Swift J201424.9+152930: discovery of a new deeply eclipsing binary with 491-s and 3.4-h modulations
D'Avanzo, P.; Campana, S.; D'Elia, V.; Moretti, A.; de Martino, D.; Belfiore, A.; Rea, N.; Sidoli, L.; Esposito, P.; Israel, G. L.; Testa, V.; Rodríguez Castillo, G. A.; Verrecchia, F.; Mapelli, M.; Piranomonte, S.; Di Stefano, R.
Italy, United States, Netherlands, Spain
Abstract
We report on the discovery of a new X-ray pulsator, Swift J201424.9+152930 (Sw J2014). Owing to its X-ray modulation at 491 s, it was discovered in a systematic search for coherent signals in the archival data of the Swift X-ray Telescope. To investigate the nature of Sw J2014, we performed multiwavelength follow-up observations with space-borne (Swift and XMM-Newton) and ground-based (the 1.5-m Loiano Telescope and the 3.6-m Telescopio Nazionale Galileo) instruments. The X-ray spectrum of Sw J2014 can be described by a hard and highly absorbed (NH ∼ 5 × 1022 cm-2) power law (Γ ∼ 1). The optical observations made it possible to single out the optical counterpart to this source, which displays several variable emission lines and total eclipses lasting ≈20 min. Total eclipses of similar length were observed also in X-rays. The study of the eclipses, allowed us to infer a second periodicity of 3.44 h, which we interpret as the orbital period of a close binary system. We also found that the period has not significantly changed over a ∼7 yr timespan. Based on the timing signatures of Sw J2014, and its optical and X-ray spectral properties, we suggest that it is a close binary hosting an accreting magnetic white dwarf. The system is therefore a cataclysmic variable of the intermediate polar type and one of the very few showing deep eclipses.