. To avoid future shortages in the provision of OST care on the system level in Germany, revisions to the legal framework seem to be necessary. In regards to adequate care for drug use-related infectious diseases and psychiatric comorbidities commonly found in opiate substituted patients, efforts are required to improve professional qualifications of physicians providing OST as well as respective interdisciplinary collaboration
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