Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

April 22, 1997
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Historic Optical Flash Fades
Credit and Copyright:
P. J. Groot (U. Amsterdam) et al., WHT, INT

Explanation: The largest telescopes in the world have scrambled to point toward this faint, fading object. Why? Because it may well be the first active optical counterpart ever found for a gamma-ray burst, and could hold the clue to the distance scale to this most enigmatic class of astronomical objects. During the past two months, multiwavelength observations, claims, and counterclaims have been exchanged at a torrential pace, as astronomers wait impatiently to see what setting houses the fading transient. Above are two pictures of the optical transient (OT), one taken on February 28th, the other about a week later on March 8th. The OT arrows show the source that faded from view during this time. The OT has been examined by large telescopes including the Hubble Space Telescope and Keck, yet researchers are still scrambling to get answers to fundamental questions about its true nature. Does the OT actually move (exhibit proper motion)? Is there a faint galaxy superposed behind the OT or is this extended emission fading too? In the face of intense scrutiny with the world's most capable telescopes, the origin of gamma-ray bursts so far remains mysterious!

Tomorrow's picture: Antlia: A New Galactic Neighbor

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
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