An unidentified TeV source in the vicinity of Cygnus OB2

Deep observation (∼113 hrs) of the Cygnus region at TeV energies using the HEGRA stereoscopic system of air Čerenkov telescopes has serendipitously revealed a signal positionally inside the core of the OB association Cygnus OB2, at the edge of the 95% error circle of the EGRET source 3EG J2033+4118, and ∼0.5° north of Cyg X-3. The source centre of gravity is RA αJ2000: 20hr32m07s± 9.2stats±2.2syss, Dec δJ2000: +41°30′30″2.0stat±0.4′sys. The source is steady, has a post-trial significance of +4.6σ, indication for extension with radius 5.6′ at the ∼3σ level, and has a differential power-law flux with hard photon index of - 1.9 ± 0.3stat ± 0.3sys. The integral flux above 1 TeV amounts ∼3% that of the Crab. No counterpart for the TeV source at other wavelengths is presently identified, and its extension would disfavour an exclusive pulsar or AGN origin. If associated with Cygnus OB2, this dense concentration of young, massive stars provides an environment conducive to multi-TeV particle acceleration and likely subsequent interaction with a nearby gas cloud. Alternatively, one could envisage γ-ray production via a jet-driven termination shock.F. A. Aharonian, ... G. P. Rowell, ... [et al

Serum Xylosyltransferase Activity in Diabetic Patients as a Possible Marker of Reduced Proteoglycan Biosynthesis

OBJECTIVE—Proteoglycan metabolism is altered in diabetic patients. The xylosyltransferases (XTs) are the initial and rate-limiting enzymes in the biosynthesis of the glycosaminoglycan chains in proteoglycans. Here, we analyzed whether the changed proteoglycan metabolism leads to altered serum XT levels in diabetic patients

The TeV Energy Spectrum of Mkn 501 Measured with the Stereoscopic Telescope System of HEGRA during 1998 and 1999

During 1997, the BL Lac object Mkn 501 went into an extraordinary state of high X-ray and TeV gamma-ray activity, lasting more than 6 months. In this paper we report on the TeV emission characteristics of the source in the subsequent years of 1998 and 1999 as measured with the Stereoscopic Cherenkov Telescope System of HEGRA (La Palma, Canary Islands). Our observations reveal a 1998-1999 mean emission level at 1 TeV of 1/3 of the flux of the Crab Nebula, a factor of 10 lower than during the year of 1997. A dataset of 122 observations hours with the HEGRA telescope system makes it possible to assess for the first time the Mkn 501 TeV energy spectrum for a mean flux level substantially below that of the Crab Nebula with reasonable statistical accuracy. Excluding the data of a strong flare, we find evidence that the 1998--1999 low-flux spectrum is substantially softer (by 0.44+-0.1(stat) in spectral index) than the 1997 time averaged spectrum. The 500 GeV to 10 TeV energy spectrum can well be described by a power law model with exponential cutoff: dN/dE ~ E^(-alpha) exp(-E/E0) with alpha=2.31+-0.22(stat), and E0=5.1 (-2.3+7.8)(stat) TeV. Within statistical accuracy, also a pure power law model gives an acceptable fit to the data: dN/dE ~ E^(-Gamma) with Gamma=2.76+-0.08(stat). After presenting the 1998-1999 TeV characteristics of the source we discuss the implications of the results.Comment: Accepted for publication in The Astrophysical Journal, Part 1, on August 4th, 200

The Energy Spectrum of TeV Gamma-Rays from the Crab Nebula as measured by the HEGRA system of imaging air Cherenkov telescopes

The Crab Nebula has been observed by the HEGRA (High-Energy Gamma-Ray Astronomy) stereoscopic system of imaging air Cherenkov telescopes (IACTs) for a total of about 200 hrs during two observational campaigns: from September 1997 to March 1998 and from August 1998 to April 1999. The recent detailed studies of system performance give an energy threshold and an energy resolution for gamma-rays of 500 GeV and ~ 18%, respectively. The Crab energy spectrum was measured with the HEGRA IACT system in a very broad energy range up to 20 TeV, using observations at zenith angles up to 65 degrees. The Crab data can be fitted in the energy range from 1 to 20 TeV by a simple power-law, which yields dJg/dE = (2.79+/-0.02 +/- 0.5) 10^{-7} E^{-2.59 +/- 0.03 +/- 0.05}, ph m^{-2} s^{-1} TeV^{-1} The Crab Nebula energy spectrum, as measured with the HEGRA IACT system, agrees within 15% in the absolute scale and within 0.1 units in the power law index with the latest measurements by the Whipple, CANGAROO and CAT groups, consistent within the statistical and systematic errors quoted by the experiments. The pure power-law spectrum of TeV gamma-rays from the Crab Nebula constrains the physics parameters of the nebula environment as well as the models of photon emission.Comment: to appear in ApJ, 29 pages, 6 figure

Simultaneous X-Ray and TeV Gamma-Ray Observations of the TeV Blazar Markarian 421 during February and May 2000

In this paper we present the results of simultaneous observations of the TeV blazar Markarian 421 (Mrk 421) at X-ray and TeV Gamma-ray energies with the Rossi X-Ray Timing Explorer (RXTE) and the stereoscopic Cherenkov Telescope system of the HEGRA (High Energy Gamma Ray Astronomy) experiment, respectively. The source was monitored from February 2nd to February 16th and from May 3rd to May 8th, 2000. We discuss in detail the temporal and spectral properties of the source. Remarkably, the TeV observations of February 7th/8th showed statistically significant evidence for substantial TeV flux variability on 30 min time scale. We show the results of modeling the data with a time dependent homogeneous Synchrotron Self-Compton (SSC) model. The X-ray and TeV gamma-ray emission strengths and energy spectra together with the rapid flux variability strongly suggest that the emission volume is approaching the observer with a Doppler factor of 50 or higher. The different flux variability time scales observed at X-rays and TeV Gamma-rays indicate that a more detailed analysis will require inhomogeneous models with several emission zones.Comment: Accepted for Publication in ApJ, 21 Pages, 5 Figure

History of medicine in Qatar

This Thesis is concerned with the history of health care and medicine in the State of Qatar. I have traced its evolution from the first man, through to the presence of Islam until oil was discovered in 1939. I then continued with close personal interest to follow the development of health and medicine in the more recent "post-oil discovery" years, in particular the last decade when Qatar matches its health and medical care with the pre-eminent services of the Arabian Gulf region (Gulf Co-operation States) and the world.The historical, cultural and political events that influenced development in the Arabian Peninsula have been many and varied causing intriguing shifts in the evolution of health practice in medicine.Traditional medicine traversed the trade routes, Islamic medical practices became firmly rooted in the Arabian Peninsula and oil wealth in the latter years empowered the Gulf States as significant buyers of modern medical technology and manpower.This thesis is organised in logical sequence with early chapters concentrating on primitive, ancient history and the pre-Islamic period. Relevant anthropological, archaeological, cultural and historical information has been outlined and analysed in the early chapters, in an attempt to identify the significant influences on the health and medical practices of the times. Plausible theories and conclusions were sought on health practices and medicine; however, a dearth of factual information necessitated some speculation on how tribal medicine and health practices were derived and disseminated throughout the region.Less speculation was necessary for the Islamic era. Islam was widespread with the daily lives and cultural practices of Muslims strictly controlled; particularly in terms of morality, marriage, dress, health and hygiene. Certain chapters describe the significant contribution of Islamic medicine to the development of medicine in general and review the impact of Islam on health practices within the Muslim society of the Arabian Peninsula including Qatar. The Arabs themselves had a profound effect on the medicine of the world, with their translations from Greek to Arabic and other languages.The remaining chapters look closely at contemporary Arab society in Qatar, from the discovery of oil to the present day

Correlated intense X-ray and TeV activity of Mrk~501 in 1998 June

We present exactly simultaneous X-ray and TeV monitoring with {\it RXTE} and HEGRA of the TeV blazar Mrk 501 during 15 days in 1998 June. After an initial period of very low flux at both wavelengths, the source underwent a remarkable flare in the TeV and X-ray energy bands, lasting for about six days and with a larger amplitude at TeV energies than in the X-ray band. At the peak of the TeV flare, rapid TeV flux variability on sub-hour timescales is found. Large spectral variations are observed at X-rays, with the 3--20 keV photon index of a pure power law continuum flattening from $\Gamma=2.3$ to $\Gamma=1.8$ on a timescale of 2--3 days. This implies that during the maximum of the TeV activity, the synchrotron peak shifted to energies $\gtrsim 50$ keV, a behavior similar to that observed during the longer-lasting, more intense flare in 1997 April. The TeV spectrum during the flare is described by a power law with photon index $\Gamma=1.9$ and an exponential cutoff at $\sim$ 4 TeV; an indication for spectral softening during the flare decay is observed in the TeV hardness ratios. Our results generally support a scenario where the TeV photons are emitted via inverse Compton scattering of ambient seed photons by the same electron population responsible for the synchrotron X-rays. The simultaneous spectral energy distributions (SEDs) can be fit with a one-zone synchrotron-self Compton model assuming a substantial increase of the magnetic field and the electron energy by a factor of 3 and 10, respectively.Comment: Accepted for publication in ApJ, Part

Policies affecting the competitiveness of dairy production in Sweden, Denmark and Germany

Denmark, Germany and Sweden are along with 24 other countries members of the European Union. Being part of the European Union also means being part of a European market. Within the union barriers for trade has been abolished in order to create more open market. This open market has also contributed towards a more globalized market for dairy products. What used to be a domestic market has become globalised with increasing trade among the members. The membership also includes a common agricultural policy (CAP) which regulates rules for animal welfare, the environment and subsidies. The common agricultural policy provides a framework for laws and legislation within the European Union. The idea of these common policies is to provide similar conditions for the market players irrespective of member country. However, each member state applies the policies a bit differently but still within the framework which affect the conditions for the producers differently. In addition to the European framework each county has its own individual system of laws, taxation and reimbursements which affect the competitiveness. Subsidies and tax reductions given to dairy farmers can be viewed as cost reducers rather than ensuring a minimum income. The subsidies enable the farmers to maintain production even if the market price is lower than the variable costs. The effect from the subsidies then make the marginal cost lower which gives the farmers a competitive advantage in form of cost advantage. The aim of this study is to investigate how subsidies and tax systems affects the competitiveness for dairy producers in Denmark, Germany and Sweden. To illustrate the effects of the different systems a case farm located in southwest Sweden has been used. The farm has 220 dairy cows and 205 hectares of agricultural land. The theory used to measure the effects from the three different systems has its basis from a dissertation by Ola Flaten (2001). The results show that there are differences in the result for the case farm when the different rules are applied. The most profitable system when applied to the case farm is the German which generates a net farm income of 277 940 Euros. The second most profitable system when applied to the case farm is the Danish which generates a net farm income of 272 870 Euros. The Swedish system generates the lowest net farm income of 271 542 Euros. In order to measure competitiveness the average cost per delivered ton milk has been used. The most competitive system when applied to the case farm is the Danish which has an average cost per delivered ton milk of 248,6 Euros. The second lowest average cost has the Swedish system which is 251,3 Euros per delivered ton milk. The highest average cost is generated by the German system which amounts to 256,3 Euros per delivered ton milk