天鹰座V1494的X射线光谱和光变曲线的演化
Evolution of X-ray spectra and light curves of V1494 Aquilae
摘要：
本文给出了新星V1494 Aql（1999#2）爆发时的六个Chandra X射线谱和光变曲线。前三次观测是在爆发后第134、187和248天用ACIS-I进行的。计数率分别为1.00、0.69和0.53 cps。我们发现ACIS光变曲线没有明显的周期性。X射线谱显示出连续发射和来自N和O的谱线。我们发现可以接受的光谱拟合使用等温APEC模型与显着增加元素丰度的O和N的所有观测。在爆发后的第248天，除了褪色的发射线外，还出现了明亮的软组分。第300、304和727天的钱德拉观测是与HRC/LETGS一起进行的。光谱由连续发射加上O和N的强发射线组成，这意味着这些元素的丰度很高。在第300天，发生了耀斑，并在第300天和第304天拍摄的光变曲线中检测到周期性振荡。这个耀斑必须起源于流出物质的深处，因为它在短时间尺度上是可变的。在耀斑前后提取的光谱非常相似，这意味着耀斑是一个非常孤立的事件。我们试图拟合黑体，多云，或APEC模型的LETG光谱失败，由于在解开连续谱和发射线组件的困难。在耀斑期间提取的光谱显示，许多谱线的强度显着增加，并出现了几条以前未检测到的谱线。此外，在耀斑之前和之后看到的一些线条在耀斑期间并不存在。在第727天，只能得到零阶的计数率，而且源太微弱，无法提取光变曲线或光谱。
英文摘要：
We present six Chandra X-ray spectra and light curves obtained for the nova V1494 Aql (1999 #2) in outburst. The first three observations were taken with ACIS-I on days 134, 187, and 248 after outburst. The count rates were 1.00, 0.69 and 0.53 cps, respectively. We found no significant periodicity in the ACIS light curves. The X-ray spectra show continuum emission and lines originating from N and O. We found acceptable spectral fits using isothermal APEC models with significantly increased elemental abundances of O and N for all observations. On day 248 after outburst a bright soft component appeared in addition to the fading emission lines. The Chandra observations on days 300, 304, and 727 were carried out with the HRC/LETGS. The spectra consist of continuum emission plus strong emission lines of O and N, implying a high abundance of these elements. On day 300, a flare occurred and periodic oscillations were detected in the light curves taken on days 300 and 304. This flare must have originated deep in the outflowing material since it was variable on short time scales. The spectra extracted immediately before and after the flare are remarkably similar, implying that the flare was an extremely isolated event. Our attempts to fit blackbody, Cloudy, or APEC models to the LETG spectra failed, owing to the difficulty in disentangling continuum and emission line components. The spectrum extracted during the flare shows a significant increase in the strengths of many of the lines and the appearance of several previously undetected lines. In addition, some of the lines seen before and after the flare are not present during the flare. On day 727 only the count rate from the zeroth order could be derived, and the source was too faint for the extraction of a light curve or spectrum.
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