Fe Kα Line Research Articles

A New Candidate of a Cluster of Galaxies, 2XMM J045637.2+522411

Abstract We present XMM-Newton and Suzaku results of an X-ray source, 2XMM J045637.2$+$522411, found during an observation of a galactic supernova remnant (SNR), G156.2$+$5.7. By comparing its radial profile with the point-spread function, we found that 2XMM J045637.2$+$522411 is an extended source. X-ray spectra exhibited a line-like structure at 5.7–5.8 keV. Since no abundant element emits an X-ray line at 5–6 keV in the rest-frame, and the most intense emission line in the 5–7 keV energy band is a Fe-K line, the line is likely to be a redshifted Fe-K line. The overall spectra can be represented by a thin-thermal plasma model with a temperature of 3–4 keV and a redshift of 0.15–0.17. No intensity variation was found in the light curve. The observational results indicate that 2XMM J045637.2$+$522411 is likely to be a cluster of galaxies.

Indirect determination of trace amounts of lithiumvia complex with iron by X-ray fluorescence spectrometry

The extremely low fluorescent yield and long-wavelength characteristic radiation are the major limitations for direct XRF determination of the elements of low atomic numbers. In the case of lithium, the determination of this element by X-ray fluorescence spectrometry (XRF) is not possible. Thus, an indirect method for the determination of lithium by X-ray fluorescence spectrometry was proposed. The method is based on the determination of lithium through iron in the potassium lithium periodatoferrate(III) complex. The complex was collected on the membrane filter and the Fe Kα line was measured by XRF. The optimum conditions for LiKFeIO6 complex formation and XRF measurement were studied. A good ratio of lithium to iron (1 to 8) and a sensitive Fe Kα line give the possibility to determine a low lithium amount. The proposed method allows the determination of 20 µg of lithium collected on a filter. The validity of the proposed method was verified with certified lithium ores. The agreement between XRF analysis and certified values is satisfactory and indicates the usefulness of the carried out method.

IS THE BLACK HOLE IN GX 339–4 REALLY SPINNING RAPIDLY?

The wide-band Suzaku spectra of the black hole binary GX 339-4, acquired in 2007 February during the Very High state, were reanalyzed. Effects of event pileup (significant within ~ 3' of the image center) and telemetry saturation of the XIS data were carefully considered. The source was detected up to ~ 300$ keV, with an unabsorbed 0.5--200 keV luminosity of ~3.8 10^{38} erg/s at 8 kpc. The spectrum can be approximated by a power-law of photon index 2.7, with a mild soft excess and a hard X-ray hump. When using the XIS data outside 2' of the image center, the Fe-K line appeared extremely broad, suggesting a high black hole spin as already reported by Miller et al. (2008) based on the Suzaku data and other CCD data. When the XIS data accumulation is further limited to >3' to avoid event pileup, the Fe-K profile becomes narrower, and there appears a marginally better solution that suggests the inner disk radius to be 5-14 times the gravitational radius (1-sigma), though a maximally spinning black hole is still allowed by the data at the 90% confidence level. Consistently, the optically-thick accretion disk is inferred to be truncated at a radius 5-32 times the gravitational radius. Thus, the Suzaku data allow an alternative explanation without invoking a rapidly spinning black hole. This inference is further supported by the disk radius measured previously in the High/Soft state.

The absorption-dominated model for the X-ray spectra of type I active galaxies: MCG–6-30-15

Abstract MCG–6-30-15 is the archetypal example of a type I active galaxy showing broad ‘red-wing’ emission in its X-ray spectrum at energies below the 6.4 keV Fe Kα emission line and a continuum excess above 20 keV. Miller et al. showed that these spectral features could be caused by clumpy absorbing material, but Reynolds et al. have argued that the observed Fe Kα line luminosity is inconsistent with this explanation unless the global covering factor of the absorber(s) is very low. However, the Reynolds et al. calculation effectively considers the only source of opacity to be the Fe K bound–free transition and neglects the opacity at the line energy: correction to realistic opacity decreases the predicted line flux by a large factor. We also discuss the interpretation of the covering factor and the possible effect of occultation by the accretion disc. Finally, we consider a model for MCG–6-30-15 dominated by clumpy absorption, which is consistent with a global covering factor of 0.45, although models that include the effects of Compton scattering are required to reach a full understanding. Variations in covering fraction may dominate the observed X-ray spectral variability.

The Ying and Yang of the M 83 Nucleus

The spiral galaxy M 83, an SB(rs)b at only 4.5 Mpc, is a privileged case for study of the detailed physics on spatial scales of a tenth of a parsec. With 3-D spectroscopic observations using CIRPASS on Gemini-S, we studied the ionized gas properties in J-band with spatial resolution of 0.″5 (Figure 1). The Paβ velocity field shows two dynamical centers, neither of them coincident with the bulge center, identified with the optical nucleus (ON) and the hidden nucleus (HN), with masses, within a radius of 10 pc, of MON = (1.8±0.4)× 107M⊙ and MHN = (1.0±0.4)× 107M⊙. Using the Paβ equivalent width together with population synthesis models, we are able to estimate the ages of both mass concentrations, TON = 8 Myr and THN =6–7 Myr. Adding complexity to this puzzling scenario, we used GMOS+Gemini imaging and spectroscopy to study the radio source J133658.3–295105 (Dottori et al. 2008) and find that Hα emission at the position of this source is redshifted by ~130 km s−1 with respect to an M 83 H II region, leading us to face the possibility of that we are witnessing the ejection of an object by gravitational recoil from the M 83 nucleus. A fit to the X-ray spectrum obtained Chandra supports the association between this source and the disk of M 83 by the presence of the Fe Kα line at 6.7 keV.

STRUCTURE OF THE ACCRETION FLOW IN BROAD-LINE RADIO GALAXIES: THE CASE OF 3C 390.3

We present XMM-Newton and Suzaku observations of the broad-line radio galaxy 3C 390.3 acquired in 2004 October and 2006 December, respectively. An archival Swift BAT spectrum from the 9 month survey is also analyzed, as well as an optical spectrum simultaneous to XMM-Newton. At soft X-rays, no absorption features are detected in the Reflection Grating Spectrometer spectrum of 3C 390.3; a narrow emission line is found at 0.564 keV, most likely originating in the narrow-line region. Both the EPIC and XIS data sets confirm the presence of an Fe Kα emission line at 6.4 keV with equivalent width (EW) = 40 eV. The Fe Kα line has a width FWHM ∼ 8800 km s^−1, consistent within a factor of 2 with the width of the double-peaked Hα line, suggesting an origin from the broad-line region. The data show for the first time a weak, broad bump extending from 5 to 7 keV. When fitted with a Gaussian, its centroid energy is 6.6 keV in the source’s rest frame with FWHM of 43,000 km s^−1 and EW of 50 eV; its most likely interpretation is emission from He-like Fe (Fe xxv), suggesting the presence of an ionized medium in the inner regions of 3C 390.3. The broadband 0.5–100 keV continuum is well described by a single power law with photon index Γ = 1.6 and cutoff energy 157 keV, plus cold reflection with strength R = 0.5. In addition, ionized reflection is required to account for the 6.6 keV bump in the broadband continuum, yielding an ionization parameter ξ ∼ 2700 erg cm s^−1; the inner radius of the ionized reflector is constrained to be larger than 20r_G, although this result depends on the assumed emissivity profile of the disk. If true, we argue that the lack of broad Fe K emission from within 20r_G indicates that the innermost regions of the disk in 3C 390.3 are obscured and/or poorly illuminated. While the spectral energy distribution (SED) of 3C 390.3 is generally dominated by accretionrelated continuum, during accretion low states the jet can significantly contribute in the optical to X-ray bands via synchrotron self-Compton emission. The Compton component is expected to extend to and peak at GeV gamma rays where it will be detected with the Fermi Gamma-Ray Space Telescope during its first few years of operation.

MULTIWAVELENGTH VARIABILITY OF THE BROAD LINE RADIO GALAXY 3C 120

We present results from a multiyear monitoring campaign of the broad-line radio galaxy 3C 120, using the Rossi X-ray Timing Explorer for nearly five years of observations. Additionally, we present coincident optical monitoring using data from several ground-based observatories. Both the X-ray and optical emission are highly variable and appear to be strongly correlated, with the X-ray emission leading the optical by 28 days. The X-ray power density spectrum is best fit by a broken power law, with a low-frequency slope of –1.2, breaking to a high-frequency slope of –2.1, and a break frequency of log νb = –5.75 Hz, or 6.5 days. This value agrees well with the value expected based on 3C 120's mass and accretion rate. We find no evidence for a second break in the power spectrum. Combined with a moderately soft X-ray spectrum (Γ = 1.8) and a moderately high accretion rate (), this indicates that 3C 120 fits in well with the high/soft variability state found in most other active galactic nuclei. Previous studies have shown that the spectrum has a strong Fe Kα line, which may be relativistically broadened. The presence of this line, combined with a power spectrum similar to that seen in Seyfert galaxies, suggests that the majority of the X-ray emission in this object arises in or near the disk, and not in the jet.

XMM-NewtonandSuzakuanalysis of the FeKcomplex in the type 1 Seyfert galaxy Mrk 509

We report on partially overlapping XMM–Newton (∼260 ks) and Suzaku (∼100 ks) observations of the iron K band in the nearby, bright type 1 Seyfert galaxy Mrk 509. The source shows a resolved neutral Fe K line, most probably produced in the outer part of the accretion disc. Moreover, the source shows further emission bluewards of the 6.4 keV line due to ionized material. This emission is well reproduced by a broad line produced in the accretion disc, while it cannot be easily described by scattering or emission from photoionized gas at rest. The summed spectrum of all XMM–Newton observations shows the presence of a narrow absorption line at 7.3 keV produced by highly ionized outflowing material. A spectral variability study of the XMM–Newton data shows an indication for an excess of variability at 6.6–6.7 keV. These variations may be produced in the red wing of the broad ionized line or by variation of a further absorption structure. The Suzaku data indicate that the neutral Fe Kα line intensity is consistent with being constant on long time-scales (of a few years), and they also confirm as most likely the interpretation of the excess blueshifted emission in terms of a broad ionized Fe line. The average Suzaku spectrum differs from the XMM–Newton one in the disappearance of the 7.3 keV absorption line and around 6.7 keV, where the XMM–Newton data alone suggested variability.

XMM-Newton observations of Seyfert galaxies from the Palomar spectroscopic survey: the X-ray absorption distribution

We present XMM-Newton spectral analysis of all 38 Seyfert galaxies from the Palomar spectroscopic sample of galaxies. These are found at distances of up to 67 Mpc and cover the absorbed 2-10 keV luminosity range ~10^38-10^43 ergs/s. Our aim is to determine the distribution of the X-ray absorption in the local Universe. Three of these are Compton-thick with column densities just above 10^24 cm^-2 and high equivalent width FeKa lines (>700 eV). Five more sources have low values of the X-ray to [OIII] flux ratio suggesting that they could be associated with obscured nuclei. Their individual spectra show neither high absorbing columns nor flat spectral indices. However, their stacked spectrum reveals an absorbing column density of N_H~10^23 cm^-2. Therefore the fraction of absorbed sources (>10^22 cm^-2 could be as high as 55+/-12%. A number of Seyfert-2 appear to host unabsorbed nuclei. These are associated with low-luminosity sources Lx < 3x10^41 ergs/s. Their stacked spectrum again shows no absorption while inspection of the \chandra images, where available, shows that contamination from nearby sources does not affect the {\it XMM-Newton} spectra in most cases. Nevertheless, such low luminosity sources are not contributing significantly to the X-ray background flux. When we consider only the brighter, $>10^{41}$ \lunits, 21 sources, we find that the fraction of absorbed nuclei rises to $75\pm19 $ % while that of Compton-thick sources to 15-20%. The fraction of Compton-thick AGN is lower than that predicted by the X-ray background synthesis model in the same luminosity and redshift range.}

Obscuring clouds playing hide-and-seek in the active nucleus H0557-385

Abstract This Letter reports on two XMM–Newton observations of the type 1 Seyfert galaxy H0557-385 obtained in 2006, which show the source at an historical low flux state, more than a factor of ∼10 lower than a previous XMM–Newton look in 2002. The low flux spectrum presents a strong Fe Kα line associated with a Compton reflection continuum. An additional spectral line around 6.6 keV is required to fit Kα emission from Fe xxv. The spectral curvature below 6 keV implies obscuration by neutral gas with a column density of ∼8 × 1023 cm-2 partially covering the primary emission, which still contributes a few per cent of the soft X-ray emission. Absorption by ionized material on the line of sight is required to fit the deep trough below 1 keV. The comparison of the two spectral states shows that the flux transition is to be ascribed entirely to intervening line-of-sight clouds with high column density.

X-Ray Spectral Variability of the Seyfert Galaxy NGC 4051 Observed with Suzaku

Abstract We report on results from a Suzaku observation of the narrow-line Seyfert 1 NGC 4051. During our observation, large-amplitude rapid variability was seen, and the averaged 2–10 keV flux was 8.1$\times$10$^{-12}$erg s$^{-1}$cm$^{-2}$ which is several times lower than the historical average. The X-ray spectrum hardens when the source flux becomes lower, confirming the trend of spectral variability known for many Seyfert 1 galaxies. The broad-band averaged spectrum and spectra in high- and low-flux intervals were analyzed. The spectra were first fitted with a model consisting of a power-law component, a reflection continuum originating in cold matter, a blackbody component, two zones of ionized absorber, and several Gaussian emission lines. The amount of reflection is rather large ($R$$\sim$ 7, where $R$$=$ 1 corresponds to reflection by an infinite slab), while the equivalent width of the Fe-K line at 6.4 keV is modest (140 eV) for the averaged spectrum. We then modeled the overall spectra by introducing partial covering for the power-law component and reflection continuum independently. The column density for the former is 1$\times$10$^{23}$cm$^{-2}$, while it is fixed at 1$\times$10$^{24}$cm$^{-2}$ for the latter. By comparing the spectra in different flux states, we could identify the causes of spectral variability.

Exploring the X-ray emission properties of the supernova remnant G67.7+1.8 and its central X-ray sources

We have studied the supernova remnant G67.7+1.8 with the Chandra X-ray observatory. The remnant’s X-ray morphology correlates well with the double-arc structure seen at radio wavelength. The X-ray spectra of the northern and southern rim of G67.7+1.8 exhibit emission line features of highly ionized metals, which suggests that most of the observed X-rays originate in a thermal plasma. We find magnesium , silicon, and sulphur overabundant relative to the solar values. Gaussian emission lines at ∼4 keV and ∼7 keV are detected. The ∼4 keV line is consistent with K-emission lines from 44 Ca and/or 44 Sc whereas the ∼7 keV line feature may arise from unresolved Fe-K lines. Chandra’s sub-arcsecond angular resolution allowed us to detect four faint point sources located within ∼1.5 arcmin of the geometrical remnant center. Among these objects, CXOU195424.75+312824.9 and CXOU195429.82+312834.1 do not have optical counterparts, leaving them as candidates for a possible compact stellar remnant.

Misalignment of the microquasar V4641 Sgr (SAX J1819.3–2525)

Abstract In the microquasar V4641 Sgr, the spin of the black hole is thought to be misaligned with the binary orbital axis. The accretion disc aligns with the black hole spin by the Lense-Thirring effect near to the black hole and further out becomes aligned with the binary orbital axis. The inclination of the radio jets and the Fe Kα line profile have both been used to determine the inclination of the inner accretion disc but the measurements are inconsistent. Using a steady-state analytical-warped disc model for V4641 Sgr, we find that the inner disc region is flat and aligned with the black hole up to about 900Rg. Thus, if both the radio jet and fluorescent emission originate in the same inner region then the measurements of the inner disc inclination should be the same.

Average Fe K$\mathsf{\alpha}$ emission from distant AGN

Context. One of the most important parameters in the XRB (X-ray background) synthesis models is the average effi ciency of accretion onto SMBH (super-massive black holes). This can be inferred from the shape of broad relativistic F e lines seen in X-ray spectra of AGN (active galactic nuclei). Several studies have tried to measure the mean Fe emission properties of AGN at different depths with very different results. Aims. We compute the mean Fe emission from a large and representative sample of AGN X-ray spectra up to redshift∼ 3.5. Methods. We developed a method of computing the rest-frame X-ray average spectrum and applied it to a large sample (more than 600 objects) of type 1 AGN from two complementary medium sensitivity surveys based on XMM-Newton data, the AXIS and XWAS samples. This method makes use of medium-to-low quality spectra without needing to fit complex models to the individual s pectra but with computing a mean spectrum for the whole sample. Extensive quality tests were performed by comparing real to simulated data, and a significance for the detection of any feature over an underlying continuum was derived. Results. We detect with a 99.9% significance an unresolved Fe Kα emission line around 6.4 keV with an EW∼ 90 eV, but we find no compelling evidence of any significant broad relativisti c emission line in the final average spectrum. Deviations fro m a power law around the narrow line are best represented by a reflection co mponent arising from cold or low-ionization material. We estimate an upper limit for the EW of any relativistic line of 400 eV at a 3σ confidence level. We also marginally detect the so-called Iw asawaTaniguchi effect on the EW for the unresolved emission line, which appears weaker for higher luminosity AGN. Conclusions. We computed an upper limit for the average relativistic Fe Kα line contribution that is significantly lower than previous ly reported values from similar analyses. Our results, however, are in excellent agreement with individual analyses of local AGN samples. We attribute this difference either to our more sophisticated method of modeling the underlying continuum, to intrinsic differences in source populations, and/or to the uneven data quality of the individual spectra of the various samples.

Suzaku broad-band spectroscopy of RX J1347.5–1145: constraints on the extremely hot gas and non-thermal emission

We present the results from the analysis of long Suzaku observations of the most X-ray luminous galaxy cluster RX J1347.5-1145 at z=0.451. Aims: We study physical properties of the hot (~20 keV) gas clump in the south-east (SE) region discovered by the Sunyaev-Zel'dovich (SZ) effect observations, to understand the gas physics of a violent cluster merger. We also explore a signature of non-thermal emission using the hard X-ray data. Results: We find that the single-temperature model fails to reproduce the continuum emission and Fe-K lines measured by XIS simultaneously. The two-temperature model with a very hot component improves the fit, although the XIS data can only give a lower bound on its temperature. We detect the hard X-ray emission in the 12-40 keV band at the 7 sigma level; however, the significance becomes marginal when the systematic error in the background estimation is included. With the Suzaku + Chandra joint analysis, we determine the temperature of the SE excess component to be 25.3^{+6.1}_{-4.5} ^{+6.9}_{-9.5} keV (90% statistical and systematic errors), which is in an excellent agreement with the previous SZ + X-ray analysis. This is the first time that the X-ray spectroscopy alone gives a good measurement of the temperature of the hot component in the SE region, which is made possible by Suzaku's unprecedented sensitivity to the wide X-ray band. These results strongly indicate that the cluster has undergone a recent, violent merger. The spectral analysis shows that the SE component is consistent with being thermal. We find the 3 sigma upper limit on the non-thermal flux, F 0.007 micro G.

A systematic look at the very high and lowhard state of GX3394: constraining the black hole spin with a new reflection model

We present a systematic study of GX 339−4 in both its very high and low hard states from simultaneous observations made with XMM‐Newton and RXTE in 2002 and 2004. The X-ray spectra of both these extreme states exhibit strong reflection signatures, with a broad, skewed Fe Kα line clearly visible above the continuum. Using a newly developed, self-consistent reflection model which implicitly includes the blackbody radiation of the disc as well as the effect of Comptonization, blurred with a relativistic line function, we were able to infer the spin parameter of GX 339−4 to be 0.935 ± 0.01 (statistical) ±0.01 (systematic) at 90 per cent confidence. We find that both states are consistent with an ionized thin accretion disc extending to the innermost stable circular orbit around the rapidly spinning black hole.

The warm absorber in NGC 5548

We study the variability of the warm absorber and the gas responsible for the emission lines in the Seyfert 1 galaxy NGC 5548 to constrain the location and physical properties of these components. Using X-ray spectra acquired using the Chandra-LETGS in 2002 and 2005, we study the variability of the ionic column densities and line intensities. We measure a lower forbidden emission line flux in 2005, while the Fe Kα line flux remains constant. The warm absorber is less ionized in 2005, which enbles its location to be constrained to within 7 pc of the central source. Using both the observed variability and the limit on the FWHM of the f line, we constrain the location of the narrow line region to a distance of 1 pc from the central source. The apparent lack of variability in the Fe Kα line flux does enable a unique explanation to be derived.

Long‐Term X‐Ray Monitoring of NGC 6251: Evidence for a Jet‐dominated Radio Galaxy

We present the first X-ray monitoring observations of the X-ray-bright FR I radio galaxy NGC 6251 observed with RXTE for 1 yr. The primary goal of this study is to shed light on the origin of the X-rays by investigating the spectral variability with model-independent methods coupled with time-resolved and flux-selected spectroscopy. The main results can be summarized as follows: (1) Throughout the monitoring campaign, NGC 6251 was in relatively high-flux state with an average 2-10 keV absorbed flux of the order of 4.5 × 10−12 erg cm−2 s−1 and a corresponding intrinsic luminosity of 6 × 1042 erg s−1. (2) The flux persistently changed with fluctuations of the order of ~2 on timescales of 20-30 days. (3) When the hardness ratio is plotted against the average count rate, there is evidence for a spectral hardening as the source brightens; this finding is confirmed by a flux-selected spectral analysis. (4) The fractional variability appears to be more pronounced in the hard energy band (5-12 keV) than in the soft one (2.5-5 keV). (5) Two month averaged and flux-limited energy spectra are adequately fitted by a power law. A Fe Kα line is never statistically required, although the presence of a strong iron line cannot be ruled out, due to the high upper limits on the line equivalent width. The inconsistency of the spectral variability behavior of NGC 6251 with the typical trend observed in Seyfert galaxies and the similarity with blazars lend support to a jet-dominated scenario during the RXTE monitoring campaign. However, a possible contribution from a disk-corona system cannot be ruled out.

X‐Ray–fluorescent Fe Kα Lines from Stellar Photospheres

X-ray spectra from stellar coronae are reprocessed by the underlying photosphere through scattering and photoionization events. While reprocessed X-ray spectra reaching a distant observer are at a flux level of only a few percent of that of the corona itself, characteristic lines formed by inner shell photoionization of some abundant elements can be significantly stronger. The emergent photospheric spectra are sensitive to the distance and location of the fluorescing radiation and can provide diagnostics of coronal geometry and abundance. Here we present Monte Carlo simulations of the photospheric -->K α1,α2 doublet arising from quasi-neutral Fe irradiated by a coronal X-ray source. Fluorescent line strengths have been computed as a function of the height of the radiation source, the temperature of the ionizing X-ray spectrum, and the viewing angle. We also illustrate how the fluorescence efficiencies scale with the photospheric metallicity and the Fe abundance. Based on the results we make three comments: (1) fluorescent Fe lines seen from pre-main-sequence stars mostly suggest flared disk geometries and/or supersolar disk Fe abundances; (2) the extreme 1400 mA line observed from a flare on V1486 Ori could be explained entirely by X-ray fluorescence if the flare itself were partially eclipsed by the limb of the star; and (3) the fluorescent Fe line detected by Swift during a large flare on II Peg is consistent with X-ray excitation and does not require a collisional ionization contribution. There is no convincing evidence supporting the energetically challenging explanation of electron impact excitation for observed stellar Fe Kα lines.

Models of the iron Kα fluorescent line and the Compton Shoulder in irradiated accretion disc spectra

We present a full set of model atmosphere equations for the accretion disc around a supermassive black hole irradiated by a hard X-ray lamp of power-law spectral distribution. Model equations allow for multiple Compton scattering of radiation on free electrons, and for large relative photon-electron energy exchange at the time of scattering. We present spectra in specific intensities integrated over the disc surface. Theoretical outgoing intensity spectra show soft X-ray excess below 1 keV, and distinct Ka and Kβ fluorescent lines of iron. We demonstrate the existence of the Compton Shoulder and claim that it can contribute to the asymmetry and equivalent widths of some observed Fe Ka lines in active galactic nuclei. Our models exhibit the effect of limb-brightening in reflected X-rays.