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X射线脉冲星SWIFT J1626的明亮耀斑。6 -5156

Bright flares from the X-ray pulsar SWIFT J1626.6-5156

P. Reig, T. Belloni, G. L. Israel, S. Campana, N. Gehrels, J. Homan

摘要:

我们对X射线脉冲星SWIFT J1626.6-5156在一次大的X射线爆发期间进行了时间和光谱分析,以揭示其性质并调查其耀斑活动。历元和脉冲折叠技术被用来推导自旋周期。利用时间平均和脉冲相位谱研究了耀斑和非耀斑状态下的光谱变化以及能量随脉冲相位的变化。功率谱的周期性和非周期性的变化进行了调查。2005年12月24日和25日观测到两次大耀斑,持续时间约为450秒。在耀斑期间,X射线强度增加了3.5倍,而峰-峰脉冲幅度从45%增加到70%。2005年12月27日观测到第三次较小的耀斑,持续时间约为180秒。在SWIFT J1626.6-5156中看到的耀斑构成了在高质量X射线双星中报道的这类事件中最短的事件。除了耀斑活动外,Pspin=15.3714+-0.0003 s的强X射线脉动也抑制了SWIFT J1626.6-5156中的X射线发射。大爆发后,光变曲线表现出强烈的长期变化,以45天为周期。我们将这种调制与系统的轨道周期或谐波联系起来。功率密度谱显示,除了脉动的谐波成分,强的带限噪声与集成的0.01-100 Hz分数均方根约40%,增加到64%,在耀斑。在非耀斑辐射中检测到特征频率为1 Hz的弱QPO(分数均方根4.7%)。SWIFT J1626.6-5156的时间(短X射线脉动,长轨道周期)和光谱(具有截止能量和中性铁线的幂律)特性是Be/X射线双星的特征。

英文摘要:

We have performed a timing and spectral analysis of the X-ray pulsar SWIFT J1626.6-5156 during a major X-ray outburst in order to unveil its nature and investigate its flaring activity. Epoch- and pulse-folding techniques were used to derive the spin period. Time-average and pulse-phase spectroscopy were employed to study the spectral variability in the flare and out-of-flare states and energy variations with pulse phase. Power spectra were obtained to investigate the periodic and aperiodic variability. Two large flares, with a duration of ~450 seconds were observed on 24 and 25 December 2005. During the flares, the X-ray intensity increased by a factor of 3.5, while the peak-to-peak pulsed amplitude increased from 45% to 70%. A third, smaller flare of duration ~180 s was observed on 27 December 2005. The flares seen in SWIFT J1626.6-5156 constitute the shortest events of this kind ever reported in a high-mass X-ray binary. In addition to the flaring activity, strong X-ray pulsations with Pspin=15.3714+-0.0003 s characterise the X-ray emission in SWIFT J1626.6-5156. After the major outburst, the light curve exhibits strong long-term variations modulated with a 45-day period. We relate this modulation to the orbital period of the system or to a harmonic. Power density spectra show, in addition to the harmonic components of the pulsation, strong band-limited noise with an integrated 0.01-100 Hz fractional rms of around 40% that increased to 64% during the flares. A weak QPO (fractional rms 4.7%) with characteristic frequency of 1 Hz was detected in the non-flare emission. The timing (short X-ray pulsations, long orbital period) and spectral (power-law with cut off energy and neutral iron line) properties of SWIFT J1626.6-5156 are characteristic of Be/X-ray binaries.

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