Fermi Gamma-ray Space Telescope

Recent results of MAXI all-sky X-ray survey on the ISS

Mutsumi Sugizaki
(N. Kawai, M. Matsuoka, T. Mihara, S. Nakahira, H. Negoro, M. Nakajima, T. Sakamoto, M. Serino, S. Sugita, S. Ueno, H. Tomida, Y. Ueda, Y. Tsuboi, W. Iwakiri, H. Tsunemi, M. Yamauchi, T. Kawamuro, K. Yamaoka, M. Shidatsu, and MAXI Team)


MAXI (Monitor of All-sky X-ray Image) is an X-ray astronomical mission that has been carried out on the ISS (International Space Station) since 2009 August. The GSC (Gas Slit Camera) on board has been scanning the whole sky every 92 minutes for over 9 years. By the systematic search for transient X-ray sources, we have discovered 21 new X-ray objects which include 7 black-hole binaries, 11 neutron-star binaries, 1 white-dwarf binary. The origins of 2 objects out of the 21 have not been identified. In the recent two years, 3 remarkable new transients that brightened up to the several Crab, MAXI J1535-571, MAXI J1820+070, and Swift J0243.6+6124, appeared. MAXI monitoring observations revealed their throughout outburst evolution. On the course of these analysis process, short transient events identified as gamma-ray bursts (GRBs) or X-ray bursts (XRBs), and recurrent events from known X-ray objects were also detected. The information about possible GRBs are sent to the GCN. we have posted 14 GCN circulars in these 2 years. We also reported important new/recurrent events in the Astronomer's Telegram and the MAXI mailing list. The MAXI all-sky source catalogs were created from the detailed image analysis. The 1st MAXI catalog (682 sources) in the high Galactic-latitude sky (Kawamuro et al. 2018) and the 1st catalog (214 sources) in the low Galactic-latitude sky (Hori et al. 2018) have been released. Since the LIGO/Virgo gravitational-wave (GW) experiments started in 2015, our MAXI team join the collaboration to search for the electromagnetic counterparts. We reported X-ray upper limits on three GW events (Kawai et al. 2017, Serino et al. 2017, Sugita et al. 2018). As for GW 170817/GRB 170817A, the GSC field of views passed through the source location a few minutes after the event. However, the GSC gas counters were turned off at that time, because the ISS was in the heavy radiation zone. The first MAXI observation of the GW 170817/GRB 170817A location was then carried out 4.6 hours later. We are now optimizing the operation scheme for the GW counterpart search. We started cooperation with NICER, the new X-ray mission on ISS started in 2017. So far, NICER observations of new transients and recurrent stellar flares detected by MAXI were carried out via e-mail communications. We develop the ISS-onboard system to enable immediate NICER observations of new MAXI transients within a few minutes, under the project named by OHMAN (On-orbit Hookup of MAXI And NICER).