MAXI
Monitor of All-sky X-ray Image (MAXI) on JEM-EF
Mission Descriptions
Overview
The Monitor of All-sky X-ray Image (MAXI) is a Japanese instrument installed on the Exposed Facility of the Japanese Experiment Module "Kibo" on the International Space Station (ISS) in August 2009. The mission's objective is to monitor X-rays from the entire sky and discover new X-ray sources and transient X-ray phenomena. MAXI is operated by a team comprising the RIKEN Institute, the Japan Aerospace Exploration Agency (JAXA), and various universities and research institutions.
About the Observation Instruments
MAXI is designed based on the observation principle of using slit cameras and one-dimensional position detection. The slit camera guides X-rays incident from a specific direction through the slit to the detector, and the one-dimensional position detector measures its position to identify the location of the X-ray source.
GSC (Gas Slit Camera)
The Gas Slit Camera (GSC) uses a large-area Xe gas proportional counter to detect X-rays in the 2-20 keV energy range. This instrument has the capability to scan over 60% of the entire sky every 92 minutes and more than 90% of the sky in a single day. The GSC enables high-sensitivity observations over a wide energy range, contributing to the rapid detection of transient X-ray phenomena.
SSC (Solid-state Slit Camera)
The Solid-state Slit Camera (SSC) uses X-ray CCDs to detect X-rays in the 0.7-7 keV energy range. Although the SSC's observation range is narrower compared to the GSC, it can scan approximately 20% of the sky. The SSC has relatively high energy resolution, enabling spectral observations of bright point sources and diffuse X-ray emissions spread across the sky.
Achievements
MAXI/GSC has the capability to transmit data to the ground in real-time, enabling the rapid detection of transient X-ray phenomena. At JAXA's Tsukuba Space Center, the MAXI transient object detection system monitors data, and if unknown objects appear or unexpected variations occur in known objects, it sends out new object information via email and through GCN (Gamma-ray Coordinates Network) and ATel (The Astronomer's Telegram). This system has established a framework in which telescopes around the world can collaborate for follow-up observations. This has made it possible to observe the details of high-density stars' outbursts (explosive activities), revealing the entire activity over periods ranging from tens to hundreds of days. Recently, the OHMAN experiment (On-Orbit Hookup of MAXI and NICER) has established a system that allows follow-up observations in as fast as about 2 minutes by directly linking with NASA's NICER X-ray telescope onboard the ISS.
Furthermore, utilizing MAXI's wide field of view, the luminosity variations of hundreds of celestial objects have been continuously observed over 15 years, and these data have been released by RIKEN. Additionally, the soft X-ray all-sky map created using the high energy resolution of MAXI/SSC has provided a more detailed distribution of X-rays across the celestial sphere.