2015MNRAS.446.3926A

We report the discovery of a quasi-periodic oscillation (QPO) at 642 mHz in an XMM-Newton observation of the ultraluminous X-ray source (ULX) IC 342 X-1. The QPO has a centroid at νQPO = 642±20 mHz, a coherence factor Q = 11.6 and an amplitude (rms) of 4.1 percent with significance of 3.6σ. The energy dependence study shows that the QPO is stronger in the energy range 0.3-5.0 keV. A subsequent observation (6 d later) does not show any signature of the QPO in the power-density spectrum. The broad-band energy spectra (0.3-40.0 keV) obtained by quasi-simultaneous observations of XMM-Newton and NuSTAR can be described well by an absorbed diskbb plus cutoffpl model. The best-fitting spectral parameters are power-law index (Γ) ∼ 1.1, cut-off energy (Ec) ∼ 7.9 keV and disc temperature (kTin) ∼ 0.33 keV where the QPO is detected. The unabsorbed bolometric luminosity is ∼ 5.34x10³⁹ erg/s. Comparing this with the well-known X-ray binary GRS 1915+105, our results are consistent with the mass of the compact object in IC 342 X-1 being in the range ∼ 20-65M_☉. We discuss the possible implications of our results.