X-ray, UV and optical time delays in the bright Seyfert galaxy Ark 120 with co-ordinated Swift and ground-based observations
A. P. Lobban, S. Zola, U. Pajdosz-Smierciak, V. Braito, E. Nardini, G. Bhatta, A. Markowitz, R. Bachev, D. Carosati, D. B. Caton, G. Damljanovic, B. Debski, J. … 展开作者
A. P. Lobban, S. Zola, U. Pajdosz-Smierciak, V. Braito, E. Nardini, G. Bhatta, A. Markowitz, R. Bachev, D. Carosati, D. B. Caton, G. Damljanovic, B. Debski, J. B. Haislip, S. M. Hu, V. Kouprianov, J. Krzesinski, D. Porquet, F. Pozo Nunez, J. Reeves, D. E. Reichart
备注：
15 pages, 9 figures, 4 tables; accepted for publication in MNRAS
We report on the results of a multiwavelength monitoring campaign of the bright, nearby Seyfert galaxy, Ark 120 using a ~50-day observing programme with Swift and a ~4-month co-ordinated ground-based observing campaign, predominantly using the Skynet Robotic Telescope Network. We find Ark 120 to be variable at all optical, UV, and X-ray wavelengths, with the variability observed to be well-correlated between wavelength bands on short timescales. We perform cross-correlation analysis across all available wavelength bands, detecting time delays between emission in the X-ray band and the Swift V, B and UVW1 bands. In each case, we find that the longer-wavelength emission is delayed with respect to the shorter-wavelength emission. Within our measurement uncertainties, the time delays are consistent with the τ~ λ^{4/3} relation, as predicted by a disc reprocessing scenario. The measured lag centroids are τ_{cent} = 11.90 +/- 7.33, 10.80 +/- 4.08, and 10.60 +/- 2.87 days between the X-ray and V, B, and UVW1 bands, respectively. These time delays are longer than those expected from standard accretion theory and, as such, Ark 120 may be another example of an active galaxy whose accretion disc appears to exist on a larger scale than predicted by the standard thin-disc model. Additionally, we detect further inter-band time delays: most notably between the ground-based I and B bands (τ_{cent} = 3.46 +/- 0.86 days), and between both the Swift XRT and UVW1 bands and the I band (τ_{cent} = 12.34 +/- 4.83 and 2.69 +/- 2.05 days, respectively), highlighting the importance of co-ordinated ground-based optical observations.
The Seyfert 1 galaxy Ark 564 was observed with Chandra high energy transmission gratings for 250 ks. We present the high resolution X-ray spectrum that shows several associated absorption lines. The photoionization model requires two warm absorbers with two different ionization states (logU=0.39\pm0.03 and logU=-0.99\pm0.13), both with moderate outflow velocities (~100 km s^-1) and relatively low line of sight column densities (logNH=20.94 and 20.11 cm^-2). The high ionization phase produces absorption lines of OVII, OVIII, NeIX, NeX, MgXI, FeXVII and FeXVIII while the low ionization phase pro…
We present \chandra high energy transmission grating spectra of the narrow-line Seyfert-1 galaxy Ark 564. The spectrum shows numerous absorption lines which are well modeled with low velocity outflow components usually observed in Seyfert galaxies \citep{Gupta2013}. There are, however, some residual absorption lines which are not accounted for by low-velocity outflows. Here we present identifications of the strongest lines as $Kα$ transitions of \oviin (two lines) and \ovin at outflow velocities of $\sim 0.1c$. These lines are detected at $6.9σ$, $6.2σ$, and $4.7σ$ respectively and cannot be d…
We present results from a detailed spectral-timing analysis of a long ~486 ks XMM-Newton observation of the bare Seyfert 1 galaxy Ark 120 which showed alternating diminution and increment in the 0.3-10 keV X-ray flux over four consecutive orbits in 2014. We study the energy-dependent variability of Ark 120 through broad-band X-ray spectroscopy, fractional root-mean-squared (rms) spectral modelling, hardness-intensity diagram and flux-flux analysis. The X-ray (0.3-10 keV) spectra are well fitted by a thermally Comptonized primary continuum with two (blurred and distant) reflection components an…
We analyse eight XMM-Newton observations of the bright Narrow-Line Seyfert 1 galaxy Arakelian 564 (Ark 564). These observations, separated by ~6 days, allow us to look for correlations between the simultaneous UV emission (from the Optical Monitor) with not only the X-ray flux but also with the different X-ray spectral parameters. The X-ray spectra from all the observations are found to be adequately fitted by a double Comptonization model where the soft excess and the hard X-ray power law are represented by thermal Comptonization in a low temperature plasma and hot corona, respectively. Apart…
We present the long-term X-ray spectral and temporal analysis of a 'bare-type AGN' Ark 120. We consider the observations from XMM-Newton, Suzaku, Swift, and NuSTAR from 2003 to 2018. The spectral properties of this source are studied using various phenomenological and physical models present in the literature. We report (a) the variations of several physical parameters, such as the temperature and optical depth of the electron cloud, the size of the Compton cloud, and accretion rate for the last fifteen years. The spectral variations are explained from the change in the accretion dynamics; (b)…
We present a detailed analysis of xmm X-ray observations of the Narrow line Seyfert-1 (NLS1) galaxy Ark 564 taken between 2000 and 2011. High-resolution X-ray spectroscopy is carried out on the resultant high signal-to-noise stacked spectrum. We find three separate photoionised warm absorbers outflowing at velocities unusually lower than typical NLS1s. Using recombination timescale estimates, improved constraints on the location of these clouds show they could be located beyond 4 pc from the central source. Our estimates of the outflow kinetics suggest that the AGN in Ark 564 is unlikely to af…
We present the first results obtained by the application of the KYNREFREV-reverberation model, which is ready for its use in XSPEC. This model computes the time dependent reflection spectra of the disc as a response to a flash of primary power-law radiation from a point source corona located on the axis of the black hole accretion disc (lamp-post geometry). Full relativistic effects are taken into account. The ionisation of the disc is set for each radius according to the amount of the incident primary flux and the density of the accretion disc. We tested the model by fitting model predictions…
We present simultaneous XMM-Newton and NuSTAR observations of the `bare' Seyfert 1 galaxy, Ark 120, a system in which ionized absorption is absent. The NuSTAR hard X-ray spectral coverage allows us to constrain different models for the excess soft X-ray emission. Among phenomenological models, a cutoff power law best explains the soft X-ray emission. This model likely corresponds to Comptonization of the accretion disk seed UV photons by a population of warm electrons: using Comptonization models, a temperature of ~0.3 keV and an optical depth of ~13 are found. If the UV-to-X-ray optxagnf mode…
Over the last few years several models have been proposed to interpret the widespread soft excess observed in the X-ray spectra of type 1 active galactic nuclei (AGN). In particular, reflection from the photoionized accretion disc blurred by relativistic effects has proven to be successful in reproducing both the spectral shape and the variability pattern of many sources. As a further test to this scenario we present the analysis of a recent ~100 ks long Suzaku observation of Arakelian 120, a prototypical 'bare' Seyfert 1 galaxy in which no complex absorption system is expected to mimic a soft…
We report the results of a six-month Swift monitoring campaign of Ark120, a prototypical bare Seyfert1 galaxy. The lack of intrinsic absorption combined with the nearly contemporaneous coverage of the UV and X-ray bands makes it possible to investigate the link between the accretion disk and the Comptonization corona. Our observations confirm the presence of substantial temporal variability, with the X-rays characterized by large-amplitude flux changes on timescales of few days, while the variations in the UV bands are smoother on timescales of several weeks. The source also shows spectral var…
We report on the detection of ultra-fast outflows in the Seyfert~1 galaxy Mrk 590. These outflows are identified through highly blue-shifted absorption lines of OVIII and NeIX in the medium energy grating spectrum and SiXIC and MgXII in the high energy grating spectrum on board Chandra X-ray observatory. Our best fit photoionization model requires two absorber components at outflow velocities of 0.176c and 0.0738c and a third tentative component at 0.0867c. The components at 0.0738c and 0.0867c have high ionization parameter and high column density, similar to other ultra-fast outflows detecte…
Newman College（纽曼学院）；Baselius College（巴瑟留斯学院）；Providence Women’s College（普罗维登斯女子学院）；St. Francis de Sales College（圣方济各沙雷氏学院）；Inter-University Centre for Astronomy & Astrophysics（大学天体物理中心）；Islamic University of Science and Technology（伊斯兰科学与技术大学）
We present the spectral/timing properties of the bare Seyfert galaxy Ark 120 through a deep ~420ks XMM-Newton campaign plus recent NuSTAR observations and a ~6-month Swift monitoring campaign. We investigate the spectral decomposition through fractional rms, covariance and difference spectra, finding the mid- to long-timescale (~day-year) variability to be dominated by a relatively smooth, steep component, peaking in the soft X-ray band. Additionally, we find evidence for variable FeK emission red-ward of the FeK-alpha core on long timescales, consistent with previous findings. We detect a cle…
We report on the results from a large observational campaign on the bare Seyfert galaxy Ark 120, jointly carried out in 2014 with XMM-Newton, Chandra, and NuSTAR. The fortunate line of sight to this source, devoid of any significant absorbing material, provides an incomparably clean view to the nuclear regions of an active galaxy. Here we focus on the analysis of the iron fluorescence features, which form a composite emission pattern in the 6$-$7 keV band. The prominent K$α$ line from neutral iron at 6.4 keV is resolved in the Chandra High-Energy Transmission Grating spectrum to a full-width a…
The spectral shape of the hard X-ray continuum of Active Galactic Nuclei (AGN) can be ascribed to inverse Compton scattering of optical/UV seed photons from the accretion disc by a hot corona of electrons. This physical process produces a polarization signal which is strongly sensitive to the geometry of the scattering medium (i.e. the hot corona) and of the radiation field. MoCA (Monte Carlo code for Comptonisation in Astrophysics) is a versatile code which allows for different geometries and configurations to be tested for Compton scattering in compact objects. A single photon approach is co…
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 AGN 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 …
The Seyfert 1 galaxy, Ark 120, is a prototype example of the so-called class of bare nucleus AGN, whereby there is no known evidence for the presence of ionized gas along the direct line of sight. Here deep ($>400$ ks exposure), high resolution X-ray spectroscopy of Ark 120 is presented, from XMM-Newton observations which were carried out in March 2014, together with simultaneous Chandra/HETG exposures. The high resolution spectra confirmed the lack of intrinsic absorbing gas associated with Ark 120, with the only X-ray absorption present originating from the ISM of our own Galaxy, with a poss…
We report flux-resolved spectroscopic analysis of the active galactic nucleus (AGN) ESO 103--035 using \textit{NuSTAR} observations. Following an earlier work, we fit the spectra using a thermal Comptonization model with a relativistic reflection component to obtain estimates of the coronal temperature for two flux levels. The coronal temperature was found to increase from 24.0$^{+6.8}_{-3.4}$ to 55.3$^{+54.6}_{-7.2}$ keV (errors at 1-$σ$ confidence level) as the flux increased from $9.8$ to $11.9 \times 10^{-11}$ erg cm$^{-2}$ s$^{-1}$ in the 3--78 keV band. A marginal variation in the high e…
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 emissio…
We present a comprehensive flux resolved spectral analysis of the bright Narrow line Seyfert I AGNs, Mrk~335 and Ark~564 using observations by XMM-Newton satellite. The mean and the flux resolved spectra are fitted by an empirical model consisting of two Comptonization components, one for the low energy soft excess and the other for the high energy power-law. A broad Iron line and a couple of low energies edges are required to explain the spectra. For Mrk~335, the 0.3 - 10 keV luminosity relative to the Eddington value, L{$_{X}$}/L$_{Edd}$, varied from 0.002 to 0.06. The index variation can be…
Variable X-ray reverberation in the rapidly accreting AGN Ark 564: the response of the soft excess to the changing geometry of the inner accretion flow
We present the results of our optical identifications of four hard X-ray sources from the Swift all-sky survey. We obtained optical spectra for each of the program objects with the 6-m BTA telescope (Special Astrophysical Observatory, Russian Academy of Sciences, Nizhnii Arkhyz), which allowed their nature to be established. Two sources (SWIFT J2237.2+6324} and SWIFT J2341.0+7645) are shown to belong to the class of cataclysmic variables (suspected polars or intermediate polars). The measured emission line width turns out to be fairly large (FWHM ~ 15-25 A), suggesting the presence of extended…
