Day 1399

Monday.

1804.04722
Testing the Weak Equivalence Principle using optical and near-infrared Crab Pulses
Leung, et al

The Weak Equivalence Principle states that the geodesics of a test particle in a gravitational field are independent of the particle's constitution.  To constrain violations of the WEP, use the one-meter telescope at Table Mountain Observatory near Los Angeles to monitor the relative arrival times of pulses from the Crab Pulsar in the optical (lambda ~ 585 nm) and near-infrared (lambda ~814 nm) using an instrument which detects single photons with nanosecond-timing resolution in those two bands.  The IR pulse arrives slightly before the visible pulse.  The 3 analysis methods give delays with statistical errors of Delta t_obs=7.41±0.58, 0.4±3.6, and 7.35±4.48 microsecond (at most 1/4000 of the pulsar period).  Attribute this discrepancy to systematic error from the fact that the visible and IR pulses have slightly different shapes.  Whether this delay emerges from the pulsar, is caused by passing through wavelength-dependent media, or is caused by a violation of the equivalence principle, unless there is a fine-tuned cancellation among these, sets the first upper limit on the differential post-Newtonian parameter at these wavelengths of Delta gamma<1.07e-10 (3 sigma).  This result falls in an unexplored region of parameter space and complements existing limits on equivalence-principle violation from fast radio bursts, gamma ray bursts, as well as previous limits from the Crab.