HEAPOW: Things that go Bump in the X-ray Night (2019 Sep 23)
Stare long enough at the X-ray sky and you'll see things you never saw before. This is especially true for the Chandra X-ray Observatory, which has been looking at pieces of the X-ray sky for over 20 years. Good examples of this adage are the Chandra Deep Field, a portion of the sky at which Chandra has stared for an equivalent exposure time of more than 85 days. The prime science goal of these Deep Field X-ray observations is to understand the evolution of supermassive black holes over cosmic time. But other, stranger things also appear from time to time. The image above shows a "true color" X-ray image of the Chandra Deep Field South observation, in which red represents low-energy X-rays, and blue high-energy X-rays. In the part of one exposure, astronomers were surprised to see a sudden bright flash of X-rays from a previously invisible source, marked as "CDF-S XT1" in the image above. This source suddenly flared into prominence and stayed bright for a fraction of a day before eventually fading into obscurity. The brightening and fading of XT1 is shown by the time series of images of the source at the bottom of the image. Other X-ray sources show transient brightenings, but this source is peculiar. The way in which the source suddenly flared and faded, along with the change in the energy of the X-rays, does not seem to fit with any known type of X-ray variable. Perhaps CDF-S XT1 might be some type of exotic phenomena: maybe an ancient exploding star producing an unusual supernova or gamma-ray burst in a distant galaxy; or a black hole swallowing a star; or perhaps a superpowerful burst from a small star in the Milky Way. None of these explanations has yet proven entirely satisfactory. It may be that this source marks the discovery of an entirely new phenomena, perhaps similar to the mysterious fast radio bursts discovered recently by radio astronomers. What other mysteries will future observations by Chandra reveal?
CXC: CDF-S XT1: Mysterious Cosmic Explosion
http://asterisk.apod.com/viewtopic.php?t=37026
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