Lensed or not lensed: Determining lensing magnifications for binary neutron star mergers from a single detection

Abstract

Advanced LIGO and Advanced Virgo could observe the first lensed gravitational wave sources in the coming years, while the future Einstein Telescope could observe hundreds of lensed events. It is, therefore, crucial to develop methodologies to distinguish between lensed from unlensed gravitational-wave observations. A lensed signal not identified as such will lead to biases during the interpretation of the source. In particular, sources will appear to have intrinsically higher masses. No robust method currently exists to distinguish between the magnification bias caused by lensing and intrinsically high-mass sources. In this work, we show how to recognize lensed and unlensed binary neutron star systems through the measurement of their tidal effects for highly magnified sources as a proof-of-principle. The proposed method could be used to identify lensed binary neutron stars, which are the chief candidate for lensing cosmography studies. We apply our method on GW190425, finding no clear evidence for or against lensing, mainly due to the poor measurement of the event's tidal effects. However, we expect that future detections with better tidal measurements can yield better constraints.

Tidal effects in the gravitational-wave phase evolution of compact binary systems to next-to-next-to-leading post-Newtonian order

“…Since Eq. (1.3) depends on both the masses and tidal deformabilities, with the masses being biased by gravitational lensing unlike the polarizabilities, the observable combination (1.3) could be used to recognize strongly lensed GW binary signals from unlensed ones with intrinsically higher masses [9]. On the other hand, assuming the absence of lensing, the simultaneous measurement of m 1 , m 2 and Λ(2) may provide an estimation of the redshift independently of electromagnetic observations [10].…”

Probing modified gravitational wave propagation with strongly lensed coalescing binaries

“…These events will have a relative time delay, of orders of minutes to months for lensing by galaxies and up to years for lensing by galaxy clusters, and a different amplitude, which reflects the fact that signals traveling through different paths undergo different amount of magnification or demagnification. The other parameters entering the waveform, such as the detector frame masses, spins, sky locations, etc., are the same (except, possibly, for a frequency-independent phase shift), and a Bayesian analysis can be performed to compare the hypothesis that two (or more) GW events belong to the same source with the hypothesis that they are unrelated [1][2][3][4][5][6][51][52][53].…”

“…Gravitational waves (GWs) propagating across cosmological distances are bent by nearby galaxies and galaxy clusters, just as light does. Signatures for lensing of GWs have been searched in the data of the O1 and O2 LIGO/Virgo observing runs [1][2][3][4][5][6] and in the O3a data [7], and no compelling evidence for lensing of GW events has been reported. With current detector sensitivity, the expected fraction of observed strong lensing events is of order 10 −4 −10 −3 , depending on assumptions of the merger rate [7] so, with the O(50) coalescences detected to date, the observation of a lensed event is unlikely (see [8] for an opposite viewpoint).…”

Gravitational-wave cosmological distances in scalar-tensor theories of gravity

“…The quantity d (GW) A is important in the context of GW lensing, a subject with interesting possibilities for GW physics -see e.g. [44,45,53,[70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][86][87][88][89][90][91][92][93][94][95][96][97][98][99] for papers discussing the topic from a variety of perspectives.…”

“…See e.g. [44,45,53,[70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][86][87][88][89][90][91][92][93][94][95][96][97][98][99] for works discussing this topic.…”