MAXI: all-sky observation from the International Space Station

TL;DR

MAXI is an all-sky X-ray monitor on the ISS that has been detecting and cataloging X-ray sources since 2009, despite technical challenges, and has discovered several new black holes and X-ray phenomena.

Contribution

This paper reports the operational experience, technical challenges, and scientific discoveries of MAXI, including the detection of new black holes and diffuse X-ray emissions over 4.5 years.

Findings

Detected 500 sources above ~0.6 mCrab in 4-10 keV

Discovered 6 of 12 new black holes

Identified two types of outburst behaviors in black holes

Abstract

Monitor of All-sky X-ray Image (MAXI) is mounted on the International Space Station (ISS). Since 2009 it has been scanning the whole sky in every 92 minutes with ISS rotation. Due to high particle background at high latitude regions the carbon anodes of three GSC cameras were broken. We limit the GSC operation to low-latitude region around equator. GSC is suffering a double high background from Gamma-ray altimeter of Soyuz spacecraft. MAXI issued the 37-month catalog with 500 sources above ~0.6 mCrab in 4-10 keV. MAXI issued 133 to Astronomers Telegram and 44 to Gammaray burst Coordinated Network so far. One GSC camera had a small gas leak by a micrometeorite. Since 2013 June, the 1.4 atm Xe pressure went down to 0.6 atm in 2014 May 23. By gradually reducing the high voltage we keep using the proportional counter. SSC with X-ray CCD has detected diffuse soft X-rays in the all-sky, such as Cygnus super bubble and north polar spur, as well as it found a fast soft X-ray nova MAXI J0158-744. Although we operate CCD with charge-injection, the energy resolution is degrading. In the 4.5 years of operation MAXI discovered 6 of 12 new black holes. The long-term behaviors of these sources can be classified into two types of the outbursts, 3 Fast Rise Exponential Decay (FRED) and 3 Fast Rise and Flat Top (FRFT). The cause of types is still unknown.