A Possible Discovery of the Optical Counterpart of the X-ray source NuSTAR J053449+2126.0

We report the observation of a possible optical counterpart to the recently discovered X-ray source NuSTAR J053449+2126.0 (J0534 in short). We observed the source location using the 1.5-m Telescope (RTT150) to search for an optical counterpart, and detected a possible optical counterpart and analysed its spectrum using the $B$, $V$, $R$, and $I$ images of J0534, and found that the possible optical counterpart of J0534 is likely to be a long-known optical source, namely PSO J083.7063+21.4333. However, this source has been misclassified as a star rather than being an extragalactic source. We determined the source distance accurately for the first time based on our spectral analysis. J0534 could be a high-redshift ($z\simeq2.2$) member of an Active Galactic Nucleus (AGN) sub-group identified as quasars. Our analysis favours an accreting black hole of mass $\sim 7\times 10^8 M_{\odot}$ as a power supply for the quasar. Further observations in optical and other wavelengths are needed to confirm its precise nature.