非稳态吸积主导X射线双星从硬态到软态的态跃迁

Hard-to-soft State Transition Dominated by Non-stationary Accretion

最近几年一些新的研究发现,X射线双星从硬态到软态的态跃迁光度和随后的软态峰值光度成正相关,而且还发现了从硬态到软态的态跃迁光度和上升时期的光度增加率成正相关,这两个经验关系表明最亮的硬态和从硬态到软态的态跃迁主要是由吸积率的变化率所表征的非稳态吸积过程所主导的。对GX 339-4的研究表明,硬X射线峰值光度由爆发前吸积盘所积累的质量决定,而且低质量X射线双星暂现源的爆发峰值光度和轨道周期的正相关关系也支持该观点,由此推断爆发或者闪耀这样的非稳态吸积过程是由吸积盘所积累的质量这个初始条件所决定的。

Different states of X-ray binaries are defined according to some observational features such as X-ray spectra and timing variabilities. The theory based on the stationary accretion was used to explain different states and state transitions, but there is a gap between the theories and observations. Some new studies show that non-stationary accretion deter- mined the luminosity of the hard-to-soft state transition. A positive correlation between the luminosity of the hard-to-soft state transition and the peak luminosity of the following soft state was found in some X-ray binaries, and then a statistical study about the sate transition luminosity showed that transient and persistent X-ray binaries follow the same positive correlation. Another positive correlation between the luminosity of the hard-to-soft state transition and the rate-of-increase of luminosity was found. These two empirical cot-relations suggest that the hard-to-soft state transition is dominated by the non-staUonary accretion which is characterized by the rate of increase of the mass accretion rate. There is a unique correlation between the peak flux in the hard X-ray and the outburst waiting time in GX 339-4, implying that the peak flux in the hard X-ray is determined by the mass accumulated before the outburst. On the other hand the statistical study about the peak luminosity of outbursts in LMXB transients showed that the peak luminosities of outbursts positively correlate with the orbital periods, which also supports that the peak luminosity is determined by the disk mass. These results suggest that the non-stationary accretion in outbursts/flares is set up by the initial condition - disk mass.