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Black hole masses from reverberation mapping
We review briefly how black hole masses are measured directly usingreverberation mapping and indirectly through scaling relationships basedon reverberation results, in particular through broad-line regionradiusluminosity relationships. We discuss the nature and originof uncertainties in these measurements, and outline current and futureefforts directed towards reducing these uncertainties.
| Confirming the high velocity outflow in PG1211+143
An XMM-Newton observation of the bright quasi-stellar object PG1211+143was previously reported to show evidence for a massive, energeticoutflow, with an outflow velocity of v ~ 0.1c based on theidentification of blueshifted absorption lines detected in both EPIC andReflection Grating Spectrometer (RGS) spectra. Subsequently, an order ofmagnitude lower velocity has been claimed from an ion-by-ion model fitto the RGS data. We show here, in a re-analysis of the highersignal-to-noise ratio EPIC data, that the high velocity is confirmed,with the resolution of additional absorption lines yielding a revisedoutflow velocity in the range ~0.13-0.15c. Confirmation of a massive andenergetic outflow in a non-BAL active galactic nucleus (AGN) hasimportant implications for metal enrichment of the intergalactic mediumand for the feedback mechanism implied by the correlation of black holeand galactic bulge masses. We note the near-Eddington luminosity ofPG1211+143 may be the critical factor in driving such an energeticoutflow, a situation likely to be common in AGN at higher redshift.
| Consistency of the black hole mass determination in AGN from the reverberation and the X-ray excess variance method
Values of black hole masses are frequently determined with the help ofthe reverberation method. This method requires a specific geometricalfactor related to the distribution of the orbits of the broad-lineregion clouds. Onken et al. determined the value f2 = 1.37+/- 0.45 from the black hole mass-dispersion relation. In this paper, wedetermine this factor using an independent mass determination from theX-ray variance method for a number of Seyfert 1 galaxies and comparingthem with the reverberation results by Peterson et al. We obtain meanvalue f2 = 1.12 +/- 0.54, consistent with Onken et al. Bothvalues are larger than the value 0.75 corresponding to a sphericalgeometry. It indicates that most probably all values of the black holemasses obtained with the use of the Kaspi et al. formulae should bemultiplied by a factor of ~1.7. This also shows that the broad-lineregion is rather flat, and hints for a dependence of the factorf2 on a source inclination seem to be present in the data.
| On the origin of the iron Kα line cores in active galactic nuclei
X-ray observations made with Chandra and XMM-Newton have shown thatthere are relatively narrow cores to the iron Kα emission lines inactive galactic nuclei (AGN). Plausible origins for this core emissioninclude the outer regions of an accretion disc, a parsec-scale moleculartorus, and the optical broad-line region (BLR). Using data from theliterature it is shown that no correlation exists between the FeKα core width and the BLR (specifically Hβ) line width. Thisshows that in general the iron Kα core emission does not arisefrom the BLR. There is a similar lack of correlation between the widthof the Fe Kα core and black hole mass. The average Kα widthis about a factor of 2 lower than the Hβ width. It therefore seemslikely that, in many cases, the narrow core arises in the torus. Thereis a very wide range of observed Fe Kα core widths, however, andthis argues for multiple origins. The simplest explanation for theobserved line profiles in AGN is that they are due to a mixing of verynarrow emission from the inner edge of the torus, and broadened emissionfrom the accretion disc, in varying proportions from object to object.
| XMM-Newton observations of the Seyfert 1 AGN H0557-385
We present XMM-Newton observations of the Seyfert 1 active galacticnucleus (AGN) H0557-385. We have conducted a study into the warmabsorber present in this source, and using high-resolution ReflectionGrating Spectrometer (RGS) data we find that the absorption can becharacterized by two phases: a phase with log ionization parameter ξof 0.50 (where ξ is in units of ergcms-1) and a column of0.2 × 1021cm-2, and a phase with log ξ of1.62 and a column of 1.3 × 1022cm-2. An ironKα line is detected. Neutral absorption is also present in thesource, and we discuss possible origins for this. On the assumption thatthe ionized absorbers originate as an outflow from the inner edge of thetorus, we use a new method for finding the volume filling factor. Bothphases of H0557-385 have small volume filling factors (<=1 per cent).We also derive the volume filling factors for a sample of 23 AGN usingthis assumption and for the absorbers with logξ > 0.7, we findreasonable agreement with the filling factors obtained through thealternative method of equating the momentum flow of the absorbers to themomentum loss of the radiation field. By comparing the filling factorsobtained by the two methods, we infer that some absorbers with logξ< 0.7 occur at significantly larger distances from the nucleus thanthe inner edge of the torus.
| Black hole masses based on reverberation mapping of the Broad-Line Region
In this contribution, we outline the fundamental assumptions anduncertainties in determining AGN black hole masses fromreverberation-mapping measurements. We attempt to explain individualsources of error and uncertainty and quantify these and identify somesystematic errors and their mitigation. We describe recent developments,including improvements to radius-luminosity relationships and resultsfrom new reverberation campaigns.
| The Hard X-Ray 20-40 keV AGN Luminosity Function
We have compiled a complete extragalactic sample based on ~25,000deg2 to a limiting flux of 3×10-11 ergscm-2 s-1 (~7000 deg2 to a flux limit of10-11 ergs cm-2 s-1) in the 20-40 keVband with INTEGRAL. We have constructed a detailed exposure map tocompensate for effects of nonuniform exposure. The flux-number relationis best described by a power law with a slope of α=1.66+/-0.11.The integration of the cumulative flux per unit area leads tof20-40 keV=2.6×10-10 ergs cm-2s-1 sr-1, which is about 1% of the known 20-40 keVX-ray background. We present the first luminosity function of AGNs inthe 20-40 keV energy range, based on 38 extragalactic objects detectedby the imager IBIS-ISGRI on board INTEGRAL. The luminosity functionshows a smoothly connected double-power-law form with an index ofγ1=0.8 below and γ2=2.1 above theturnover luminosity of L*=2.4×1043 ergss-1. The emissivity of all INTEGRAL AGNs per unit volume isW20-40keV(>1041 ergss-1)=2.8×1038 ergs s-1h370 Mpc-3. These results areconsistent with those derived in the 2-20 keV energy band and do notshow a significant contribution by Compton-thick objects. Because thesample used in this study is truly local (z¯=0.022), only limitedconclusions can be drawn for the evolution of AGNs in this energy band.
| On the Fraction of X-Ray-obscured Quasars in the Local Universe
Recent wide-area hard X-ray and soft gamma-ray surveys have shown thatthe fraction of X-ray-obscured active galactic nuclei (AGNs) in thelocal universe significantly decreases with intrinsic luminosity. Inthis Letter we point out that two corrections have to be made to thesamples: (1) radio-loud AGNs have to be excluded, since their X-rayemission might be dominated by the jet component, and (2) Compton-thicksources have to be excluded too, since their hard X-ray and softgamma-ray emission are also strongly attenuated by Compton scattering.The soft gamma-ray-selected AGN samples obtained by Swift and INTEGRALprovide the best opportunity to study the fraction of obscured AGNs inthe local universe in the least biased way. We choose these samples tocheck if the corrections could alter the above result on the fraction ofobscured AGNs. We find that before the corrections both samples showsignificant anticorrelation between LX and NH,indicating an obvious decrease in the fraction of obscured AGNs withluminosity. However, after the corrections, we find only marginalevidence of anticorrelation (at the 98% confidence level) in the Swiftsample and no evidence at all in the INTEGRAL sample, which consists ofa comparable number of objects. We conclude that current samples onlyshow a marginal decrease in the fraction of obscured AGNs in the localuniverse and that much larger samples are required in order to reach amore robust conclusion.
| A Comprehensive Search for Gamma-Ray Lines in the First Year of Data from the INTEGRAL Spectrometer
We have carried out an extensive search for gamma-ray lines in the firstyear of public data from the spectrometer (SPI) on the INTEGRAL mission.INTEGRAL has spent a large fraction of its observing time in theGalactic plane with particular concentration in the Galactic center (GC)region (~3 Ms in the first year). Hence the most sensitive searchregions are in the Galactic plane and center. The phase space of thesearch spans the energy range 20-8000 keV and line widths from 0 to 1000keV (FWHM). It includes both diffuse and pointlike emission. We havesearched for variable emission on timescales down to ~1000 s. Diffuseemission has been searched for on a range of different spatial scalesfrom ~20° (the approximate field of view of the spectrometer) up tothe entire Galactic plane. Our search procedures were verified by therecovery of the known gamma-ray lines at 511 and 1809 keV at theappropriate intensities and significances. We find no evidence for anypreviously unknown gamma-ray lines. The upper limits range from afew×10-5 to a few×10-2 cm-2s-1 depending on line width, energy, and exposure; regions ofstrong instrumental background lines were excluded from the search.Comparison is made between our results and various prior predictions ofastrophysical lines.
| Fe K Emission and Absorption in the XMM-EPIC Spectrum of the Seyfert Galaxy IC 4329a
We present a detailed analysis of the XMM-Newton long-look of theSeyfert galaxy IC 4329a. The Fe K bandpass is dominated by two resolvedpeaks at 6.4 and 7.0 keV, consistent with neutral or near-neutral FeKα and Kβ emission. There is a prominent redward asymmetry inthe 6.4 keV line, which could indicate emission from a Compton shoulder.Alternatively, models using dual relativistic disk lines are found todescribe the emission profile well. A low-inclination, moderatelyrelativistic dual disk-line model is possible if the contribution fromnarrow components, due to distant material, is small or absent. Ahigh-inclination, moderately relativistic profile for each peak ispossible if there are roughly equal contributions from both the broadand narrow components. Combining the XMM-Newton data with RXTEmonitoring data, we explore the time-resolved spectral behavior ontimescales from hours to 2 years. We find no strong evidence forvariability of the Fe K line flux on any timescale, likely due to theminimal level of continuum variability. We detect, at high significance,a narrow absorption line at 7.68 keV. This feature is most likely due toFe XXVI Kα absorption blueshifted to ~0.1c relative to thesystemic velocity, suggesting a high-velocity, highly ionized outflowcomponent. As is often the case with similar outflows seen inhigh-luminosity quasars, the power associated with the outflowrepresents a substantial portion of the total energy budget of the AGN.The outflow could arise from a radiatively driven disk wind, or it maybe in the form of a discrete, transient blob of ejected material.
| On the X-Ray Baldwin Effect for Narrow Fe Kα Emission Lines
Most active galactic nuclei (AGNs) exhibit a narrow Fe Kα line at~6.4 keV in the X-ray spectra, due to the fluorescent emission from coldmaterial far from the inner accretion disk. Using XMM-Newtonobservations, Page et al. found that the equivalent width (EW) of thenarrow Fe Kα line decreases with increasing luminosity(EW~L-0.17+/-0.08), suggesting a decrease in the coveringfactor of the material emitting the line (presumably the torus). Bycombining the archival Chandra HETG observations of 34 type 1 AGNs withXMM observations in the literature, we build a much larger sample with101 AGNs. We find a similar X-ray Baldwin effect in the sample(EW~L-0.2015+/-0.0426) however, we note that theanticorrelation is dominated by the radio-loud AGNs in the sample, whoseX-ray spectra might be contaminated by the relativistic jet. Excludingthe radio-loud AGNs, we find a much weaker anticorrelation(EW~L-0.1019+/-0.0524). We present Monte Carlo simulationsshowing that such a weak anticorrelation can be attributed to therelative short timescale variations of the X-ray continuum.
| The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements
We have obtained high-resolution images of the central regions of 14reverberation-mapped active galactic nuclei (AGNs) using the HubbleSpace Telescope Advanced Camera for Surveys High Resolution Camera toaccount for host-galaxy starlight contamination of measured AGNluminosities. We measure the host-galaxy starlight contribution to thecontinuum luminosity at 5100 Å through the typical ground-basedslit position and geometry used in the reverberation-mapping campaigns.We find that removing the starlight contribution results in asignificant correction to the luminosity of each AGN both for lowerluminosity sources, as expected, but also for the higher luminositysources such as the PG quasars. After accounting for the host galaxystarlight, we revisit the well-known broad-line region radius-luminosityrelationship for nearby AGNs. We find the power-law slope of therelationship for the Hβ line to be 0.518+/-0.039, shallower thanwhat was previously reported and consistent with the slope of 0.5expected from the naive theoretical assumption that all AGNs have, onaverage, the same ionizing spectrum and the same ionization parameterand gas density in the Hβ line-emitting region.
| BeppoSAX View of Radio-loud Active Galactic Nuclei
A systematic analysis of a large sample of radio-loud active galacticnuclei (AGNs) available in the BeppoSAX public archive has beenperformed. The sample includes 3 narrow-line radio galaxies (NLRGs), 10broad-line radio galaxies (BLRGs), 6 steep-spectrum radio quasars(SSRQs), and 16 flat-spectrum radio quasars (FSRQs). According to theunified models, these classes correspond to objects with increasingviewing angles. As expected, the presence of a nonthermal beamedcomponent emerges clearly in FSRQs. This class shows in fact afeatureless continuum (with the exception of 3C 273) and a significantlyflatter average spectral slope. However, traces of a nonthermalDoppler-enhanced radiation are elusive in the other classes. We findthat the iron line equivalent widths (EWs) are generally weaker inradio-loud AGNs than in Seyfert 1 galaxies, and we confirm the presenceof an X-ray Baldwin effect; that is, a decrease of EW with the 2-10 keVluminosity from Seyfert galaxies to BLRGs and quasars. Since theEW-L2-10 keV anticorrelation is present also in radio-quietAGNs alone, this effect cannot be ascribed entirely to a strongly beamedjet component. Possible alternative interpretations are explored.
| INTEGRAL and RXTE Observations of Centaurus A
INTEGRAL and RXTE performed three simultaneous observations of thenearby radio galaxy Centaurus A in 2003 March, 2004 January, and 2004February with the goals of investigating the geometry and emissionprocesses via the spectral/temporal variability of the X-ray/low-energygamma-ray flux, and intercalibration of the INTEGRAL instruments withrespect to those on RXTE. Cen A was detected by both sets of instrumentsfrom 3 to 240 keV. When combined with earlier archival RXTE results, wefind the power-law continuum flux and the line-of-sight column depthvaried independently by 60% between 2000 January and 2003 March.Including the three archival RXTE observations, the iron-line flux wasessentially unchanging, and from this we conclude that theiron-line-emitting material is distant from the site of the continuumemission, and that the origin of the iron-line flux is still an openquestion. Taking X-ray spectral measurements from satellite missionssince 1970 into account, we discover a variability in the column depthbetween 1.0×1023 and 1.5×1023cm-2 separated by approximately 20 yr, and suggest thatvariations in the edge of a warped accretion disk viewed nearly edge-onmight be the cause. The INTEGRAL OSA 4.2 calibration of JEM-X, ISGRI,and SPI yields power-law indices consistent with the RXTE PCA and HEXTEvalues, but the indices derived from ISGRI alone are about 0.2 greater.Significant systematics are the limiting factor for INTEGRAL spectralparameter determination.
| Determining Central Black Hole Masses in Distant Active Galaxies and Quasars. II. Improved Optical and UV Scaling Relationships
We present four improved empirical relationships useful for estimatingthe central black hole mass in nearby AGNs and distant luminous quasarsalike using either optical or UV single-epoch spectroscopy. These massscaling relationships between line widths and luminosity are based onrecently improved empirical relationships between the broad-line regionsize and luminosities in various energy bands and are calibrated to theimproved mass measurements of nearby AGNs based on emission-linereverberation mapping. The mass scaling relationship based on theHβ line luminosity allows mass estimates for low-redshift sourceswith strong contamination of the optical continuum luminosity by stellaror nonthermal emission, while that based on the C IV λ1549 linedispersion allows mass estimates in cases where only the line dispersion(as opposed to the FWHM) can be reliably determined. We estimate thatthe absolute uncertainties in masses given by these mass scalingrelationships are typically around a factor of 4. We include in anappendix mass estimates for all of the Bright Quasar Survey (PG) quasarsfor which direct reverberation-based mass measurements are notavailable.Based in part on observations made with the NASA/ESA Hubble SpaceTelescope, obtained from the Data Archive at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| The First INTEGRAL AGN Catalog
We present the first INTEGRAL AGN catalog, based on observationsperformed from launch of the mission in 2002 October until 2004 January.The catalog includes 42 AGNs, of which 10 are Seyfert 1, 17 are Seyfert2, and 9 are intermediate Seyfert 1.5. The fraction of blazars is rathersmall, with five detected objects, and only one galaxy cluster and nostarburst galaxies have been detected so far. A complete subset consistsof 32 AGNs with a significance limit of 7 σ in the INTEGRAL ISGRI20-40 keV data. Although the sample is not flux limited, thedistribution of sources shows a ratio of obscured to unobscured AGNs of1.5-2.0, consistent with luminosity-dependent unified models for AGNs.Only four Compton-thick AGNs are found in the sample. Based on theINTEGRAL data presented here, the Seyfert 2 spectra are slightly harder(Γ=1.95+/-0.01) than Seyfert 1.5 (Γ=2.10+/-0.02) and Seyfert1 (Γ=2.11+/-0.05).
| INTEGRAL IBIS Extragalactic Survey: Active Galactic Nuclei Selected at 20-100 keV
Analysis of International Gamma-Ray Astrophysics Laboratory (INTEGRAL)Core Programme and public open-time observations performed up to 2005April provides a sample of 62 active galactic nuclei in the 20-100 keVband above a flux limit of ~1.5×10-11 ergscm-2 s-1. Most (42) of the sources in the sampleare Seyfert galaxies, almost equally divided between type 1 and type 2objects; six are blazars, and 14 are still unclassified. Excluding theblazars, the average redshift of our sample is 0.021, while the meanluminosity is logL=43.45. We find that absorption is present in 65% ofthe objects, with 14% of the total sample due to Compton-thick activegalaxies. In agreement with both Swift BAT team results and 2-10 keVstudies, the fraction of absorbed objects decreases with the 20-100 keVluminosity. All Seyfert 2's in our sample are absorbed, as are 33% ofSeyfert 1's. The present data highlight the capability of INTEGRAL toprobe the extragalactic gamma-ray sky and to find new and/or absorbedactive galaxies.Based on observations obtained with INTEGRAL, an ESA project withinstruments and science data center funded by ESA member states(especially the PI countries: Denmark, France, Germany, Italy,Switzerland, Spain), the Czech Republic, and Poland and with theparticipation of Russia and the US.
| Statistics of relativistically broadened Fe Kα lines in AGN
We present preliminary results on the properties of relativisticallybroadened Fe Kα lines in a collection of more then 100 ActiveGalactic Nuclei (AGN) observed by the XMM-Newton EPIC-pn camera. Ourmain conclusions can be summarized as follows: a) we detect broad linesin about 25% of the sample objects. This fraction increases to 42± 13 % if we consider only objects with more than 104counts in the hard (2-10 keV) band, and to 50 ± 32 % for thesmall sub-sample (6 objects) of type 1 Piccinotti AGN with optimalXMM-Newton exposure (at least 2 × 105 counts in thehard band); b) we find no significant difference in the detection rateof broad lines between obscured and unobscured AGN; c) the strongestrelativistic profiles are measured in low-luminosity (L_X <1043 erg s-1) AGN; d) Equivalent Widths (EWs)associated with relativistic profiles in stacked spectra are150 eV for all luminosity classes; e)models of relativistically broadened iron line profiles (kyrline,\cite{dovciak05}), which include full relativistic treatment of theaccretion disk emission around a Kerr black hole in the strong gravityregime, yield an average disk inclination angle≃30°, and a radial dependence of the disk emissivityprofile ≃-3. The distribution of EW is very broad, with < log(EW) > = 2.4 and σ_{log (EW)} = 1.4. We estimate that aninvestment of about 1 Ms of XMM-Newton time would be required to putthese results on a sound statistical basis.
| Search for narrow energy-shifted lines in AGN spectra in the XMM-Newton archive
Thanks to the large effective area and the spectral resolution ofcurrent X-ray satellites, the detection of X-ray narrow spectralfeatures in the 5-7 keV band is becoming commonplace in many AGNobservations. Such lines, both in emission and in absorption, are mostlyinterpreted as arising from Iron atoms. When observed with somedisplacement from their rest frame position, these lines carry thepotential to study the motion of circumnuclear gas in AGN, providing adiagnostic of the effects of the gravitational field of the centralblack hole. These narrow features have been often found with marginalstatistical significance. A systematic search for narrow features intype1 AGN is being performed on all spectra available in the XMM-Newtonarchive with the aim to estimate the significance of the features withMonte Carlo simulations of synthetic spectra. The project andpreliminary results are presented. http://xmm.esac.esa.int/external/xmm_data_acc/xsa/index.shtml
| Relativistic blue- and red-shifted absorption lines in AGNs
Current, accumulating evidence for (mildly) relativistic blue- andred-shifted absorption lines in AGNs is reviewed. XMM-Newton and Chandrasensitive X-ray observations are starting to probe not only thekinematics (velocity) but also the dynamics (accelerations) of highlyionized gas flowing in-and-out from, likely, a few gravitational radiifrom the black hole. It is thus emphasized that X-ray absorption-linespectroscopy provides new potential to map the accretion flows nearblack holes, to probe the launching regions of relativisticjets/outflows, and to quantify the cosmological feedback of AGNs.Prospects to tackle these issues with future high energy missions arebriefly addressed.
| The Spiral Host Galaxy of the Double Radio Source 0313-192
We present new Hubble Space Telescope (HST), Gemini South, and Chandraobservations of the radio galaxy 0313-192, which hosts a 350 kpc doublesource and jets, even though previous data have suggested that it is aspiral galaxy. We measure the bulge scale and the luminosity, radial,and vertical profiles of disk starlight and consider the distributionsof H II regions and absorbing dust. In each case the HST data confirmits classification as an edge-on spiral galaxy, the only such systemknown to produce such an extended radio source of this kind. The Gemininear-IR images and Chandra spectral fit reveal a strongly obscuredcentral active galactic nucleus (AGN), seen through the entireinterstellar medium path length of the disk and showing X-ray evidenceof additional absorption from warm or dense material close to thecentral object. We consider several possible mechanisms for producingsuch a rare combination of AGN and host properties, some combination ofwhich may be at work. These include an unusually luminous bulge(suggesting a black hole of mass ~8×108Msolar), the orientation of the jets near the pole of thegas-rich disk, and some evidence of a weak gravitational interactionthat has warped the disk and could have enhanced fueling of the centralengine. We detect an X-ray counterpart of the kiloparsec-scale radio jetemerging to the south; jet/counterjet limits on both radio and X-rayregimes allow them to be symmetric if seen more than 15° from theplane of the sky, still consistent with the jet axes being within~30° of the poles of the gas-rich galaxy disk. A linear or disklikeemission-line structure is seen around the nucleus, inclined by ~20°to the stellar disk but nearly perpendicular to the jets; this mayrepresent the aftermath of a galaxy encounter, in which gas isphotoionized by a direct view of the nuclear continuum.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS5-26555 made with the Chandra X-Ray Observatory;and obtained at the Gemini Observatory, which is operated by AURA, Inc.,under a cooperative agreement with the National Science Foundation (NSF)on behalf of the Gemini partnership: the NSF (United States), theParticle Physics and Astronomy Research Council (United Kingdom), theNational Research Council (Canada), CONICYT (Chile), the AustralianResearch Council (Australia), CNPq (Brazil), and CONICET (Argentina).
| The Host Galaxies of Narrow-Line Seyfert 1 Galaxies: Nuclear Dust Morphology and Starburst Rings
We present a study of the nuclear morphology of a sample of narrow- andbroad-line Seyfert 1 galaxies (NLS1s and BLS1s, respectively) based onbroadband images in the Hubble Space Telescope archives. In our previousstudy we found that large-scale stellar bars at >1 kpc from thenucleus are more common in NLS1s than BLS1s. In this paper we find thatNLS1s preferentially have grand-design dust spirals within ~1 kpc oftheir centers. We also find that NLS1s have a higher fraction of nuclearstar-forming rings than BLS1s. We find that many of the morphologicaldifferences are due to the presence or absence of a large-scale stellarbar within the spiral host galaxy. In general, barred Seyfert 1 galaxiestend to have grand-design dust spirals at their centers, confirming theresults of other researchers. The high fraction of grand-design nucleardust spirals and stellar nuclear rings observed in NLS1s' host galaxiessuggests a means for efficient fueling of their nuclei to support theirhigh Eddington ratios.
| Systematic effects in measurement of black hole masses by emission-line reverberation of active galactic nuclei: Eddington ratio and inclination
Context: .Scatter around the relationship between central black holemasses in active galactic nuclei (AGNs) obtained byreverberation-mapping methods and host-galaxy bulge velocity dispersionindicates that the masses are uncertain typically by a factor of aboutthree. Aims: .In this paper, we try to identify the sources andsystematics of this uncertainty. Methods: .We characterize thebroad Hβ emission-line profiles by the ratio of their full-width athalf maximum (FWHM) to their line dispersion, i.e., the second moment ofthe line profile. We use this parameter to separate thereverberation-mapped AGNs into two populations, the first with narrowerHβ lines that tend to have relatively extended wings, and thesecond with broader lines that are relatively flat-topped. The firstpopulation is characterized by higher Eddington ratios than the second.Within each population, we calibrate the black-hole mass scale bycomparison of the reverberation-based mass with that predicted by thebulge velocity dispersion. We also use the distribution of ratios of thereverberation-based mass to the velocity-dispersion mass prediction in acomparison with a "generalized thick disk" model in order to see ifinclination can plausibly account for the observed distribution.Results: .We find that the line dispersion is a less biased parameter ingeneral than FWHM for black hole mass estimation, although we show thatit is possible to empirically correct for the bias introduced by usingFWHM to characterize the emission-line width. We also argue thatinclination effects are apparent only in some small subset of thereverberation-based mass measurements; it is primarily the objects withthe narrowest emission lines that seem to be most strongly affected. Conclusions: .Our principal conclusion is that the Hβ profile issensitive primarily to Eddington ratio, but that inclination effectsplay a role in some cases.
| The structure and X-ray radiation spectra of illuminated accretion disks in AGN. III. Modeling fractional variability
Context: .Random magnetic flares above the accretion disks of ActiveGalactic Nuclei can account for the production of the primary radiationand for the rapid X-ray variability that have been frequently observedin these objects. The primary component is partly reprocessed in thedisk atmosphere, forming a hot spot underneath the flare source andgiving rise to distinct spectral features. Aims: .Extending thework of Czerny et al. (2004, A&A, 420, 1), we model the fractionalvariability amplitude due to distributions of hot spots co-orbiting onthe accretion disk around a supermassive black hole. We compare ourresults to the observed fractional variability spectrum of the Seyfertgalaxy MCG-6-30-15. Methods: .According to defined radialdistributions, our code samples random positions for the hot spotsacross the disk. The local spot emission is computed as reprocessedradiation coming from a compact primary source above the disk. Thestructure of the hot spot and the anisotropy of the re-emission aretaken into account. We compute the fractional variability spectraexpected from such spot ensembles and investigate dependencies on theparameters describing the radial spot distribution. We consider thefractional variability F{ var} with respect to the spectralmean and the so-called point-to-point definition F{ pp}. Ourmethod includes relativistic corrections due to the curved space-time inthe vicinity of a rotating supermassive black hole at the disk center;the black hole's angular momentum is a free parameter and is subject tothe fitting procedure. Results: .We confirm that therms-variability spectra involve intrinsic randomness at a significantlevel when the number of flares appearing during the total observationtime is too small. Furthermore, the fractional variability expressed byF{ var} is not always compatible with F{ pp}. Inthe special case of MCG-6-30-15, we can reproduce the short-timescalevariability and model the suppressed variability in the energy range ofthe Kα line without any need to postulate reprocessing fartheraway from the center. The presence of the dip in the variabilityspectrum requires an increasing rate of energy production by the flarestoward the center of the disk. The depth of the feature is wellrepresented only if we assume a fast rotation of the central black holeand allow for considerable suppression of the primary flare emission.The modeled line remains consistent with the measured equivalent widthof the iron Kα line complex. The model can reproduce thefrequently observed suppression of the variability in the spectral rangearound 6.5 keV, thereby setting constraints on the black hole spin andon the disk inclination.
| Spectral line variability amplitudes in active galactic nuclei
We present the results of a long-term variability campaign of verybroad-line AGNs with line widths broader than FWHM > 5000 kms-1. The main goal of our investigation was to study whetherthe widths of the optical broad emission lines are correlated with theoptical intensity variations on timescales of years. Our AGN sampleconsisted of 10 objects. We detected a significant correlation betweenoptical continuum variability amplitudes and Hβ emission linewidths (FWHM) and, to a lesser degree, between Hβ line intensityvariations and Hβ equivalent widths. We add the spectroscopic dataof variable AGNs from the literature to supplement our sample. The AGNsfrom other optical variability campaigns with different line-widthshelped to improve the statistical significance of our very broad-lineAGN sample. After including the data on 35 additional galaxies, thecorrelation between optical continuum variability amplitudes and Hβemission line widths becomes even more significant and the probabilitythat this is a random correlation drops to 0.7 percent.
| Modeling the warm absorber in active galactic nuclei
We present a wide grid of models for the structure and transmissionproperties of warm absorbers in active galactic nuclei (AGN). Contraryto commonly used constant density models, our absorbing cloud is assumedto be under constant total (gas plus radiation) pressure. Thisassumption implies the coexistence of material at different temperaturesand ionization states, which is a natural consequence of pressure andthermal equilibrium. Our photoionization code allows us to compute theprofiles of the density, the temperature, the gas pressure, theradiation pressure and the ionization state across the cloud, and tocalculate the radiative transfer of continuum and lines includingCompton scattering. Therefore, equivalent widths of both saturated andunsaturated lines are properly modeled. For each pair of the incidentspectrum slope and the ionization parameter at the cloud surface thereis a natural upper limit to the total column densities of the cloud dueto thermal instabilities. These maximum values are comparable to theobservational constraints on the column density of warm absorbers whichmay give support to constant total pressure models. In all models wenote considerable absorption around 6.4 keV which modifies the intrinsicrelativistically broadened iron line profile originating in an accretiondisk illuminated atmosphere. Our models can be applied to fitting thespectroscopic data from the XMM-Newton and Chandra satellites.
| Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
This review discusses the current status of supermassive black holeresearch, as seen from a purely observational standpoint. Since theearly ‘90s, rapid technological advances, most notably the launchof the Hubble Space Telescope, the commissioning of the VLBA andimprovements in near-infrared speckle imaging techniques, have not onlygiven us incontrovertible proof of the existence of supermassive blackholes, but have unveiled fundamental connections between the mass of thecentral singularity and the global properties of the host galaxy. It isthanks to these observations that we are now, for the first time, in aposition to understand the origin, evolution and cosmic relevance ofthese fascinating objects.
| XMM-Newton spectroscopy of high-redshift quasars
XMM-Newton observations of 29 high-redshift (z > 2) quasars,including seven radio-quiet, 16 radio-loud and six broad absorption line(BAL) objects, are presented; due to the high redshifts, the rest-frameenergy bands extend up to ~30-70 keV. Over 2-10 keV, the quasars can bewell fitted in each case by a simple power law, with no strong evidencefor iron emission lines. The lack of iron lines is in agreement bothwith dilution by the radio jet emission (for the radio-loud quasars) andthe X-ray Baldwin effect. No Compton reflection humps at higher energies(i.e. above 10 keV in the rest frame) are detected either. Over thebroad-band (0.3-10 keV), approximately half (nine out of 16) of theradio-loud quasars are intrinsically absorbed, with the values ofNH generally being 1 × 1022 to 2 ×1022cm-2 in the rest frames of the objects. Noneof the seven radio-quiet objects shows excess absorption, while four ofthe six BAL quasars are absorbed. The radio-loud quasars have flattercontinuum slopes than their radio-quiet counterparts(ΓRL~ 1.55; ΓRQ~ 1.98 over 2-10 keV),while, after modelling the absorption, the underlying photon index forthe six BAL quasars is formally consistent with the non-BAL radio-quietobjects.
| Constraints on hot metals in the vicinity of the Galaxy
We have searched for evidence of soft X-ray absorption by hot metals inthe vicinity of the Galaxy in the spectra of a small sample of 15 type Iactive galactic nuclei (AGN) observed with the high-resolution X-raygratings on board Chandra. This is an extension of our previous surveyof hot OVII and OVIII absorbing gas in the vicinity of the Galaxy. Thestrongest absorption signatures within a few hundred km s-1of their rest-frame energies are most likely to be due to warm absorbingoutflows from the nearest AGN, which are back-lighting the local hotgas. We emphasize that absorption signatures in the spectra of somedistant AGN that are kinematically consistent with the recessionalvelocity of the AGN are most likely to be due to hot local gas. Alongthe sightline towards PG 1211+143, PDS 456 and MCG-6-30-15 there is avery large absorbing Fe column density which is kinematically consistentwith absorption by hot, local Fe. The sightlines to these three AGN passthrough the limb of the Northern Polar Spur (NPS), a local bubble formedfrom several supernovae which, if rich in Fe, may account for a largelocal Fe column.We obtain limits on the column density of local, highly ionized N, Ne,Mg, Si along all of the sightlines in our sample. We correlate thecolumn density limits with those of highly ionized O along the samesightlines. Assuming the hot local gas is in collisionally ionizedequilibrium, we obtain limits on the temperature and relative abundancesof the metals in the hot local gas. Our limits on the ionic columndensities in the local hot gas seem to be consistent with those observedin the hot halo gas of edge-on normal spiral galaxies.
| The relationship between X-ray variability amplitude and black hole mass in active galactic nuclei
We have investigated the relationship between the X-ray variabilityamplitude and black hole mass for a sample of 46 radio-quiet activegalactic nuclei observed by ASCA. 33 of the objects in our sampleexhibited significant variability over a time-scale of ~40 ks. Wedetermined the normalized excess variance in the 2-10 keV light curvesof these objects and found a significant anticorrelation between excessvariance and black hole mass. Unlike most previous studies, we havequantified the variability using nearly the same time-scale for allobjects. Moreover, we provide a prescription for estimating theuncertainties in variance which accounts both for measurementuncertainties and for the stochastic nature of the variability. We alsopresent an analytical method to predict the excess variance from a modelpower spectrum accounting for binning, sampling and windowing effects.Using this, we modelled the variance-mass relation assuming all objectshave a universal twice-broken power spectrum, with the position of thebreaks being dependent on mass. This accounts for the general form ofthe variance-mass relationship but is formally a poor fit and there isconsiderable scatter. We investigated this scatter as a function of theX-ray photon index, luminosity and Eddington ratio. After accounting forthe primary dependence of excess variance on mass, we find nosignificant correlation with either luminosity or X-ray spectral slope.We do find an anticorrelation between excess variance and the Eddingtonratio, although this relation might be an artefact owing to theuncertainties in the mass measurements. It remains to be establishedthat enhanced X-ray variability is a property of objects with steepX-ray slopes or large Eddington ratios. Narrow-line Seyfert 1 galaxies,in particular, are consistent with being more variable than theirbroad-line counterparts solely because they tend to have smaller masses.
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