We have started an immediate X-ray follow-up observation program named "OHMAN (On-orbit Hookup of MAXI and NICER)" on August 10, 2022, and the first coordinated observation was successfully completed on September 13, 2022. This project consists of two instruments on-board the International Space Station (ISS); JAXA's MAXI all-sky monitor to detect sudden bursts in X-ray phenomena that occur anywhere at any time across the sky, and NASA's NICER high-precision X-ray telescope that can then turn towards these identified targets immediately. The search for these transient X-ray bursts and the follow-up observation are fully automated on the ISS, which reduces the follow-up time from 3 hours on the ground to 10 minutes. OHMAN is expected to provide new insights into rapidly dimming X-ray objects within an hour after the burst.
OHMAN is an international joint project carried out in the Japan-US Open Platform Partnership Program (JP-US OP3). Its software development was supported by the "S (small) Class Program" of the Institute of Space and Astronautical Science (ISAS), so that the MAXI data are automatically analyzed, and alerts are sent to NICER using a computer installed on the ISS. The S Class Program is an open call to maximize results with a limited budget, and OHMAN was a very suitable project to realize innovative observations through only software improvements.
Researchers and students affiliated with ISAS contributed to the development of OHMAN. Development of the communication processing module and design of the software was carried out by NAKAHIRA Satoshi, associate senior researcher of the Science Satellite Operation and Data Application Unit (C-SODA). The software update from Windows 7 to Windows 10 was made by Nakahira and Professor EBISAWA Ken and graduate student NAGATSUKA Tomoki (University of Tokyo's Graduate School of Science) of the Department of Astrophysics. They made a significant contribution to start OHMAN on the ISS.
MAXI's data archive is available from DARTS (https://darts.isas.jaxa.jp/) at ISAS/JAXA. To maximize the use of MAXI's real-time observation data, we are updating the public data archive within about 10 minutes from the observation. It will allow researchers worldwide to validate and conduct a detailed analysis of the X-ray transients discovered by MAXI.