X-ray eclipse time delays in 4U 2129+47
Campana, S.; Israel, G.; Stella, L.; Papitto, A.; Burderi, L.; Bozzo, E.; Lazzati, D.; Mangano, V.; Perna, R.; Falanga, M.; di Salvo, T.
Italy, France, United States
Abstract
Aims:4U 2129+47 was discovered in the early 80's and classified as an accretion disk corona source due to its broad and partial X-ray eclipses. The 5.24 h binary orbital period was inferred from the X-ray and optical light curve modulation, implying a late K or M spectral type companion star. The source entered a low state in 1983, during which the optical modulation disappeared and an F8 IV star was revealed, suggesting that 4U 2129+47 might be part of a triple system. The nature of 4U 2129+47 has since been investigated, but no definitive conclusion has been reached.
Methods: Here, we present timing and spectral analyses of two XMM-Newton observations of this source, carried out in May and June, 2005.
Results: We find evidence for a delay between two mid-eclipse epochs measured ~22 days apart, and we show that this delay can be naturally explained as being due to the orbital motion of the binary 4U 2129+47 around the center of mass of a triple system. This result thus provides further support in favor of the triple nature of 4U 2129+47.