HEAPOW: EXTraS! The X-ray Sky is Variable! (2020 Mar 09)
Astronomical archives of space-based X-ray data from the XMM-Newton X-ray Observatory, the Chandra X-ray Observatory, and other, older X-ray observatories (like ROSAT) are gold mines of information on the high energy properties of normal stars, galaxies, galaxy clusters, exploding stars, black holes, neutron stars and white dwarfs, and (perhaps) even cosmic objects not yet identified. XMM has been observing the X-ray sky from space for the past 20 years and is still going strong, and, since it's one of the most sensitive X-ray observatories ever flown, its archive of observed X-ray sources is enormous. Some enterprising astronomical treasure hunters have now combed through the entire XMM-Newtons archive to understand the unsteady X-ray sky and to characterize its extent, timescales, and variability amplitudes. These scientists have created a database of this variability information, which they call EXTraS, which stands for "Exploring the X-ray Transient and variable Sky". The image above shows one example, highlighting the X-ray variations from two sources in a galaxy far, far away. The plots on the left show the fast changes of a compact X-ray source in the disk of this spiral galaxy which brightens by more than a factor of three with period of only 1.2 seconds. On the right, plots show dips in the X-ray brightness of a source near the center of the galaxy, as documented in 4 different observations from 2007 (top) to 2011 (bottom). Scientific treasure hunters are scouring the EXTraS database looking for unusal objects, finding marvelous, unexpected things, like the discovery of an X-ray superflare from an L dwarf, one of the smallest stars known. What other oddities lurk in EXTraS? Take a look for yourself.
EXTraS (Exploring the X-ray Transient and variable Sky)
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