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arXiv 2107.05660astro-ph.HE
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2020年8月至10月期间对$γ$ -射线闪耀耀变体BL Lacertae的NICER、NuSTAR和Swift跟踪观测

NICER, NuSTAR, and Swift follow-up observations of the $γ$-ray flaring blazar BL Lacertae in 2020 August-October

Filippo D'Ammando

摘要:

在一段来自BL Lacertae的强烈$γ$射线耀斑活动期间,我们组织了雨燕,中子星内部成分探测器(NICER)和核光谱望远镜阵列(NuSTAR)的后续观测。在2020年8月11日至10月16日期间,Swift-XRT(X射线望远镜)对该源进行了监测,显示其变化幅度为65,通量在1.0 $\times$ 10 $^{-11}$和65.3 $\times$ 10 $^{-11}$ erg cm $^{-2}$ s $^{-1}$之间变化。2020年10月6日,Swift-XRT在其历史最大X射线通量期间观察到了该源。一个软时,更明亮的行为已被观察到的XRT,这表明一个日益重要的同步辐射在X射线光谱的一部分,在这个明亮的状态覆盖的XRT。在Swift-XRT和NICER观测中都观察到了软X射线的快速变化,最小变化时间尺度分别为60和240 s,倍增时间尺度分别为274和1008 s,这表明发射区域非常紧凑(1.1 $\times$ 10 $^{14}$和4.0 $\times$ 10 $^{14}$ cm)。在硬X射线,$\sim$ 5.5 ks的最小可变性时间尺度已被NuSTAR观察到。我们报告了2020年10月11日至12日期间BL Lacertae的首次同时NICER和NuSTAR观测。NICER和NuSTAR联合谱符合破幂律,在$\sim$ 2.7 keV处,光子指数在2.10以下和1.60以上有显著差异,表明在宽带X射线谱中存在两种不同的发射成分(即同步辐射和逆康普顿辐射)。离开总氢柱密度向BL Lacertae自由变化,值N $_{H,tot}$ =(2.58 $\pm$ 0.09)$\times$ 10 $^{21}$ cm $^{-2}$已被估计。

英文摘要:

During a period of strong $γ$-ray flaring activity from BL Lacertae, we organized Swift, Neutron star Interior Composition Explorer (NICER), and Nuclear Spectroscopic Telescope Array (NuSTAR) follow-up observations. The source has been monitored by Swift-XRT (X-ray Telescope) between 2020 August 11 and October 16, showing a variability amplitude of 65, with a flux varying between 1.0 $\times$ 10$^{-11}$ and 65.3 $\times$ 10$^{-11}$ erg cm$^{-2}$ s$^{-1}$. On 2020 October 6, Swift-XRT has observed the source during its historical maximum X-ray flux. A softer-when-brighter behaviour has been observed by XRT, suggesting an increasing importance of the synchrotron emission in the X-ray part of the spectrum covered by XRT during this bright state. Rapid variability in soft X-rays has been observed with both the Swift-XRT and NICER observations with a minimum variability time-scale of 60 and 240 s, and a doubling time-scale of 274 and 1008 s, respectively, suggesting very compact emitting regions (1.1 $\times$ 10$^{14}$ and 4.0 $\times$ 10$^{14}$ cm). At hard X-rays, a minimum variability time-scale of $\sim$ 5.5 ks has been observed by NuSTAR. We report the first simultaneous NICER and NuSTAR observations of BL Lacertae during 2020 October 11-12. The joint NICER and NuSTAR spectra are well fitted by a broken power law with a significant difference of the photon index below (2.10) and above (1.60) an energy break at $\sim$ 2.7 keV, indicating the presence of two different emission components (i.e, synchrotron and inverse Compton) in the broad band X-ray spectrum. Leaving the total hydrogen column density toward BL Lacertae free to vary, a value of N$_{H,tot}$ = (2.58 $\pm$ 0.09) $\times$ 10$^{21}$ cm$^{-2}$ has been estimated.

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