Following the discovery of 3:2 resonance quasi-periodic oscillations ( QPOs ) in M82X-1 ( Pasham et al .
2014 ) , we have constructed power density spectra ( PDS ) of all 15 ( sufficiently long ) XMM-Newton observations of the ultraluminous X-ray source NGC1313X-1 ( L _ { X } \approx 2 \times 10 ^ { 40 } erg/sec ) .
We detect a strong QPO at a frequency of 0.29 \pm 0.01 Hz in data obtained on 2012 December 16 .
Subsequent searching of all the remaining observations for a 3:2/2:3 frequency pair revealed a feature at 0.46 \pm 0.02 Hz on 2003 Dec 13 ( frequency ratio of 1.59 \pm 0.09 ) .
The global significance of the 0.29 Hz feature considering all frequencies between 0.1 and 4 Hz is > 3.5 \sigma .
The significance of the 0.46 \pm 0.02 Hz QPO is > 3.5 \sigma for a search at 2/3 and 3/2 of 0.29 Hz .
We also detect lower frequency QPOs ( 32.9 \pm 2.6 and 79.7 \pm 1.2 mHz ) .
All the QPOs are super-imposed on a continuum consisting of flat-topped , band-limited noise , breaking into a power-law at a frequency of 16 \pm 3 mHz and white noise at \gtrsim 0.1 Hz .
NGC1313X-1 ’ s PDS is analogous to stellar-mass black holes ’ ( StMBHs ) PDS in the so-called steep power-law state , but with the respective frequencies ( both QPOs and break frequencies ) scaled down by a factor of \sim 1000 .
Using the inverse mass-to-high-frequency QPO scaling of StMBHs , we estimate NGC1313X-1 ’ s black hole mass to be 5000 \pm 1300 M _ { \odot } , consistent with an inference from the scaling of the break frequency .
However , the implied Eddington ratio , L _ { Edd } > 0.03 \pm 0.01 , is significantly lower compared to StMBHs in the steep power-law state ( L _ { Edd } \gtrsim 0.2 ) .