Spectral variability in M74 ULX-1

We conducted an extensive long-term spectral and timing study on the Ultraluminous X-ray source M74 X-1, using data taken between 2001 and 2021 by Chandra and XMM-Newton X-ray observatories. Our analysis reveals variations in the presence of flares across different observations. Flaring observations exhibit two-component spectra at a lower average flux level. On the other hand, the non-flaring observations display single-component spectra at a higher average flux level. These spectra are best described by the diskbb+comptt, diskbb+diskbb, and diskpbb models. With the diskbb+comptt model, we obtain a low plasma temperature (Te ~ 2.0 keV) and a high optical depth of the corona, typical of ULXs, in contrast with the high temperature and low optical depth seen in Galactic Black Hole Binaries. Using the diskbb + diskbb model, we get cool and hot temperatures of Tin(cool) = 0.38^{+0.08}_{-0.06} keV and Tin(hot) = 1.67^{+0.18}_{-0.13} keV, respectively, suggesting two temperature emitting regions indicating possible presence of outflowing wind along with the accretion disk. We found a Gaussian feature at E_{line} = 0.96^{+0.05}_{-0.11} keV with sigma = 0.11^{+0.13}_{-0.06} keV in flaring observations, indicative of powerful optically thick outflows, which is not significant in non-flaring observations. This variation can be explained by changes in wind funnel geometry with the accretion rate. Additionally, using the hot diskbb component from the diskbb + diskbb model, we estimate the mass of the compact object to be M = 7.1^{+1.4}_{-1.3} Mo, classifying it as a stellar-mass black hole and confirming super-Eddington accretion in the system.