Speaker
Description
After more than 10 attempts to fly an X-ray polarimeter, aimed at revitalizing the field, with early efforts based on Bragg diffraction and Thomson scattering and yielding a single positive (and fundamental) result in the mid-1980s, the innovative use of the photoelectric effect in gas detectors led to the development of the Gas Pixel Detector, specifically designed for astronomical polarimetry.
Finally, NASA approved IXPE in January 2017, and the NASA–ASI Small Explorer mission was successfully launched in early December 2021. IXPE is still in operation, providing a wealth of scientifically outstanding results across all classes of X-ray–emitting celestial sources.
The next step beyond IXPE requires significant improvements in several key areas: larger mirror effective area and enhanced angular resolution, a broader energy band to access a wider range of physical phenomena through polarimetry, and a substantially faster repointing capability to capture the polarization of transient sources.
This vision is embodied in Europe by EXPO (Enhanced X-ray Polarimetry Observatory) a proposed M-8 mission waiting for selection outcome for phase-0 by ESA and in USA by Lynx2030 under consideration for angular resolution at the 1–2 arcsecond level and mirror effective areas on the order of square meters. In China the enhanced X-ray Timing-Polarimetry mission (eXTP) with a projected launch in 2030 will augment the number of sources observed by IXPE being sensitive in the same energy band.
At higher energies indeed, Compton Scattering takes the role and while at lower energies photoelectric effect allows for fine imaging polarimetry this is not possible above about 20-30 keV. Anyhow the use of new generations of ASICs coupled to solid state detectors may overcome the situation. XL-Calibur, AstroSat-CZTI, XPOSAT-POLIX and the future Polar-2 and COSI are making (or will) use of Compton/Thomson scattering for non-imaging polarimetry.
In this talk, I will present the main scientific results obtained by IXPE, discuss its limitations, and outline how these can be overcome by EXPO and Lynx 2030. I will also discuss Compton polarimeters highlighting also the astrophysical potential enabled by this new generation of high-throughput X-ray missions.
| Name of the speaker | Paolo Soffitta (INAF-IAPS), on behalf of large teams |
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