The atmospheric Cherenkov gamma-ray telescope MAGIC, designed for a low-energy threshold, has detected very-high-energy gamma rays from a giant flare of the distant Quasi-Stellar Radio Source (in ...short: radio quasar) 3C 279, at a distance of more than 5 billion light-years (a redshift of 0.536). No quasar has been observed previously in very-high-energy gamma radiation, and this is also the most distant object detected emitting gamma rays above 50 gigaelectron volts. Because high-energy gamma rays may be stopped by interacting with the diffuse background light in the universe, the observations by MAGIC imply a low amount for such light, consistent with that known from galaxy counts.
We analyze the timing of photons observed by the MAGIC telescope during a flare of the active galactic nucleus Mkn 501 for a possible correlation with energy, as suggested by some models of quantum ...gravity (QG), which predict a vacuum refractive index ≃1+(E/MQGn)n, n=1,2. Parametrizing the delay between γ-rays of different energies as Δt=±τlE or Δt=±τqE2, we find τl=(0.030±0.012) s/GeV at the 2.5-σ level, and τq=(3.71±2.57)×10−6 s/GeV2, respectively. We use these results to establish lower limits MQG1>0.21×1018 GeV and MQG2>0.26×1011 GeV at the 95% C.L. Monte Carlo studies confirm the MAGIC sensitivity to propagation effects at these levels. Thermal plasma effects in the source are negligible, but we cannot exclude the importance of some other source effect.
Microquasars are binary star systems with relativistic radio-emitting jets. They are potential sources of cosmic rays and can be used to elucidate the physics of relativistic jets. We report the ...detection of variable gamma-ray emission above 100 gigaelectron volts from the microquasar LS I 61 + 303. Six orbital cycles were recorded. Several detections occur at a similar orbital phase, which suggests that the emission is periodic. The strongest gamma-ray emission is not observed when the two stars are closest to one another, implying a strong orbital modulation of the emission or absorption processes.
We report on the results from the observations in the very high energy band (VHE; unk greater than or equal to 100 GeV) of the black hole X-ray binary (BHXB) Cygnus X-1. The observations were ...performed with the MAGIC telescope, for a total of 40 hr during 26 nights, spanning the period between 2006 June and November. Searches for steady Y-ray signals yielded no positive result, and upper limits to the integral flux ranging between 1% and 2% of the Crab Nebula flux, depending on the energy, have been established. We also analyzed each observation night independently, obtaining evidence of Y-ray signals at the 4.0 sigma significance level (3.2 sigma after trial correction) for 154 minutes of effective on-time (EOT) on September 24 between 20:58 and 23:41 UTC, coinciding with an X-ray flare seen by RXTE, Swift, and INTEGRAL. A search for faster-varying signals within a night resulted in an excess with a significance of 4.9 sigma (4.1 sigma after trial correction) for 79 minutes EOT between 22:17 and 23:41 UTC. The measured excess is compatible with a pointlike source at the position of Cygnus X-1 and excludes the nearby radio nebula powered by its relativistic jet. The differential energy spectrum is well fitted by an unbroken power law described as dN/(dA dt dE) = (2.3 plus or minus 0.6) x 10- super(12)(E/1TeV) super(-3.2 plus or minus 0.6). This is the first experimental evidence of VHE emission from a stellar mass black hole and therefore from a confirmed accreting X-ray binary.
The PILATUS detector module was characterized in the PTB laboratory at BESSY II comparing modules with 320 μm thick and newly developed 450 μm and 1000 μm thick silicon sensors. Measurements were ...carried out over a wide energy range, in-vacuum from 1.75 keV to 8.8 keV and in air from 8 keV to 60 keV. The quantum efficiency (QE) was measured as a function of energy and the spatial resolution was measured at several photon energies both in terms of the modulation transfer function (MTF) from edge profile measurements and by directly measuring the point spread function (PSF) of a single pixel in a raster scan with a pinhole beam. Independent of the sensor thickness, the measured MTF and PSF come close to those for an ideal pixel detector with the pixel size of the PILATUS detector (172 × 172 μm2). The measured QE follows the values predicted by calculation. Thicker sensors significantly enhance the QE of the PILATUS detectors for energies above 10 keV without impairing the spatial resolution and noise-free detection. In-vacuum operation of the PILATUS detector is possible at energies as low as 1.75 keV.
Hydroxymethylglutaryl coenzyme A reductase inhibitors (statins), which exhibit beneficial cerebrovascular effects by modulating inflammation and nitric oxide production, have not been evaluated in ...acute aneurysmal subarachnoid hemorrhage (SAH) patients. The effect of prior statin use on 14-day functional outcome and on prevention of vasospasm-induced delayed cerebral ischemia (DCI) or stroke during hospitalization was analyzed.
We conducted a 1:2 matched (age, admission Hunt and Hess grade, vascular disease/risk history) cohort study of 20 SAH patients on statins and 40 SAH controls. The primary outcome was functional outcome at 14 days (Modified Lawton Physical Self-Maintenance Scale and Barthel Index scale scores). Secondary outcomes were 14-day mortality, Modified Rankin Scale score, DCI, DCI supported by angiography/transcranial Doppler TCD, cerebral infarctions of any type, and TCD highest mean velocity elevation.
Statin users demonstrated a significant protective effect on 14-day Barthel Index scale and Modified Lawton Physical Self-Maintenance Scale scores (77 +/- 10 versus 39 +/- 8, P = 0.003; 12 +/- 7 versus 19 +/- 9, P = 0.03, respectively). Moreover, statin users demonstrated a significantly lower incidence of DCI and DCI supported by angiography/TCD (10% versus 43%, P = 0.02; 5% versus 35%, P = 0.01, respectively), cerebral infarctions of any type (25% versus 63%, P = 0.01), and baseline-to-final TCD highest mean velocity change of 50 cm/s or greater (18% versus 51%, P = 0.03).
SAH statin users demonstrated significant improvement in 14-day functional outcome, a significantly lower incidence of DCI and cerebral infarctions of any type, as well as prevention of TCD highest mean velocity elevation. However, we did not find a significant statin impact on mortality or global outcome (Modified Rankin Scale) in this small sample. This study provides clinical evidence for the potential therapeutic benefit of statins after acute SAH.
The Cherenkov light flashes produced by extensive air showers are very short in time. A high bandwidth and fast digitizing readout, therefore, can minimize the influence of the background from the ...light of the night sky, and improve the performance in Cherenkov telescopes. The time structure of the Cherenkov image can further be used in single-dish Cherenkov telescopes as an additional parameter to reduce the background from unwanted hadronic showers. A description of an analysis method which makes use of the time information and the subsequent improvement on the performance of the MAGIC telescope (especially after the upgrade with an ultra fast 2 GSamples/s digitization system in February 2007) will be presented. The use of timing information in the analysis of the new MAGIC data reduces the background by a factor two, which in turn results in an enhancement of about a factor 1.4 of the flux sensitivity to point-like sources, as tested on observations of the Crab Nebula.
The MAGIC collaboration has studied the high-frequency-peaked BL Lac object 1ES 1218+30.4, at a redshift z = 0.182, using the MAGIC imaging air Cerenkov telescope located on the Canary Island of La ...Palma. A gamma-ray signal was observed with 6.4 s significance. The differential energy spectrum for an energy threshold of 120 GeV can be fitted by a simple power law, yielding F sub(E)(E) = (8.1 c 2.1) x 10 super(-7) E/(250 GeV) super(-3.0c0.4) TeV super(-1) m super(-2) s super(-1). During the 6 days of observation in 2005 January, no time variability on timescales of days was found within the statistical errors. The observed integral flux above 350 GeV is nearly a factor of 2 below the upper limit reported by the Whipple collaboration in 2003.
During its first data cycle, between 2005 and the beginning of 2006, the fast repositioning system of the MAGIC telescope allowed the observation of nine different gamma-ray bursts as possible ...sources of very high energy gamma -rays. These observations were triggered by alerts from Swift, HETE-2, and INTEGRAL; they started as quickly as possible after the alerts and lasted for several minutes, with an energy threshold varying between 80 and 200 GeV, depending on the zenith angle of the burst. No evidence for gamma signals was found, and upper limits for the flux were derived for all events using the standard analysis chain of MAGIC. For the bursts with measured redshifts, the upper limits are compatible with a power-law extrapolation, when the intrinsic fluxes are evaluated taking into account the attenuation due to the scattering in the metagalactic radiation field.
Geiger-mode Avalanche Photodiodes (G-APD) bear the potential to significantly improve the sensitivity of Imaging Air Cherenkov Telescopes (IACT). We are currently building the First G-APD Cherenkov ...Telescope (FACT) by refurbishing an old IACT with a mirror area of 9.5 square meters and are constructing a new, fine-pixelized camera using novel G-APDs. The main goal is to evaluate the performance of a complete system by observing very high energy gamma-rays from the Crab Nebula. This is an important field test to check the feasibility of G-APD-based cameras to replace at some time the PMT-based cameras of planned future IACTs like AGIS and CTA. In this article, we present the basic design of such a camera as well as some important details.
PDF
