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arXiv 0905.4809astro-ph.HEastro-ph.SR
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低质量X射线双星4U 1636-53中一个非常罕见的三峰I型X射线爆发

A very rare triple-peaked type-I X-ray burst in the low-mass X-ray binary 4U 1636-53

Guobao Zhang, Mariano Mendez, Diego Altamirano, Tomaso M. Belloni, Jeroen Homan

摘要:

利用Rossi X射线计时探测器(RXTE)在低质量X射线双星(LMXB)4U 1636-53中发现了一个三峰X射线爆发。这是使用RXTE从任何LMXB报告的第一个三峰爆发,也是从任何来源观察到的第二个此类爆发。(The前一次也来自4U 1636-53,是用EXOSAT观测到的。从时间分辨光谱的拟合,我们发现这不是一个半径膨胀爆发,并且在X射线光变曲线中看到的相同的三峰模式也存在于爆发的热光变曲线中。类似于以前在这个来源的双峰爆发中观察到的情况,在爆发期间,发射区的半径稳步增加,在这之间的短时间内,半径或多或少保持不变。温度首先急剧上升,然后在整个爆发中下降,也显示出三个峰值。温度曲线中的第一个和最后一个峰值分别明显地出现在X射线和热辐射光变曲线中的第一个和最后一个峰值之前和之后。我们在这次爆发中没有发现明显的振荡。这一三峰爆发,以及EXOSAT观测到的爆发和该源的双峰爆发,都发生在4U 1636-53在色图中占据相对较窄的区域时,对应于相对较高的(推断的)质量吸积率。目前没有模型能够解释多峰爆发。

英文摘要:

We have discovered a triple-peaked X-ray burst from the low-mass X-ray binary (LMXB) 4U 1636-53 with the Rossi X-ray Timing Explorer (RXTE). This is the first triple-peaked burst reported from any LMXB using RXTE, and it is only the second burst of this kind observed from any source. (The previous one was also from 4U 1636-53, and was observed with EXOSAT.) From fits to time-resolved spectra, we find that this is not a radius-expansion burst, and that the same triple-peaked pattern seen in the X-ray light curve is also present in the bolometric light curve of the burst. Similar to what was previously observed in double-peaked bursts from this source, the radius of the emitting area increases steadily during the burst, with short periods in between during which the radius remains more or less constant. The temperature first increases steeply, and then decreases across the burst also showing three peaks. The first and last peak in the temperature profile occur, respectively, significantly before and significantly after the first and last peaks in the X-ray and bolometric light curves. We found no significant oscillations during this burst. This triple-peaked burst, as well as the one observed with EXOSAT and the double-peak bursts in this source, all took place when 4U 1636-53 occupied a relatively narrow region in the colour-colour diagram, corresponding to a relatively high (inferred) mass-accretion rate. No model presently available is able to explain the multiple-peaked bursts.

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