An Atypical Low-frequency Quasiperiodic Oscillation Detected in the Hard State of MAXI J1348–630 with Insight-HXMT

Based on the Insight-HXMT archival data, we have detected a new atypical low-frequency quasiperiodic oscillation (LFQPO) in the black hole X-ray binary MAXI J1348−630. The new LFQPO is detected in all three instruments of Insight-HXMT with a combined significance of 3 σ –5 σ , covering a wide energy range of 1–100 keV. The fractional rms seems to decrease with energy. It exclusively appears in the hard state during both the main and mini outburst, spanning an X-ray intensity range by a factor of 10, and a very narrow hardness range. The frequency of this new type of LFQPO is moderately stable, in the range of 0.08–0.15 Hz. We discussed different models for the LFQPO, and found none can explain the observed properties of this new type of LFQPO.