Double white dwarf ZTF J0538+1953 as the brightest verification binary for space laser interferometers

TL;DR

This paper reports the measurement of orbital decay in the ultrashort-period white dwarf binary ZTF J0538+1953, establishing it as the brightest verification binary for space laser interferometers like LISA and TianQin, with significant implications for gravitational wave detection.

Contribution

The study provides the first measurement of orbital period decrease in ZTF J0538+1953, refining its chirp mass and confirming its status as a prime verification binary for space-based gravitational wave observatories.

Findings

Measured orbital period decrease rate of $dP/dt=-(1.16\pm 0.22) imes 10^{-11}$ s/s.

Derived a chirp mass of $0.434\pm 0.05 M_\odot$, 30% higher than previous spectroscopic estimates.

Identified ZTF J0538+1953 as the brightest Galactic verification binary for LISA and TianQin with high SNRs.

Abstract

A decrease in the orbital period of the ultrashort-period binary white dwarf \ZTF, which is one of the Galactic verification binaries in the millihertz frequency range for planned space laser interferometers, has been measured. Based on photometric observations carried out on the 2.5-m telescope of the Caucasian Mountain Observatory of the Sternberg Astronomical Institute of Moscow State University (CMO SAI MSU), a diagram \textit{O-C} is constructed. It can be described by quadratic elements of the brightness variation, which correspond to a decrease rate of the orbital period of the system of $dP/dt=-(1.16\pm 0.22)\times 10^{-11}$ s/s. The decrease rate of the orbital period in the quadrupole approximation for the emission of gravitational waves by a binary system corresponds to its chirp mass $\mathcal{M}=0.434\pm 0.05 M_\odot$, which turned out to be $\sim 30\%$ higher than the value obtained earlier from spectroscopic mass determination. The chirp mass of \ZTF inferred from the measured orbital decay rate makes this system the brightest Galactic verification binary for LISA and TianQin space interferometers with a signal-to-noise ratio of $\approx 119$ and $\approx 30$ over 5 years and 2.5 years of observations, respectively.