  Recently LIGO and VIRGO collaborations reported about observation of
gravitational-wave signal corresponding to the inspiral and merger of two black
holes, resulting into formation of the final black hole. It was shown that the
observations are consistent with the Einstein theory of gravity with high
accuracy limited mainly by the statistical error. Angular momentum and mass of
the final black hole were determined with rather large allowance of tens of
percents. Here we shall show that this indeterminacy in the range of the
black-hole parameters allows for some not negligible deformations of the Kerr
spacetime leading to the same frequencies of black-hole ringing. This means
that at the current precision of the experiment there remain some possibilities
for alternative theories of gravity.

General Relativity and Quantum Cosmology;High Energy Astrophysical Phenomena;High Energy Physics - Theory