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arXiv 2009.00630astro-ph.HE
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光学和UV波段发射$γ$射线的窄线Seyfert 1星系的短时标变率

Short time-scale variability of $γ$-ray-emitting narrow-line Seyfert 1 galaxies in optical and UV bands

Filippo D'Ammando

摘要:

我们报告了由紫外线和光学望远镜(UVOT)在{ \em Neil Gehrels Swift Observatory}卫星上进行的所有光学和紫外线(UV)观测的单次曝光的第一次系统分析,该卫星可在2019年4月的6个$γ$ -射线发射窄线Seyfert 1星系(NLSy 1)。在1H 0323+342、SBS 0846+513、PMN J 0948 +0022和PKS 2004-447的18次观察中,在小时时间尺度上检测到了显著的快速变异性,共34起事件。特别是,我们报告的第一次检测到显着的变化,在短时间尺度(3-6 ks)的光学PKS 2004-447,和UV的1H 0323+342和PMN J 0948 +0022。观察到1H 0323+342、SBS 0846+513、PMN J 0948 +0022的最短变异性时间尺度,和PKS 2004-447(假设多普勒因子δ = 10)给出了发射区域大小的下限,在9.7 $\times$ 10 $^{14}$之间(对于SBS 0846+513)和1.6 $\times$ 10 $^{15}$ cm(对于1H 0323+342),表明在这些事件期间的光学和UV发射产生于喷流内的致密区域。这些观测提供了明确的证据,相对论光束同步辐射在这些来源,类似耀变体。2009年6月23日,观察到PMN J 0948 +0022的显著变异性,在$\sim$ 1.6 h内,从v到w2过滤器,从$\sim$ 1.1 mag增加到0.4 mag,在可比时间内,在初始水平下降。在较低频率下观察到的这种和其他事件的较高分数通量变化表明,同步辐射在较高频率下受到吸积盘热辐射的污染更大。

英文摘要:

We report the first systematic analysis of single exposures of all optical and ultraviolet (UV) observations performed by the UltraViolet and Optical Telescope (UVOT) on board the {\em Neil Gehrels Swift Observatory} satellite available up to 2019 April of six $γ$-ray-emitting narrow-line Seyfert 1 galaxies (NLSy1). Rapid variability has been significantly detected on hours time-scale for 1H 0323+342, SBS 0846+513, PMN J0948+0022, and PKS 2004-447 in 18 observations for a total of 34 events. In particular, we report the first detection of significant variability on short time-scale (3-6 ks) in optical for PKS 2004-447, and UV for 1H 0323+342 and PMN J0948+0022. The shortest variability time-scale observed for 1H 0323+342, SBS 0846+513, PMN J0948+0022, and PKS 2004-447 (assuming a Doppler factor delta = 10) gives a lower limit on the size of emission region between 9.7 $\times$ 10$^{14}$ (for SBS 0846+513) and 1.6 $\times$ 10$^{15}$ cm (for 1H 0323+342), suggesting that the optical and UV emission during these events is produced in compact regions within the jet. These observations provide unambiguous evidence about the relativistically beamed synchrotron emission in these sources, similar to blazars. A remarkable variability has been observed for PMN J0948+0022 on 2009 June 23 with an increase from $\sim$1.1 to 0.4 mag going from v to w2 filter in $\sim$1.6 h and a decrease at the initial level in a comparable time. The higher fractional flux change observed for this and other events at lower frequencies suggests that the synchrotron emission is more contaminated by thermal emission from accretion disc at higher frequencies.

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