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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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SDSS J1042-0018:a Broad Line AGN but Misclassified as an HⅡGalaxy in the BPT Diagram by Flux Ratios of Narrow Emission Lines

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Research in Astronomy and Astrophysics 2022年第4期22卷 114-122页

作者： Yi Cao Si-Dan Zhao Xing-Yu Zhu Hai-Chao Yu Yi-Wei Wang Xue-Guang Zhang School of Physics and Technology Nanjing Normal UniversityNanjing 210023China

In this paper,we discuss properties of SDSS J1042-0018 which is a broad line active galactic nucleus(AGN)but misclassified as an H II galaxy in the BPT diagram(SDSS J1042-0018 is called a misclassified broad line AGN).The emission lines around Hαand around Hβare well described by different model functions,considering broad Balmer lines to be described by Gaussian or Lorentz *** model functions lead to different determined narrow emission line fiuxes,but the different narrow emission line fiux ratios lead SDSS J1042-0018 as an H II galaxy in the BPT *** order to explain the unique properties of the misclassified broad line AGN SDSS J1042-0018,two methods are proposed,the star-forming contributions and the compressed narrow emission line regions with high electron densities near to critical densities of forbidden emission ***,the strong star-forming contributions can be preferred in SDSS *** misclassified broad line AGN SDSS J1042-0018,well explained by star-forming contributions,could provide further clues on the applications of BPT diagrams to the normal broad line AGNs.

关键词： active galaxies active galactic nuclei emission line galaxies Quasars

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The parameters of binary black hole system in PKS 1510-089

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Chinese Physics B 2007年第3期16卷 876-880页

作者：李娟樊军辉袁聿海 Centre for Astrophysics Guangzhou University Guangzhou 510006 China

Observations of PKS 1510-089 indicate the existence of a deep flux minimum with a timescale of -35 min and an interval of about 336 ± 14 d. A binary black hole system is proposed to be at the nucleus of this object. The secondary black hole orbits around the primary black hole. The minimum is caused by the periodic eclipse of the primary black hole by the secondary black hole. Based on the observations of PKS 1510-089, we estimate the parameters of the binary black hole system. The masses for the primary and secondary black holes are 1.37 × 10^9M⊙（M⊙ is the solar mass） and 1.37 × 10^7M⊙, and the major axis for this pair being about 0.1 parsec（pc）.

关键词： active galaxies black hole individual (PKS1510-089)

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On the M-σ Relationship and SMBH Mass Estimates of Selected Nearby galaxies

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International Journal of Astronomy and Astrophysics 2013年第3期3卷 1-9页

作者： Alper K.Ates Can Battal Kilinc Cafer Ibanoglu Astronomy and Space Sciences Department Ege UniversityIzmirTurkey

Super massive black holes are believed to influence galactic evolution and dynamics. A histogram of SMBH masses for different redshift regimes may reveal clues on how the SMBH evolve in time. A prominent method for SMBH mass estimation is based on the linear correlation between the bulge velocity dispersion and the SMBH mass. Known as M-σ relationship, this method is known to provide reasonable but not very accurate mass estimates due to considerable scatter in data. In order to increase the precision, we surveyed the literature and gathered SMBH and velocity dispersion data for low redshift (z 0.02) spiral galaxies. We report the M-σ relationship for low redshift spiral galaxies as, By using this refined M-σ relationship we measured 32 SMBH masses and determined upper and lower mass boundaries and the mass histogram for spiral galaxies in a narrow redshift regime (0.016 z < 0.017). The spectroscopic data are obtained from The SLOAN Digital Survey and The National Observatory of Turkey (TUG). The targets are selected within a low redshift range for discernible [OIII] lines. TUG observations are carried out on the RTT150 1.5 m telescope using TUG Faint Object Spectrographic Camera and the SLOAN data are obtained from the 7th data release of the survey. We measured the bandwidths of narrow [OIII] lines, which are shown to be indicative in estimating stellar bulge velocity dispersion and estimated the central black hole masses from the refined version of the empirical M-σ relationship. The estimated masses vary between 9.51 × 106 - 2.36 × 108 solar masses.

关键词： galaxies active galaxies AGN SMBH Stellar Velocity Dispersion Bulge Velocity Dispersion

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