Constraints on differential Shapiro delay between neutrinos and photons from IceCube-170922A

TL;DR

This paper uses the coincident detection of a high-energy neutrino and gamma-ray flare from TXS 0506+056 to constrain violations of Einstein's Weak Equivalence Principle by comparing Shapiro delays, setting bounds on differences in gravitational coupling.

Contribution

It provides the first constraints on WEP violations for TeV neutrinos using astrophysical observations of neutrino-photon coincidences.

Findings

WEP violation parameter |_{ u}-_{ m EM}|<5.5 imes 10^{-2}

Shapiro delay of about 6300 days estimated for the event

Time difference between neutrino and photon arrival constrained to 175 days

Abstract

On 22nd September 2017, the IceCube Collaboration detected a neutrino with energy of about 290 TeV from the direction of the gamma-ray blazar TXS 0506+056, located at a distance of about 1.75 Gpc. During the same time, enhanced gamma-ray flaring was also simultaneously observed from multiple telescopes, giving rise to only the second coincident astrophysical neutrino/photon observation after SN 1987A. We point out that for this event, both neutrinos and photons encountered a Shapiro delay of about 6300 days along the way from the source. From this delay and the relative time difference between the neutrino and photon arrival times, one can constrain violations of Einstein's Weak Equivalence Principle (WEP) for TeV neutrinos. We constrain such violations of WEP using the Parameterized Post-Newtonian (PPN) parameter $\gamma$, which is given by $|\gamma_{\rm {\nu}}-\gamma_{\rm{EM}}|<5.5 \times 10^{-2}$, after assuming time difference of 175 days between neutrino and photon arrival times.