Finding the Electromagnetic Counterparts of Cosmological Standard Sirens

The gravitational waves (GWs) emitted during the coalescence of black holes (SMBHs) in the mass range similar to 10(4) -10(7) M-circle dot/(1 + z) will be detectable out to high redshifts the future Laser Interferometer Space Antenna (LISA). The distance direction to these "standard sirens'' can be inferred directly from GW signal, with a precision that depends on the masses, spins, and of the merging system. In a given cosmology, the LISA-measured distance translates into a redshift shell. We calculate the and shape of the corresponding three-dimensional error volume in an electromagnetic counterpart to a LISA event could be found, into account errors in the background cosmology ( as expected by time LISA flies), weak gravitational lensing (de) magnification due inhomogeneities along the line of sight, and potential-peculiar velocities. Weak-lensing errors largely exceed other of uncertainties (by a factor of similar to 7 for typical at z = 1). Under the plausible assumption that SMBH-SMBH are accompanied by gas accretion leading to Eddington-limited activity, we then compute the number of quasars that would be in a typical three-dimensional LISA error volume, as a function BH mass and event redshift. Low redshifts offer the best to identify quasar counterparts to cosmological standard. For mergers of similar to 4; (10(5)-10(7)) M-circle dot SMBHs, LISA error volume will typically contain a single near-Eddington at z similar to 1. If SMBHs are spinning rapidly, the error is smaller and may contain a unique quasar out to redshift z to 3. This will allow a straightforward test of the hypothesis GW events are accompanied by bright quasar activity and, if the proves correct, will guarantee the identification of a quasar counterpart to a LISA event, with a B-band luminosity of-B similar to (10(10)-10(11)) L-circle dot. Robust counterpart would allow unprecedented tests of the physics of SMBH, such as precision measurements of the Eddington ratio. They clarify the role of gas as a catalyst in SMBH coalescences and also offer an alternative method to constrain cosmological.