Grazing incidence mirrors for X–ray astronomy are usually designed in the parabola-hyperbola (Wolter I) configuration. This design allows for optimal images on-axis, which however degrade rapidly with the off-axis angle. Mirror surfaces described by polynomia (with terms higher than order two), have been put forward to improve the performances over the field of view. Here we present a refined p...

High energy gamma-ray astronomy has recently made significant progresss through ground-based instruments like the H.E.S.S. array of imaging atmospheric Cherenkov telescopes. The unprecedented angular resolution and the large field of view has allowed to spatially resolve for the first time the morphology of gamma-ray sources in the TeV energy range. The experimental technique is described and t...

We report the discovery of an X-ray luminous galaxy cluster at z = 1.26. RXJ0848.9+4452 was selected as an X-ray cluster candidate in the ROSAT Deep Cluster Survey, on the basis of its spatial extent. Deep optical and near-IR imaging have revealed a galaxy overdensity around the peak of the X-ray Based in part on observations obtained at the W.M. Keck Observatory Based in part on observations o...

We obtained 98 R-band and 18 B, r, i images of the optical afterglow of GRB 060526 (z = 3.21) with the MDM 1.3m, 2.4m, and the PROMPT telescopes in Cerro Tololo over the 5 nights following the burst trigger. Combining these data with other optical observations reported in GCN and the Swift-XRT observations, we compare the optical and X-ray afterglow light curves of GRB 060526. Both the optical ...

INTRODUCTION In future satellite missions for X-ray astronomy, hard X-ray imaging will become one of the major observation techniques. It allows astronomers to observe the distribution of hard X-ray objects in the Universe with a high sensitivity. Since hard X-rays can penetrate thick absorbing materials, astronomers are able to discover many massive black holes embedded in thick gas. High-ener...