Massive stars and their impacts on their surrounding interstellar medium drive the stellar feedback process, one of the main astrophysical issues in the context of galaxy evolution and cosmic chemical evolution. Radioactivity from 26Al adds a unique diagnostic tool for its investigation in nearby massive-star regions. The Orion region hosts one of the closest such regions at a distance of ~400 pc there is hardly a more suitable and closer target region. COMPTEL had provided a measurement of 26Al 1809 keV emission from this region, confirming this opportunity. An interesting offset of the diffuse and extended 26Al emission source from its likely sources suggests champagne-like outflow from the OB1 association stars into the Eridanus cavity. HI filaments in radio emission, X-ray emission seen with XMM-Newton, and GeV emission seen with Fermi-LAT, all support this; together with Gaia details on the stellar population this is an ideal setting for a multi-messenger study of feedback, to study the ISM as it is shaped by massive stars and the interaction of massive stars with their surrounding ISM in a new way: With INTEGRAL gamma-ray measurements we can constrain 26Al ejection from massive stars in mass and velocity, and due to their proximity and location on the near side of molecular clouds and at the edge of a large cavity, we can compare the locations of massive stars to the morphology of the ISM and the emission pattern of 26Al radioactivity. Analysis of previous INTEGRAL observations has obtained a firm detection of the expected signal from 26Al. With our proposed multi-year deepening of exposure (3 Ms in AO-18) we aim to improve our measure of the line shape and thus kinematics of this nearby 26Al source. With these observations we can also search for annihilation radiation, and for nuclear deexcitation gamma-rays in the MeV range, both valuable diagnostics of the structure of superbubble interiors, and >30 Fermi sources are within our target region.
The INTEGRAL (International Gamma-Ray Astrophysics Laboratory) mission, launched by the European Space Agency (ESA) on October 17, 2002, was designed to study high-energy phenomena in the universe. INTEGRAL was operating until february 2025 and it was equipped with three high-energy instruments: the Imager on Board the INTEGRAL Satellite (IBIS), the Spectrometer on INTEGRAL (SPI), and the JEM-X (Joint European Monitor for X-rays). Its Optical Monitoring Camera (OMC) provided optical V-band magnitude measurements, complementing the high-energy observations.
