Reobserving the extreme-ultraviolet emission from abell 2199: in situ measurement of background distribution by offset pointing

摘要

The EUV excess emission from the clusters A2199 and A1795 remains an unexplained astrophysical phe- nomenon. There has been many unsuccessful attempts to " trivialize" the findings. In this Letter, we present direct evidence proving that the most recent of such attempts, which attributes the detected signals to a background nonuniformity effect, is likewise excluded. We address the issue by a reobservation of A2199 that features a new filter orientation, usage of a more sensitive part of the detector, and, most crucially, the inclusion of a background pointing at -2° offset-the first in situ measurement of its kind.