Self-Lensing Signals in Binary Systems Containing White Dwarfs with Neutron star or Stellar-mass Black hole Companions

TL;DR

This study evaluates the properties and detectability of self-lensing signals in binary systems with white dwarfs and neutron star or black hole companions using TESS and Roman data, highlighting potential detection prospects.

Contribution

It provides analytical and simulated analysis of self-lensing signals in WD+NS/BH systems, estimating their probabilities and detectability with current and future space telescopes.

Findings

Self-lensing signals are more probable in systems with low-mass WDs and massive NSs/BHs.

TESS can potentially detect at least one self-lensing event from these systems.

Roman's detection capability for these signals is effectively zero.

Abstract

Light curves from binary systems containing white dwarfs with neutron star or stellar-mass black hole companions (WD+NS and WD+BH) with edge-on orbital planes potentially show self-lensing/eclipsing signals. Here, we evaluate the properties and detectability of these signals in the NASA's Transiting Exoplanet Survey Satellite (TESS), and the Nancy Grace Roman Space Telescope (Roman) observations. WD+NS systems with orbital periods $T\lesssim25~$days mostly have considerable finite-source sizes with the normalized source radii $\rho_{\star}\gtrsim1$. WD+BH systems with $T\gtrsim3$ days have $\rho_{\star}\lesssim1$, and $\rho_{\star}\sim0.01$ for BHs with a few tens solar-mass. Our analytical calculations show the probabilities of occurring self-lensing signals in WD+NS and WD+BH systems are $\sim10^{-3},~10^{-2}$, and maximize for systems with low-mass WDs revolving massive NSs/BHs. We simulate their light curves and generate synthetic data for them by applying the observing protocols of these two satellites. We assume self-lensing signals are detectable if (i) $1\leq T\leq T_{\rm{obs}}$ (where $T_{\rm{obs}}=62~\rm{and}~27.4$ days are the Roman and TESS continuous observing windows), (ii) $\rm{SNR}\ge3,~6$, their signals are (iii) deeper than twice the photometric error, and (iv) covered by at least one datum. Systems with detectable self-lensing signals in the TESS and Roman observations on average have small inclination angles $i\lesssim0.2^{\circ}$, with the orbital periods $\sim6,~19~$days, and their signals last $\sim[6,~30]~\rm{minutes}$. The TESS and Roman efficiencies for detecting these signals are $\sim2-6\times10^{-4}$ and $\sim2-12\times10^{-10}$. Although detecting these self-lensing signals by Roman is impossible, the TESS telescope potentially manifests at least one self-lensing signal due to these binary systems, if $8\%,~\rm{and}~3\%$ of WDs have NS and BH companions.