August 11, 2017: Dr. Gregory Sivakoff (University of Alberta) and colleagues have requested AAVSO observers' assistance in observing the black hole X-ray transient LMXB V404 Cyg in support of Chandra observations taking place TONIGHT. The Chandra schedule is
2017 Aug 11 23:49:04.072 - 2017 Aug 12 13:42:14.730 UTC
Four AAVSO members listed as co-authors in Nature paper
V404 Cygni has been known as a variable star residing in the constellation Cygnus since the 18th century. It was believed to be a nova, a compact binary system containing a white dwarf primary and a sun-like secondary star, that undergoes unpredictable episodes of dramatic brightening - or 'outbursts' - before settling back down to quiescence for decades, until the next outburst.
July 1, 2015: In AAVSO Alert Notice 522 on the upcoming observations of the black hole X-ray binary V404 Cyg by HST, the date of the detection by the Swift satellite was incorrectly given as 2015 June 16.77197 UT (Barthelmy et al., GCN Circular 17929). The correct date is 2015 June 15.77197 UT.
Our sincere apologies for this error!
Correction: In the text below, the date of the detection by the Swift satellite was incorrectly given as 2015 June 16.77197 UT. The correct date is 2015 June 15.77197 UT.
Our sincere apologies for this error!
July 1, 2015:
Campaign extended until further notice: As V404 Cyg's behavior following outbursts is clearly unpredictable, AAVSO observers are asked to continue obtaining multicolor photometry as well as visual observations. - April 2017
June 18, 2015: V404 Cyg, an X-ray nova and a low mass X-ray binary (LMXB) with black hole component, is undergoing its first reported X-ray and optical outburst since 1989. Large scale, rapid variations are being reported in wavelengths from X-ray to radio by professional and amateur astronomers worldwide.
