MAXI/SSC All-sky maps from 0.7 keV to 4 keV

TL;DR

This paper presents all-sky diffuse X-ray background maps from 0.7 to 4 keV using MAXI/SSC data, revealing structures consistent with previous ROSAT observations and providing new insights into the Galactic diffuse emission.

Contribution

First all-sky diffuse X-ray maps in multiple energy bands derived from MAXI/SSC data, enabling comparison with ROSAT and revealing extended structures in the Galactic X-ray emission.

Findings

Detection of a bright arc-like structure at 0.7--1.0 keV similar to ROSAT results

Identification of a larger, elongated elliptical structure centered near the Galactic center

Spectral analysis indicating thin thermal plasma with ~0.31 keV temperature

Abstract

By accumulating data from the Solid-state Slit Camera (SSC) on board the MAXI mission for 2 years from 2009 to 2011, diffuse X-ray background maps were obtained in energies of 0.7--1.0, 1.0--2.0, and 2.0--4.0 keV. They are the first ones that were derived with a solid-state instrument, and to be compared with the previous ROSAT all sky survey result. While the SSC map in the highest energy band is dominated by point sources and the Galactic Diffuse X-ray emission, that in 0.7--1.0 keV reveals an extended X-ray structure, of which the brightness distribution is very similar to that observed with ROSAT about 20 years before. Like in the ROSAT result, the emission is dominated by a bright arc-like structure, which appears to be a part of a circle of $\sim 50^\circ$ radius centered at about $(l, b) \sim (340^\circ, 15^\circ)$. In addition, the SSC map suggests a fainter and larger ellipse, which is elongated in the north-south direction and roughly centered at the Galactic center. The spectrum of these structures is explained as thin thermal emission from a plasma, with a temperature of $\sim 0.31$ keV and an abundance of $\sim0.3$ Solar. Based on SSC observation conditions including the low Solar activity, the Solar Wind Charge Exchange signals are estimated to be negligible in the present SSC maps, as well as in the $>0.56$ keV ROSAT map. A brief discussion is given to the obtained results.