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As a novel X-ray focusing technology, lobster eye micro-pore optics (MPO) feature both a wide observing field of view and true imaging capability, promising sky monitoring with significantly improved sensitivity and spatial resolution in soft X-rays. Since first proposed by Angel (1979), the optics have been extensively studied, developed and trialed over the past decades. In this Letter, we report on the first-light results from a flight experiment of the Lobster Eye Imager for Astronomy ($LEIA$), a pathfinder of the wide-field X-ray telescope of the Einstein Probe mission. The piggyback imager, launched in July 2022, has a mostly un-vignetted field of view of $18.6^\circ \times 18.6^\circ $. Its spatial resolution is in the range of 4$-$7 arcmin in FWHM and the focal spot effective area is 2$-$3 cm$^2$, both showing only mild fluctuations across the field of view. We present images of the Galactic center region, Sco X-1 and the diffuse Cygnus Loop nebular taken in snapshot observations over 0.5$-$4 keV. These are truly wide-field X-ray images of celestial bodies observed, for the first time, by a focusing imaging telescope. Initial analyses of the in-flight data show excellent agreement between the observed images and the on-ground calibration and simulations. The instrument and its characterization are briefly described, as well as the flight experiment. The results provide a solid basis for the development of the present and proposed wide-field X-ray missions using lobster eye MPO., Comment: 11 pages, 4 figures. Accepted for publication in Astrophysical Journal Letter

This paper presents a numerical study onfree-surface flow in curved open channel. An improved SIMPLEC algorithm with velocity-pressure-free-surface coupled correction is developed and validated. Such algorithm differs from the traditional SIMPLEC algorithm and includes three correction equations which are named as the velocity correction equation, the free-surface correction equation derived from the continuity equation with the kinematic boundary conditions on the free-surface and the bottom bed, and the pressure correction equation taking the same formulation as the traditional SIMPLEC algorithm does. In this study, the improved method is used to solve the incompressible, three-dimensional, Reynolds-averaged Navier–Stokes equation set combined with the standard k–ɛ model and/or the low Reynolds number k–ɛ model for free-surface viscous flow in curved open channels. The power law scheme (POW) is used to discretize the convection terms in these equations with a finite-volume method. The practical cases studied are free-surface flow through the 180° curved open channel with different hydraulic discharge rates. The comparisons between computations and experiments reveal that the model is capable of predicting the detailed velocity field, including changes in secondary motion, the distribution of bed shear, and the variations of flow depth in both the transverse and the longitudinal directions. In summary, the improved SIMPLEC algorithm is feasible and effective for numerical study of free-surface viscous flows in curved open channels.