Characterization of the emitting and absorbing media around the nucleus of the active galaxy UGC 11763 using XMM-Newton data (original) (raw)
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An X-ray bright nucleus in the low-surface-brightness galaxy UGC 6614
Monthly Notices of the Royal Astronomical Society, 2010
We report a study of the X-ray emission from the nuclear region of the low surface brightness (LSB) galaxy UGC 6614. Very little is known about the central objects in LSB galaxies especially their X-ray properties and X-ray spectra. In this study we have used XMM-Newton archival data to study the characteristics of the X-ray spectrum and the X-ray flux variability of the AGN in the LSB galaxy UGC 6614. The nucleus of UGC 6614 is very bright in X-ray emission with an absorption corrected 0.2-10.0 keV luminosity of ∼1.1× 10 42 erg s −1. The X-ray spectrum is found to be power-law type with a moderate column density. A short time scale of intensity variation and large X-ray flux is indicative of the presence of a black hole at the centre of this galaxy. Using the method of excess variance, we have determined the black hole mass to be ∼ 0.12 × 10 6 M ⊙. The X-ray spectral properties are similar to that of the Seyfert I type AGNs. Our study thus demonstrates that although LSB galaxies are poor in star formation, they may harbour AGNs with X-ray properties comparable to that seen in more luminous spiral galaxies.
X-ray spectroscopy of the broad-line radio galaxy 3C 111
Monthly Notices of the Royal Astronomical Society, 1998
We present an ASCA observation of the broad line radio galaxy 3C 111. The Xray spectrum is well described by a model consisting of a photoelectrically-absorbed power-law form. The inferred absorbing column density is significantly greater than expected on the basis of 21-cm measurements of Galactic H i. Whilst this may be due intrinsic absorption from a circumnuclear torus or highly warped accretion disk, inhomogeneities and molecular gas within the foreground giant molecular cloud may also be responsible for some of this excess absorption. We also claim a marginal detection of a broad iron Kα line which is well explained as being a fluorescent line originating from the central regions of a radiatively-efficient accretion disk. This line appears weak in comparison to those found in (radio-quiet) Seyfert nuclei. We briefly discuss the implications of this fact.
The soft X-ray absorption lines of the Seyfert 1 galaxy MCG-6-30-15
Monthly Notices of the Royal Astronomical Society, 2004
The absorption lines in the soft X-ray spectrum of MCG-6-30-15 are studied using the Reflection Grating Spectrometer data from the 2001 XMM-Newton 320 ks observation. A line search of the full time-averaged spectrum reveals 51 absorption lines and one emission line. The equivalent widths of the lines are measured and the majority of the lines identified. We find lines produced by a broad range of charge states for several elements, including almost all the charge states of oxygen and iron, suggesting a broad range of ionization parameters is present in the warm absorber. The equivalent widths of the lines are broadly consistent with the best fitting warm absorber models from Turner et al. (2003). The equivalent widths of the absorption lines allow confidence limits on the column density of the species to be determined. For O VII a column density of 10 18.36-10 18.86 cm −2 is found. This column density of O VII, when combined with the inferred Fe I absorption, is sufficient to explain the drop in flux at 0.7 keV as being due to absorption from the warm absorber. Fitting O I K-edge absorption to the spectrum reveals a column of 10 17.51 − 10 17.67 cm −2 of O I, suggesting an Fe:O ratio of ∼1:2, consistent with the neutral iron being in the form of iron oxide dust. Variability is seen in a few absorption lines, but the majority of the absorption features, including the prominent absorption edges, stay constant throughout the observation despite variability in the continuum flux.
Multiwavelength Observations of Radio Galaxy 3C 120 with XMM‐Newton
The Astrophysical Journal, 2005
We present XMM-Newton observations of the radio galaxy 3C 120, which we use to study the nature and geometry of the X-ray and UV-emitting regions. Contemporaneous radio, mm-wave, and optical data provide additional constraints on the spectral energy distribution and physical state of the active galactic nucleus. The hard X-ray spectrum contains a marginally resolved Fe i Kα emission line with FWHM= 9, 000 ± 3, 000 km s −1 and an equivalent width of 57 ± 7 eV. The line arises via fluorescence in a broad-line region with covering fraction of 0.4. There is no evidence of relativistically broad Fe Kα, contrary to some previous reports. The normal equivalent widths of the X-ray and optical emission lines exclude a strongly beamed synchrotron component to the hard X-ray and optical continua. There is an excess of 0.3-2 keV soft Xray continuum over an extrapolation of the hard X-ray power-law, which may arise in a disk corona. Analysis of an archival Chandra image shows that extended emission from the jet and other sources contributes < 3% of the total X-ray flux. A break in the X-ray spectrum below 0.6 keV indicates an excess neutral hydrogen column density of N H = 1.57 ± 0.03 × 10 21 cm −2. However, the neutral absorber must have an oxygen abundance of < 1/50 of the solar value to explain the absence of an intrinsic or intervening O i edge. There is no ionized absorption in the soft X-ray spectrum, but there is a weak, narrow O viii Lyα emission line. We do not detect previously claimed O viii absorption from the intervening intergalactic medium. Radio observations at 37 GHz show a fast, high frequency flare starting 7 days after the XMM-Newton observation. However, this has no obvious effect on the X-ray spectrum. The X-ray spectrum, including the soft excess, became harder as the X-ray flux decreased, with an estimated pivot energy of 40 keV. The UV and soft X-ray fluxes are strongly correlated over the 120 ks duration of the XMM-Newton observation. This is qualitatively consistent with Comptonization of UV photons by a hot corona.
2008
We present a detailed spectral analysis of point-like X-ray sources in the XMM-COSMOS field. Our sample of 135 sources only includes those that have more than 100 net counts in the 0.3-10 keV energy band and have been identified through optical spectroscopy. The majority of the sources are well described by a simple power-law model with either no absorption (76%) or a significant intrinsic, absorbing column (20%). The remaining ∼ 4% of the sources require a more complex modeling by incorporating additional components to the power-law. For sources with more than 180 net counts (bright sample), we allowed both the photon spectral index Γ and the equivalent hydrogen column N H to be free parameters. For fainter sources, we fix Γ to the average value and allow N H to vary. The mean spectral index of the 82 sources in the bright sample is < Γ >= 2.06±0.08, with an intrinsic dispersion of ∼ 0.24. Each of these sources have fractional errors on the value of Γ below 20%. As expected, the distribution of intrinsic absorbing column densities is markedly different between AGN with or without broad optical emission lines. We find within our sample four Type-2 QSOs candidates (L X > 10 44 erg s −1 , N H > 10 22 cm −2 ), with a spectral energy distribution well reproduced by a composite Seyfert-2 spectrum, that demonstrates the strength of the wide field XMM/COSMOS survey to detect these rare and underrepresented sources. In addition, we have identified a Compton-thick (N H > 1.5 × 10 24 cm −2 ) AGN at z=0.1248. Its X-ray spectrum is well fitted by a pure reflection model and a significant Fe Kα line at rest-frame energy of 6.4 keV.
An X-ray spectral study of 24 type 1 active galactic nuclei
Monthly Notices of the Royal Astronomical Society, 1997
I present a study of the X-ray spectral properties of a sample containing 24 type 1 active galactic nuclei using the medium spectral resolution of ASCA. The sample consists of 20 radio-quiet objects (18 Seyfert 1 galaxies and two radio-quiet quasars) and four radio-loud objects (three broad-line radio galaxies and one radio-loud quasar). A simple power-law continuum absorbed by Galactic material provides a very poor description of the spectra of most objects. Deviations from the power-law form are interpreted in terms of X-ray reprocessing/absorption processes. In particular, at least half of the objects show K-shell absorption edges of warm oxygen (Ovii and Oviii) characteristic of optically thin, photoionized material along the line of sight to the central engine, the so-called warm absorber. The amount and presence of this absorption are found to depend on either the luminosity or radio properties of the objects: luminous and/or radio-loud objects are found to possess less ionized absorption. This ambiguity exists because the radio-loud objects are also amongst the most luminous of the sample. It is also found that objects with significant optical reddening display deep Ovii edges. The converse is true with two possible exceptions (NGC 3783 and NGC 3516). Coupled with other evidence resulting from detailed study of particular objects, this suggests the existence of dusty warm plasma. A radiatively driven outflow originating from the molecular torus is probably the source of this plasma. Rapid variability of the warm absorber also points to there being another component closer to the central source and probably situated within the broad-line region (BLR). Independent evidence for such an optically thin, highly ionized BLR component comes from detailed optical/UV studies. Spectral features at energies characteristic of cold iron Kalpha emission are common. Such emission is expected to arise from the fluorescence of cold iron in optically thick material when illuminated by the primary X-ray continuum. Radio-quiet objects have iron emission well described as originating either from the inner regions of an accretion disc or, in a small number of cases, from the molecular torus. Two of the radio-loud objects (3C 120 and 3C 382) have a much broader feature which presents problems for the relativistic disc model. The presence of radio jets may be important in forming this spectral feature.
XMM‐Newton Archival Study of the Ultraluminous X‐Ray Population in Nearby Galaxies
The Astrophysical Journal, 2006
We present the results of an archival XMM-Newton study of the bright X-ray point sources (L X > 10 38 erg s −1 ) in 32 nearby galaxies. From our list of approximately 100 point sources, we attempt to determine if there is a low-state counterpart to the Ultraluminous X-ray (ULX) population, searching for a soft-hard state dichotomy similar to that known for Galactic X-ray binaries and testing the specific predictions of the IMBH hypothesis. To this end, we searched for "low-state" objects, which we defined as objects within our sample which had a spectrum well fit by a simple absorbed power law, and "high-state" objects, which we defined as objects better fit by a combined blackbody and a power law. Assuming that "low-state" objects accrete at approximately 10% of the Eddington luminosity and that "high-state" objects accrete near the Eddington luminosity we further divided our sample of sources into low and high state ULX sources. We classify 16 sources as low-state ULXs and 26 objects as high-state ULXs. As in Galactic black hole systems, the spectral indices, Γ, of the lowstate objects, as well as the luminosities, tend to be lower than those of the high-state objects. The observed range of blackbody temperatures for the high state is 0.1-1 keV, with the most luminous systems tending toward the lowest temperatures. We therefore divide our high-state ULXs into candidate IMBHs (with blackbody temperatures of approximately 0.1 keV) and candidate stellar mass BHs (with blackbody temperatures of approximately 1.0 keV). A subset of the candidate stellar mass BHs have spectra that are well-fit by a Comptonization model, a property similar of Galactic BHs radiating in the "very-high" state near the Eddington limit.
Astronomy and Astrophysics, 2003
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 Kα 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 Kα 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 ξ of ∼ 2 to ∼ −2 where ξ 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.
Multi-wavelength studies of the broad line radio galaxies IGR J21247+5058 and 3C 390.3
We present a multi-wavelength study of two broad line radio galaxies: IGR J21247+5058, one of the brightest AGN discovered by INTEGRAL, and 3C 390.3, also extensively observed by INTEGRAL. All the available INTEGRAL, XMM-Newton and Swift data were analysed, covering the 0.3-200 keV range. The spectral energy distribution of IGR J21247+5058 was extracted from the total observed spectrum in the IR to UV bands, using a blackbody model to account for the emission of a star in the line of sight. The broad band X-ray spectrum of IGR J21247+5058 can be described by a cut-off (E C = 206 +180 −61 keV) power law (Γ = 1.56 +0.09 −0.07 ) plus a reflection component (R = 0.8 +0.5 −0.4 ), absorbed by a double layer of partially covering neutral material. The X-ray spectrum of 3C 390.3 can be represented by an absorbed power law (N H ≃ 4.5 × 10 20 cm −2 , Γ = 1.78 +0.02 −0.02 ) plus a blackbody component (kT ≃ 150 eV). Both radio galaxies show weak Kα iron lines. The spectral energy distribution of IGR J21247+5058 shows the presence of two peaks, one in the near infrared and one in the X-rays. While the X-ray peak may be due to inverse Comptonisation of synchrotron photons, the one in the IR is likely due to thermal emission. The spectral energy distribution of 3C 390.3 shows two strong peaks in the IR and X-rays and a third peak in the UV, whose height varies considerably between XMM-Newton and Swift observations.
Broad-band study of hard X-ray-selected absorbed active galactic nuclei
Monthly Notices of the Royal Astronomical Society, 2012
In this paper we report on the broadband X-ray properties of a complete sample of absorbed Seyfert galaxies hard X-ray selected with INTEGRAL. Our sample is composed of 33 sources, of which 15 are newly discovered AGN above 20 keV (IGR sources) while 18 are already known type 2 AGN ("known"). For 17 sources (15 IGR + 2 "known" sources) we have performed a broadband analysis using both XMM-Newton, and INTEGRAL-IBIS data. To have a full view of the complete sample we have then complemented the analysis of the 16 remaining sources with already existing broadband studies in the same range. The high quality broadband spectra are well reproduced with an absorbed primary emission with a high energy cutoff and its scattered fraction below 2-3 keV, plus the Compton reflection features (Compton hump and Fe line emission). This study permitted a very good characterization of the primary continuum and, in turn, of all the spectral features. A high energy cutoff is found in 30% of the sample, with an average value below 150 keV, suggesting that this feature has to be present in the X-ray spectra of obscured AGN. The hard X-ray selection favours the detection of more obscured sources, with the log N H average value of 23.15 (standard deviation of 0.89). The diagnostic plot N H vs F corr (2-10 keV)/F(20-100 keV) allowed the isolation of the Compton thick objects, and may represent a useful tool for future hard X-ray observations of newly discovered AGN. We are unable to associate the reflection components (both continuum and Fe line) with the absorbing gas as a torus (as envisaged in the Unified Model), a more complex scenario being necessary. In the Compton thin 2 A. De Rosa et al. sources, a fraction (but not all) of the Fe K line needs to be produced in a gas located closer to the black hole than the Compton thick torus, and this is possibly associated with the optical Broad Line Region, responsible also for the absorption. We still need a Compton thick medium (not intercepting the line of sight) likely associated to a torus, which contributes to the Fe line intensity and produces the observed reflection continuum above 10 keV. The so-called Iwasawa-Taniguchi effect can not be confirmed with our data. Finally, the comparison with a sample of unobscured AGN shows that, type 1 and type 2 (once corrected for absorption) Seyfert are characterized by the same nuclear/accretion properties (luminosity, bolometric luminosity, Eddington ratio), supporting the "unified" view.