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.
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.
Ground-based Cherenkov telescopes have made in recent years important contributions to high energy gamma-ray astronomy. A lower energy threshold, considerably below 100
GeV, and improved sensitivity ...will be key parameters to extend their role. A lower threshold will permit these instruments to cover wavelengths with good overlap with satellite experiments, thus providing essential complementary information.
The latest generation of Imaging Air Cherenkov Telescopes was built with this criterion in mind. Preliminary studies concerning further progress in the same direction have started.
We discuss in this contribution the astrophysics and physics arguments for lowering the observable energy threshold as far as the Cherenkov technique permits, and the ensuing complementarity to results obtained with a GLAST-like satellite.
Development of a 10-inch HPD with integrated readout electronics Braem, A.; Chesi, E.; Joram, C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2003, Volume:
504, Issue:
1-3
Journal Article
Peer reviewed
Open access
A round 10-in. diameter Hybrid Photodiode (HPD) with spherical entrance window is under development for Cherenkov imaging applications in cosmic ray astronomy. The HPD adopts the fountain focusing ...electron optics, which, as already demonstrated in the 5 inch Pad HPD, allows for a linear demagnification of the image over practically the full tube diameter. Self-triggering front-end electronics providing also sparse readout capability, has been tested. High-efficiency Rb2Te cathodes have been produced on a UV extended borosilicate glass windows with very thin conductive underlayers of Indium Tin Oxide. We report on the design of the 10-in. HPD, the fabrication procedure and first tests of a 5-in. HPD with Rb2Te photocathode and 2048 channels.
The MAGIC telescope took data of very high energy gamma -ray emission from the blazar Markarian 421 (Mrk 421) between 2004 November and 2005 April. We present a combined analysis of data samples ...recorded under different observational conditions, dowr to gamma -ray energies of 100 GeV. The flux was found to vary between 0.5 and 2 crab (integrated above 200 GeV), considered a low state when compared to known data. Although the flux varied day by day, no short-term variability was observed, although there is some indication that not all nights show an equally quiescent state. The results at higher energies were found to be consistent with previous observations. A clear correlation is observed between gamma -ray and X-ray fluxes, whereas no significant correlation between gamma -ray and optical data is seen. The spectral energy distribution between 100 GeV and 3 TeV shows a clear deviation from a power law, more clearly and at lower flux than previous observations at higher energies. The deviation persists after correcting for the effect of attenuation by the extragalactic background light, and most likely is source-inherent. There is a rather clear indication of an inverse Compton peak around 100 GeV. The spectral energy distribution of Mrk 421 can be fitted by a one-zone synchrotron self-Compton model, suggesting once again a leptonic origin of the very high energy gamma -ray emission from this blazar.
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