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More than softer-when-brighter: The X-ray powerlaw spectral variability in NGC 4051

Science China(Physics,Mechanics & Astronomy) 2020年第12期63卷 102-112页

作者： Yun-Jing Wu Jun-Xian Wang Zhen-Yi Cai Jia-Lai Kang Teng Liu Zheng Cai CAS Key Laboratory for Research in galaxies and Cosmology Department of AstronomyUniversity of Science and Technology of ChinaHefei 230026China School of Astronomy and Space Science University of Science and Technology of ChinaHefei 230026China Department of Astronomy Tsinghua UniversityBeijing 100084China Max-Planck-Institut für Extraterrestrische Physik Garching bei Munchen D-85748Germany

The powerlaw X-ray spectra of active galactic nuclei at moderate to high accretion rates normally appear softer when they brighten,for which the underlying mechanisms are yet *** XMM-Newton observations and excluding photons<2 keV to avoid contamination from the soft excess,in this work we scrutinize the powerlaw spectral variability of NCG 4051 from two new *** first find that a best-fit"softer-when-brighter"relation is statistically insufficient to explain the observed spectral variabilities,and intervals deviated from the empirical relation are clearly visible in the light curve of 2-4 ke V/4-10 keV count rate *** deviations are seen not only between but also within individual XMM-Newton exposures,consistent with random variations of the corona geometry or inner structure(with timescales as short as^1 ks),in addition to those behind the smooth"softer-when-brighter"*** further find the"softer-when-brighter"trend gradually weakens with the decreasing timescale(from^100 ks down to 0.5 ks).These findings indicate that the powerlaw spectral slope is not solely determined by its *** propose a two-tier geometry,including flares/nano-flares on top of the inner disc and an embedding extended corona(heated by the flares,in analogy to solar corona)to explain the observations together with other observational clues in *** spectral variabilities could be due to individual flares/nano-flares,while slow ones are driven by the variations in the global activity of inner disc region(akin to the variation of solar activity,but not the accretion rate)accompanied with heating/cooling and inflation/contraction of the extended corona.

关键词： active galaxies X-ray seyfert galaxies

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UV and X-ray variability of the narrow-line seyfert 1 galaxy Ark 564

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Research in Astronomy and Astrophysics 2016年第7期16卷 69-76页

作者： Savithri H.Ezhikode Gulab C.Dewangan Ranjeev Misra Shruti Tripathi Ninan Sajeeth Philip Ajit K.Kembhavi Department of Physics St. Thomas College Kozhencherry Kerala 689641 India Inter-University Centre for Astronomy & Astrophysics Post Bag 4 Ganeshkhind Pune 411 007 India Physics Department Bishop's University 2600 College Street Sherbrooke QC J1M1Z7 Canada

We analyze eight XMM-Newton observations of the bright Narrow Line seyfert 1 galaxy Arakelian 564（Ark 564）. These observations, separated bye^6 days, allow us to look for correlations between the simultaneous ultraviolet（UV） emission（from th Optical Monitor） with not only the X-ray flux but also with different X-ray spectral parameters. The X-ray spectra from all the observations are found to be adequately fitted by a double Comptonization model where the soft excess and the hard X-ray power law are represented by thermal Comptonization in a low temperature plasma and hot corona, respectively. Apart from the fluxes of each component, the hard X-ray power law index is found to be variable. These results suggest that the variability is associated with changes in the geometry of the inner region. The UV emission is found to be variable and well correlated with the high energy index while the correlations with the fluxes of each component are found to be weaker. Using viscous timescale arguments we rule out the possibility that the UV variation is due to the fluctuating accretion rate in the outer disk. If the UV variation is driven by X-ray reprocessing, then our results indicate that the strength of the X-ray reprocessing depends more on the geometry of the X-ray producing inner region rather than on the X-ray luminosity alone.

关键词： galaxies active galaxies seyfert galaxies individual(Ark 564) X-rays galaxies

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