Comparing X-ray color selection in separating X-ray binary classes using Color-Color-Intensity diagrams

TL;DR

This study evaluates the effectiveness of Color-Color-Intensity diagrams, using MAXI data, in distinguishing black hole from neutron star X-ray binaries, confirming the method's universality across different instruments and color definitions.

Contribution

It tests and confirms the reliability of Color-Color-Intensity diagrams with MAXI data, extending previous findings beyond RXTE/ASM and exploring optimal color definitions for classification.

Findings

Color-Color-Intensity diagrams can distinguish black holes from neutron stars.

Certain energy bands are more effective for classifying individual sources.

The method shows universality across different instruments and color definitions.

Abstract

X-ray binaries exhibit a wide range of properties but there are few accepted methods to determine the nature of the compact object. Color-Color-Intensity diagrams have been suggested as a means of distinguishing between systems containing black holes from those containing neutron stars. However, this technique has been verified with data from only one instrument (RXTE/ASM) with a single set of X-ray colors defined using data available only in pre-determined energy bands. We test a selection of X-ray colors with a more sensitive instrument to determine the reliability of this method. We use data from the MAXI Gas Slit Camera, which allows users to specify energy-bands. We test X-ray colors that have been previously defined in the literature as well as ones that we define specifically in this paper. A representative set of systems are used to construct Color-Color-Intensity diagrams in each set of colors to determine which are best for separating different classes. For studying individual sources certain bands are more effective than others. For a specified energy range, the separation of soft states in black hole binaries was possible only where both soft and hard colors included information from the lowest energy band. We confirm that Color-Color-Intensity diagrams can distinguish between systems containing black holes or neutron stars in all X-ray colors tested; this suggests an universality in the accretion processes governing these different classes. We suggest possible physical processes driving different classes of X-ray binaries to different locations in Color-Color-Intensity diagrams.