Mass of cosmologically distant object in Earth frame The original paper on GW 150914 in PRL 116,06112 (2016), talks about black hole masses in the source frame and the detector frame, indicating that the black hole masses in the detector frame are scaled up by a factor of $1+z$, where z in the redshift (Table 1). I am having trouble understanding the physical meaning of "source mass in the detector (Earth) frame." How would an observer on Earth measure the mass of a cosmologically distant object? I guess they would measure the resulting effect on the metric tensor, the curvature of  space time. Is that right? Qualitatively, why would they see greater curvature? Does this have something to do with the fact that the cosmological scale factor on Earth is less than the cosmological scale factor at the source?
There is some related discussion in the Stack Exchange here
 A: The dynamics of black hole mergers contains only one length scale/time scale, set by the total mass of the binary. This means two mergers with the same parameters ( spin, mass ratio, etc.) but different total masses, produce exactly the same signal up to an overall scaling. This also means that the total mass of an observed black hole merger is completely degenerate with the red shift of the signal. The “detector frame” mass of an observed merger signal is a technical shorthand for the mass inferred assuming zero redshift.
Note that this degeneracy between total mass and redshift is universal to any purely gravitational method of measuring the mass. Besides measuring (and matching) the gravitational wave signal, this includes any method involving measuring the orbital periods, precession, eccentricity, etc.
A: Gravitational signals experience cosmological redshift in the same way light does.
Think of a spectral line for a distant object: we observe it with a "detector-frame" wavelength $\lambda = \lambda_0 (1+z)$, while its "source-frame" wavelength is $\lambda_0$.
You know that the signal from a binary coalescence depends heavily on the chirp mass, which is the main factor determining its frequency.
So, when a gravitational signal is cosmologically redshifted it will be shifted in frequency - each of its components will be changed to $f = f_0 / (1+z)$.
This will be the signal our detectors pick up!
So, if we do parameter estimation and figure out what is our best estimate for the chirp mass $\mathcal{M}$ without accounting for cosmological redshift, what we are measuring is called "detector-frame mass".
Because of the degeneracy at play, measuring source-frame masses - the masses of the objects in their own center-of-mass frame - is difficult, but they are the "real" quantities we would like to know, since the source frame mass is the one which is related to black hole formation and evolution.
