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Variable X-ray Signals from Massive Black Hole Binaries

Presentation #106.10 in the session Multi-Messenger Astrophysics - Poster Session.

Published onMay 03, 2024
Variable X-ray Signals from Massive Black Hole Binaries

We present a simple model for the electromagnetic (EM) variability for accreting supermassive black hole binaries (SMBHB). Systems with total masses in the 105-7 M range, which will ultimately merge in the LISA frequency band, first spend hundreds of thousands of years with orbital periods of weeks to months. We argue that this is a “sweet spot” for current and near-future time domain EM surveys searching for periodic sources as a way of identifying SMBHB candidates. At higher masses (107-9 Msun), SMBHB systems are expected to dominate the stochastic gravitational wave signal recently discovered by a number of pulsar timing array (PTA) collaborations. The most massive and nearby subset of this population should ultimately be detected as individually resolvable sources with PTA. For both the pre-LISA and PTA systems, the X-ray counterparts will be relatively bright, nearby, long-lived, and periodic on time scales that allow for many cycles during a multi-year observing campaign, making it much easier to rule out red-noise imposters. Coupled with cosmological simulations of black hole formation and merger models, we can also predict expected rates for detecting these systems with wide-field X-ray surveys.

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