Boutloukos et al .
( 2006 ) discovered twin-peak quasi-periodic oscillations ( QPOs ) in 11 observations of the peculiar Z-source Circinus X-1 .
Among several other conjunctions the authors briefly discussed the related estimate of the compact object mass following from the geodesic relativistic precession model for kHz QPOs .
Neglecting the neutron star rotation they reported the inferred mass M _ { 0 } = 2.2 \pm 0.3 M _ { \odot } .
We present a more detailed analysis of the estimate which involves the frame-dragging effects associated with rotating spacetimes .
For a free mass we find acceptable fits of the model to data for ( any ) small dimensionless compact object angular momentum j = cJ / GM ^ { 2 } .
Moreover , quality of the fit tends to increase very gently with rising j .
Good fits are reached when M \sim M _ { 0 } [ 1 + 0.55 ( j + j ^ { 2 } ) ] .
It is therefore impossible to estimate the mass without the independent knowledge of the angular momentum and vice versa .
Considering j up to 0.3 the range of the feasible values of mass extends up to 3 M _ { \sun } .
We suggest that similar increase of estimated mass due to rotational effects can be relevant for several other sources .