超巨星X射线双星SAX. 6 -1703中30天偏心周期的发现
Discovery of an eccentric 30 days period in the supergiant X-ray binary SAX J1818.6-1703 with INTEGRAL
摘要：
SAX J 1818.6 -1703是一个闪烁的瞬态X射线源，是BeppoSAX于1998年在观测银河系中心时偶然发现的。该源被确认为一颗高质量X射线双星，伴随着一颗OB超巨星。该源具有短暂而明亮的耀斑和异常低的静态能级，表明强度动态范围高达1 e 3 -4，因此被归类为超巨星快速X射线瞬变。触发经典SGXB和最近发现的SFXT类之间观察到的不同时间行为的机制仍有争议。长轨道（>15 d）的发现应有助于区分排放模型并带来限制。我们分析了SAX J1818.6-1703上的存档INTEGRAL数据。我们建立了短期和长期的光变曲线，并进行了时序分析，以研究不同时间尺度上的SAX J1818.6-1703的时间行为。INTEGRAL揭示了一个异常长的轨道周期为30.0+/-0.2 d，在短暂的SGXB SAX J1818.6-1703中经历了一个约6 d的吸积阶段。这意味着一个椭圆轨道，并限制了可能的超巨星光谱类型在B0.5- 1 I之间，偏心率e~0.3-0.4（对于超巨星的平均基本参数）。在吸积阶段，源表现得像经典的SGXB。观测到的X射线通量的巨大变化可以通过恒星风中形成的大团块的吸积来解释。我们的分析加强了模型预测SFXTs的行为SGXB，但不同的轨道参数，从而不同的时间行为。
英文摘要：
SAX J1818.6-1703 is a flaring transient X-ray source serendipitously discovered by BeppoSAX in 1998 during an observation of the Galactic centre. The source was identified as a High-Mass X-ray Binary with an OB SuperGiant companion. Displaying short and bright flares and an unusually very-low quiescent level implying intensity dynamical range as large as 1e3-4, the source was classified as a Supergiant Fast X-ray Transient. The mechanism triggering the different temporal behaviour observed between the classical SGXBs and the recently discovered class of SFXTs is still debated. The discovery of long orbits (>15 d) should help to discriminate between emission models and bring constraints. We analysed archival INTEGRAL data on SAX J1818.6-1703. We built short- and long-term light curves and performed timing analysis in order to study the temporal behaviour of SAX J1818.6-1703 on different time scales. INTEGRAL revealed an unusually long orbital period of 30.0+/-0.2 d and an elapsed accretion phase of ~6 d in the transient SGXB SAX J1818.6-1703. This implies an elliptical orbit and constraints the possible supergiant spectral type between B0.5-1I with eccentricities e~0.3-0.4 (for average fundamental parameters of supergiant stars). During the accretion phase, the source behaved like classical SGXBs. The huge variations of the observed X-ray flux can be explained through accretion of macro-clumps formed within the stellar wind. Our analysis strengthens the model which predicts that SFXTs behave as SGXBs but with different orbital parameters, thus different temporal behaviour.
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