A nova, discovered before dawn on April 21st, has flared to 9th magnitude along the border of Sagittarius and Ophiuchus.
Word has spread worldwide among dedicated skywatchers that there's a possible 9th-magnitude nova in Sagittarius near the Ophiuchus border. Its coordinates (17h 45m 28s, declination –23° 5′ 23″) place it 4° west of the Trifid Nebula (Messier 20).
Announced yesterday by the IAU's Central Bureau for Astronomical Telegrams, the "new star" was initially designated PNV J17452791-2305213 but now answers to Nova Sagittarii 2012. It was first spotted at magnitude 9.6 by Stanislav Korotkiy (Ka-Dar Observatory, Barybino, Russia) and Kirill Sokolovsky (Astro Space Center, Moscow State University) on a trio of images they'd taken with a 135-mm telephoto lens and ST-8300M digital camera. They've posted their discovery images here.
A prediscovery image from Xingming Observatory in China shows that the star was magnitude 10.2 just four hours earlier, though Korotkiy and Sokolovskiy report nothing at that location brighter than 14th magnitude in images taken three days earlier. Follow-up observations taken this morning by Italian observers Ernesto Guido, Nick Howes, and Giovanni Sostero using a remotely controlled telescope in Mayhill, New Mexico, show the star had brightened slightly to magnitude 9.1.
The Italians also note on their Remanzacco Observatory website that a 16th-magnitude star is cataloged within a fraction of an arcsecond of the outburst's position.
A 25-minute observation late on April 21st by NASA's Swift spacecraft did not detect any X-rays, common in nova eruptions. This suggests to observers that "the observable part of the nova shell is expanding rather uniformly with no shocks strong enough to produce bright X-ray emission."