The X-Ray and Optical Light Curves of A0620-00 (V616 Mon)

Abstract

A complete X-ray light curve for the transient source A0620-00 has been constructed using Ariel V data. This curve is characterized by a sharp initial rise with a pre-maximum “dip” (Elvis et al. 1975) and by a two-sloped flux decrease (0.034 mag day−1 up to October 1975 and 0.053 mag day−1 thereafter). In early 1976 a factor of ten increase in flux lasting for about two months dominates the light curve until the final, abrupt decline around mid-March. Two other small flux increases were detected, a short one in September 1975 (20% increase) and a longer one in October 1975 (50% increase) just at the time of the change in slope. Several intensity minima are present in the light curve near minimum flux and are probably related to the 8-day cycle reported by Matilsky et al. (1976) and Chevalier et al.(1976). The amplitude of these minima seems to increase with decreasing flux level. An exception is a sharp “dip” (25% decrease) observed in November 1975.