Gamma-ray bursts (GRBs) rank among the most powerful explosions in the Universe, releasing immense energy in intense flashes of gamma rays. The most distant GRBs originate from the era when the first stars and galaxies formed. Detecting them allows astronomers to probe the early Universe and understand how the first heavy elements formed and how the earliest stellar populations lived and died. Missions like HiZ-GUNDAM, a satellite planned for launch in the 2030s by the Japan Aerospace Exploration Agency (JAXA), aim to detect these distant explosions in real time.
However, detecting GRBs presents a major challenge. These explosions appear unpredictably across the sky, and their afterglows fade rapidly. Astronomers must therefore detect each burst quickly and determine its position immediately so that other telescopes can observe it. Wide-field X-ray monitors provide one solution, as they can observe large regions of the sky and determine the direction of incoming signals. Some designs use lobster-eye X-ray optics, inspired by the way lobsters’ compound eyes collect light from many directions simultaneously. Yet building a single optical system from multiple lobster-eye segments and aligning them precisely remains a difficult technical task.
In the Journal of Astronomical Telescopes, Instruments, and Systems , researchers addressed this challenge by developing a practical method to align lobster-eye X-ray optics for space telescopes. The team led by Hatsune Goto from Kanazawa University, Japan, designed and tested an alignment strategy for EAGLE, the wide-field X-ray monitor planned for the HiZ-GUNDAM mission.
EAGLE uses devices called Micro Pore Optics (MPOs), which are thin glass plates with microscopic channels. When X-rays enter at a shallow angle, they reflect off the channel walls and focus onto a detector, forming a distinctive cross-shaped image. The position of that cross tells astronomers where in the sky the X-rays came from. A single EAGLE module uses nine MPO segments arranged on a curved surface, and getting all segments to focus as close as possible to the same point is critical. Even slightly misalignments cause their images to fall at different positions on the detector, reducing localization accuracy.
To determine how precisely the segments needed to be aligned, the research team first conducted Monte Carlo simulations. They found that keeping inter-segment offsets within five arcminutes (about one-twelfth of a degree) was enough to meet the mission’s localization goal of three arcminutes. With that target in hand, they physically tested seven MPO segments at the 27-meter X-ray beamline at the Institute of Space and Astronautical Science under JAXA, measuring each segment's focal length and how its focused image shifted with the angle of incoming X-rays.
Based on these measurements, the team selected four segments with closely matched focal lengths and minimal distortion and mounted them on a prototype structure representing one EAGLE module. Using small precision motors, the researchers adjusted the tilt of each segment in real time while monitoring the X-ray images. Through repeated cycles of measurement and adjustment, they brought all four segments into precise alignment. “The estimated incident angles exhibited systematic uncertainties of less than three arcminutes over more than 95% of the field of view. This level of performance satisfies the localization requirement for the EAGLE instrument when considering systematic errors intrinsic to the MPO-based detection system,” Goto said.
These results open the door to scaling the proposed approach toward a full nine-segment array and, eventually, the 16-module EAGLE instrument. “Our present results demonstrate the feasibility of precise MPO alignment in a segmented lobster-eye optics system and provide practical feedback for the design, alignment strategy, and mechanical tolerance definition of future engineering and flight models of the EAGLE X-ray optics,” Goto said. Future work will include testing the optics under thermal and vibration conditions that simulate launch and spaceflight, evaluating performance across a broader range of X-ray energies, and refining the calibration methods used to reconstruct source directions.
If EAGLE successfully meets its performance targets, HiZ-GUNDAM will be able to precisely localize distant GRBs, enabling astronomers to study these fascinating cosmic explosions in detail.
Read the Gold Open Access paper by Goto et al., “Construction and mechanical alignment method of wide-field X-ray monitor with lobster-eye optics onboard HiZ-GUNDAM,” J. Astron. Telesc. Intrum. Syst. 12(1) 014007 doi: 10.1117/1.JATIS.12.1.014007
Not applicable
Construction and mechanical alignment method of wide-field X-ray monitor with lobster-eye optics onboard HiZ-GUNDAM
26-Mar-2026