Never throw away old data! Cygnus X-1's fast X-ray variability behaviour in the 70s revisited - SSW

NEVER THROW AWAY OLD DATA! CYGNUS X-1'S FAST X-RAY VARIABILITY BEHAVIOUR IN THE 70S REVISITED - ERIK KUULKERS

Apollo 15 (and 16) did not only bring people to the Moon, but also experiments to study our neighbour and its environment. Onboard the Command and Service Modules (CSM's) were X-ray experiments, to explore the Lunar surface chemistry. These data, covering about 10% of the Lunar surface has been extensively used to study Lunar formation history and geological evolution. However, when traveling back to Earth, the experiments were also used for X-ray astronomy. These data had to be retrieved from a tape dump binary file. One of the extra-Solar sources observed is the famous black-hole X-ray binary Cygnus X-1.
X-ray states in X-ray binaries are mainly defined by their spectra and timing behaviour; these states correspond to different accretion regimes of the compact object. With the advent of high-throughput, high-time resolution experiments (such as onboard ASTROSAT, EXOSAT, Ginga, NICER, RXTE) emphasis has been shifting to study X-ray variability at high time resolution (typically less than milliseconds). For most of the earlier X-ray experiments in the 1960's and 1970's information is only available down to about milliseconds. We show that for Cygnus X-1, X-ray data taken with second to subsecond time resolution can uniquely help in defining its X-ray states. This is done by using digitized light curves and power density spectra as presented in the literature, from Uhuru (the 1st X-ray satellite), SAS-3 and HEAO-1, and various rocket experiments, in the 1970's, as well as newly analysed data from the X-ray experiment onboard Apollo 15 and the Netherlands Astronomical Satellite (ANS; the Netherlands 1st satellite).