We have detected sub-TeV gamma-ray emission from the direction of the Galactic center (GC) using the CANGAROO-II Imaging Atmospheric Cerenkov Telescope. We detected a statistically significant excess at energies greater than 250 GeV. The flux was 1 order of magnitude lower than that of the Crab Nebula at 1 TeV with a soft spectrum proportional to . The signal centroid is consistent with the GC direction, and the Ϫ4.6‫5.0ע‬E observed profile is consistent with a pointlike source. Our data suggest that the GeV source 3EG J1746Ϫ2851 is identical to this TeV source, and we study the combined spectra to determine the possible origin of the gammaray emission. We also obtain an upper limit on the cold dark matter density in the Galactic halo.

We have detected gamma-ray emission at the 6 σ level at energies greater than 500 GeV from the supernova remnant RX J0852.0−4622 (G266.2−1.2) using the

Magnetic field is ubiquitous in the Universe and it plays essential roles in various astrophysical phenomena, yet its real origin and evolution are poorly known. This article reviews current understanding of magnetic fields in the interstellar medium, the Milky Way Galaxy, external galaxies, active galactic nuclei, clusters of galaxies, and the cosmic web. Particularly, the review concentrates on the achievements that have been provided by centimeter and meter wavelength radio observations. The article also introduces various methods to analyze linear polarization data, including synchrotron radiation, Faraday rotation, depolarization, and Faraday tomography.

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RM CLEAN is a standard method to reconstruct the distribution of cosmic magnetic fields and polarized sources along the line of sight (LOS) from observed polarization spectrum. This method is similar to the CLEAN algorithm for aperture synthesis radio telescope images but it is rather unclear in what cases RM CLEAN works well. In this paper, we evaluate the performance of RM CLEAN by simulating spectro-polarimetric observations of two compact sources located in the same LOS, varying the relative initial polarization angle and Faraday depth systematically. Especially, we focus on if the two polarized sources can be resolved in the Faraday depth space and how well the source parameters can be estimated. We confirm the previous studies that two sources cannot be resolved when they are closely located in the Faraday depth space for specific values of the relative initial polarization angle. Further, we calculate the chi-square value for the fit between the mock data of polarization spectrum and the one from RM CLEAN. Then we find that the chi-squared value is not always significantly large even when RM CLEAN gives wrong results.