Discovery of a Quasi-Periodic Oscillation in the Ultraluminous X-ray Source IC 342 X-1: XMM-Newton Results

TL;DR

This paper reports the discovery of a quasi-periodic oscillation in the ultraluminous X-ray source IC 342 X-1, providing insights into its spectral properties and possible black hole mass, based on XMM-Newton and NuSTAR observations.

Contribution

The study is the first to identify a QPO in IC 342 X-1 and links its spectral characteristics to black hole mass estimates, advancing understanding of ULX variability.

Findings

QPO at 642 mHz detected with high significance

Spectral modeling suggests a black hole mass of 20-65 solar masses

QPO is energy-dependent and transient, not always present

Abstract

We report the discovery of a quasi-periodic oscillation (QPO) at 642 mHz in an {\it XMM-Newton} observation of the ultraluminous X-ray source (ULX) IC 342 X-1. The QPO has a centroid at $\nu_{QPO} = 642 \pm 20$ mHz, a coherence factor of $ Q = 11.6$, and an amplitude (rms) of 4.1\% with significance of $3.6\sigma$. The energy dependence study shows that the QPO is stronger in the energy range 0.3 - 5.0 keV. A subsequent observation (6 days later) does not show any signature of the QPO in the power density spectrum. The broadband energy spectra (0.3 - 40.0 keV) obtained by quasi-simultaneous observations of {\it XMM-Newton} and {\it NuSTAR} can be well described by an absorbed {\it diskbb} plus {\it cutoffpl} model. The best fitted spectral parameters are power-law index ($\Gamma$) $\sim$ 1.1, cutoff energy ($E_c$) $\sim$ 7.9 keV and disc temperature ($kT_{in}$) $\sim$ 0.33 keV, where the QPO is detected. The unabsorbed bolometric luminosity is $\sim$ 5.34$\times$ 10$^{39}$ erg~s$^{-1}$. Comparing 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 $\sim 20 - 65 ~ M_\odot$. We discuss the possible implications of our results.