Abstract
ABSTRACT Compact Galactic Binary Systems with orbital periods of a few hours are expected to be detected in gravitational waves (GW) by Laser Interferometer Space Antenna (LISA) or a similar mission. At present, these so-called verification binaries provide predictions for GW frequency and amplitude. A full polarization prediction would provide a new method to calibrate LISA and other GW observatories, but requires resolving the orientation of the binary on the sky, which is not currently possible. We suggest a method to determine the elusive binary orientation and hence predict the GW polarization, using km-scale optical intensity interferometry. The most promising candidate is CD–30° 11223, consisting of a hot helium subdwarf with mB = 12 and a much fainter white dwarf companion, in a nearly edge-on orbit with period 70.5 min. We estimate that the brighter star is tidally stretched by 6 per cent. Resolving the tidal stretching would provide the binary orientation. The resolution needed is far beyond any current instrument, but not beyond current technology. We consider scenarios where an array of telescopes with km-scale baselines and/or the Very Large Telescope (VLT) and Extremely Large Telescope (ELT) are equipped with recently developed kilopixel sub-ns single-photon counters and used for intensity interferometry. We estimate that a team-up of the VLT and ELT could measure the orientation to ±1° at 2σ confidence in 24 h of observation.
Highlights
Gravitational-wave detections are so far all transient events with no advance warning
We propose a ‘multimessenger’ method to predict the gravitational waves (GW) polarization that would be observed by Laser Interferometer Space Antenna (LISA) when probing a binary system, and in particular the system CD−30◦ 11223, which is the optically brightest and most widely spaced of the LISA verification binaries (Kupfer et al 2018)
We consider Array for CHerenkov Shower Observations (ACHSO) in a scenario corresponding to the planned configuration for Cherenkov Telescope Array (CTA) (South), with 99 telescopes (4851 different baselines) spread over 4 km2
Summary
Gravitational-wave detections are so far all transient events with no advance warning This will change when laser interferometers in space make lower frequency gravitational waves (GW) detectable, because some Galactic binaries (known as LISA verification binaries) are predicted to be detectable via GW (Stroeer & Vecchio 2006). The GW polarization of a LISA verification binary could be predicted if the orientation of the system in the sky (inclination and position angle) were somehow measured from its electromagnetic radiation. This is where intensity interferometry comes into play. By varying the separation between the telescopes, they showed that it is possible to measure the spatial
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