S. Shah

Using electromagnetic observations to aid gravitational-wave parameter estimation of compact binaries observed with LISA

We present a first-stage study of the e ect of using knowledge from electromagnetic (EM) observations in the gravitational wave (GW) data analysis of Galactic binaries that are predicted to be observed by the new Laser Interferometer Space Antenna in the lowfrequency range, 10 4 Hz < f < 1Hz. In particular, we examine the extent to which the accuracy of GW parameter estimation improves if we use available information from EM data. We do this by investigating whether correlations exist between the GW parameters that describe these binaries and whether some of these parameters are also available from EM observations. We used verification binaries, which are known as the guaranteed sources for eLISA and will test the functioning of the instrument. We find that of the seven parameters that characterise such a binary, only a few are correlated. The most useful result is the strong correlation between amplitude and inclination, which can be used to constrain the parameter uncertainty in amplitude by making use of the constraint of inclination from EM measurements. The improvement can be up to a factor of 6:5, but depends on the signal-to-noise ratio of the source data. Moreover, we find that this strong correlation depends on the inclination. For mildly face-on binaries ( . 45 ), EM data on inclination can improve the estimate of the GW amplitude by a significant factor. However, for edge-on binaries ( 90 ), the inclination can be determined accurately from GW data alone, thus GW data can be used to select systems that will likely be eclipsing binaries for EM follow-up.

Using electromagnetic observations to aid gravitational-wave parameter estimation of compact binaries observed with LISA II: The effect of knowing the sky position

In this follow-up paper, we continue our study of the e ect of using knowledge from electromagnetic observations in the gravitational wave (GW) data analysis of Galactic binaries that are predicted to be observed by the new Laser Interferometer Space Antenna (LISA) in the low-frequency range, 10 4 Hz < f < 1 Hz. In the first paper, we have shown that the strong correlation between amplitude and inclination can be used for mildly inclined binaries to improve the uncertainty in amplitude, and that this correlation depends on the inclination of the system. In this paper we investigate the overall e ect of the other orientation parameters, namely the sky position and the polarisation angle. We find that after the inclination, the ecliptic latitude of the source has the strongest e ect in determining the GW parameter uncertainties. We ascertain that the strong correlation we found previously only depends on the inclination of the source and not on the other orientation parameters. We find that knowing the sky position of the source from electromagnetic data can reduce the GW parameter uncertainty up to a factor of 2, depending on the inclination and the ecliptic latitude of the system. Knowing the sky position and inclination can reduce the uncertainty in amplitude by a factor larger than 40. We also find that unphysical errors in the inclinations, which we found when using the Fisher matrix, can a ect the corresponding uncertainties in the amplitudes, which need to be corrected.

Ultra-compact binaries as gravitational wave sources

Ultra-compact binaries are among the most numerous sources in the millihertz gravitational wave band, and as such represent one of the primary sources for LISA-like detectors (gravitational wave interferometers in space). Already there are almost 60 ultra-compact binaries that have been detected by electromagnetic means, and more are being discovered in dedicated searches as time goes on. Prominent in this population is the doubly-degenerate white dwarf system J0651, whose orbital decay has been measured and shown to track accurately with the predicted evolution due to the emission of gravitational wave emission. This paper reviews the current understanding of the ultra-compact binary population, recent progress in electromagnetic studies, and prospects for multi-messenger astronomy of these systems once a LISA-like detector is operational.