arXiv subjects

J. N. Reeves

Publications and source records attributed to J. N. Reeves.

At least 55 records · Page 3Linked to original sources

arXiv2014

Ultra-fast outflows in radio-loud active galactic nuclei

Recent X-ray observations show absorbing winds with velocities up to mildly-relativistic values of the order of ~0.1c in a limited sample of 6 broad-line radio galaxies. They are observed as blue-shifted Fe XXV-XXVI K-shell absorption lines, similarly to the ultra-fast outflows (UFOs) reported in Seyferts and quasars. In this work we extend the search for such Fe K absorption lines to a larger sample of 26 radio-loud AGNs observed with XMM-Newton and Suzaku. The sample is drawn from the Swift BAT 58-month catalog and blazars are excluded. X-ray bright FR II radio galaxies constitute the majority of the sources. Combining the results of this analysis with those in the literature we find that UFOs are detected in >27% of the sources. However, correcting for the number of spectra with insufficient signal-to-noise, we can estimate that the incidence of UFOs is this sample of radio-loud AGNs is likely in the range f=(50+/-20)%. A photo-ionization modeling of the absorption lines with XSTAR allows to estimate the distribution of their main parameters. The observed outflow velocities are broadly distributed between v_out<1,000 km s^-1 and v_out~0.4c, with mean and median values of v_out~0.133c and v_out~0.117c, respectively. The material is highly ionized, with an average ionization parameter of logξ~4.5 erg s^-1 cm, and the column densities are larger than N_H > 10^22 cm^-2. Overall, these characteristics are consistent with the presence of complex accretion disk winds in a significant fraction of radio-loud AGNs and demonstrate that the presence of relativistic jets does not preclude the existence of winds, in accordance with several theoretical models.

astro-ph.HE↗

arXiv2014

Revealing the location and structure of the accretion disk-wind in PDS456

We present evidence for the rapid variability of the high velocity iron K-shell absorption in the nearby ($z=0.184$) quasar PDS456. From a recent long Suzaku observation in 2013 ($\sim1$Ms effective duration) we find that the the equivalent width of iron K absorption increases by a factor of $\sim5$ during the observation, increasing from $<105$eV within the first 100ks of the observation, towards a maximum depth of $\sim500$eV near the end. The implied outflow velocity of $\sim0.25$c is consistent with that claimed from earlier (2007, 2011) Suzaku observations. The absorption varies on time-scales as short as $\sim1$ week. We show that this variability can be equally well attributed to either (i) an increase in column density, plausibly associated with a clumpy time-variable outflow, or (ii) the decreasing ionization of a smooth homogeneous outflow which is in photo-ionization equilibrium with the local photon field. The variability allows a direct measure of absorber location, which is constrained to within $r=200-3500$$\rm{r_{g}}$ of the black hole. Even in the most conservative case the kinetic power of the outflow is $\gtrsim6\%$ of the Eddington luminosity, with a mass outflow rate in excess of $\sim40\%$ of the Eddington accretion rate. The wind momentum rate is directly equivalent to the Eddington momentum rate which suggests that the flow may have been accelerated by continuum-scattering during an episode of Eddington-limited accretion.

astro-ph.HE↗

arXiv2014

The puzzling X-ray continuum of the quasar MR 2251-178

We report on a comprehensive X-ray spectral analysis of the nearby radio-quiet quasar MR 2251-178, based on the long-look (~ 400 ks) XMM-Newton observation carried out in November 2011. As the properties of the multiphase warm absorber (thoroughly discussed in a recent, complementary work) hint at a steep photoionizing continuum, here we investigate into the nature of the intrinsic X-ray emission of MR 2251-178 by testing several physical models. The apparent 2-10 keV flatness as well as the subtle broadband curvature can be ascribed to partial covering of the X-ray source by a cold, clumpy absorption system with column densities ranging from a fraction to several x10^23 cm^-2. As opposed to more complex configurations, only one cloud is required along the line of sight in the presence of a soft X-ray excess, possibly arising as Comptonized disc emission in the accretion disc atmosphere. On statistical grounds, even reflection with standard efficiency off the surface of the inner disc cannot be ruled out, although this tentatively overpredicts the observed ~ 14-150 keV emission. It is thus possible that each of the examined physical processes is relevant to a certain degree, and hence only a combination of high-quality, simultaneous broadband spectral coverage and multi-epoch monitoring of X-ray spectral variability could help disentangling the different contributions. Yet, regardless of the model adopted, we infer for MR 2251-178 a bolometric luminosity of ~ 5-7 x 10^45 erg/s, implying that the central black hole is accreting at ~ 15-25 per cent of the Eddington limit.

astro-ph.HE↗

arXiv2013

Variability of the High Velocity Outflow in the Quasar PDS 456

We present a comparison of two Suzaku X-ray observations of the nearby (z=0.184), luminous ($L_{bol} \sim 10^{47}$ erg s$^{-1}$) type I quasar, PDS456. A new 125ks Suzaku observation in 2011 caught the quasar during a period of low X-ray flux and with a hard X-ray spectrum, in contrast to a previous 190ks Suzaku observation in 2007 when the quasar appeared brighter and had a steep ($Γ>2$) X-ray spectrum. The 2011 X-ray spectrum contains a pronounced trough near 9\,keV in the quasar rest frame, which can be modeled with blue-shifted iron K-shell absorption, most likely from the He and H-like transitions of iron. The absorption trough is observed at a similar rest-frame energy as in the earlier 2007 observation, which appears to confirm the existence of a persistent high velocity wind in PDS 456, at an outflow velocity of $0.25-0.30$c. The spectral variability between 2007 and 2011 can be accounted for by variations in a partial covering absorber, increasing in covering fraction from the brighter 2007 observation to the hard and faint 2011 observation. Overall the low flux 2011 observation can be explained if PDS 456 is observed at relatively low inclination angles through a Compton thick wind, originating from the accretion disk, which significantly attenuates the X-ray flux from the quasar.

astro-ph.HE↗

arXiv2013

A High Resolution View of the Warm Absorber in the Quasar MR2251-178

High resolution X-ray spectroscopy of the warm absorber in the nearby quasar, MR2251-178 (z = 0.06398) is presented. The observations were carried out in 2011 using the Chandra High Energy Transmission Grating and the XMM-Newton Reflection Grating Spectrometer, with net exposure times of approximately 400 ks each. A multitude of absorption lines from C to Fe are detected, revealing at least 3 warm absorbing components ranging in ionization parameter from log(ξ/erg cm s^-1) = 1-3 and with outflow velocities < 500 km/s. The lowest ionization absorber appears to vary between the Chandra and XMM-Newton observations, which implies a radial distance of between 9-17 pc from the black hole. Several broad soft X-ray emission lines are strongly detected, most notably from He-like Oxygen, with FWHM velocity widths of up to 10000 km/s, consistent with an origin from Broad Line Region (BLR) clouds. In addition to the warm absorber, gas partially covering the line of sight to the quasar appears to be present, of typical column density N_H = 10^23 cm^-2. We suggest that the partial covering absorber may arise from the same BLR clouds responsible for the broad soft X-ray emission lines. Finally the presence of a highly ionised outflow in the iron K band from both 2002 and 2011 Chandra HETG observations appears to be confirmed, which has an outflow velocity of -15600 \pm 2400 km/s. However a partial covering origin for the iron K absorption cannot be excluded, resulting from low ionization material with little or no outflow velocity.

astro-ph.CO↗

arXiv2013

An outburst scenario for the X-ray spectral variability in 3C 111

We present a combined Suzaku and Swift BAT broad-band E=0.6-200keV spectral analysis of three 3C 111 observations obtained in 2010. The data are well described with an absorbed power-law continuum and a weak (R~0.2) cold reflection component from distant material. We constrain the continuum cutoff at E_c~150-200keV, which is in accordance with X-ray Comptonization corona models and supports claims that the jet emission is only dominant at much higher energies. Fe XXVI Lyαemission and absorption lines are also present in the first and second observations, respectively. The modelling and interpretation of the emission line is complex and we explore three possibilities. If originating from ionized disc reflection, this should be emitted at r_in> 50r_g or, in the lamp-post configuration, the illuminating source should be at a height of h> 30r_g over the black hole. Alternatively, the line could be modeled with a hot collisionally ionized plasma with temperature kT = 22.0^{+6.1}_{-3.2} keV or a photo-ionized plasma with logξ=4.52^{+0.10}_{-0.16} erg s^{-1} cm and column density N_H > 3x10^23 cm^{-2}. However, the first and second scenarios are less favored on statistical and physical grounds, respectively. The blue-shifted absorption line in the second observation can be modelled as an ultra-fast outflow (UFO) with ionization parameter logξ=4.47^{+0.76}_{-0.04} erg s^{-1} cm, column density N_H=(5.3^{+1.8}_{-1.3})x 10^{22} cm^{-2} and outflow velocity v_out = 0.104+/-0.006 c. Interestingly, the parameters of the photo-ionized emission model remarkably match those of the absorbing UFO. We suggest an outburst scenario in which an accretion disc wind, initially lying out of the line of sight and observed in emission, then crosses our view to the source and it is observed in absorption as a mildly-relativistic UFO.

astro-ph.HE↗

arXiv2013

Unification of X-ray winds in Seyfert galaxies: from ultra-fast outflows to warm absorbers

The existence of ionized X-ray absorbing layers of gas along the line of sight to the nuclei of Seyfert galaxies is a well established observational fact. This material is systematically outflowing and shows a large range in parameters. However, its actual nature and dynamics are still not clear. In order to gain insights into these important issues we performed a literature search for papers reporting the parameters of the soft X-ray warm absorbers (WAs) in 35 type 1 Seyferts and compared their properties to those of the ultra-fast outflows (UFOs) detected in the same sample. The fraction of sources with WAs is >60%, consistent with previous studies. The fraction of sources with UFOs is >34%, >67% of which also show WAs. The large dynamic range obtained when considering all the absorbers together allows us, for the first time, to investigate general relations among them. In particular, we find significant correlations indicating that the closer the absorber is to the central black hole, the higher the ionization, column, outflow velocity and consequently the mechanical power. The absorbers continuously populate the whole parameter space, with the WAs and the UFOs lying always at the two ends of the distribution. This strongly suggest that these absorbers, often considered of different types, could actually represent parts of a single large-scale stratified outflow observed at different locations from the black hole. The observed parameters and correlations are consistent with both radiation pressure through Compton scattering and MHD processes contributing to the outflow acceleration, the latter playing a major role. Most of the absorbers, especially the UFOs, have a sufficiently high mechanical power to significantly contribute to AGN feedback.

astro-ph.HE↗

arXiv2012

The Global Implications of the Hard X-ray Excess in Type 1 AGN

Recent evidence for a strong 'hard excess' of flux at energies > 20 keV in some Suzaku observations of type 1 Active Galactic Nuclei (AGN) has motivated an exploratory study of the phenomenon in the local type 1 AGN population. We have selected all type 1 AGN in the Swift Burst Alert Telescope (BAT) 58-month catalog and cross-correlated them with the holdings of the Suzaku public archive. We find the hard excess phenomenon to be a ubiquitous property of type 1 AGN. Taken together, the spectral hardness and equivalent width of Fe K alpha emission are consistent with reprocessing by an ensemble of Compton-thick clouds that partially cover the continuum source. In the context of such a model, ~ 80 % of the sample has a hardness ratio consistent with > 50% covering of the continuum by low-ionization, Compton-thick gas. More detailed study of the three hardest X-ray spectra in our sample reveal a sharp Fe K absorption edge at ~ 7 keV in each of them, indicating that blurred reflection is not responsible for the very hard spectral forms. Simple considerations place the distribution of Compton-thick clouds at or within the optical broad line region.

astro-ph.HE↗

arXiv2012

Decoupling absorption and continuum variability in the Seyfert 2 NGC 4507

We present the results of the Suzaku observation of the Seyfert 2 galaxy NGC 4507. This source is one of the X-ray brightest Compton-thin Seyfert 2s and a candidate for a variable absorber. Suzaku caught NGC 4507 in a highly absorbed state characterised by a high column density (NH \sim8 x10^23 cm^-2), a strong reflected component (R\sim 1.9) and a high equivalent width Fe K alpha emission line (EW\sim 500 eV). The Fe K alpha emission line is unresolved at the resolution of the Suzaku CCDs (sigma < 30 eV or FWHM < 3000 km s^-1) and most likely originates in a distant absorber. The Fe K beta emission line is also clearly detected and its intensity is marginally higher than the theoretical value for low ionisation Fe. A comparison with previous observations performed with XMM-Newton and BeppoSAX reveals that the X-ray spectral curvature changes on a timescale of a few months. We analysed all these historical observations, with standard models as well as with a most recent model for a toroidal reprocessor and found that the main driver of the observed 2-10 keV spectral variability is a change of the line-of-sight obscuration, varying from \sim4x10^23 cm^-2 to \sim9 x 10^23 cm^-2. The primary continuum is also variable, although its photon index does not appear to vary, while the Fe K alpha line and reflection component are consistent with being constant across the observations. This suggests the presence of a rather constant reprocessor and that the observed line of sight NH variability is either due to a certain degree of clumpiness of the putative torus or due to the presence of a second clumpy absorber.

astro-ph.HE↗

arXiv2012

Direct Measurement of the X-ray Time-Delay Transfer Function in Active Galactic Nuclei

The origin of the observed time lags, in nearby active galactic nuclei (AGN), between hard and soft X-ray photons is investigated using new XMM-Newton data for the narrow-line Seyfert I galaxy Ark 564 and existing data for 1H0707-495 and NGC 4051. These AGN have highly variable X-ray light curves that contain frequent, high peaks of emission. The averaged light curve of the peaks is directly measured from the time series, and it is shown that (i) peaks occur at the same time, within the measurement uncertainties, at all X-ray energies, and (ii) there exists a substantial tail of excess emission at hard X-ray energies, which is delayed with respect to the time of the main peak, and is particularly prominent in Ark 564. Observation (i) rules out that the observed lags are caused by Comptonization time delays and disfavors a simple model of propagating fluctuations on the accretion disk. Observation (ii) is consistent with time lags caused by Compton-scattering reverberation from material a few thousand light-seconds from the primary X-ray source. The power spectral density and the frequency-dependent phase lags of the peak light curves are consistent with those of the full time series. There is evidence for non-stationarity in the Ark 564 time series in both the Fourier and peaks analyses. A sharp `negative' lag (variations at hard photon energies lead soft photon energies) observed in Ark 564 appears to be generated by the shape of the hard-band transfer function and does not arise from soft-band reflection of X-rays. These results reinforce the evidence for the existence of X-ray reverberation in type I AGN, which requires that these AGN are significantly affected by scattering from circumnuclear material a few tens or hundreds of gravitational radii in extent.

astro-ph.HE↗

arXiv2012

A Suzaku survey of Fe K lines in Seyfert 1 AGN

We construct full broadband models in an analysis of Suzaku observations of nearby Seyfert 1 AGN (z<0.2) with exposures >50ks and with greater than 30000 counts in order to study their iron line profiles. This results in a sample of 46 objects and 84 observations. After a full modelling of the broadband Suzaku and Swift-BAT data (0.6-100 keV) we find complex warm absorption is present in 59% of the objects in this sample which has a significant bearing upon the derived Fe K region parameters. Meanwhile 35% of the 46 objects require some degree of high column density partial coverer in order to fully model the hard X-ray spectrum. We also find that a large number of the objects in the sample (22%) require high velocity, high ionization outflows in the Fe K region resulting from Fe XXV and Fe XXVI. A further four AGN feature highly ionized Fe K absorbers consistent with zero outflow velocity, making a total of 14/46 (30%) AGN in this sample showing evidence for statistically significant absorption in the Fe K region. Narrow Fe K alpha emission from distant material at 6.4 keV is found to be almost ubiquitous in these AGN. Examining the 6-7 keV Fe K region we note that narrow emission lines originating from Fe XXV at 6.63-6.70 keV and from Fe XXVI at 6.97 keV are present in 52% and 39% of objects respectively. Our results suggest statistically significant relativistic Fe K alpha emission is detected in 23 of 46 objects (50%) at >99.5% confidence, measuring an average emissivity index of q=2.4\pm0.1 and equivalent width EW=96\pm10 eV using the relline model. When parameterised with a Gaussian we find an average line energy of 6.32\pm0.04 keV, sigma width=0.470\pm0.05 keV and EW=97\pm19 eV. Where we can place constraints upon the black hole spin parameter a, we do not require a maximally spinning black hole in all cases.

astro-ph.HE↗

arXiv2012

X-ray evidence for ultra-fast outflows in local AGNs

X-ray evidence for ultra-fast outflows (UFOs) has been recently reported in a number of local AGNs through the detection of blue-shifted Fe XXV/XXVI absorption lines. We present the results of a comprehensive spectral analysis of a large sample of 42 local Seyferts and 5 Broad-Line Radio Galaxies (BLRGs) observed with XMM-Newton and Suzaku. We detect UFOs in >40% of the sources. Their outflow velocities are in the range 0.03-0.3c, with a mean value of ~0.14c. The ionization is high, in the range logxi~3-6 erg s^{-1} cm, and also the associated column densities are large, in the interval ~10^{22}-10^{24} cm^{-2}. Overall, these results point to the presence of highly ionized and massive outflowing material in the innermost regions of AGNs. Their variability and location on sub-pc scales favor a direct association with accretion disk winds/outflows. This also suggests that UFOs may potentially play a significant role in the AGN cosmological feedback besides jets and their study can provide important clues on the connection between accretion disks, winds and jets.

astro-ph.HE↗

arXiv2012

Modeling the Fe K Line Profiles in Type I AGN with a Compton-Thick Disk Wind

We have modeled a small sample of Seyfert galaxies that were previously identified as having simple X-ray spectra with little intrinsic absorption. The sources in this sample all contain moderately broad components of Fe K-shell emission and are ideal candidates for testing the applicability of a Compton-thick accretion-disk wind model to AGN emission components. Viewing angles through the wind allow the observer to see the absorption signature of the gas, whereas face-on viewing angles allow the observer to see the scattered light from the wind. We find that the Fe K emission line profiles are well described with a model of a Compton-thick accretion-disk wind of solar abundances, arising tens to hundred of gravitational radii from the central black hole. Further, the fits require a neutral component of Fe K alpha emission that is too narrow to arise from the inner part of the wind, and likely comes from a more distant reprocessing region. Our study demonstrates that a Compton-thick wind can have a profound effect on the observed X-ray spectrum of an AGN, even when the system is not viewed through the flow.

astro-ph.CO↗

arXiv2012

Observations of Outflowing UV Absorbers in NGC 4051 with the Cosmic Origins Spectrograph

We present new Hubble Space Telescope (HST)/Cosmic Origins Spectrograph observations of the Narrow-Line Seyfert 1 galaxy NGC 4051. These data were obtained as part of a coordinated observing program including X-ray observations with the Chandra/High Energy Transmission Grating (HETG) Spectrometer and Suzaku. We detected nine kinematic components of UV absorption, which were previously identified using the HST/Space Telescope Imaging Spectrograph. None of the absorption components showed evidence for changes in column density or profile within the \sim 10 yr between the STIS and COS observations, which we interpret as evidence of 1) saturation, for the stronger components, or 2) very low densities, i.e., n_H < 1 cm^-3, for the weaker components. After applying a +200 km s^-1 offset to the HETG spectrum, we found that the radial velocities of the UV absorbers lay within the O VII profile. Based on photoionization models, we suggest that, while UV components 2, 5 and 7 produce significant O VII absorption, the bulk of the X-ray absorption detected in the HETG analysis occurs in more highly ionized gas. Moreover, the mass loss rate is dominated by high ionization gas which lacks a significant UV footprint.

astro-ph.CO↗

arXiv2012

Study of LINER sources with broad H(alpha) emission. Spectral energy distribution and multiwavelength correlations

(Abridged) We attempt to infer the accretion mechanism and radiative processes giving rise to the SEDs of a well-defined optically-selected sample of LINERs showing a definite detection of broad Halpha emission (LINER 1s). We construct SEDs for six LINER~1s with simultaneous UV and X-ray fluxes, and we looked for multiwavelength, radio to X-ray and UV to X-ray, correlations. At a given X-ray luminosity, the average SED of the six LINER 1s in our sample: (1) resembles the SED of radio-loud quasars in the radio band, ~-2.7, (2) exhibits a weak UV bump, ~-1.17+-0.02 with a dispersion sigma=0.01, and (3) displays a X-ray spectrum similar to radio-quiet quasars. The bolometric luminosities inferred from the SEDs are extremely faint, at least two orders of magnitude lower than AGN. The X-ray bolometric correction, kappa_(2-10 keV), of our sample is lower than in the case of AGN, with a mean value of 16. We find a strong anticorrelation between the radio loudness parameter, R_X, and the Eddington ratio for our sample, confirming previous results. Moreover, we find a positive correlation between the radio luminosity and the X-ray luminosity which places AGN-powered LINERs, on a radio-power scale, right between low luminosity Seyferts and low luminosity radio galaxies. We complement our alpha_ox list with values derived on a well defined sample of UV-variable LINERs, and establish a strong positive correlation between alpha_ox (considering negative values) and the Eddington ratio, in contrast to the correlation found for luminous AGN. Lastly, we tested two different fundamental planes existing in the literature on our sample, in an attempt to put constraints on the debated origin of the X-ray emission, "RIAF versus jet". The results came contradictory with one pointing toward a RIAF-dominated X-ray emission process and the other pointing toward a jet domination.

astro-ph.CO↗

arXiv2012

The Suzaku view of highly-ionised outflows in AGN

We are conducting a systematic study of highly-ionised outflows in AGN using archival Suzaku data. To date we have analysed 59 observations of 45 AGN using a combined energy-intensity contour plot and Montecarlo method. We find that ~36% (16/45) of sources analysed so far show largely unambigous signatures (i.e., Montecarlo proabilities of >95%) of highly-ionised, high-velocity absorption troughs in their X-ray spectra. From XSTAR fitting we find that, overall, the properties of the absorbers are very similar to those found recently by Tombesi et al. (2010,2011) with XMM-Newton for the same phenomenon.

astro-ph.GA↗

arXiv2012

Evidence for ultra-fast outflows in radio-quiet AGNs: III - location and energetics

Using the results of a previous X-ray photo-ionization modelling of blue-shifted Fe K absorption lines on a sample of 42 local radio-quiet AGNs observed with XMM-Newton, in this letter we estimate the location and energetics of the associated ultra-fast outflows (UFOs). Due to significant uncertainties, we are essentially able to place only lower/upper limits. On average, their location is in the interval ~0.0003-0.03pc (~10^2-10^4 r_s) from the central black hole, consistent with what is expected for accretion disk winds/outflows. The mass outflow rates are constrained between ~0.01-1 M_{\odot} yr^{-1}, corresponding to >5-10% of the accretion rates. The average lower-upper limits on the mechanical power are log\dot{E}_K~42.6-44.6 erg s^{-1}. However, the minimum possible value of the ratio between the mechanical power and bolometric luminosity is constrained to be comparable or higher than the minimum required by simulations of feedback induced by winds/outflows. Therefore, this work demonstrates that UFOs are indeed capable to provide a significant contribution to the AGN cosmological feedback, in agreement with theoretical expectations and the recent observation of interactions between AGN outflows and the interstellar medium in several Seyferts galaxies.

astro-ph.HE↗

arXiv2011

New insights on the accretion disk-winds connection in radio-loud AGNs from Suzaku

From the spectral analysis of long Suzaku observations of five radio-loud AGNs we have been able to discover the presence of ultra-fast outflows with velocities ~0.1c in three of them, namely 3C 111, 3C 120 and 3C 390.3. They are consistent with being accretion disk winds/outflows. We also performed a follow-up on 3C 111 to monitor its outflow on ~7days time-scales and detected an anti-correlated variability of a possible relativistic emission line with respect to blue-shifted Fe K features, following a flux increase. This provides the first direct evidence for an accretion disk-wind connection in an AGN. The mass outflow rate of these outflows can be comparable to the accretion rate and their mechanical power can correspond to a significant fraction of the bolometric luminosity and is comparable to their typical jet power. Therefore, they can possibly play a significant role in the expected feedback from AGNs and can give us further clues on the relation between the accretion disk and the formation of winds/jets.

astro-ph.HE↗