Comment on "On the recurrence times of neutron star X-ray binary transients and the nature of the Galactic Center quiescent X-ray binaries"

TL;DR

This paper critiques a recent claim disputing the black hole nature of certain X-ray binaries near the Galactic Center, clarifying misunderstandings about recurrence times and population data, and reaffirming their original conclusions.

Contribution

It provides a detailed rebuttal to TM22's arguments, clarifying the evidence supporting black hole candidates and correcting misconceptions about neutron star X-ray binary properties.

Findings

Most of the 12 sources are likely black hole low-mass X-ray binaries.

Misunderstandings about neutron star recurrence times are addressed and corrected.

The original classification of sources as black hole candidates is reaffirmed.

Abstract

In 2018, we reported our discovery of a dozen quiescent X-ray binaries in the central parsec (pc) of the Galaxy (Hailey et al. 2018). In a recent follow-up paper (Mori et al. 2021), we published an extended analysis of these sources and other X-ray binaries (XRBs) in the central pc and beyond, showing that most if not all of the 12 non-thermal sources are likely black hole low-mass X-ray binary (BH-LMXB) candidates. In response, Maccarone et al. 2022 (TM22 hereafter) argued, primarily on the claim that neutron star low-mass X-ray binaries (NS-LMXBs) often do not have short outburst recurrence times (<~ 10 yr), that they cannot be excluded as a designation for the 12 quiescent X-ray binary sources. TM22 cites three main factors in their study: (1) X-ray outburst data of NS transients detected by RXTE and MAXI, (2) the Galactic population of NS-LMXBs, and (3) (persistently) quiescent NS-LMXBs in globular clusters. We address these arguments of TM22 and correct their misunderstandings of our work and the literature, even though most of these points have already been thoroughly addressed by Mori et al. 2021. We also correct TM22's assertion that our arguments are based solely on NS transients' recurrence times.