The DIANA project delivered advances that push beyond the current state of the art in three major areas: multi-wavelength constraints on accretion flows, mid-infrared views of compact objects, and theoretical modelling of radiation-pressure–dominated disks in neutron stars.
A first key achievement was the combination of fast infrared variability with time-dependent X-ray polarimetry of accreting compact objects—an approach that had never been attempted before. Although Sco X-1 exhibited very low X-ray polarization, the fast IR analysis revealed strong sub-second variability, and the lack of correlated polarization changes places the tightest constraints so far on short-timescale geometric fluctuations in a neutron-star accretion flow. This result challenges the expectation—based on initial expectations—that radiation-pressure–dominated inner disks should produce detectable polarization swings. DIANA therefore provides evidence that the geometry of bright neutron-star systems is more stable than previously assumed.
Beyond neutron stars, DIANA contributed to ground-breaking IXPE campaigns on two black hole transients (MAXI J1744-294 and GRS 1739–278). These observations yielded some of the clearest constraints to date on the disc inclination and black hole spin derived from X-ray polarization. The measurements reveal a coherent picture of the inner flow geometry in these systems and strengthen the case that polarimetry can break degeneracies present in spectral modelling alone. Together with the broader IXPE collaboration, these results are helping reshape the theoretical framework used to describe the corona–jet configuration in black hole X-ray binaries.
The project also produced results that significantly extend the multi-wavelength view of compact objects, enabled by the first mid-infrared observations of X-ray binaries with JWST. DIANA contributed to the discovery of a powerful outflow in quiescence from A0620–00, the first of its kind ever detected in a stellar-mass black hole system, and to the identification of synchrotron emission in the soft state of GX 339–4, a result that overturns the textbook expectation that jets are fully quenched in disc-dominated phases. These findings demonstrate that the mid-IR band hosts rich, previously inaccessible diagnostics of jet and outflow physics.
On the theoretical side, DIANA delivered a major step forward by developing the first version of GLADIS-NS, a radiation-pressure–instability code tailored for accreting neutron stars. The project successfully incorporated X-ray irradiation of the disk, a key physical ingredient that had never been included in instability models for neutron stars. Preliminary simulations show that irradiation can strongly reshape the predicted variability patterns, opening a new pathway to connect theoretical predictions with observations from IXPE, JWST, and high-speed infrared instruments. The code will be made openly available, ensuring long-term impact and community uptake.
Finally, through workshops, invited talks, and close collaboration with IXPE and JWST teams, DIANA helped stimulate dialogue between observers and theorists working on accretion physics. The project has therefore not only produced new scientific results but also strengthened the methodological and collaborative foundations needed for the next generation of multi-wavelength and polarimetric studies of compact objects.
