X射线瞬态SAXJ-2609与INTEGRAL的活性恢复
Renewed activity from the X-ray transient SAXJ 1810.8-2609 with INTEGRAL
摘要：
本文报道了2007年8月对中子星低质量X射线双星SAXJ1810.8 -2609的积分观测结果。这次爆发是1998年以来的第一次爆发，在20-100 keV的能量范围内，得到的光度为1.1-2.6x10^36 erg s-1。这种低爆发光度和约5 × 10 ^-12兆太阳/年的长期平均吸积率表明SAXJ 1810.8-2609是一个微弱的软X射线瞬变。在通量增加的过程中，光谱与热康普顿化模型一致，等离子体温度为~23-30 keV，光学深度为~1.2-1.5，与系统的光度无关。这是一个典型的低硬光谱状态的X射线发射归因于软种子光子的热，光学薄的电子等离子体的上散射。在衰变期间，光谱具有不同的形状，高能量尾部与单一幂律相容。这证实了BeppoSAX号卫星在前一次爆发期间观察到的类似行为，在硬X射线光谱中没有可见的截止。INTEGRAL/JEM-X仪器在2007年秋季观察到4次X射线爆发。第一个具有最高的峰值通量（在3--25 keV能量范围内约为3.5Crab），对于LEdd约为3.8x10^38 erg s^-1的情况，源的距离上限约为5.7 kpc。观测到的重现时间约为1.2天，持续通量中发射的总能量与爆发中发射的总能量之比（约为73）使我们能够得出结论，爆发燃料由氢和氦的混合物组成，X>0.4。
英文摘要：
We report on the results of INTEGRAL observations of the neutron star low mass X-ray binary SAX J1810.8-2609 during its latest active phase in August 2007. The current outburst is the first one since 1998 and the derived luminosity is 1.1-2.6x10^36 erg s-1 in the 20-100 keV energy range. This low outburst luminosity and the long-term time-average accretion rate of ~5x10^-12Msolar/yr suggest that SAXJ 1810.8-2609 is a faint soft X-ray transient. During the flux increase, spectra are consistent with a thermal Comptonization model with a temperature plasma of ~23-30 keV and an optical depth of ~1.2-1.5, independent from luminosity of the system. This is a typical low hard spectral state for which the X-ray emission is attributed to the upscattering of soft seed photons by a hot, optically thin electron plasma. During the decay, spectra have a different shape, the high energy tail being compatible with a single power law. This confirm similar behavior observed by BeppoSAX during the previous outburst, with absence of visible cutoff in the hard X-ray spectrum. INTEGRAL/JEM-X instrument observed four X-ray bursts in Fall 2007. The first one has the highest peak flux (~3.5Crab in 3--25 keV) giving an upper limit to the distance of the source of about 5.7 kpc, for a LEdd~3.8x10^38 erg s^-1. The observed recurrence time of ~1.2 days and the ratio of the total energy emitted in the persistent flux to that emitted in the bursts (~73) allow us to conclude that the burst fuel was composed by mixed hydrogen and helium with X>0.4.
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