Both the high density medium that characterizes the central regions of starburst galaxies and its power to accelerate particles up to relativistic energies make these objects good candidates for ...γ-ray sources. In this paper we present a self-consistent model of the multifrequency emission of the starburst galaxy NGC 253 from radio to γ-rays. The model agrees with all current measurements and provides predictions for the high energy behavior of the NGC 253 central region. In particular, we discuss prospects for observations with the HESS array (and comparison with their recently obtained data) and GLAST satellite.
We have proposed that the interaction between relativistic protons resulting from Fermi first order acceleration in the superbubble of a stellar OB association or in other nearby accelerators and ...ions residing in single stellar winds of massive stars could lead to TeV sources without strong counterparts at lower energies. Here we refine this analysis in several directions. We study collective wind configurations produced by a number of massive stars, and obtain densities and expansion velocities of the stellar wind gas that is to be target of hadronic interactions. We study the expected γ-ray emission from these regions, considering in an approximate way the effect of cosmic ray modulation. We compute secondary particle production (electrons from knock-on interactions and electrons and positrons from charged pion decay), and solve the loss equation with ionization, synchrotron, bremsstrahlung, inverse Compton and expansion losses. We provide examples where configurations can produce sources for GLAST satellite and the MAGIC/HESS/VERITAS telescopes in non-uniform ways, i.e., with or without the corresponding counterparts. We show that in all cases we studied, no EGRET source is expected. We comment on HESS J1303-631 and on Cygnus OB 2 and Westerlund 1 as two associations where this scenario could be tested.
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.
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.
Aims.We searched for very high energy (VHE) γ-ray emission from the supernova remnant Cassiopeia A Methods.The shell-type supernova remnant Cassiopeia A was observed with the 17 m MAGIC telescope ...between July 2006 and January 2007 for a total time of 47 h. Results.The source was detected above an energy of 250 GeV with a significance of 5.2σ and a photon flux above 1 TeV of (7.3 ± $0.7_{\rm stat}$ ± $2.2_{\rm sys})$ $\times$ 10-13 cm-2s-1. The photon spectrum is compatible with a power law dN/dE $\propto$ $E^{-\Gamma}$ with a photon index Γ = 2.3 ± $0.2_{\rm stat}$ ± $0.2_{\rm sys}$. The source is point-like within the angular resolution of the telescope.
The paper describes an application of the tree classification method Random Forest (RF), as used in the analysis of data from the ground-based gamma telescope MAGIC. In such telescopes, cosmic ...gamma-rays are observed and have to be discriminated against a dominating background of hadronic cosmic-ray particles. We describe the application of RF for this gamma/hadron separation. The RF method often shows superior performance in comparison with traditional semi-empirical techniques. Critical issues of the method and its implementation are discussed. An application of the RF method for estimation of a continuous parameter from related variables, rather than discrete classes, is also discussed.
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.
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