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Register a new userOrigin of the Broad Iron Line Feature and the Soft X-ray Variation in Seyfert Galaxies
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Many Seyfert galaxies are known to exhibit significant X-ray spectral variations and seemingly broad iron K-emission line features. In this paper, we show that the variable partial covering model, which has been successfully proposed for MCG-6.30-15 (Miyakawa, Ebisawa & Inoue 2012) and 1H0707.495 (Mizumoto, Ebisawa & Sameshima 2014), can also explain the spectral variations in 2-10 keV as well as the broad iron line features in 20 other Seyfert galaxies observed with Suzaku. In this model, the absorbed spectral component through the optically-thick absorbing clouds has a significant iron K-edge, which primarily accounts for the observed seemingly broad iron line feature. Fluctuation of the absorbing clouds in the line of sight of the extended X-ray source results in variation of the partial covering fraction, which causes an anti-correlation between the direct (not covered) spectral component and the absorbed (covered) spectral component below ~10 keV. Observed spectral variation in 2-10 keV in a timescale of less than ~day is primarily explained by such variations of the partial covering fraction, while the intrinsic soft X-ray luminosity is hardly variable.
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The X-ray spectrum of GRS 1915+105 is known to have a ``broad iron spectral feature in the spectral hard state. Similar spectral features are often observed in Active Galactic Nuclei (AGNs) and other black-hole binaries (BHBs), and several models have been proposed for explaining it. In order to distinguish spectral models, time variation provides an important key. In AGNs, variation amplitude has been found to drop significantly at the iron K-energy band at timescales of ~10 ks. If spectral variations of black-holes are normalized by their masses, the spectral variations of BHBs at timescales of sub-seconds should exhibit similar characteristics to those of AGNs. In this paper, we investigated spectral variations of GRS 1915+105 at timescales down to ~10 ms. This was made possible for the first time with the Suzaku XIS Parallel-sum clocking (P-sum) mode, which has the CCD energy-resolution as well as a time-resolution of 7.8 ms. Consequently, we found that the variation amplitude of GRS 1915+105 does not drop at the iron K-energy band at any timescales from 0.06 s to 63000 s, and that the entire X-ray flux and the iron feature are independently variable at timescales of hours. These are naturally understood in the framework of the ``partial covering model, in which variation timescales of the continuum flux and partial absorbers are independent. The difference of energy dependence of the variation amplitude between AGN and BHB is presumably due to different mechanisms of the outflow winds, i.e., the partial absorbers are due to UV-line driven winds (AGN) or thermally-driven winds (BHB).
We present for the first time the timing and spectral analyses for a narrow-line Seyfert 1 galaxy, SBS 1353+564, using it{XMM-Newton} and it{Swift} multi-band observations from 2007 to 2019. Our main results are as follows: 1) The temporal variability of SBS 1353+564 is random, while the hardness ratio is relatively constant over a time span of 13 years; 2) We find a prominent soft X-ray excess feature below 2 keV, which cannot be well described by a simple blackbody component; 3) After comparing the two most prevailing models for interpreting the origin of the soft X-ray excess, we find that the relativistically smeared reflection model is unable to fit the data above 5 keV well and the X-ray spectra do not show any reflection features, such as the Fe Kalpha emission line. However, the warm corona model can obtain a good fitting result. For the warm corona model, we try to use three different sets of spin values to fit the data and derive different best-fitting parameter sets; 4) We compare the UV/optical spectral data with the extrapolated values of the warm corona model to determine which spin value is more appropriate for this source, and we find that the warm corona model with non-spin can sufficiently account for the soft X-ray excess in SBS 1353+564.
We present a detailed comparative systematic study using a sample of 221 Narrow-line Seyfert 1 (NLSy1) galaxies in comparison to a redshift matched sample of 154 Broad-line Seyfert 1 (BLSy1) galaxies based on their observations using ROSAT and/or XMM-Newton telescopes in soft X-ray band (0.1-2.0 keV). A homogeneous analysis is carried out to estimate their soft X-ray photon indices ($Gamma^{s}_{X}$) and its correlations with other parameters of nuclear activities such as Eddington ratios (R$_mathrm{Edd}$), bolometric luminosities (L$_mathrm{bol}$), black hole masses (M$_mathrm{BH}$) and the widths of the broad component of H$beta$ lines (FWHM(H$beta$)). In our analysis, we found clear evidence of the difference in the $Gamma^{s}_{X}$ and R$_mathrm{Edd}$ distributions among NLSy1 and BLSy1 galaxies, with steeper $Gamma^{s}_{X}$ and higher R$_mathrm{Edd}$ for the former. Such a difference also exists in the spectral indices distribution in hard X-ray ($Gamma^{h}_{X}$), based on the analysis of 53 NLSy1 and 46 BLSy1 galaxies in the 2-10 keV energy band. The difference in R$_mathrm{Edd}$ distributions does exist even after applying the average correction for the difference in the inclination angle of NLSy1 and BLSy1 galaxies. We also estimated R$_mathrm{Edd}$, based on SED fitting of 34 NLSy1 and 30 BLSy1 galaxies over the 0.3-10 keV energy band and found that results are still consistent with R$_mathrm{Edd}$ estimates based on the optical bolometric luminosity. Our analysis suggests that the higher R$_mathrm{Edd}$ in NLSy1 is responsible for its steeper X-ray spectral slope compared to the BLSy1, consistent with the disc-corona model as proposed for the luminous AGNs.
Narrow-line Seyfert,1 galaxies (NLS1s) with very small broad-line widths (say, FWHM(hb) $la $ 1200,kms) represent the extreme type of Seyfert,1 galaxies that have small black hole masses (mbh) and/or high Eddington ratios (redd). Here we study the X-ray properties of a homogeneously and optically selected sample of 13 such objects, termed as very narrow line Seyfert,1 galaxies (VNLS1s), using archival xmm data. It is found that the Fe K$alpha$ emission line is at most weak in these objects. A soft X-ray excess is ubiquitous, with the thermal temperatures falling within a strict range of 0.1--0.2,keV. Our result highlights the puzzling independence of the thermal temperature by extending the relations to even smaller FWHM(hb), i.e., smaller mbh ($sim 10^6$ msun) and/or higher redd. The excess emission can be modeled by a range of viable models, though the disk reflection and Comptonization models generally give somewhat better fits over the smeared absorption and the $p$-free models. At the Eddington ratios around unity and above, the X-ray spectral slopes in the 2--10,keV band are systematically flatter than the Risaliti et al.s predictions of the relationship with redd suggested previously. Short timescale (1--2 hours) X-ray variability is common, which, together with the variability amplitude computed for some of the objects, are supportive of the scenario that NLS1s are indeed AGN with relatively small mbh.
We use publicly available XMM-Newton data to systematically compare the hard X-ray photon indices, $Gamma_{rm 2-10 keV}$ and the iron K$alpha$ emission lines of narrow-line (NL) and broad-line Seyfert 1 (BLS1) galaxies. We compile a flux-limited ($f_{rm 2-10 keV} geq 1 times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$) sample including 114 radio-quiet objects, with the 2-10 keV luminosity ranging from 10$^{41}$ to 10$^{45}$ erg s$^{-1}$. Our main results are: 1) NLS1s and BLS1s show similar luminosity distributions; 2) The weighted mean of $Gamma_{rm 2-10 keV}$ of NLS1s, BLS1s and the total sample is $2.04pm0.04$, $1.74pm0.02$, $1.84pm0.02$, respectively; a significant anti-correlation between ga and FWHMH$beta$ suggests that $Gamma_{rm 2-10 keV} > 2.0$ may be taken to indicate X-ray luminous NLS1 type; 3) The 6.4 keV narrow iron K$alpha$ lines from NLS1s are generally weaker than that from BLS1s; this would indicate a smaller covering factor of the dusty tori in NLS1s, if the line emission originates from the inner boundary region of the dusty torus in an AGN; 4) all the broadened iron K$alpha$ lines with intrinsic width $sigma>0.5$ keV correspond to FWHMhb $leq 4000 ~kms$.
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