Workshop Purpose

Accreting black holes (BHs) power various energetic phenomena in the Universe, emitting electromagnetic radiation across all wavelengths. Among these, X-rays originate from the innermost regions near the central BH. Studying the X-ray signals from these objects is key to understanding BHs, accretion processes, and their impact on their host environments. Over the last few decades, X-ray spectral and timing observations have significantly improved our understanding of these objects. However, spectral and timing techniques are often subject to model degeneracies and significant systematic uncertainties due to unknown geometries of the emission region. This prevents us from addressing key questions such as the distribution of BH spins.

The launch of Imaging X-ray Polarimetry Explorer (IXPE) in 2021 reopened the X-ray polarimetric window after more than 40 years of dormancy. It provides geometry-sensitive X-ray polarization data, which are crucial for breaking model degeneracies in spectral and timing analysis. IXPE has observed more than 10 accreting BHs, yielding important results. However, a synergy framework that can fully integrate the power of spectral, timing, and polarimetric data to break model degeneracies is still lacking. Moreover, IXPE observations have raised new puzzles that challenge our traditional understanding of accretion systems. The goals of the international team are to develop a synergy framework/strategy and to resolve these puzzles.