Observation of gravitational waves ( GWs ) in two different frequency bands is referred to as multiband GW astronomy .
With the planned Laser Interferometric Space Antenna ( LISA ) operating in the 10 ^ { -4 } -0.1 Hz range , and third generation ( 3G ) ground-based detectors such as the Cosmic Explorer ( CE ) and Einstein Telescope ( ET ) , operating in the 1 – 10 ^ { 4 } Hz range , multiband GW astronomy could be a reality in about a decade .
In this paper we present the potential of multiband observations of intermediate mass binary black holes ( IMBBHs ) of component masses { \sim } 10 ^ { 2 } – 10 ^ { 3 } M _ { \odot } to test general relativity ( GR ) .
We show that mutiband observations of IMBBHs would permit multiparameter tests of GR—tests where more than one post-Newtonian ( PN ) coefficient is simultaneously measured yielding more rigorous constraints on possible modifications to GR .
We also find that the improvement due to multibanding can often be much larger than the best of the bounds from either of the two observatories .
The origin of this result , as we shall demonstrate , can be traced to the lifting of degeneracies among the various parameters when the information from LISA and 3G are taken together .
We obtain the best multiband bounds for an IMBBH with a total redshifted mass of 200 M _ { \odot } and a mass ratio of 2 .
For single-parameter tests , this system at 1 Gpc would allow us to constrain the deviations on all the PN coefficients to below 10 % and derive simultaneous bounds on the first seven PN coefficients to below 50 % ( with low spins ) .