arXiv subjects

J. S. Kaastra

Publications and source records attributed to J. S. Kaastra.

At least 145 records · Page 8Linked to original sources

arXiv2004

Chandra-LETGS observation of Mrk 279: modeling the AGN internal structure

We present the Chandra-LETGS analysis of Mrk 279, a bright Seyfert 1 galaxy. The spectrum shows a variety of features arising from different physical environments in the vicinity of the black hole. We detect three absorption components, located at the redshift of the source. One of them is likely to arise from the host galaxy. An additional component due to absorption by a collisionally ionized gas at z=0 is also observed. Such an absorption can be produced in the outskirts of our Galaxy or in the local group. The emission spectrum is rich in narrow and broad emission features. We tested the hypothesis that the broad emission lines originate in the Broad Line Region (BLR), as studied in the UV band. We find that at least 2 components with different ionization parameters are necessary to simultaneously interpret the broad emission line measured in the UV (by HST-STIS and FUSE) and in the X-rays.

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arXiv2004

XMM-Newton observations of the heavily absorbed Seyfert 1 galaxy IC 4329A

We detect seven distinct absorbing systems in the high-resolution X-ray spectrum of the Seyfert 1 galaxy IC 4329A, taken with XMM-Newton. Firstly we detect absorption due to cold gas in our own Galaxy and warm gas in the Galactic halo or the Local Group. This local warm gas is only detected through O VII absorption, from which we deduce a temperature between 0.03 and 0.2 keV. In IC 4329A we detect absorption from the host galaxy as well as from a warm absorber, close to the nucleus, which has 4 components. The absorption from the host galaxy is well modeled by neutral material. The warm absorber detected in IC 4329A is photoionized and has an ionization range between log $ξ$ = -1.37 and log $ξ$ = 2.7. A broad excess is measured at the O VIII Ly$α$ and N VII Ly$α$ emission lines, which can be modeled by either disklines or multiple Gaussians. From the lightcurve we find that the source changed luminosity by about 20 % over the 140 ks observation, while the spectral shape, i.e. the softness ratio did not vary. In the EPIC spectra a narrow Fe K$α$ and Fe XXVI Ly$α$ emission line are detected. The narrowness of the Fe K$α$ line and the fact that there is no evidence for flux variability between different observations leads us to conclude that the Fe K$α$ line is formed at a large distance from the central black hole.

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arXiv2004

X-ray/UV campaign on the Mrk 279 outflow: density diagnostics in Active Galactic Nuclei using O V K-shell absorption lines

One of the main problems in modeling the ionised outflows in Active Galactic Nuclei is the unknown distance of the outflowing wind to the central source. Only if the density is known this distance can be determined through the ionisation parameter. Here we study density diagnostics based upon O V transitions. O V is known to have metastable levels that are density dependent. We study the population of those levels under photoionisation equilibrium conditions and determine for which parameter range they can have a significant population. We find that resonance line trapping plays an important role in reducing the critical densities above which the metastable population becomes important. We investigate the K-shell absorption lines from these metastable levels. Provided that there is a sufficient population of the metastable levels, the corresponding K-shell absorption lines are detectable and are well separated from the main absorption line originating from the ground state. We then present the Chandra LETGS spectrum of the Seyfert 1 galaxy Mrk 279 that may show for the first time the presence of these metastable level absorption lines. A firm identification is not yet possible due to both uncertainties in the observed wavelength of the strongest line as well as uncertainties in the predicted wavelength. If the line is indeed due to absorption from O V, then we deduce a distance to the central source of one light week to a few light months, depending upon the importance of additional heating processes.

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arXiv2004

X-ray spectroscopy on Abell 478 with XMM-Newton

We report the results from a spatially resolved spectroscopy study with XMM-Newton on the relaxed cluster of galaxies Abell 478. From the EPIC data we extract a temperature profile and radial abundance profiles for Ne, Mg, Si, S, Ca, Fe and Ni. The abundance profiles follow the same trends as observed in other clusters. The spectra of the core of the cluster can be best fitted with a multi-temperature model. We argue that this multi-temperature behavior is mostly due to projection effects, because of the strong temperature gradient in the core. Contributions from other effects, for example, intrinsic temperature stratification cannot be fully excluded. For the first time we measure an underabundance of oxygen in the Galactic absorption component toward a cluster. The measured oxygen abundance in this absorber is about 0.5 times the solar oxygen abundance as determined by Anders & Grevesse (1989).

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arXiv2004

XMM-Newton study of A3562 and its immediate Shapley environs

Using the mosaic of six XMM-Newton observations, we study the hydrodynamic state of the A3562, a cluster in the center of the Shapley Supercluster. The X-ray image reveals a sharp surface brightness gradient within the core of A3562, a 200 kpc ridge extending to the south-west. A nearby group, SC1329-313, imaged within this program also exhibits a tail aligned with the ridge. Study of the pressure and entropy identified the ridge with a 40% pressure enhancement. An associated Mach number of 1.15 relative to a polytropic sound speed for a 5 keV plasma requires the velocity of the group to be 1400 km/s, while the projected velocity difference between the cluster and the group amounts to 1200-1500 km/s. Apparent disruption of the group, if attributed to the ram pressure, also requires the velocity of the group in the cluster frame to amount to 1700+/-150 km/s. The sharp surface brightness gradient at the center is identified with a contact discontinuity, which together with dove tails in the the large-scale entropy distribution reveals a sloshing of the BCG in response to the passage of the SC1329-313 group. Using the extent of the low-entropy tails in A3562 we estimate the amplitude of sloshing motion to be 200/h_70 kpc and the oscillation frequency 1 Gyr.

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arXiv2004

Simultaneous X-ray and Ultraviolet spectroscopy of the Seyfert galaxy NGC 5548. III. X-ray time variability

The Seyfert 1 galaxy NGC 5548 was observed for a week by Chandra using both the HETGS and LETGS spectrometers. In this paper we study the time variability of the continuum radiation. During our observation, the source showed a gradual increase in flux over four days, followed by a rapid decrease and flattening of the light curve afterwards. Superimposed upon these relatively slow variations several short duration bursts or quasi-periodic oscillations occured with a typical duration of several hours and separation between 0.6-0.9 days. The bursts show a delay of the hard X-rays with respect to the soft X-rays of a few hours. We interprete these bursts as due to a rotating, fluctuating hot spot at approximately 10 gravitational radii; the time delay of the hard X-rays from the bursts agree with the canonical picture of Inverse Compton scattering of the soft accretion disk photons on a hot medium that is relatively close to the central black hole.

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arXiv2004

The elemental abundances in the intracluster medium as observed with XMM-Newton

XMM-Newton observations of 19 galaxy clusters are used to measure the elemental abundances and their spatial distributions in the intracluster medium. The sample mainly consists of X-ray bright and relaxed clusters with a cD galaxy. Along with detailed Si, S and Fe radial abundance distributions within 300-700 kpc in radius, the O abundances are accurately derived in the central region of the clusters. The Fe abundance maxima towards the cluster center, possibly due to the metals from the cD galaxy,are spatially resolved. The Si and S abundances also exhibit central increases in general, resulting in uniform Fe-Si-S ratios within the cluster. In contrast, the O abundances are in general uniform over the cluster. The mean O to Fe ratio within the cluster core is sub-solar, while that of the cluster scale is larger than the solar ratio. These measurements indicate that most of the Fe-Si-S and O in the intracluster medium have different origins, presumably in supernovae Ia and II, respectively. The obtained Fe and O mass are also used to discuss the past star formation history in clusters.

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arXiv2003

XMM-Newton observation of the Seyfert 1 ESO 198-G24

We present the results from an XMM-Newton observation (January 24, 2001) of the bright Seyfert 1 galaxy ESO 198-G24 (z=0.045). We found that this Seyfert has an intrinsic 2-10 keV luminosity of about 10^44 erg s-1. This source shows no intrinsic absorption in addition to the Galactic absorption (N_{H}~3 x 10^20 cm-2). We found both with EPIC and RGS that this source possesses significantly steeper spectra below ~ 1.5-2 keV than observed at higher X-ray energies, the so-called soft X-ray excess. The RGS spectra reveal no significant narrow absorption lines suggesting that if there is a warm absorber, it either has a relatively low column density, or a very high ionization parameter. The RGS data are well described by the combination of a power-law, a modified black body continuum, and weak relativistic lines of O VIII, and C VI Lyalpha. However other interpretations are not definitely excluded. The 2-10 keV energy band is well fitted by an absorbed power-law with a photon spectral index of Gamma=1.77 +/- 0.04 (consistent with the typical Gamma~1.7 found in Seyfert 1 galaxies). We found the presence of a narrow Gaussian emission line at 6.41 keV (i.e < Fe XVII) with a moderate equivalent width of about 60-70 eV, and we found an upper limit for a broad component, if any, of 75 eV. We also found a weak absorption edge associated with cold iron with an optical depth of about 0.2.

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arXiv2003

Spatially resolved X-ray spectroscopy of cooling clusters of galaxies

We present spatially resolved X-ray spectra taken with the EPIC cameras of XMM-Newton of a sample of 17 cooling clusters and three non-cooling clusters for comparison. The deprojected spectra are analyzed with a multi-temperature model, independent of any a priori assumptions about the physics behind the cooling and heating mechanisms. All cooling clusters show a central decrement of the average temperature, most of them of a factor of ~2. At each radius within the cooling region the gas is non-isothermal. The differential emission measure distribution peaks near the maximum (ambient) temperature, and steeply declines towards lower temperatures, proportional to T^3, or alternatively a cut-off at about a quarter to half of the maximum temperature. In general, we find a poor correlation between radio flux of the central galaxy and the temperature decrement of the cooling flow. This is interpreted as evidence that except for a few cases heating by a central AGN is not the most common cause of weak cooling flows. We investigate the role of heat conduction by electrons and find that the theoretically predicted conductivity rates are not high enough to balance radiation losses. The differential emission measure distribution has remarkable similarities with the predictions from coronal magnetic loop models. Also the physical processes involved (radiative cooling, thermal conduction along the loops, gravity) are similar for clusters loops and coronal loops. If coronal loop models apply to clusters, we find that a few hundred loops per scale height should be present. The typical loop sizes deduced from the observed emission measure distribution are consistent with the characteristic magnetic field sizes deduced from Faraday rotation measurements.

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arXiv2003

Synoptic study of the SMC SNRs using XMM-Newton

We present a detailed X-ray spectral analysis of 13 supernova remnants (SNR) in the Small Magellanic Cloud (SMC). We apply both single-temperature non-equilibrium ionisation models and models based on the Sedov similarity solution, where applicable. We also present detailed X-ray images of individual SNRs, which reveal a range of different morphological features. Eight remnants, viz DEM S 32, IKT 2, HFPK 419, IKT 6, IKT 16, IKT 18 and IKT 23, are consistent with being in their Sedov evolutionary phase. IKT 6 and IKT 23 both have a clear shell like morphology with oxygen-rich X-ray emitting material in the centre. We draw attention to similarities between these two remnants and the well studied, oxygen-rich remnant IKT 22 (SNR 0102-72.3) and propose that they are more evolved versions of IKT 22. IKT 4, IKT 5, DEM S 128 and IKT 5 are evolved remnants which are in, or in the process of entering, the radiative cooling stage. We argue that the X-ray emission from these four remnants is most likely from the ejecta remains of type Ia SNe. Our modeling allow us to derive estimates for physical parameters, such as densities, ages, masses and initial explosion energies. Our results indicate that the average SMC hydrogen density is a factor of ~6 lower as compared to the Large Magellanic Cloud. This has obvious implications for the evolution and luminosities of the SMC SNRs. We also estimate the average SMC gas phase abundances for the elements O, Ne, Mg, Si and Fe.

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arXiv2003

Can a Dusty Warm Absorber Model Reproduce the Soft X-ray Spectra of MCG-6-30-15 and Mrk 766?

XMM-Newton RGS spectra of MCG-6-30-15 and Mrk 766 exhibit complex discrete structure, which was interpreted in a paper by Branduardi-Raymont et al. (2001) as evidence for the existence of relativistically broadened Lyman alpha emission from carbon, nitrogen, and oxygen, produced in the inner-most regions of an accretion disk around a Kerr black hole. This suggestion was subsequently criticized in a paper by Lee et al. (2001), who argued that for MCG-6-30-15, the Chandra HETG spectrum, which is partially overlapping the RGS in spectral coverage, is adequately fit by a dusty warm absorber model, with no relativistic line emission. We present a reanalysis of the original RGS data sets in terms of the Lee et al. (2001) model, and demonstrate that spectral models consisting of a smooth continuum with ionized and dust absorption alone cannot reproduce the RGS spectra of both objects. The original relativistic line model with warm absorption proposed by Branduardi-Raymont et al. (2001) provides a superior fit to the RGS data, both in the overall shape of the spectrum and in the discrete absorption lines. Limits on the amount of X-ray absorption by dust particles are discussed. We also discuss a possible theoretical interpretation for the putative relativistic Lyman alpha line emission in terms of the photoionized surface layers of the inner regions of an accretion disk.

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arXiv2003

Chandra LETGS and XMM-Newton observations of NGC 4593

In this paper, we analyze spectra of the Seyfert 1 galaxy NGC 4593 obtained with the Chandra Low Energy Transmission Grating Spectrometer (LETGS), the Reflection Grating Spectrometer (RGS) and the European Photon Imaging Camera's (EPIC) onboard of XMM-Newton. The two observations were separated by ~7 months. In the LETGS spectrum we detect a highly ionized warm absorber corresponding to an ionization state of 400x10^{-9} W m, visible as a depression at 10-18 Å. This depression is formed by multiple weak Fe and Ne lines. A much smaller column density was found for the lowly ionized warm absorber, corresponding to xi = 3x10^{-9} W m. However, an intermediate ionization warm absorber is not detected. For the RGS data the ionization state is hard to constrain. The EPIC results show a narrow Fe Kalpha line.

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arXiv2003

XMM-Newton discovery of O VII emission from warm gas in clusters of galaxies

XMM-Newton recently discovered O VII line emission from ~2 million K gas near the outer parts of several clusters of galaxies. This emission is attributed to the Warm-Hot Intergalactic Medium. The original sample of clusters studied for this purpose has been extended and two more clusters with a soft X-ray excess have been found. We discuss the physical properties of the warm gas, in particular the density, spatial extent, abundances and temperature.

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arXiv2003

Simultaneous UV and X-ray Spectroscopy of the Seyfert 1 Galaxy NGC 5548. I. Physical Conditions in the UV Absorbers

We present new UV spectra of the nucleus of the Seyfert 1 galaxy NGC 5548, which we obtained with the Space Telescope Imaging Spectrograph at high spectral resolution, in conjunction with simultaneous Chandra X-ray Observatory spectra. Taking advantage of the low UV continuum and broad emission-line fluxes, we have determined that the deepest UV absorption component covers at least a portion of the inner, high-ionization narrow-line region (NLR). We find nonunity covering factors in the cores of several kinematic components, which increase the column density measurements of N V and C IV by factors of 1.2 to 1.9 over the full-covering case; however, the revised columns have only a minor effect on the parameters derived from our photoionization models. For the first time, we have simultaneous N V and C IV columns for component 1 (at -1040 km/s), and find that this component cannot be an X-ray warm absorber, contrary to our previous claim based on nonsimultaneous observations. We find that models of the absorbers based on solar abundances severely overpredict the O VI columns previously obtained with the Far Ultraviolet Spectrograph, and present arguments that this is not likely due to variability. However, models that include either enhanced nitrogen (twice solar) or dust, with strong depletion of carbon in either case, are successful in matching all of the observed ionic columns. These models result in substantially lower ionization parameters and total column densities compared to dust-free solar-abundance models, and produce little O VII or O VIII, indicating that none of the UV absorbers are X-ray warm absorbers.

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arXiv2003

High resolution spectroscopy and emission line imaging of DEM L 71 with XMM-Newton

The X-ray emission from the supernova remnant DEM L 71 is measured and analysed using the high-resolution cameras and spectrometers on board XMM-Newton. The spectrum from the outer shell is reproduced very well by two plasma components of kT = 0.3 and 0.8 keV. The abundance value from this shell is consistent with the average LMC values. More extreme temperature variations are possibly indicated by spatial variations in the O VII forbidden/resonance line ratio, which could imply that in some regions the plasma is cooling dramatically and recombining. However, an alternative and equally interesting possibility is that the variation in forbidden/resonance ratios is due to resonant scattering, which would reduce resonance line emission along lines of sight with a high O VII column density. The inner region is hotter (kT = 1.1 keV) and shows enhanced Fe and Si abundances. We estimate the Fe and Si ejecta mass to be 0.7-1.1 M_sun and 0.1--0.15 M_sun, respectively. The morphology, mass estimates and abundances strongly suggest that DEM L 71 is the result of a type Ia explosion, as indicated by previous measurements.

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arXiv2003

Multiwavelength studies of the Seyfert 1 galaxy NGC7469. II - X-ray and UV observations with XMM-Newton

We present an XMM-Newton observation of NGC 7469, including studies of the X-ray and UV variability, 0.2-10 keV spectral continuum, Fe K-alpha emission line and the first-ever high-resolution X-ray spectrum of the soft X-ray warm absorber. We compare the properties of this X-ray warm absorber with the UV warm absorber as seen in a FUSE observation one year previously. The 0.2-10 keV spectral continuum is best fitted by a power-law plus two blackbody model. An Fe K-alpha emission line is visible which consists of a single narrow component and is well-modelled by a simple gaussian. Narrow absorption and emission lines in the soft X-ray RGS spectrum demonstrate the existence of a multi-phase warm absorber with a range in log xi of ~ 2 to ~ -2 where xi is in erg cm s^-1. The warm absorber is blueshifted by several hundred km s^-1. The highest-ionisation phase of the absorber is the best constrained and has an overall equivalent Hydrogen column of order 10^20 cm^-2; we find that its ionisation parameter is consistent with that of the warm emitter which generates the narrow emission lines. We identify this high ionisation absorber with the low-velocity phase of the UV absorber observed by FUSE.

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arXiv2003

XMM-NEWTON High Resolution Spectroscopy of NGC 5548

We analyze a 137 ks exposure X-ray spectrum of the Seyfert 1 galaxy NGC 5548 obtained with the XMM-Newton Reflection Grating Spectrometer. Due to the long exposure time, the spectrum is of higher statistical quality than the previous observations of this AGN. Therefore, we detect for the first time in NGC 5548 inner-shell transitions from O III to O VI ions, and the Unresolved Transition Array of M-shell iron. The warm absorber found from this X-ray observation spans three orders of magnitude in ionization parameter. We detect O III, which is as lowly ionized as the warm absorber detected in the UV band, to Fe XXIV. For O VI the column density determined from our X-ray data is an order of magnitude larger than the column density measured in previous UV observations. We conclude that there is substantially more low ionized material than previously deduced from UV observations. However, only a few percent of the warm absorber detected in the X-rays is lowly ionized. A 99.9 % significant increase in the derived absorbing column density with higher ionization states is observed. The outflow velocities determined from the X-ray absorption lines are consistent with those deduced from the UV lines, evidence, together with the detection of O VI, that the X-ray and UV warm absorber are different manifestations of the same phenomenon. From a simple mass conservation argument, we indicate that our data set is consistent with an outflow with small opening angle formed due to instabilities in the accretion disk. Possible due to uncertainties in the radiative transport mechanism, an apparent deviant iron to oxygen abundance is detected. No strong relativistically broadened emission lines of O VIII, N VII and C VI were detected.

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arXiv2002

High resolution soft X-ray spectroscopy of the elliptical galaxy NGC 5044. Results from the reflection grating spectrometer on-board XMM-Newton

The results from an X-ray spectroscopic study of the giant elliptical galaxy NGC5044 in the center of a galaxy group are presented. The line dominated soft X-ray spectra (mainly Fe-L and O VIII Ly_a) from the diffuse gas are resolved for the first time in this system with the Reflection Grating Spectrometers on-board XMM-Newton and provide a strong constraint on the temperature structure. The spectra integrated over 2' (\sim 20kpc) in full-width can be described by a two temperature plasma model of 0.7keV and 1.1keV. Most of the latter component is consistent with originating from off-center regions. Compared to the isobaric cooling flow prediction, the observation shows a clear cut-off below a temperature of 0.6 +-0.1keV. Furthermore, the Fe and O abundances within the central 10--20kpc in radius are accurately measured to be 0.55+-0.05 and 0.25+-0.1 times the solar ratios, respectively. The observed cut-off temperature of this galaxy and other central galaxies in galaxy groups and clusters are compared with the scale of the galaxy and properties of the surrounding intra-cluster medium. Based on this comparison, the origin of the lack of predicted cool emission is discussed.

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