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arXiv 1003.3460astro-ph.HE
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超爱丁顿瞬态XTE J1701-462中子星的快速冷却

Rapid Cooling of the Neutron Star in the Quiescent Super-Eddington Transient XTE J1701-462

Joel K. Fridriksson, Jeroen Homan, Rudy Wijnands, Mariano Mendez, Diego Altamirano, Edward M. Cackett, Edward F. Brown, Tomaso M. Belloni, Nathalie Degenaar, Walter H. G. Lewin

摘要:

我们介绍了Rossi X射线定时探测器和雨燕观测在2006-2007年的超爱丁顿中子星(NS)瞬态XTE J1701-462爆发的最后三个星期,以及钱德拉和XMM-牛顿观测涵盖了随后的静止期的前800天。源从活跃吸积迅速过渡到平静,在~13天内光度下降了3个数量级以上。在静止期间获得的光谱表现出热分量,假定起源于从NS表面的发射,和一个不确定的起源,这表明大的和不规则的变化的非热分量。我们解释所观察到的衰减推断的有效表面温度的NS在平静的冷却NS地壳后,被加热,并带来了热平衡的核心在爆发。数据的解释是复杂的,因为温度明显暂时升高,大约220天进入静止期,可能是由于额外的吸积激增。我们推导出推断温度的指数衰减时间尺度约为120(+30/-20)天(不包括受暂时增加影响的观测)。这个短时间尺度表明一个高导电性的NS地壳。需要进一步的观测来确认地壳是否仍在缓慢冷却,或者已经与地核达到热平衡,表面温度约为125 eV。后者意味着在8.8千秒差距的假设距离下,一个高的平衡热光度约为5x 10 ^{33} erg/s。

英文摘要:

We present Rossi X-Ray Timing Explorer and Swift observations made during the final three weeks of the 2006-2007 outburst of the super-Eddington neutron star (NS) transient XTE J1701-462, as well as Chandra and XMM-Newton observations covering the first ~800 days of the subsequent quiescent phase. The source transitioned quickly from active accretion to quiescence, with the luminosity dropping by over 3 orders of magnitude in ~13 days. The spectra obtained during quiescence exhibit both a thermal component, presumed to originate in emission from the NS surface, and a non-thermal component of uncertain origin, which has shown large and irregular variability. We interpret the observed decay of the inferred effective surface temperature of the NS in quiescence as the cooling of the NS crust after having been heated and brought out of thermal equilibrium with the core during the outburst. The interpretation of the data is complicated by an apparent temporary increase in temperature ~220 days into quiescence, possibly due to an additional spurt of accretion. We derive an exponential decay timescale of ~120 (+30/-20) days for the inferred temperature (excluding observations affected by the temporary increase). This short timescale indicates a highly conductive NS crust. Further observations are needed to confirm whether the crust is still slowly cooling or has already reached thermal equilibrium with the core at a surface temperature of ~125 eV. The latter would imply a high equilibrium bolometric thermal luminosity of ~5x10^{33} erg/s for an assumed distance of 8.8 kpc.

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