Testing the Weak Equivalence Principle with the Binary Neutron Star Merger GW 170817: The Gravitational Contribution of the Host Galaxy

Abstract

The successful detection of the binary neutron star merger GW 170817 and its electromagnetic counterparts has provided an opportunity to explore the joint effect of the host galaxy and the Milky Way (MW) on the weak equivalence principle (WEP) test. In this paper, using the Navarro–Frenk–White profile and the Hernquist profile, we present an analytic model to calculate the galactic potential, in which the possible locations of the source from the observed angle offset and the second supernova kick are accounted for. We show that the upper limit of Δγ is 10−9 for the comparison between GW 170817 and a gamma-ray burst (GRB 170817A), and it is 10−4 for the comparison between GW 170817 and a bright optical transient (SSS 17a, now with the IAU identification of AT 2017gfo). These limits are more stringent by one to two orders of magnitude than those determined solely using the measured MW potential in the literature. We demonstrate that the WEP test is strengthened by the contribution from the host galaxy to the Shapiro time delay. Meanwhile, we also find that large natal kicks produce a maximum deviation of about 20% from the results with a typical kick velocity of 400 to ∼500 km s−1. Finally, we analyze the impact from the halo mass of NGC 4993 with a typical 0.2 dex uncertainty and find that the upper limit of Δγ, with a maximum mass , is nearly two times more stringent than that of the minimum mass .

Constraints on Equivalence Principle Violation from Gamma Ray Bursts

“…The majority of previous attempts to constrain violations of the WEP via ∆γ ij with GRBs [18,[51][52][53][54], FRBs [6,[55][56][57][58], Supernovae [59,60], Gravitational Waves [61][62][63][64][65][66][67][68][69], Blazar Flares [70][71][72][73][74] or Pulsars [75][76][77][78] have assumed that the gravitational potential is dominated by the contribution from the Milky Way and/or other massive objects such as the Laniakea supercluster. This has two major shortcomings for distant sources: firstly the gravitational potential in Equation 2 should be a fluctuation about the cosmological mean (and thus can take either sign, unlike in the multiple-source approximation where it is strictly additive), and secondly the long range behaviour of the gravitational potential means that we cannot neglect the large-scale distribution of mass [8,9].…”

Testing Fundamental Physics with Astrophysical Transients

“…These constraints can be further improved using the likely associations of high-energy neutrinos with the flaring blazars [168][169][170][171] or GRBs [172]. Besides the neutrino-photon sectors, the coincident detections of GW events with electromagnetic counterparts also provided multimessenger tests of the WEP, extending the WEP tests with GWs and photons [100,[173][174][175][176][177][178][179][180]. For example, with the assumption that the arrival time delay between GW170817 and GRB 170817A (∼ 1.7 s) from a binary neutron star merger is mainly due to the gravitational potential of the Milky Way outside a sphere of 100 kpc, Abbott et al [174] derived −2.6 × 10 −7 ≤ γ g − γ γ ≤ 1.2 × 10 −6 .…”

Consistent equivalence principle tests with fast radio bursts

“…There is a number of papers (e.g. Krauss & Tremaine 1988;Wei et al 2015Wei et al , 2016aWu et al 2016Wu et al , 2017Yang et al 2017;Yu et al 2018;Xing et al 2019;Yao et al 2020) dealing with this type of measurements, which all rely on measuring the Shapiro time delay (Shapiro 1964) for different messengers. The most recent ones focus on gravitational waves, gamma-ray bursts or FRBs.…”