Speaker
Description
"From December 2019 to February 2022, SRG/eROSITA has scanned the whole sky at 0.2-8 keV, with
highest sensitivity in the soft (0.2-2.3 keV) X-ray band. Although designed primarily for cosmological studies, the eROSITA mission is also ideally suited for studying our immediate astronomical environment: the discovery of cometary X-ray emission has made us aware that we are observing the sky through regions of soft diffuse X-ray emission, powered by charge exchange between solar wind heavy ions and tenuous amounts of gas. Such gas in the Earth's exosphere creates an extended cloud of geocoronal X-ray emission, and interstellar gas streaming through the solar system causes the inner heliosphere to glow in soft X-rays. These foreground emission components have severely complicated the unambiguous interpretation of the diffuse soft X-ray sky to date. Now this situation has greatly improved: its wide field of view, high sensitivity to soft X-rays and high spectral resolution make eROSITA the perfect instrument for studying the diffuse soft X-ray sky, and observing from a distance of ~1.5 million km, eROSITA is unaffected by geocoronal X-rays. By having mapped the sky four times, starting at solar minimum, it becomes possible to isolate the heliospheric component. This allows us to obtain unprecedentedly detailed insights into the spatial, spectral, and temporal properties of the X-ray emission caused by the solar wind over a major part of the solar cycle, and to use it for mapping the flow of interstellar matter through the heliosphere. By subtracting the heliospheric component we can also reconstruct for the first time the sky as it would appear from outside the solar system. One immediate result is that, after removing all foreground components, even the darkest regions exhibit significant flux, providing solid evidence for the presence of a hot interstellar medium around the Sun on a scale of hundreds of parsecs. Given eROSITA’s improved capacity to disentangle foreground components, its data could also enable more sensitive searches for faint features potentially linked to dark matter, such as the debated 3.5 keV line."