The astronomers calculated the object's rotation period by measuring small periodic fluctuations in brightness. (keckobservatory.org)
The energy spectrum and periodic fluctuations of the X-rays, recorded by the INTEGRAL satellite, suggest they are coming from young binary... (newscientist.com)
But there's also a stronger response due to truly stronger periodic fluctuations recently, especially for the precession frequencies and the unidentified 100,000 - year fluctuation. (tamino.wordpress.com)