Fig. 11.
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Hardness ratio comparison. Top panel: hardness ratio of each FXT candidate (using the Bayesian BEHR code; Park et al. 2006) at 1σ confidence level. Bottom panel: hardness-ratio distributions of our final samples of FXTs (orange histogram), compared to the X-ray transients classified as “stars” by Criterion 2 using Gaia (filled cyan histogram) and the sources identified previously as distant FXTs (blue histogram) by Paper I.
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