Abstract
We propose a concept of multiplexing lobster-eye (MuLE) optics to achieve significant reductions in the number of focal plane imagers in lobster-eye (LE) wide-field X-ray monitors. In the MuLE configuration, an LE mirror is divided into several segments and the X-rays reflected on each of these segments are focused on a single image sensor in a multiplexed configuration. If each LE segment assumes a different rotation angle, the azimuthal rotation angle of a cross-like image reconstructed from a point source by the LE optics identifies the specific segment that focuses the X-rays on the imager. With a focal length of 30 cm and LE segments with areas of 10 x 10 cm^2, ~1 sr of the sky can be covered with 36 LE segments and only four imagers (with total areas of 10 x 10 cm^2). A ray tracing simulation was performed to evaluate the nine-segment MuLE configuration. The simulation showed that the flux (0.5 to 2 keV) associated with the 5-sigma detection limit was ~2 x 10^-10 erg cm^-2 s^-1 (10 mCrab) for a transient with a duration of 100 s. The simulation also showed that the direction of the transient for flux in the range of 14 to 17 mCrab at 0.6 keV was determined correctly with 99.7% confidence limit. We conclude that the MuLE configuration can become an effective on-board device for small satellites for future X-ray wide-field transient monitoring.
Highlights
Wide-field x-ray monitors have been proven to be indispensable devices in time-domain astronomy in recent years
One of the possible configurations of the multiplexing lobster-eye (MuLE) optics consists of nine tiled segments, as shown in Fig. 3, in which an azimuthal rotation angle of each LE segment increments 10 deg from 0 deg to 80 deg
Imager sized aScan angles are measured from the center of the FoV of each LE segment. bShadows induced by the radial spokes are included. cThese values were obtained from our silicon–microelectromechanical systems (Si–MEMS) manufacturing experience. d4k × 4k square pixels
Summary
Wide-field x-ray monitors have been proven to be indispensable devices in time-domain astronomy in recent years. Tamagawa et al.: Multiplexing lobster-eye optics: a concept for wide-field x-ray. In multimessenger astronomy, the use of a device that constantly monitors the universe with a wide field-of-view (FoV) in the x-ray energy band is essential. Lobster-eye (LE) optics[13] represents the best possible observation equipment for missions that require a wide FoV and increased sensitivity. The all-sky monitor mission LOBSTER requires a detector area spanning 5000 cm[2] to cover ∼1∕4 of the entire sky.[17] In this study, we describe the design, feasibility, and performance evaluation of a newly proposed idea of LE optics to reduce the number of imagers
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