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arXiv 1402.6015astro-ph.HE
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Fermi/GBM探测SGR J1550-5418爆发的时间分辨光谱

Time resolved spectroscopy of SGR J1550-5418 bursts detected with Fermi/GBM

G. Younes, C. Kouveliotou, A. J. van der Horst, M. G. Baring, J. Granot, A. L. Watts, P. N. Bhat, A. Collazzi, N. Gehrels, N. Gorgone, E. Gogus, D. Gruber, S. G… 展开作者

G. Younes, C. Kouveliotou, A. J. van der Horst, M. G. Baring, J. Granot, A. L. Watts, P. N. Bhat, A. Collazzi, N. Gehrels, N. Gorgone, E. Gogus, D. Gruber, S. Grunblatt, D. Huppenkothen, Y. Kaneko, A. von Kienlin, M. van der Klis, L. Lin, J. Mcenery, T. van Putten, R. A. M. J. Wijers

摘要:

我们报告的时间分辨光谱的63个最明亮的爆发SGR J1550-5418,检测费米/伽马射线暴监测器在其2008-2009年的强烈爆发插曲。我们进行了频谱分析下降到4毫秒的时间尺度,表征的频谱演变的爆发。使用康普顿化模型,我们发现峰值能量E_peak与通量反相关,而低能光子指数在通量极限F~10^-5 erg s-1 cm-2时保持恒定在-0.8。在此通量值以上,E_peak与通量的相关性改变了符号,并且指数与通量正相关,在最大通量处达到1。利用双黑体模型,我们发现两个发射区的面积和通量正相关。此外,我们在这里首次研究了温度和面积随通量的变化。我们发现,面积-kT关系在最低通量R^2 \propto kT^-4处遵循恒定光度线,在较高通量($F>10^-5.5 erg s-1 cm-2)处出现突变。高kT组件的面积随着通量的增加而增加,同时其温度降低,我们解释为由于绝热冷却过程。另一方面,低kT分量的区域在最高通量处似乎饱和,接近R_max~30 km。假设SGR爆发是由地壳地震引起的,并把R_max作为发射光子对等离子体火球的最大半径,我们把这个饱和半径与磁层的最小激发半径联系起来,并给出了SGR J 1550 -5418的内部磁场的下限,B_int>~ 4.5 × 10^15 G。

英文摘要:

We report on time-resolved spectroscopy of the 63 brightest bursts of SGR J1550-5418, detected with Fermi/Gamma-ray Burst Monitor during its 2008-2009 intense bursting episode. We performed spectral analysis down to 4 ms time-scales, to characterize the spectral evolution of the bursts. Using a Comptonized model, we find that the peak energy, E_peak, anti-correlates with flux, while the low-energy photon index remains constant at -0.8 up to a flux limit F~10^-5 erg s-1 cm-2. Above this flux value the E_peak-flux correlation changes sign, and the index positively correlates with flux reaching 1 at the highest fluxes. Using a two black-body model, we find that the areas and fluxes of the two emitting regions correlate positively. Further, we study here for the first time, the evolution of the temperatures and areas as a function of flux. We find that the area-kT relation follows lines of constant luminosity at the lowest fluxes, R^2 \propto kT^-4, with a break at higher fluxes ($F>10^-5.5 erg s-1 cm-2). The area of the high-kT component increases with flux while its temperature decreases, which we interpret as due to an adiabatic cooling process. The area of the low-kT component, on the other hand, appears to saturate at the highest fluxes, towards R_max~30 km. Assuming that crust quakes are responsible for SGR bursts and considering R_max as the maximum radius of the emitting photon-pair plasma fireball, we relate this saturation radius to a minimum excitation radius of the magnetosphere, and put a lower limit on the internal magnetic field of SGR J1550-5418, B_int>~4.5x10^15 G.

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