Orateur
Description
The LISA constellation offers a unique opportunity to detect Massive Black Hole Binaries (MBHBs), with a sensitivity band that is particularly well suited to these sources. Their detection will allow us to trace the origins, growth and merger histories of massive black holes, to explore the fundamental nature of gravity and black holes and to probe the rate of expansion of the Universe using these sources as standard sirens [Colpi, 2024].
To fully exploit MBHB observations, rapid and reliable sky localization is crucial [Mangiagli, 2022], as it enables the triggering of alerts for electromagnetic observatories through the Low-Latency Alert Pipeline (LLAP), complementing the observation of these complex systems with a multi-messenger approach. In this context, we present a fast and agnostic localization method.
This approach relies on the construction of an observable, the coronagraphic variable κ derived from linear combinations of Sagnac-type channels [Costa, 2025]. The principle is as follows : when the direction and frequency parameters injected into the observable exactly match the true source parameters, the gravitational-wave signal is canceled within the κ variable.
Localization is thus performed by scanning the celestial sphere to identify the configuration that minimizes the spectral power of the signal.
Preliminary results from the implementation of this approach within the NullStream pipeline have already proven promising for MBHBs [Costa, 2025]. We are now working to improve the accuracy of this localization. Moreover, since the method is fast owing to its agnostic nature, it is naturally well suited to integration within the Low-Latency Alert Pipeline (LLAP).
Finally, as this remains to be investigated, one may ask how the sky localization obtained through the Coronagraphic method could later be used to constrain full Bayesian parameter estimation.