We present the results of our study of the X-ray spectrum for the source X-6 in the nearby galaxy M33 obtained for the first time at energies above 10 keV from the data of the NuSTAR orbital telescope .
The archival Swift -XRT data for energy coverage below 3 keV have been used , which has allowed the spectrum of M33 X-6 to be constructed in the wide energy range 0.3–20 keV .
The spectrum of the source is well described by the model of an optically and geometrically thick accretion disk with a maximum temperature of \sim 2 keV and an inner radius of \sim 5 \cos ^ { -1 / 2 } \theta km ( where \theta is the unknown disk inclination angle with respect to the observer ) .
There is also evidence for the presence of an additional hard component in the spectrum .
The X-ray luminosity of M33 X-6 measured for the first time in the wide energy range 0.3–20 keV is \sim 2 \times 10 ^ { 38 } erg s ^ { -1 } , with the luminosity in the hard 10–20 keV X-ray band being \sim 10 % of the source’s total luminosity .
The results obtained suggest that X-6 may be a Z -source , i.e. , an X-ray binary with subcritical accretion onto a weakly magnetized neutron star .