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arXiv 2102.11633astro-ph.HE
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射电强窄线塞弗特1星系PKS 2004-447的第一次GeV耀斑

The first GeV flare of the radio-loud narrow-line Seyfert 1 galaxy PKS 2004-447

Andrea Gokus, Vaidehi S. Paliya, Sarah M. Wagner, Sara Buson, Filippo D'Ammando, Philip G. Edwards, Matthias Kadler, Manuel Meyer, Roopesh Ojha, Jamie Stevens, Jörn Wilms

摘要:

2019年10月25日,费米大面积望远镜观测到了来自射电大声窄线塞弗特1(NLSy 1)星系PKS 2004 $-$ 447($z=0.24$)的第一个伽马射线耀斑。我们报告了ATCA,Neil Gehrels Swift天文台,XMM-Newton和NuSTAR分别进行的无线电,光学紫外线和X射线波段的后续观测以及我们的多波长分析。我们研究了所有能带的变化,并另外产生了不同时间装仓的$γ$射线光变曲线,以研究耀斑期间短时间尺度上的变化。我们研究的X射线光谱从0.5 $-$ 50千电子伏的光谱形状与吸收的功率定律。我们分析多波长数据集之前,期间和之后的耀斑和比较这些与低活动状态的源通过建模各自的SED与一个区域同步逆康普顿辐射模型。最后,我们将我们的结果与以前从其他$γ$ -响亮的NLSy 1星系观察到的伽马射线耀斑进行了比较。在伽马射线能量(0.1 $-$ 300 GeV)下,耀斑在3小时的分箱中达到了总最大通量$(2.7\pm0.6)\times10^{-6}$ ~ph~cm $^{-2}$ ~s $^{-1}$。耀斑期间的光子指数为$Γ_{0.1-300\mathrm{GeV}}=2.42\pm0.09$,这对应于各向同性伽马射线光度$(2.9\pm0.8)\times10^{47}\,\mathrm{erg}\,\mathrm{s}^{-1}$。从9月底到11月中旬的$γ$射线、X射线和光学-紫外光变曲线显示出显著的变化,我们发现在$γ$射线能量下通量倍增时间为$\sim 2.2$ ~小时的迹象。在耀斑期间,SED表现出很大的康普顿优势。虽然光学紫外范围的增加可以用增强的同步辐射来解释,但$γ$射线通量的增加可以用喷流的体积洛伦兹因子的增加来解释,这与在闪烁的伽马射线耀变体中观察到的情况类似。

英文摘要:

On 2019 October 25, the Fermi-Large Area Telescope observed the first gamma-ray flare from the radio-loud narrow-line Seyfert 1 (NLSy 1) galaxy PKS 2004$-$447 ($z=0.24$). We report on follow-up observations in the radio, optical-UV, and X-ray bands that were performed by ATCA, the Neil Gehrels Swift observatory, XMM-Newton, and NuSTAR, respectively, and our multi-wavelength analysis. We study the variability across all energy bands and additionally produce $γ$-ray light curves with different time binnings to study the variability on short timescales during the flare. We examine the X-ray spectrum from 0.5$-$50 keV by describing the spectral shape with an absorbed power law. We analyse multi-wavelength datasets before, during, and after the flare and compare these with a low activity state of the source by modelling the respective SEDs with a one-zone synchrotron inverse Compton radiative model. Finally, we compare our results to gamma-ray flares previously observed from other $γ$-loud NLSy 1 galaxies. At gamma-ray energies (0.1$-$300 GeV) the flare reached a total maximum flux of $(2.7\pm0.6)\times10^{-6}$~ph~cm$^{-2}$~s$^{-1}$ in 3-hour binning. With a photon index of $Γ_{0.1-300\mathrm{GeV}}=2.42\pm0.09$ during the flare, this corresponds to an isotropic gamma-ray luminosity of $(2.9\pm0.8)\times10^{47}\,\mathrm{erg}\,\mathrm{s}^{-1}$. The $γ$-ray, X-ray, and optical-UV light curves covering the end of September to the middle of November show significant variability, and we find indications for flux-doubling times of $\sim 2.2$~hours at $γ$-ray energies. During the flare, the SED exhibits large Compton dominance. While the increase in the optical-UV range can be explained by enhanced synchrotron emission, the elevated $γ$-ray flux can be accounted for by an increase in the bulk Lorentz factor of the jet, similarly observed for flaring gamma-ray blazars.

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