Multiplexing lobster-eye optics: a concept for wide-field X-ray monitoring

TL;DR

This paper introduces a multiplexing lobster-eye (MuLE) optical design that reduces the number of imagers needed for wide-field X-ray monitoring, enabling efficient detection of transient X-ray sources with fewer sensors.

Contribution

The paper proposes a novel MuLE configuration that segments lobster-eye optics and uses multiplexing to minimize the number of focal plane imagers required.

Findings

Simulated MuLE configuration can cover ~1 sr of sky with 4 imagers.

Detected transient flux limit of ~2 x 10^-10 erg cm^-2 s^-1 (0.5-2 keV).

Transient source direction can be determined with 99.7% confidence.

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.