Using Gravitational‐Wave Standard Sirens

Abstract

Gravitational waves (GWs) from supermassive binary black hole (BBH) inspirals are potentially powerful standard sirens (the GW analog to standard candles) (Schutz 1986(Schutz , 2002. Because these systems are well-modeled, the space-based GW observatory LISA will be able to measure the luminosity distance (but not the redshift) to some distant massive BBH systems with 1-10% accuracy. This accuracy is largely limited by pointing error: GW sources generally are poorly localized on the sky. Localizing the binary independently (e.g., through association with an electromagnetic counterpart) greatly reduces this positional error. An electromagnetic counterpart may also allow determination of the event's redshift. In this case, BBH coalescence would constitute an extremely precise (better than 1%) standard candle visible to high redshift. In practice, gravitational lensing degrades this precision, though the candle remains precise enough to provide useful information about the distance-redshift relation. Even if very rare, these GW standard sirens would complement, and increase confidence in, other standard candles.

Reducing the weak lensing noise for the gravitational wave Hubble diagram using the non-Gaussianity of the magnification distribution

“…This question has been considered by several authors, including [12,[28][29][30][31], with the importance of weak lensing as the dominant effect in limiting LISA's distance-measurement accuracy first being stressed by Hughes and Holz [32]. The main result of this paper-that previous analyses considerably underestimated the improvement in D L -accuracy that comes from combining several measurements-suggests a reexamination of the LISA case.…”

“…where D is the distance, L is the intrinsic luminosity, F is the measured flux, and is the magnification; with N sources, this uncertainty is reduced by a factor of ffiffiffiffi N p [9,12]. Since the last term dominates for GW sources and is significant for high-z SNe, there is great motivation to try to reduce it.…”

Sources of Gravitational Waves: Theory and Observations

“…Weak gravitational lensing would bias distance measurements of individual sources [383], but a large population of events, as might be expected in the case of ET, can average out lensing biases [379]. If the host galaxy of a merger event is identified and its redshift measured, then we can use a population of binary coalescence events to infer cosmological parameters.…”

Short GRB and binary black hole standard sirens as a probe of dark energy

“…Because of lensing errors, small numbers of LISA sources will generally be unable to constrain dark energy parameters significantly [6]. The effects of lensing diminish significantly at lower redshifts, so a single SMBBH inspiral at z < 0:5 observed by LISA could measure the Hubble constant to & 1% and w to & 10%.…”