ALBERT

Description: We examine simultaneous X-ray and UV light curves from multi-epoch 8 d XMM–Newton observations of the narrow line Seyfert 1 galaxy 1H 0707–495. The simultaneous observations reveal that both X-ray and UV emission are variable and that the amplitude of the X-ray variations is significantly greater than that of the UV variations in both epochs. Using a discrete correlation function the X-ray and UV light curves were examined for correlation on time-scales up to 7 d. Low-significance (~95 per cent confidence) correlations with the UV leading the X-ray variations are observed. The lack of a significant correlation between the UV and X-ray bands seems consistent with the X-ray source being centrally compact and dominated by light bending close to the black hole. In addition, multiband X-ray light curves were examined for correlations on similar time-scales. Highly significant (〉99.9 per cent confidence) correlations were observed at zero lag consistent with previous studies of this active galactic nucleus.

Description: X-ray reverberation, where light-travel time delays map out the compact geometry around the inner accretion flow in supermassive black holes, has been discovered in several of the brightest, most variable and well-known Seyfert galaxies. In this work, we expand the study of X-ray reverberation to all Seyfert galaxies in the XMM–Newton archive above a nominal rms variability and exposure level (a total of 43 sources). Approximately 50 per cent of sources exhibit iron K reverberation, in that the broad iron K emission line responds to rapid variability in the continuum. We also find that on long time-scales, the hard band emission lags behind the soft band emission in 85 per cent of sources. This ‘low-frequency hard lag’ is likely associated with the coronal emission, and so this result suggests that most sources with X-ray variability show intrinsic variability from the nuclear region. We update the known iron K lag amplitude versus black hole mass relation, and find evidence that the height or extent of the coronal source (as inferred by the reverberation time delay) increases with mass accretion rate.

Description: We examine simultaneous X-ray and UV light curves from multi-epoch 8 d XMM–Newton observations of the narrow line Seyfert 1 galaxy 1H 0707–495. The simultaneous observations reveal that both X-ray and UV emission are variable and that the amplitude of the X-ray variations is significantly greater than that of the UV variations in both epochs. Using a discrete correlation function the X-ray and UV light curves were examined for correlation on time-scales up to 7 d. Low-significance (~95 per cent confidence) correlations with the UV leading the X-ray variations are observed. The lack of a significant correlation between the UV and X-ray bands seems consistent with the X-ray source being centrally compact and dominated by light bending close to the black hole. In addition, multiband X-ray light curves were examined for correlations on similar time-scales. Highly significant (〉99.9 per cent confidence) correlations were observed at zero lag consistent with previous studies of this active galactic nucleus.

Description: The recent detection of X-ray reverberation lags, especially in the Fe Kα line region, around active galactic nuclei (AGN) has opened up the possibility of studying the time-resolved response (reflection) of hard X-rays from the accretion disc around supermassive black holes. Here, we use general relativistic transfer functions for reflection of X-rays from a point source located at some height above the black hole to study the time lags expected as a function of frequency and energy in the Fe Kα line region. We explore the models and the dependence of the lags on key parameters such as the height of the X-ray source, accretion disc inclination, black hole spin and black hole mass. We then compare these models with the observed frequency- and energy-dependence of the Fe Kα line lag in NGC 4151. Assuming the optical reverberation mapping mass of 4.6 10 7 M , we get a best fit to the lag profile across the Fe Kα line in the frequency range (1-2) x 10 – 5  Hz for an X-ray source located at a height $h = 7^{+2.9}_{-2.6} R_G$ with a maximally spinning black hole and an inclination i 〈 30°.

Description: In the past five years, a flurry of X-ray reverberation lag measurements of accreting supermassive black holes have been made using the XMM–Newton telescope in the 0.3–10 keV energy range. In this work, we use the NuSTAR ( Nuclear Spectroscopic Telescope Array ) telescope to extend the lag analysis up to higher energies for two Seyfert galaxies, SWIFT J2127.4+5654 and NGC 1365. X-ray reverberation lags are due to the light travel time delays between the direct continuum emission and the reprocessed emission from the inner radii of an ionized accretion disc. XMM–Newton has been particularly adept at measuring the lag associated with the broad Fe K emission line, where the gravitationally redshifted wing of the line is observed to respond before the line centroid at 6.4 keV, produced at larger radii. Now, we use NuSTAR to probe the lag at higher energies, where the spectrum shows clear evidence for Compton reflection, known as the Compton ‘hump’. The XMM–Newton data show Fe K lags in both SWIFT J2127.4+5654 and NGC 1365. The NuSTAR data provide independent confirmation of these Fe K lags, and also show evidence for the corresponding Compton hump lags, especially in SWIFT J2127.4+5654. These broad-band lag measurements confirm that the Compton hump and Fe K lag are produced at small radii. At low frequencies in NGC 1365, where the spectrum shows evidence for eclipsing clouds in the line of sight, we find a clear negative (not positive) lag from 2 to 10 keV, which can be understood as the decrease in column density from a neutral eclipsing cloud moving out of our line of sight during the observation.

Description: Reverberation lags in active galactic nuclei (AGN) were first discovered in the NLS1 galaxy, 1H0707–495. We present a follow-up analysis using 1.3 Ms of data, which allows for the closest ever look at the reverberation signature of this remarkable source. We confirm previous findings of a hard lag of ~100 s at frequencies ~ [0.5–4]  x 10 –4 Hz, and a soft lag of ~30 s at higher frequencies, ~ [0.6–3]  x 10 –3 Hz. These two frequency domains clearly show different energy dependences in their lag spectra. We also find evidence for a signature from the broad Fe Kα line in the high-frequency lag spectrum. We use Monte Carlo simulations to show how the lag and coherence measurements respond to the addition of Poisson noise and to dilution by other components. With our better understanding of these effects on the lag, we show that the lag-energy spectra can be modelled with a scenario in which low-frequency hard lags are produced by a compact corona responding to accretion rate fluctuations propagating through an optically thick accretion disc, and high-frequency soft lags are produced by short light-travel delay associated with reflection of coronal power-law photons off the disc.

Description: We present results obtained from the time-resolved X-ray spectral analysis of the Narrow-Line-Seyfert 1 galaxy SWIFT J2127.4+5654 during a ~130 ks XMM–Newton observation. We reveal large spectral variations, especially during the first ~90 ks of the XMM–Newton exposure. The spectral variability can be attributed to a partial eclipse of the X-ray source by an intervening low-ionization/cold absorbing structure (cloud) with column density $N_{\rm {H}} = 2.0^{+0.2}_{-0.3}\times 10^{22}$ cm –2 which gradually covers and then uncovers the X-ray emitting region with covering fraction ranging from zero to ~43 per cent. Our analysis enables us to constrain the size, number density and location of the absorbing cloud with good accuracy. We infer a cloud size (diameter) of D c ≤ 1.5 10 13 cm, corresponding to a density of n c ≥ 1.5 10 9 cm –3 at a distance of R c ≥ 4.3 10 16 cm from the central black hole. All of the inferred quantities concur to identify the absorbing structure with one single cloud associated with the broad line region of SWIFT J2127.4+5654. We are also able to constrain the X-ray emitting region size (diameter) to be D s ≤ 2.3 10 13 cm which, assuming the black hole mass estimated from single-epoch optical spectroscopy (1.5 10 7 M ), translates into D s ≤ 10.5 gravitational radii ( r g ) with larger sizes (in r g ) being associated with smaller black hole masses, and vice versa. We also confirm the presence of a relativistically distorted reflection component off the inner accretion disc giving rise to a broad relativistic Fe K emission line and small soft excess (small because of the high Galactic column density), supporting the measurement of an intermediate black hole spin in SWIFT J2127.4+5654 that was obtained from a previous Suzaku observation.

Description: We use archival XMM–Newton observations of Ark 564 and Mrk 335 to calculate the frequency-dependent time lags for these two well-studied sources. We discover high-frequency Fe K lags in both sources, indicating that the red wing of the line precedes the rest-frame energy by roughly 100 and 150 s for Ark 564 and Mrk 335, respectively. Including these two new sources, Fe K reverberation lags have been observed in seven Seyfert galaxies. We examine the low-frequency lag-energy spectrum, which is smooth, and shows no feature of reverberation, as would be expected if the low-frequency lags were produced by distant reflection off circumnuclear material. The clear differences in the low- and high-frequency lag-energy spectra indicate that the lags are produced by two distinct physical processes. Finally, we find that the amplitude of the Fe K lag scales with black hole mass for these seven sources, consistent with a relativistic reflection model where the lag is the light travel delay associated with reflection of continuum photons off the inner disc.

Description: Relativistically blueshifted absorption features of highly ionized ions, the so-called ultrafast outflows (UFOs), have been detected in the X-ray spectra of a number of accreting supermassive black holes. If these features truly originate from accretion disc winds accelerated to more than 10 per cent of the speed of light, their energy budget is very significant and they can contribute to or even drive galaxy-scale feedback from active galactic nuclei (AGNs). However, the UFO spectral features are often weak due to high ionization of the outflowing material, and the inference of the wind physical properties can be complicated by other spectral features in AGNs such as relativistic reflection. Here we study a highly accreting narrow-line Seyfert 1 galaxy PG 1448+273. We apply an automated, systematic routine for detecting outflows in accreting systems and achieve an unambiguous detection of a UFO in this AGN. The UFO absorption is observed in both soft and hard X-ray bands with the XMM–Newton observatory. The velocity of the outflow is (26 900 ± 600) km s−1 (∼0.09c), with an ionization parameter of $log (xi / extrm {erg~cm~s}^{-1})=4.03_{-0.08}^{+0.10}$ and a column density above 1023 cm−2. At the same time, we detect weak warm absorption features in the spectrum of the object. Our systematic outflow search suggests the presence of further multiphase wind structure, but we cannot claim a significant detection considering the present data quality. The UFO is not detected in a second, shorter observation with XMM–Newton, indicating variability in time, observed also in other similar AGNs.