This paper presents the first credible detection of apsidal motion in the binary system CrB. To my knowledge this is the first time that such a classic measurement (through eclipse timing) has been performed in the X-ray domain. Because of the deep X-ray eclipse at the time of secondary optical minimum and the 24 hour availability of satellite-based observatories, the required timing measurements can easily be performed. The significance of the detected periastron advance is quite large; the probability for the periastron advance being greater than zero is 0.986. At the moment the observed time difference between secondary and primary minima is 4.8 seconds with an error of 2.1 seconds. I expect that this value can be significantly improved upon in a few years when new, more sensitive X-ray observatories allow uninterrupted coverage of eclipse ingress and egress; a determination of with an accuracy of 0.1 seconds, i.e., an order of magnitude better, appears certainly feasible. For the time being the measured periastron advance of 4.8 2.1 sec is consistent with our knowledge of the primary component of the CrB system. The relativistic contribution to the total periastron advance, 0.95 seconds, amounts to 17 % of the measured effect, and may amount to 24 % of the total.
© European Southern Observatory (ESO) 1998
Online publication: April 15, 1998