A Consistency Relation for the Observed Galaxy Bispectrum and the Local
  non-Gaussianity from Relativistic Corrections
  We obtain a consistency relation for the observed three-point correlator of
galaxies. It includes relativistic effects and it is valid in the squeezed
limit. Furthermore, the consistency relation is non-perturbative and can be
used at arbitrarily small scales for the short modes. Our results are also
useful to compute the non-linear relativistic corrections which induce a signal
in the observations that might be misinterpreted as primordial non-Gaussianity
with a local shape. We estimate the effective local non-Gaussianity parameter
from the relativistic corrections. The exact value depends on the redshift and
the magnification bias. At redshift of $ z = 1$, in the absence of
magnification bias, we get $\,\, f^{\rm GR}_{\rm NL} \simeq - 3.7 $.
