69 research outputs found
Primary prevention of cardiovascular diseases: a cost study in family practices
Background: Considering the scarcity of health care resources and the high costs associated with cardiovascular diseases, we investigated the spending on cardiovascular primary preventive activities and the prescribing behaviour of primary preventive cardiovascular medication (PPCM) in Dutch family practices (FPs). Methods. A mixed methods design was used, which consisted of a questionnaire (n = 80 FPs), video recordings of hypertension- or cholesterol-related general practitioner visits (n = 56), and the database of Netherlands Information Network of General Practic
Discovery of the Binary Pulsar PSR B1259-63 in Very-High-Energy Gamma Rays around Periastron with H.E.S.S
We report the discovery of very-high-energy (VHE) gamma-ray emission of the
binary system PSR B1259-63/SS 2883 of a radio pulsar orbiting a massive,
luminous Be star in a highly eccentric orbit. The observations around the 2004
periastron passage of the pulsar were performed with the four 13 m Cherenkov
telescopes of the H.E.S.S. experiment, recently installed in Namibia and in
full operation since December 2003. Between February and June 2004, a gamma-ray
signal from the binary system was detected with a total significance above 13
sigma. The flux was found to vary significantly on timescales of days which
makes PSR B1259-63 the first variable galactic source of VHE gamma-rays
observed so far. Strong emission signals were observed in pre- and
post-periastron phases with a flux minimum around periastron, followed by a
gradual flux decrease in the months after. The measured time-averaged energy
spectrum above a mean threshold energy of 380 GeV can be fitted by a simple
power law F_0(E/1 TeV)^-Gamma with a photon index Gamma =
2.7+-0.2_stat+-0.2_sys and flux normalisation F_0 = (1.3+-0.1_stat+-0.3_sys)
10^-12 TeV^-1 cm^-2 s^-1. This detection of VHE gamma-rays provides unambiguous
evidence for particle acceleration to multi-TeV energies in the binary system.
In combination with coeval observations of the X-ray synchrotron emission by
the RXTE and INTEGRAL instruments, and assuming the VHE gamma-ray emission to
be produced by the inverse Compton mechanism, the magnetic field strength can
be directly estimated to be of the order of 1 G.Comment: 10 pages, 8 figures, accepted in Astronomy and Astrophysics on 2 June
2005, replace: document unchanged, replaced author field in astro-ph entry -
authors are all members of the H.E.S.S. collaboration and three additional
authors (99+3, see document
Observations of Mkn 421 in 2004 with H.E.S.S. at large zenith angles
Mkn 421 was observed during a high flux state for nine nights in April and
May 2004 with the fully operational High Energy Stereoscopic System (H.E.S.S.)
in Namibia. The observations were carried out at zenith angles of
60--65, which result in an average energy threshold of 1.5 TeV
and a collection area reaching 2~km at 10~TeV. Roughly 7000 photons from
Mkn~421 were accumulated with an average gamma-ray rate of 8 photons/min. The
overall significance of the detection exceeds 100 standard deviations. The
light-curve of integrated fluxes above 2~TeV shows changes of the diurnal flux
up to a factor of 4.3. For nights of high flux, intra-night variability is
detected with a decay time of less than 1 hour. The time averaged energy
spectrum is curved and is well described by a power-law with a photon index
\egamm and an exponential cutoff at \ecut~TeV and an average integral flux
above 2~TeV of 3 Crab flux units. Significant variations of the spectral shape
are detected with a spectral hardening as the flux increases. Contemporaneous
multi-wavelength observations at lower energies (X-rays and gamma-rays above
~GeV) indicate smaller relative variability amplitudes than seen
above 2~TeV during high flux state observed in April 2004.Comment: 5 pages, 4 figures, published in A&
Very high energy gamma rays from the direction of Sagittarius A*.
We report the detection of a point-like source of very high energy (VHE) -rays coincident within 1' of Sgr A *, obtained with the HESS array of Cherenkov telescopes. The -rays exhibit a power-law energy spectrum with a spectral index of and a flux above the 165 GeV threshold of m -2 s -1. The measured flux and spectrum differ substantially from recent results reported in particular by the CANGAROO collaboration
Discovery of extended VHE gamma-ray emission from the asymmetric pulsar wind nebula in MSH 15-52 with H.E.S.S
The Supernova Remnant MSH 15-52 has been observed in very high energy (VHE)
gamma-rays using the H.E.S.S. 4-telescope array located in Namibia. A gamma-ray
signal is detected at the 25 sigma level during an exposure of 22.1 hours live
time. The image reveals an elliptically shaped emission region around the
pulsar PSR B1509-58, with semi-major axis 6' in the NW-SE direction and
semi-minor axis 2' approximately. This morphology coincides with the diffuse
pulsar wind nebula as observed at X-ray energies by ROSAT. The overall energy
spectrum from 280 GeV up to 40 TeV can be fitted by a power law with photon
index Gamma = 2.27 +/- 0.03(stat.) +/- 0.20(syst.). The detected emission can
be plausibly explained by inverse Compton scattering of accelerated
relativistic electrons with soft photons.Comment: 5 pages, 3 figures, accepted by A&A letter
Serendipitous discovery of the unidentified extended TeV gamma-ray source HESS J1303-631
The serendipitous discovery of an unidentified extended TeVgamma-ray source
close to the galactic plane named HESS J1303-631 at a significance of 21
standard deviations is reported. The observations were performed between
February and June 2004 with the H.E.S.S. stereoscopic system of Cherenkov
telescopes in Namibia. HESS J1303-631 was discovered roughly 0.6 deg north of
the binary system PSR B1259-63/SS 2883, the target object of the initial
observation campaign which was also detected at TeV energies in the same field
of view. HESS J1303-631 is extended with a width of an assumed intrinsic
Gaussian emission profile of sigma = (0.16 +- 0.02) deg and the integral flux
above 380 GeV is compatible with constant emission over the entire
observational period of (17 +- 3)% of the Crab Nebula flux. The measured energy
spectrum can be described by a power-law dN/dE ~ E^-Gamma with a photon index
of Gamma = 2.44 +- 0.05_stat +- 0.2_syst. Up to now, no counterpart at other
wavelengths is identified. Various possible TeV production scenarios are
discussed.Comment: 9 pages, 8 figures, accepted in Astronomy and Astrophysic
Simultaneous observations of PKS 2155-304 with H.E.S.S., Fermi, RXTE and ATOM: spectral energy distributions and variability in a low state
We report on the first simultaneous observations that cover the optical,
X-ray, and high energy gamma-ray bands of the BL Lac object PKS 2155-304. The
gamma-ray bands were observed for 11 days, between 25 August and 6 September
2008, jointly with the Fermi Gamma-ray Space Telescope and the H.E.S.S.
atmospheric Cherenkov array, providing the first simultaneous MeV-TeV spectral
energy distribution with the new generation of gamma-ray telescopes. The ATOM
telescope and the RXTE and Swift observatories provided optical and X-ray
coverage of the low-energy component over the same time period. The object was
close to the lowest archival X-ray and Very High Energy state, whereas the
optical flux was much higher. The light curves show relatively little (~30%$)
variability overall when compared to past flaring episodes, but we find a clear
optical/VHE correlation and evidence for a correlation of the X-rays with the
high energy spectral index. Contrary to previous observations in the flaring
state, we do not find any correlation between the X-ray and VHE components.
Although synchrotron self-Compton models are often invoked to explain the SEDs
of BL Lac objects, the most common versions of these models are at odds with
the correlated variability we find in the various bands for PKS 2155-304.Comment: Accepted for publication in the Astrophysical Journa
H.E.S.S. observations of PKS 2155-304
The high-frequency peaked BL Lac PKS 2155-304 at redshift z = 0.117 has been detected with high significance (∼45σ) at energies greater than 160 GeV, using the H.E.S.S. stereoscopic array of imaging air-Cherenkov telescopes in Namibia. A strong signal is found in each of the data sets corresponding to the dark periods of July and October, 2002, and June-September, 2003. The observed flux of VHE gamma rays shows variability on time scales of months, days, and hours. The monthly-averaged integral flux above 300 GeV varies between 10% and 60% of the flux observed from the Crab Nebula. Energy spectra are measured for these individual periods of data taking and are characterized by a steep power law with a time-averaged photon index of Γ = 3.32 ± 0.06. An improved x2 per degree of freedom is found when either a power law with an exponential cutoff energy or a broken power law are fit to the time-averaged energy spectrum. However, the significance of the improvement is marginal (∼2σ). The suggested presence of features in the energy spectrum may be intrinsic to the emission from the blazar, or an indication of absorption of TeV gamma rays by the extragalactic infrared background light.F. Aharonian, A. G. Akhperjanian, K.-M. Aye, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, D. Berge, P. Berghaus, K. Bernlöhr, O. Bolz, C. Boisson, C. Borgmeier, F. Breitling, A. M. Brown, J. Bussons Gordo, P. M. Chadwick, V. R. Chitnis, L.-M. Chounet, R. Cornils, L. Costamante, B. Degrange, A. Djannati-Ataï, L.O'C. Drury, T. Ergin, P. Espigat, F. Feinstein, P. Fleury, G. Fontaine, S. Funk, Y. A. Gallant, B. Giebels, S. Gillessen, P. Goret, J. Guy, C. Hadjichristidis, M. Hauser, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, W. Hofmann, M. Holleran, D. Horns, O. C. de Jager, I. Jung, B. Khélifi, Nu. Komin, A. Konopelko, I. J. Latham, R. Le Gallou, M. Lemoine, A. Lemière, N. Leroy, T. Lohse, A. Marcowith, C. Masterson, T. J. L. McComb, M. de Naurois, S. J. Nolan, A. Noutsos, K. J. Orford, J. L. Osborne, M. Ouchrif, M. Panter, G. Pelletier, S. Pita, M. Pohl, G. Pühlhofer, M. Punch, B. C. Raubenheimer, M. Raue, J. Raux, S. M. Rayner, I. Redondo, A. Reimer, O. Reimer, J. Ripken, M. Rivoal, L. Rob, L. Rolland, G. Rowell, V. Sahakian, L. Saugé, S. Schlenker, R. Schlickeiser, C. Schuster, U. Schwanke, M. Siewert, H. Sol, R. Steenkamp, C. Stegmann, J.-P. Tavernet, C. G. Théoret, M. Tluczykont, D. J. van der Walt, G. Vasileiadis, P. Vincent, B. Visser, H. J. Völk and S. J. Wagne
Discovery of VHE gamma rays from PKS 2005-489
The high-frequency peaked BL Lac PKS 2005-489 (z = 0.071) was observed in 2003 and 2004 with the HESS stereoscopic array of imaging atmospheric-Cherenkov telescopes in Namibia. A signal was detected at the 6.7σ level in the 2004 observations (24.2 h live time), but not in the 2003 data set (27.3 h live time). PKS 2005-489 is the first blazar independently discovered by HESS to be an emitter of VHE photons, and only the second such blazar in the Southern Hemisphere. The integral flux above 200 GeV observed in 2004 is (6.9 ± 1.0 stat ± 1.4 syst) × 10 -12 cm -2 s -1, corresponding to ∼2.5% of the flux observed from the Crab Nebula. The 99% upper limit on the flux in 2003, I(>200 GeV) < 5.2 × 10 -12 cm -2 s -1, is smaller than the flux measured in 2004, suggesting an increased level of activity in 2004. However, the data show no evidence for significant variability on any time scale less than a year. An energy spectrum is measured and is characterized by a very soft power law (photon index of Γ = 4.0 ± 0.4). © ESO 2005.Aharonian, F... Rowell, G... et al
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