A. Markowitz

X-ray spectral variability and rapid variability of the soft X-ray spectrum Seyfert 1 galaxies Arakelian 564 and Ton S180

The bright, soft X-ray spectrum Seyfert 1 galaxies Ark 564 and Ton S180 were monitored for 35 days and 12 days, respectively, with ASCA and RXTE (and EUVE for Ton S180). These represent the most intensive X-ray monitoring of any such soft-spectrum Seyfert 1 to date. Light curves were constructed for Ton S180 in six bands spanning 0.1-10 keV and for Ark 564 in five bands spanning 0.7-10 keV. The short-timescale (hours-days) variability patterns were very similar across energy bands, with no evidence of lags between any of the energy bands studied. The fractional variability amplitude was almost independent of energy band, unlike hard-spectrum Seyfert 1 galaxies, which show stronger variations in the softer bands. It is difficult to simultaneously explain soft Seyfert galaxies stronger variability, softer spectra, and weaker energy dependence of the variability relative to hard Seyfert galaxies. There was a trend for soft- and hard-band light curves of both objects to diverge on the longest timescales probed (~weeks), with the hardness ratio showing a secular change throughout the observations. This is consistent with the fluctuation power density spectra that showed relatively greater power on long timescales in the softest bands. The simplest explanation of all of these is that two continuum emission components are visible in the X-rays: a relatively hard, rapidly variable component that dominates the total spectrum and a slowly variable soft excess that only shows up in the lowest energy channels of ASCA. Although it would be natural to identify the latter component with an accretion disk and the former with a corona surrounding it, a standard thin disk could not get hot enough to radiate significantly in the ASCA band, and the observed variability timescales are much too short. It also appears that the hard component may have a more complex shape than a pure power law. The most rapid factor of 2 flares and dips occurred within ~1000 s, in Ark 564 and a bit more slowly in Ton S180. The speed of the luminosity changes rules out viscous or thermal processes and limits the size of the individual emission regions to 15 Schwarzschild radii (and probably much less), that is, to either the inner disk or small regions in a corona.

Flaring Behavior of the Quasar 3C 454.3 Across the Electromagnetic Spectrum

We analyze the behavior of the parsec-scale jet of the quasar 3C 454.3 during pronounced flaring in 2005-2008. Three major disturbances propagated down the jet along different trajectories with Lorentz factors Γ > 10. The disturbances show a clear connection with millimeter-wave outbursts, in 2005 May/June, 2007 July, and 2007 December. High-amplitude optical events in the R-band light curve precede peaks of the millimeter-wave outbursts by 15-50 days. Each optical outburst is accompanied by an increase in X-ray activity. We associate the optical outbursts with propagation of the superluminal knots and derive the location of sites of energy dissipation in the form of radiation. The most prominent and long lasting of these, in 2005 May, occurred closer to the black hole, while the outbursts with a shorter duration in 2005 autumn and in 2007 might be connected with the passage of a disturbance through the millimeter-wave core of the jet. The optical outbursts, which coincide with the passage of superluminal radio knots through the core, are accompanied by systematic rotation of the position angle of optical linear polarization. Such rotation appears to be a common feature during the early stages of flares in blazars. We find correlations between optical variations and those at X-ray and γ-ray energies. We conclude that the emergence of a superluminal knot from the core yields a series of optical and high-energy outbursts, and that the millimeter-wave core lies at the end of the jets acceleration and collimation zone. We infer that the X-ray emission is produced via inverse Compton scattering by relativistic electrons of photons both from within the jet (synchrotron self-Compton) and external to the jet (external Compton, or EC); which one dominates depends on the physical parameters of the jet. A broken power-law model of the γ-ray spectrum reflects a steepening of the synchrotron emission spectrum from near-IR to soft UV wavelengths. We propose that the γ-ray emission is dominated by the EC mechanism, with the sheath of the jet supplying seed photons for γ-ray events that occur near the millimeter-wave core.

Long-Term X-Ray Spectral Variability in Seyfert 1 Galaxies

Direct time-resolved spectral fitting has been performed on continuous Rossi X-Ray Timing Explorer monitoring of seven Seyfert 1 galaxies to study their broadband spectral variability and Fe Kα variability characteristics on timescales of days to years. Variability in the Fe Kα line is not detected in some objects but is present in others; e.g., in NGC 3516, NGC 4151, and NGC 5548 there are systematic decreases in line flux by factors of ~2-5 over 3-4 years. The Fe Kα line varies less strongly than the broadband continuum, but, like the continuum, exhibits stronger variability toward longer timescales. Relatively less model-dependent broadband fractional variability amplitude (Fvar) spectra also show weaker line variability compared with the continuum variability. Comparable systematic long-term decreases in the line and continuum are present in NGC 5548. Overall, however, there is no evidence for correlated variability between the line and continuum, severely challenging models in which the line tracks continuum variations modified only by a light-travel time delay. Local effects such as the formation of an ionized skin at the site of line emission may be relevant. The spectral fitting and Fvar spectra both support spectral softening as continuum flux increases.

Correlated long term optical and x-ray variations in NGC 5548

We combine the long-term optical light curve of the Seyfert 1 galaxy NGC 5548 with the X-ray light curve measured by the Rossi X-Ray Timing Explorer over 6 years, to determine the relationship between the optical and X-ray continua. The X-ray light curve is strongly correlated with the optical light curve on long (~1 yr) timescales. The amplitude of the long-term optical variability in NGC 5548 is larger than that of the X-ray variability (after accounting for the host galaxy contribution), implying that X-ray reprocessing is not the main source of the optical/X-ray correlation. The correlated X-ray and optical variations in NGC 5548 may be caused by instabilities in the inner part of the accretion flow, where both the X-ray and the optical emission regions may be located.

A Suzaku survey of Fe K lines in Seyfert 1 active galactic nuclei

We construct full broad-band models in an analysis of Suzaku observations of nearby Seyfert 1 active galactic nuclei (AGN) (z ≤ 0.2) with exposures >50 ks and with greater than 30 000 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 broad-band Suzaku and Swift-Burst Alert Telescope data (0.6–100 keV), we find complex warm absorption is present in 59 per cent of the objects in this sample which has a significant bearing upon the derived Fe K region parameters. Meanwhile 35 per cent 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 per cent) 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 per cent) AGN in this sample showing evidence for statistically significant absorption in the Fe K region. Narrow Fe Kα 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 per cent of objects, respectively. Our results suggest statistically significant relativistic Fe Kα emission is detected in 23 of 46 objects (50 per cent) at >99.5 per cent confidence, measuring an average emissivity index of q = 2.4 ± 0.1 and equivalent width  eV using the relline model. When parametrized with a Gaussian we find an average line energy of 6.32 ± 0.04 keV, σwidth = 0.470 ± 0.05 keV and  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.

A Suzaku survey of Fe K lines in Seyfert 1 AGN

We construct full broad-band models in an analysis of Suzaku observations of nearby Seyfert 1 active galactic nuclei (AGN) (z ≤ 0.2) with exposures >50 ks and with greater than 30 000 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 broad-band Suzaku and Swift-Burst Alert Telescope data (0.6–100 keV), we find complex warm absorption is present in 59 per cent of the objects in this sample which has a significant bearing upon the derived Fe K region parameters. Meanwhile 35 per cent 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 per cent) 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 per cent) AGN in this sample showing evidence for statistically significant absorption in the Fe K region. Narrow Fe Kα 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 per cent of objects, respectively. Our results suggest statistically significant relativistic Fe Kα emission is detected in 23 of 46 objects (50 per cent) at >99.5 per cent confidence, measuring an average emissivity index of q = 2.4 ± 0.1 and equivalent width  eV using the relline model. When parametrized with a Gaussian we find an average line energy of 6.32 ± 0.04 keV, σwidth = 0.470 ± 0.05 keV and  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.

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 the Seyfert galaxy IC 4329a. The Fe K bandpass is dominated by two resolved peaks at 6.4 and 7.0 keV, consistent with neutral or near-neutral Fe Kα and Kβ emission. There is a prominent redward asymmetry in the 6.4 keV line, which could indicate emission from a Compton shoulder. Alternatively, models using dual relativistic disk lines are found to describe the emission profile well. A low-inclination, moderately relativistic dual disk-line model is possible if the contribution from narrow components, due to distant material, is small or absent. A high-inclination, moderately relativistic profile for each peak is possible if there are roughly equal contributions from both the broad and narrow components. Combining the XMM-Newton data with RXTE monitoring data, we explore the time-resolved spectral behavior on timescales from hours to 2 years. We find no strong evidence for variability of the Fe K line flux on any timescale, likely due to the minimal level of continuum variability. We detect, at high significance, a narrow absorption line at 7.68 keV. This feature is most likely due to Fe XXVI Kα absorption blueshifted to ~0.1c relative to the systemic velocity, suggesting a high-velocity, highly ionized outflow component. As is often the case with similar outflows seen in high-luminosity quasars, the power associated with the outflow represents a substantial portion of the total energy budget of the AGN. The outflow could arise from a radiatively driven disk wind, or it may be in the form of a discrete, transient blob of ejected material.

An RXTE Survey of Long-Term X-Ray Variability in Seyfert 1 Galaxies

Data from the first three years of RXTE observations have been systematically analyzed to yield a set of 300 day 2-10 keV light curves with similarly uniform, ~5 day sampling, for a total of nine Seyfert 1 galaxies. This is the first X-ray variability survey to probe consistently timescales longer than a few days in a large number of active galactic nuclei (AGNs). Comparison to ASCA data covering a similar band but much shorter (1 day) timescales shows that all the AGNs are more strongly variable on long timescales than on short timescales. This increase is greatest for the highest luminosity sources. The well-known anticorrelation between source luminosity and variability amplitude is both stronger and shallower in power-law slope when measured on long timescales. This is consistent with a picture in which the X-ray variability of Seyfert 1 galaxies can be can be described by a single, universal fluctuation power-density shape for which the cutoff moves to longer timescales for higher luminosity sources. All of the Seyfert 1 galaxies exhibit stronger variability in the relatively soft 2-4 keV band than in the harder 7-10 keV band. This effect is much too pronounced to be explained by simple models based either on the dilution of the power-law continuum by the Compton reflection component or on the hard X-rays being produced in a static, pair-dominated, plane-parallel Comptonizing corona.

Iron line profiles in Suzaku spectra of bare Seyfert galaxies

We methodically model the broad-band Suzaku spectra of a small sample of six ‘bare’ Seyfert galaxies: Ark 120, Fairall 9, MCG −02-14-009, Mrk 335, NGC 7469 and SWIFT J2127.4+5654. The analysis of bare Seyferts allows a consistent and physical modelling of active galactic nuclei due to a weak amount of any intrinsic warm absorption, removing the degeneracy between the spectral curvature due to warm absorption and the red wing of the Fe K region. Through effective modelling of the broad-band spectrum and investigating the presence of narrow neutral or ionized emission lines and reflection from distant material, we obtain an accurate and detailed description of the Fe K line region using models such as LAOR, KERRDISK and KERRCONV. Results suggest that ionized emission lines at 6.7 and 6.97 keV (particularly Fe XXVI )a re relatively common, and the inclusion of these lines can greatly affect the parameters obtained with relativistic models, i.e. spin, emissivity, inner radius of emission and inclination. Moderately broad components are found in all objects, but typically the emission originates from tens of rg, rather than within <6 rg of the black hole. Results obtained with KERRDISK line profiles suggest an average emissivity of q ∼ 2.3 at intermediate spin values with all objects ruling out the presence of a maximally spinning black hole at the 90 per cent confidence level. We also present new spin constraints for Mrk 335 and NGC 7469 with intermediate values of a = 0.70 +0.12 −0.01 and 0.69 +0.09 −0.09 , respectively.

Suzaku Observations of the Hard X-ray Variability of MCG-6-30-15: the Effects of Strong Gravity Around a Kerr Black Hole

Suzaku has, for the first time, enabled the hard X-ray variability of the Seyfert 1 galaxy MCG-6-30-15 to be measured. The variability in the 14-45 keV band, which is dominated by a strong reflection hump, is quenched relative to that at a few keV. This directly demonstrates that the whole reflection spectrum is much less variable than the power-law continuum. The broadband spectral variability can be decomposed into two components - a highly variable power-law and constant reflection - as previously inferred from other observations in the 2-10 keV band. The strong reflection and high iron abundance give rise to a strong broad iron line, which requires the inner disc radius to be at about 2 gravitational radii. Our results are consistent with the predictions of the light bending model which invokes the very strong gravitational effects expected very close to a rapidly spinning black hole.