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 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.
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.
We report the detection of a new source of very high energy (VHE; unk greater than or equal to 100 Gev) Y-ray emission located close to the Galactic plane, MA J0616+225, which is spatially coincident ...with supernova remnant IC 443. The observations were carried out with the MAGIC telescope unk 2005 December-2006 January and 2006 December-2007 January. Here we present results from this source, leading to a VHE Y-ray unk statistical significance of 5.7 sigma in the 2006/2007 data and a measured differential Y-ray flux consistent with a power law, described as unk(dAdtdE) = (1.0 plus or minus 0.2) x 10 super(11)(E/0.4TeV)-3.1 plus or minus 0.3 cm super(-2) s super(-1) Tev super(-1). we briefly discuss the observational technique used and the unk implemented for the data analysis. The results are placed in the context of the multiwavelength emission and the molecular environment region of IC 443.
The very high energy (VHE; E > 100 GeV) blazar Markarian 501 (Mrk 501) has a well-studied history of extreme spectral variability and is an excellent laboratory for studying the physical processes ...within the jets of active galactic nuclei. However, there are few detailed multiwavelength studies of Mrk 501 during its quiescent state, due to its low luminosity. A short-term multiwavelength study of Mrk 501 was coordinated in 2009 March, focusing around a multi-day observation with the Suzaku X-ray satellite and including Delta *g-ray data from VERITAS, MAGIC, and the Fermi Gamma-ray Space Telescope with the goal of providing a well-sampled multiwavelength baseline measurement of Mrk 501 in the quiescent state. The results of these quiescent-state observations are compared to the historically extreme outburst of 1997 April 16, with the goal of examining variability of the spectral energy distribution (SED) between the two states. The derived broadband SED shows the characteristic double-peaked profile. We find that the X-ray peak shifts by over two orders of magnitude in photon energy between the two flux states while the VHE peak varies little. The limited shift in the VHE peak can be explained by the transition to the Klein-Nishina (KN) regime. Synchrotron self-Compton models are matched to the data and the implied KN effects are explored.
COMPET is an innovative implementation of a small animal PET scanner using a novel block detector geometry, allowing for a high resolution and high sensitivity. One detector block is built up from ...layers of long LYSO crystals. Perpendicular and interleaved between the crystals, Wave Length Shifting (WLS) fibers are used. The scintillation light created by a gamma ray interacting with a crystal is measured with Geiger mode Avalanche Photo Diodes (GAPDs) at one end of the crystals. A small part of the scintillation light escapes the crystals and enters the WLS, where it has a certain probability to be absorbed and re-emitted at a longer wavelength. This light is measured at one end of the WLS by a GAPD. With this setup, the point of interaction (POI) of the gamma ray is deduced, allowing for the 3D reconstruction of the interaction point between the gamma ray and the detector. Thus, not only photoelectric interactions are used to reconstruct the line of responses (LOR) for each event, but also Compton scattered gamma-rays are included. Using 4 such modules, the total detector comprises a total amount of 1080 readout channels, where 600 are used for the crystals and 480 for the WLS. The central point source resolution was deduced from Monte Carlo simulation to be below 1 mm FWHM in transaxial direction. The sensitivity to detect coincident gamma rays emitted at the centre of the field of view is up to 16%. With its compact geometry, high point source resolution, high sensitivity and its low amount of readout channels, the COMPET detector geometry provides a promising detector layout for future preclinical PET scanners.
The MAGIC collaboration observed BL Lacertae for 22.2 hr during 2005 August to December and for 26 hr during 2006 July to September. The source is the historical prototype and eponym of a class of ...low-frequency-peaked BL Lacertae (LBL) objects. A very high energy (VHE) gamma -ray signal was discovered with a 5.1 a excess in the 2005 data. Above 200 GeV, an integral flux of (0.6 plus or minus 0.2) x 10 super(-11) cm super(-2)8 super(-1) was measured, corresponding to approximately 3% of the Crab flux. The differential spectrum between 150 and 900 GeV is rather steep with a photon index of -3.6 plus or minus 0.5. The light curve shows no significant variability during the observations in 2005. For the first time a clear detection of VHE gamma -ray emission from an LBL object was obtained with a signal below previous upper limits. The 2006 data show no significant excess. This drop in flux follows the observed trend in optical activity.
Recently, the Galactic center has been reported to be a source of very high energy (VHE) g-rays by the CANGAROO, VERITAS, and HESS experiments. The energy spectra as measured by these experiments ...show substantial differences. In this Letter we present MAGIC observations of the Galactic center, resulting in the detection of a differential g-ray flux consistent with a steady, hard-slope power law, described as dN sub(g)/(dA dt dE) = (2.9 c 0.6) x 10 super(-12)(E/TeV) super(-2.2c0.2) cm super(-2) s super(-1) TeV super(-1). The g-ray source is centered at (R.A., decl.) = (17 super(h)45 super(m)20 super(s), -292'). This result confirms the previous measurements by the HESS experiment and indicates a steady source of TeV g-rays. We briefly describe the observational technique used and the procedure implemented for the data analysis, and we discuss the results in the perspective of different models proposed for the acceleration of the VHE g-rays.
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