Broadband X-ray Spectral Study of Ultra-luminous X-ray Source M81 X--6

Abstract: Ultra-luminous X-ray sources (ULXs) are a class of extra-galactic, point-like, off-nuclear X-ray sources with X-ray luminosity from $\sim 10^{39}$~erg s$^{-1}$ to $10^{41}$~erg s$^{-1}$. We investigated the temporal and broadband X-ray spectral properties of the ULX M81~X--6 using simultaneous \textit{Suzaku} and \textit{NuSTAR} observations. To understand the nature of the source, we searched for pulsating signals from the source using the \textit{NuSTAR} observation. However, we failed to identify any strong pulsating signals from the source. Alternatively, the broadband spectral modelling with accreting magnetic neutron star continuum model provides a statistically acceptable fit, and the inferred spectral parameters and X-ray colours are consistent with other pulsating ULXs. Thus, our analysis suggests that M81~X--6 is another candidate ULX pulsar.