Long-term X-ray outbursts studies of 42 transient low mass X-ray binaries using MAXI and Swift/BAT: Black Hole-Neutron Star distinction

In this work, using ~13 years of publicly available data from MAXI and Swift/BAT transient monitoring campaign, we have studied long-term source evolution of 42 transient low-mass X-ray binaries in 2-4 keV, 10-20 keV, and 15-50 keV respectively. The sample consists of 11 confirmed black hole X-ray binaries (BHXBs), 10 black hole candidates (BHC), and 21 neutron star X-ray binaries (NSXBs). Outbursts and flaring activities studied over 13 years show that 19/21 NSXBs spend significantly longer time in the hard state (observations for which hardness ratio is > 0.2) while only 15/21 BHXB+BHC spend significantly longer time in the soft state (observations for which hardness ratio is < 0.2). The frequency distribution of the hardness ratio clearly shows two distinct distributions for BHXBs and NSXBs, with their peaks clearly separated: NSXBs prefer harder values, while BHXBs prefer softer values of hardness. Candidate sources mostly show a `q' diagram in the HID and prefer to align with the HID distribution of black holes except for MAXI J1848-015. MAXI J1848-015 shows HID distribution similar to NSXBs. Therefore, long-term MAXI and Swift/BAT evolution of X-ray binaries may be used to distinguish black holes from neutron stars.