MAXI2

MAXI2 is a second‑generation X‑ray astronomy instrument developed by the Japanese Aerospace Exploration Agency (JAXA) for use on the International Space Station (ISS). It is part of the Monitor of All‑sky X‑ray Image (MAXI) series, which began in 2009 with the original MAXI. MAXI2 builds on the earlier design by incorporating a larger detector array and improved angular resolution, enabling more precise localization of transient X‑ray sources such as gamma‑ray bursts, supernovae, and accreting compact objects.

The instrument uses a set of coded‐mask cameras constructed from cadmium zinc telluride (CZT) detectors. These detectors are arranged in a 2‑dimensional grid and are sensitive to X‑ray photons in the 2–30 keV energy range. MAXI2’s coded‑mask optics provide a field of view covering up to 30% of the sky at any given time, allowing continuous monitoring of the X‑ray sky from orbit.

MAXI2 was launched aboard the Japanese H-IIA‑01 rocket in 2021 and installed on the Japanese Experiment Module (KIBO) of the ISS. Its primary scientific objectives include detecting and localizing transient X‑ray events, mapping the distribution of persistent X‑ray sources, and contributing to multi‑wavelength studies of astrophysical phenomena. Data generated by MAXI2 are publicly released through the JAXA data archive, facilitating collaboration among the global astronomical community.

Operation of MAXI2 involves a combination of Earth‑pointed scans and 360° sky surveys. The instrument’s real‑time data processing pipeline extracts source positions and fluxes, and sends alerts to ground‑based observatories within minutes of detection. Over the course of its mission, MAXI2 has detected hundreds of variable X‑ray sources and contributed to the discovery of several new gamma‑ray burst counterparts.

In addition to its scientific role, MAXI2 serves as a technological demonstrator for future high‑energy astronomical instruments, providing valuable experience in space‑borne detector development, coded‑mask imaging, and autonomous data handling systems.