Andrew Lobban

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.

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.

Assessing black hole spin in deep Suzaku observations of Seyfert 1 AGN

We present a broad-band analysis of deep Suzaku observations of nearby Seyfert 1 active galactic nuclei (AGN): Fairall 9, MCG-6-30-15, NGC 3516, 3783 and 4051. The use of deep observations (exposures >200 ks) with high signal-to-noise ratio allows the complex spectra of these objects to be examined in full, taking into account features such as the soft excess, reflection continuum and complex absorption components. After a self-consistent modelling of the broad-band data (0.6-100.0 keV, also making use of Burst Alert Telescope data from Swift), the subtle curvature which may be introduced as a consequence of warm absorbers has a measured affect upon the spectrum at energies > 3 keV and the Fe K region. Forming a model (including absorption) of these AGN allows the true extent to which broadened disc line emission is present to be examined and as a result the measurement of accretion disc and black hole parameters which are consistent over the full 0.6-100.0 keV energy range. Fitting relativistic line emission models appears to rule out the presence of maximally spinning black holes in all objects at the 90 per cent confidence level, in particular MCG-6-30-15 at >99.5 per cent confidence. Relativistic Fe K line emission is only marginally required in NGC 3516 and not required in NGC 4051, over the full energy bandpass. None the less, statistically significant broadened 6.4 keV Fe Kα emission is detected in Fairall 9, MCG-6-30-15 and NGC 3783 yielding black hole spin estimates of a = 0.67 +0.10 -0.11 , a = 0.49 +0.20 -0.12 and a < -0.04, respectively, when fitted with disc emission models.

Spectral variability and reverberation time delays in the Suzaku X-ray spectrum of NGC 4051

Long-exposure Suzaku X-ray observations of the nearby active galaxy NGC 4051 from 2005 and 2008 are analysed, in an attempt to reach a self-consistent understanding of both the spectral variability on long time-scales and the broad-band variability at high time resolution. The techniques of principal components analysis and a maximum likelihood method of power spectrum analysis are used. In common with other type I active galactic nuclei (AGN), the spectral variability is dominated by a varying-normalization power-law component together with a quasi-steady, hard-spectrum offset component that contains Fe K atomic features. NGC 4051 displays a strong excess over a power law at energies of above 20 keV, some fraction of which also appears to vary with the power-law continuum. The fast time-scale power spectrum has a shape generally consistent with previous determinations, with the previously known dependence on broad-band photon energy, but in the new data significant differences are found between the low and high flux states of the source, demonstrating that the power spectrum is non-stationary. Frequency-dependent time lags between the hard and soft bands of up to 970 ± 225 s are measured. The existence of the observed time lags excludes the possibility that the hard spectral component originates as reflection from the inner accretion disc. We instead show that the time lags and their frequency and energy dependence may be explained simply by the effects of reverberation in the hard band, caused by reflection from a thick shell of material with maximum lags of about 10 000 s. If the reflecting material surrounds the AGN, it extends to a distance of about 1.5 x 10 14 cm, 600 gravitational radii, from the illuminating source and the global covering factor is C g ≳ 0.44, confirming previous suggestions that type I AGN have high covering factors of absorbing and reflecting material. Given the spectral and timing similarities with other type I AGN, we infer that this source structure is common in the type I population.

Contemporaneous Chandra HETG and Suzaku X-ray observations of NGC 4051

We present the results of a deep 300 ks Chandra HETG observation of the highly variable narrow-line Seyfert Type 1 galaxy NGC 4051. The HETG spectrum reveals 28 significant soft X-ray ionised lines in either emission or absorption; primarily originating from H-like and Helike K-shell transitions of O, Ne, Mg and Si (including higher order lines and strong forbidden emission lines from O VII and Ne IX) plus high ionisation L-shell transitions from Fe XVII to Fe XXII and lower ionisation inner-shell lines (e.g. O VI). Modelling the data with XSTAR requires four distinct ionisation zones for the gas, all outflo wing with velocities <1 000 km s 1 . A selection of the strongest emission/absorption lines app ear to be resolved with FWHM of �600 km s 1 . We also present the results from a quasi-simultaneous 350 ks Suzaku observation of NGC 4051 where the XIS spectrum reveals strong evidence for blueshifted absorption lines at �6.8 and �7.1 keV, consistent with previous findings. Modelling with XSTAR suggests that this is the signature of a highly ionised, high vel ocity outflow (log � = 4.1 +0.2 0.1 ; vout � 0.02c) which potentially may have a significant effect on the host g alaxy environment via feedback. Finally, we also simultaneously model the broad-band 2008 XIS+HXD Suzaku data with archival Suzaku data from 2005 when the source was observed to have entered an extended period of low flux in an attempt to analyse the cause of the long-term spectral variability. We find that we can account for this by a llowing for large variations in the normalisation of the intrinsic power-law component which may be interpreted as being due to significant changes in the covering fraction of a Compton-th ick partial-coverer obscuring the central continuum emission.

Evidence for a truncated accretion disc in the low-luminosity Seyfert galaxy, NGC 7213?

We present the broad-band 0.6–150 keV Suzaku and Swift BAT spectra of the low-luminosity Seyfert galaxy, NGC 7213. The time-averaged continuum emission is well fitted by a single power law of photon index � = 1.75, and from consideration of the Fermi flux limit we constrain the high-energy cut-off to be 350 keV < Ecut < 25 MeV. Line emission from both near-neutral iron Kα at 6.39 keV and highly ionized iron, from Fe XXV and Fe XXVI, is strongly detected in the Suzaku spectrum, further confirming the results of previous observations with Chandra and XMM–Newton. We find the centroid energies for the emission from Fe XXV and Fe XXVI to be 6.60 and 6.95 keV respectively, with the latter appearing to be resolved in the Suzaku spectrum. From modelling, we show that the Fe XXV and Fe XXVI emission can result from a highly photoionized plasma, with a column density of NH ∼ 3 × 10 23 cm −2 . A Compton reflection component, e.g. originating from an optically thick accretion disc or a Compton-thick torus, appears either very weak or absent in this active galactic nucleus (AGN), subtending <1 sr to the X-ray source, consistent with previous findings. Indeed, the absence of Compton reflection from either neutral or ionized material coupled with the lack of any relativistic Fe K signatures in the spectrum suggests that an inner, optically thick accretion disc is absent in this source. Instead, the accretion disc could be truncated with the inner regions perhaps replaced by a Compton-thin radiatively inefficient accretion flow (RIAF). Thus, the Fe XXV and Fe XXVI emission could both originate in ionized material perhaps at the transition region between the hot, inner flow and the cold, truncated accretion disc on the order of 10 3 –10 4 gravitational radii from the black hole. The origin for the unresolved neutral Fe Kα emission is then likely to be further out, perhaps originating in the optical broad-line region or a Compton-thin pc-scale torus.

X-ray timing analysis of the quasar PG 1211+143

We report on a timing analysis of a new ~630ks XMM-Newton observation of the quasar, PG 1211+143. We find a well-defined X-ray power spectrum with a well-detected bend at ~7e-5 Hz, consistent with the established bend-timescale--black-hole-mass correlation for luminous, accreting black holes. We find the linear rms-flux relation commonly observed in accreting black hole systems and investigate the energy-dependence of the rms. The fractional rms is roughly constant with energy on short timescales (< 1 day; within observations) whereas there is enhanced soft band variability on long timescales (between observations typically spaced by a few days). Additionally, we also report on the optical--UV variability using the OM on-board XMM-Newton and a ~2-month-long overlapping monitoring programme with Swift. We find that, although there is little UV variability within observations (<1 day), UV variations of a few per cent exist on time-scales of ~days--weeks.

A deep X-ray view of the bare AGN Ark 120. I. Revealing the Soft X-ray Line Emission

J.N. Reeves acknowledges financial support via Chandra grant number GO4-15092X. J.N. Reeves and T.J. Turner both acknowledge support from NASA grant NNX15AF12G. D. Porquet acknowledges financial support from the French GDR PCHE and from the European Union Seventh Framework Program (FP7/2007-2013) under grant agreement number 312789. J.N. Reeves, E. Nardini, and A. Lobban also acknowledge the financial support of the STFC. This research is based on observations obtained with the XMM-Newton and ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA) and on observations made by the Chandra X-ray Observatory. This research has made use of the CIAO software provided by the Chandra X-ray Center (CXC).

Imprints of a high-velocity wind on the soft X-ray spectrum of PG1211+143

XMM–Newton is a space science mission developed and operated by the European Space Agency. We acknowledge in particular the excellent work of ESA staff at the European Space Astronomy Center in Madrid in successfully planning and conducting the relevant XMM–Newton observations. The UK Science and Technology Facilities Council funded the posts of AL and MC.