Publication Search Results

ID: 158661
Type: article
Authors: Balasubramaniam, K.; Stawarz, L.; Marchenko, V.; Sobolewska, Magorzata A.; Cheung, C. C.; Siemiginowska, Aneta; Thimmappa, R.; Kosmaczewski, E.
Abstract: We present an analysis of the new, deep (94 ksec) Chandra ACIS-S observation of radio-loud active galaxy CGCG 292-057, characterized by a LINER-type nucleus and a complex radio structure that indicates intermittent jet activity. On the scale of the host galaxy bulge, we detected excess X-ray emission with a spectrum best fit by a thermal plasma model with a temperature of ˜0.8 keV. We argue that this excess emission results from compression and heating of the hot diffuse fraction of the interstellar medium displaced by the expanding inner, ˜20 kpc-scale lobes observed in this restarted radio galaxy. The nuclear X-ray spectrum of the target clearly displays an ionized iron line at ˜6.7 keV, and is best fitted with a phenomenological model consisting of a power-law (photon index ? 1.8) continuum absorbed by a relatively large amount of cold matter (hydrogen column density ?0.7 × 10²³ cm^-2), and partly scattered (fraction ˜3%) by ionized gas, giving rise to a soft excess component and Ka line from iron ions. We demonstrate that the observed X-ray spectrum, particularly the equivalent width of Fe XXV Ka (of order 0.3 keV) can in principle, be explained in a scenario involving a Compton-thin gas located at the scale of the broad-lined region in this source and photoionized by nuclear illumination. We compare the general spectral properties of the CGCG 292-057 nucleus, with those of other nearby LINERs studied in X-rays.

ID: 157705
Type: article
Authors: Kosmaczewski, E.; Stawarz, Ł.; Siemiginowska, Aneta; Cheung, C. C.; Ostorero, L.; Sobolewska, Malgorzata; Kozieł-Wierzbowska, D.; Wójtowicz, A.; Marchenko, V.
Abstract: We present a systematic analysis of the mid-infrared (MIR) properties of the youngest radio galaxies, based on low-resolution data provided by the Wide-field Infrared Survey Explorer and IRAS satellites. We restrict our analysis to sources with available X-ray data that constitute the earliest phase of radio galaxy evolution, I.e., those classified as gigahertz-peaked spectrum and/or compact symmetric objects. In our sample of 29 objects, we find that the host galaxies are predominantly red/yellow ellipticals, with some of them displaying distorted morphology. We find a variety of MIR colors and observe that the sources in which the MIR emission is dominated by the ISM component uniformly populate the region occupied by galaxies with a wide range of pronounced (≥0.5M_☉ yr^-1) star formation activity. We compare the MIR color distribution in our sample to that in the general population of local active galactic nuclei (AGNs), in the population of evolved FR II radio galaxies, and also in the population of radio galaxies with recurrent jet activity. We conclude that the triggering of radio jets in AGNs does not differentiate between elliptical hosts with substantially different fractions of young stars; instead, there is a relationship between the jet duty cycle and the ongoing star formation. The distribution of the subsample of our sources with z < 0.4 on the low-resolution MIR versus absorption-corrected X-ray luminosity plane is consistent with the distribution of a sample of local AGNs. Finally, we comment on the star formation rates of the two γ-ray-detected sources in our sample, 1146+596 and 1718-649.

ID: 157802
Type: article
Authors: Olejak, A.; Belczynski, K.; Bulik, T.; Sobolewska, Malgosia
Abstract: Aims: We present an open-access database that includes a synthetic catalog of black holes (BHs) in the Milky Way, divided by the components disk, bulge, and halo. Methods: To calculate the evolution of single and binary stars, we used the updated population synthesis code StarTrack. We applied a new model of the star formation history and chemical evolution of Galactic disk, bulge, and halo that was synthesized from observational and theoretical data. This model can be easily employed for other studies of population evolution. Results: We find that at the current Milky Way (disk+bulge+halo) contains about 1.2 × 10⁸ single BHs with an average mass of about 14 M_☉, and 9.3 × 10⁶ BHs in binary systems with an average mass of 19 M_☉. We present basic statistical properties of the BH population in three Galactic components such as the distributions of BH masses, velocities, or the numbers of BH binary systems in different evolutionary configurations. Conclusions: The metallicity of a stellar population has a significant effect on the final BH mass through the stellar winds. The most massive single BH in our simulation of 113 M_☉ originates from a merger of a BH and a helium star in a low-metallicity stellar environment in the Galactic halo. We constrain that only ∼0.006% of the total Galactic halo mass (including dark matter) can be hidden in the form of stellar origin BHs. These BHs cannot be detected by current observational surveys. We calculated the merger rates for current Galactic double compact objects (DCOs) for two considered common-envelope models: ∼3-81 Myr^-1 for BH-BH, ∼1-9 Myr^-1 for BH-neutron star (NS), and ∼14-59 Myr^-1 for NS-NS systems. We show the evolution of the merger rates of DCOs since the formation of the Milky Way until the current moment with the new star formation model of the Galaxy. Data files are available on our website, http://https://bhc.syntheticuniverse.org/.

ID: 157703
Type: article
Authors: Snios, Bradford; Siemiginowska, Aneta; Sobolewska, Małgosia; Cheung, C. C.; Kashyap, Vinay; Migliori, Giulia; Schwartz, Daniel A.; Stawarz, Łukasz; Worrall, Diana M.
Abstract: We present a comprehensive analysis of Chandra X-ray observations of 15 young radio quasars at redshifts 4.5 ⁴⁵ erg s^-1. The optical-X-ray power-law spectral index ${\alpha }_{\mathrm{ox}}$ is calculated for each source using optical/UV data available in the literature. The ${\alpha }_{\mathrm{ox}}$ -UV relationship is compared with other quasar surveys, and an anticorrelation is observed that agrees with independent estimates. Rest-frame radio and X-ray luminosities are established for the sample, and a correlation between the luminosities is detected. These multiwavelength results reinforce a lack of spectral evolution for quasars over a broad redshift range. We additionally identify three quasars from our multiwavelength analysis that are statistically significant outliers, with one source being a Compton-thick candidate in the early universe, and discuss each in detail.

ID: 154427
Type: article
Authors: Ruan, John J.; Anderson, Scott F.; Eracleous, Michael; Green, Paul J.; Haggard, Daryl; MacLeod, Chelsea L.; Runnoe, Jessie C.; Sobolewska, Malgosia A.
Abstract: Despite their factor of ̃10⁸ difference in black hole mass, several lines of evidence suggest possible similarities between black hole accretion flows in active galactic nuclei (AGN) and Galactic X-ray binaries. However, it is still unclear whether the geometry of the disk- corona system in X-ray binaries directly scales up to AGN and whether this analogy still holds in different accretion states. We test this AGN/X-ray binary analogy by comparing the observed correlations between the UV-to-X-ray spectral index (α _OX) and Eddington ratio in AGN to those predicted from observations of X-ray binary outbursts. This approach probes the geometry of their disk-corona systems as they transition between different accretion states. We use new Chandra X-ray and ground-based rest-UV observations of faded "changing-look" quasars to extend this comparison to lower Eddington ratios of ) and Eddington ratio in AGN to those predicted from observations of X-ray binary outbursts. This approach probes the geometry of their disk-corona systems as they transition between different accretion states. We use new Chandra X-ray and ground-based rest-UV observations of faded "changing-look" quasars to extend this comparison to lower Eddington ratios of ^-2, where observations of X-ray binaries predict a softening of α _OX in AGN. We find that the observed correlations between the α _OX and Eddington ratio of AGN displays a remarkable similarity to accretion state transitions in prototypical X-ray binary outbursts, including an inversion of this correlation at a critical Eddington ratio of ̃10^-2. Our results suggest that the structures of black hole accretion flows directly scale across a factor of ̃10⁸ in black hole mass and across different accretion states, enabling us to apply theoretical models of X-ray binaries to explain AGN phenomenology.

ID: 154566
Type: article
Authors: Ryan, J. L.; Siemiginowska, Aneta; Sobolewska, Magorzata A.; Grindlay, Jonathan
Abstract: Characteristic variability timescales in blazar γ-ray light curves can provide insights into the physical processes responsible for γ-ray variability. The power spectral density (PSD) is capable of revealing such timescales, which may appear as breaks or periodicities. Continuous-time autoregressive moving-average (CARMA) models can be used to accurately estimate a light curve's PSD. Through a light-curve simulation study, we develop a methodology to identify PSD breaks using CARMA models. Using this methodology, we study the γ-ray light curves of 13 bright blazars observed with the Fermi Large Area Telescope in the 0.1-300 GeV band over 9.5 yr. We present the blazar γ-ray PSDs, which provide evidence for low-frequency breaks on timescales ̃1 yr in four sources, and an additional high-frequency break on a timescale ̃9 days in one source.

ID: 154719
Type: article
Authors: Sobolewska, Małgosia; Siemiginowska, Aneta; Guainazzi, Matteo; Hardcastle, Martin; Migliori, Giulia; Ostorero, Luisa; Stawarz, Łukasz
Abstract: Compact symmetric objects (CSOs) have been observed with Chandra and XMM-Newton to gain insights into the initial stages of a radio source evolution and to probe the black hole activity at the time of relativistic outflow formation. However, there have been no CSO observations to date at the hard X-ray energies (>10 keV), impeding our ability to robustly constrain the properties of the intrinsic X-ray emission and of the medium surrounding the young expanding jets. We present the first hard X-ray observation of a CSO performed with the Nuclear Spectroscopic Telescope Array (NuSTAR). Our target, OQ +208, is detected up to 30 keV, and thus we establish CSOs as a new class of the NuSTAR sources. We analyze the NuSTAR data jointly with our new Chandra and archival XMM-Newton data and find that a young (̃250 yr old) radio jet spanning the length of 10 pc coexists with cold obscuring matter, consistent with a dusty torus, with an equivalent hydrogen column density of N _H = 10²³-10²⁴ cm^-2. The primary X-ray emission is characterized by a photon index of Γ ̃ 1.45 and an intrinsic 0.5-30 keV luminosity of L ≃ 10⁴³ erg s^-1. The results of our spectral modeling and broad-line optical classification of the source suggest a porous structure of the obscuring torus. Alternatively, the source may belong to the class of optically unobscured/X-ray-obscured active galactic nucleus. The observed X-ray emission is too weak compared to that predicted by the expanding radio lobes model, leaving an accretion disk corona or jets as the possible origins of the X-ray emission from this young radio galaxy.

ID: 150434
Type: article
Authors: Sobolewska, Małgosia; Siemiginowska, Aneta; Guainazzi, Matteo; Hardcastle, Martin; Migliori, Giulia; Ostorero, Luisa; Stawarz, Łukasz
Abstract: Compact symmetric objects (CSOs) show radio features such as jets, lobes, and hot spots that are contained within the central 1 kpc region of their host galaxy. Thus, they are thought to be among the progenitors of large-scale radio galaxies. A debate regarding whether the CSOs are compact primarily because they are young or because they are surrounded by a dense medium impacting their expansion is ongoing. Until now, attempts to discriminate between the environmental and genuine youthfulness scenarios have been inconclusive. We present a study of three CSOs selected on the basis of their puzzling X-ray absorbing properties in prior Beppo-SAX and/or Chandra X-ray Observatory data. Our new XMM-Newton observations unambiguously confirm the nature of their X-ray absorbers. Furthermore, for the first time, our X-ray data reveal the existence of a population of CSOs with intrinsic hydrogen column density N _H > 10²³ cm^‑2 that is different from the population of X-ray unabsorbed CSOs. The two groups appear to be separated in the linear size versus radio power plane. This finding suggests that a dense medium in X-ray obscured CSOs may be able to confine the radio jets. Alternatively, X-ray obscured CSOs could be seen as radio brighter than their unobscured counterparts either because they reside in a dense environment or because they have larger jet powers. Our results help constrain the origin of the X-ray emission and the location and size of the X-ray obscurer in CSOs, and indicate that the environment may play a key role during the initial expansion of a radio source.

ID: 148985
Type: article
Authors: Goyal, A.; Stawarz, L.; Zola, S.; Marchenko, V.; Soida, M.; Nilsson, K.; Ciprini, S.; Baran, A.; Ostrowski, M.; Wiita, P. J.; Gopal-Krishna; Siemiginowska, Aneta; Sobolewska, M.; Jorstad, S.; Marscher, A.; Aller, M. F.; Aller, H. D.; Hovatta, T.; Caton, D. B.; Reichart, D.; Matsumoto, K.; Sadakane, K.; Gazeas, K.; Kidger, M.; Piirola, V.; Jermak, H.; Alicavus, F.; Baliyan, K. S.; Baransky, A.; Berdyugin, A.; Blay, P.; Boumis, P.; Boyd, D.; Bufan, Y.; Campas Torrent, M.; Campos, F.; Carrillo Gómez, J.; Dalessio, J.; Debski, B.; Dimitrov, D.; Drozdz, M.; Er, H.; Erdem, A.; Escartin Pérez, A.; Fallah Ramazani, V.; Filippenko, A. V.; Gafton, E.; Garcia, F.; Godunova, V.; Gómez Pinilla, F.; Gopinathan, M.; Haislip, J. B.; Haque, S.; Harmanen, J.; Hudec, R.; Hurst, G.; Ivarsen, K. M.; Joshi, A.; Kagitani, M.; Karaman, N.; Karjalainen, R.; Kaur, N.; Koziel-Wierzbowska, D.; Kuligowska, E.; Kundera, T.; Kurowski, S.; Kvammen, A.; LaCluyze, A. P.; Lee, B. C.; Liakos, A.; Lozano de Haro, J.; Moore, J. P.; Mugrauer, M.; Naves Nogues, R.; Neely, A. W.; Ogloza, W.; Okano, S.; Pajdosz, U.; Pandey, J. C.; Perri, M.; Poyner, G.; Provencal, J.; Pursimo, T.; Raj, A.; Rajkumar, B.; Reinthal, R.; Reynolds, T.; Saario, J.; Sadegi, S.; Sakanoi, T.; Salto González, J. L.; Sameer; Simon, A. O.; Siwak, M.; Schweyer, T.; Soldán Alfaro, F. C.; Sonbas, E.; Strobl, J.; Takalo, L. O.; Tremosa Espasa, L.; Valdes, J. R.; Vasylenko, V. V.; Verrecchia, F.; Webb, J. R.; Yoneda, M.; Zejmo, M.; Zheng, W.; Zielinski, P.; Janik, J.; Chavushyan, V.; Mohammed, I.; Cheung, C. C.; Giroletti, M.
Abstract: We present the results of our power spectral density analysis for the BL Lac object OJ 287, utilizing the Fermi-LAT survey at high-energy gamma-rays, Swift-XRT in X-rays, several ground-based telescopes and the Kepler satellite in the optical, and radio telescopes at GHz frequencies. The light curves are modeled in terms of continuous-time autoregressive moving average (CARMA) processes. Owing to the inclusion of the Kepler data, we were able to construct for the first time the optical variability power spectrum of a blazar without any gaps across ~6 dex in temporal frequencies. Our analysis reveals that the radio power spectra are of a colored-noise type on timescales ranging from tens of years down to months, with no evidence for breaks or other spectral features. The overall optical power spectrum is also consistent with a colored noise on the variability timescales ranging from 117 years down to hours, with no hints of any quasi-periodic oscillations. The X-ray power spectrum resembles the radio and optical power spectra on the analogous timescales ranging from tens of years down to months. Finally, the gamma-ray power spectrum is noticeably different from the radio, optical, and X-ray power spectra of the source: we have detected a characteristic relaxation timescale in the Fermi-LAT data, corresponding to ~150 days, such that on timescales longer than this, the power spectrum is consistent with uncorrelated (white) noise, while on shorter variability timescales there is correlated (colored) noise.

ID: 144729
Type: article
Authors: Wiktorowicz, Grzegorz; Sobolewska, Malgorzata; Lasota, Jean-Pierre; Belczynski, Krzysztof
Abstract: Recently, several ultraluminous X-ray (ULX) sources were shown to host a neutron star (NS) accretor. We perform a suite of evolutionary calculations, which show that, in fact, NSs are the dominant type of ULX accretor. Although black holes (BH) dominate early epochs after the star-formation burst, NSs outweigh them after a few 100 Myr and may appear as late as a few gigayears after the end of the star-formation episode. If star formation is a prolonged and continuous event (I.e., not a relatively short burst), NS accretors dominate the ULX population at any time in the solar metallicity environment, whereas BH accretors dominate when the metallicity is sub-solar. Our results show a very clear (and testable) relation between the companion/donor evolutionary stage and the age of the system. A typical NSULX consists of a ~ 1.3 {M}_? NS and ~ 1.0 {M}_? Red Giant. A typical BH ULX consists of a ~ 8 {M}_? BH and ~ 6 {M}_? main-sequence star. Additionally, we find that the very luminous ULXs ({L}_X? {10}⁴¹ erg s^-1) are predominantly BH systems (~ 9 {M}_? ) with Hertzsprung-gap donors (~ 2 {M}_? ). Nevertheless, some NSULX systems may also reach extremely high X-ray luminosities (?10⁴¹ erg s^-1).

ID: 139611
Type: article
Authors: Migliori, G.; Siemiginowska, Aneta; Sobolewska, Magorzata A.; Loh, A.; Corbel, S.; Ostorero, L.; Stawarz, Ł.
Abstract: We report the γ-ray detection of a young radio galaxy, PKS 1718-649, belonging to the class of compact symmetric objects (CSOs), with the Large Area Telescope (LAT) on board the Fermi satellite. The third Fermi Gamma-ray LAT catalog (3FGL) includes an unassociated γ-ray source, 3FGL J1728.0-6446, located close to PKS 1718-649. Using the latest Pass 8 calibration, we confirm that the best-fit 1σ position of the γ-ray source is compatible with the radio location of PKS 1718-649. Cross-matching of the γ-ray source position with the positions of blazar sources from several catalogs yields negative results. Thus, we conclude that PKS 1718-649 is the most likely counterpart to the unassociated LAT source. We obtain a detection test statistics TS ˜ 36 (>5σ) with a best-fit photon spectral index Γ = 2.9 ± 0.3 and a 0.1-100 GeV photon flux density F _{0.1-100 GeV} = (11.5 ± 0.3) × 10^-9 ph cm^-2 s^-1. We argue that the linear size (˜2 pc), the kinematic age (˜100 years), and the source distance (z = 0.014) make PKS 1718-649 an ideal candidate for γ-ray detection in the framework of the model proposing that the most compact and the youngest CSOs can efficiently produce GeV radiation via inverse-Compton scattering of the ambient photon fields by the radio lobe non-thermal electrons. Thus, our detection of the source in γ-rays establishes young radio galaxies as a distinct class of extragalactic high-energy emitters and yields a unique insight on the physical conditions in compact radio lobes interacting with the interstellar medium of the host galaxy.

ID: 139795
Type: article
Authors: Siemiginowska, Aneta; Sobolewska, Malgosia; Migliori, Giulia; Guainazzi, Matteo; Hardcastle, Martin; Ostorero, Luisa; Stawarz, Lukasz
Abstract: We present the first results from our X-ray study of young radio sources classified as compact symmetric objects (CSOs). Using the Chandra X-ray Observatory we observed six CSOs for the first time in X-rays, and re-observed four CSOs already observed with XMM-Newton or BeppoSAX. We also included six other CSOs with archival data to built a pilot study of a sample of the 16 CSO sources observed in X-rays to date. All the sources are nearby, z\lt 1, and the age of their radio structures (\lt 3000 yr) has been derived from the expansion velocity of their hot spots. Our results show the heterogeneous nature of the CSOs’ X-ray emission, indicating a complex environment associated with young radio sources. The sample covers a range in X-ray luminosity, {L}_2{--10{keV}}~ {10}⁴¹–10⁴⁵ erg s^-1, and intrinsic absorbing column density of {N}_{{H}}? {10}²¹–10²² cm^-2. In particular, we detected extended X-ray emission in 1718-649 a hard photon index of {{G }}? 1 in 2021+614 and 1511+0518 consistent with either a Compton-thick absorber or non-thermal emission from compact radio lobes, and in 0710+439 an ionized iron emission line at {E}_{rest}=(6.62+/- 0.04) keV and EW ~ 0.15–1.4 keV, and a decrease by an order of magnitude in the 2–10 keV flux since the 2008 XMM-Newton observation in 1607+26. We conclude that our pilot study of CSOs provides a variety of exceptional diagnostics and highlights the importance of deep X-ray observations of large samples of young sources. This is necessary in order to constrain theoretical models for the earliest stage of radio source evolution and to study the interactions of young radio sources with the interstellar environment of their host galaxies.

ID: 138581
Type: article
Authors: Adhikari, T. P.; Rózanska, A.; Sobolewska, Magorzata A.; Czerny, B.
Abstract: In this paper we model the observed absorption measure distribution (AMD) in Mrk 509, which spans three orders of magnitude in ionization level with a single-zone absorber in pressure equilibrium. AMD is usually constructed from observations of narrow absorption lines in radio-quiet active galaxies with warm absorbers. We study the properties of the warm absorber in Mrk 509 using recently published broadband spectral energy distribution observed with different instruments. This spectrum is an input in radiative transfer computations with full photoionization treatment using the titan code. We show that the simplest way to fully reproduce the shape of AMD is to assume that the warm absorber is a single zone under constant total pressure. With this assumption, we found theoretical AMD that matches the observed AMD determined on the basis of the 600 ks reflection grating spectrometer XMM-Newton spectrum of Mrk 509. The softness of the source spectrum and the important role of the free-free emission breaks the usual degeneracy in the ionization state calculations, and the explicit dependence of the depths of AMD dips on density open a new path to the density diagnostic for the warm absorber. In Mrk 509, the implied density is of the order of 10⁸ cm^-3.

ID: 127257
Type: article
Authors: Kelly, Brandon C.; Becker, Andrew C.; Sobolewska, Malgosia; Siemiginowska, Aneta; Uttley, Phil
Abstract: We present the use of continuous-time autoregressive moving average (CARMA) models as a method for estimating the variability features of a light curve, and in particular its power spectral density (PSD). CARMA models fully account for irregular sampling and measurement errors, making them valuable for quantifying variability, forecasting and interpolating light curves, and variability-based classification. We show that the PSD of a CARMA model can be expressed as a sum of Lorentzian functions, which makes them extremely flexible and able to model a broad range of PSDs. We present the likelihood function for light curves sampled from CARMA processes, placing them on a statistically rigorous foundation, and we present a Bayesian method to infer the probability distribution of the PSD given the measured light curve. Because calculation of the likelihood function scales linearly with the number of data points, CARMA modeling scales to current and future massive time-domain data sets. We conclude by applying our CARMA modeling approach to light curves for an X-ray binary, two active galactic nuclei, a long-period variable star, and an RR Lyrae star in order to illustrate their use, applicability, and interpretation.

ID: 123023
Type: article
Authors: Sobolewska, Magorzata A.; Siemiginowska, Aneta; Kelly, B. C.; Nalewajko, K.
Abstract: We study the ?-ray variability of 13 blazars observed with the Fermi/Large Area Telescope (LAT). These blazars have the most complete light curves collected during the first four years of the Fermi sky survey. We model them with the Ornstein-Uhlenbeck (OU) process or a mixture of the OU processes. The OU process has power spectral density (PSD) proportional to 1/f ^? with ? changing at a characteristic timescale, ?₀, from 0 (? Gt ?₀) to 2 (? Lt ?₀). The PSD of the mixed OU process has two characteristic timescales and an additional intermediate region with 0 ). The PSD of the mixed OU process has two characteristic timescales and an additional intermediate region with 0 ). The PSD of the mixed OU process has two characteristic timescales and an additional intermediate region with 0 ₀ ~= 25 days and ?₀ ~= 43 days, respectively, in the observer's frame), which are longer than the soft X-ray timescales detected in blazars and Seyfert galaxies. We find that the mixed OU process approximates the light curves of the remaining 10 blazars better than the OU process. We derive limits on their long and short characteristic timescales, and infer that their Fermi/LAT PSD resemble power-law functions. We constrain the PSD slopes for all but one source in the sample. We find hints for sub-hour Fermi/LAT variability in four flat spectrum radio quasars. We discuss the implications of our results for theoretical models of blazar variability.

ID: 118384
Type: article
Authors: Trichas, Markos; Green, Paul J.; Constantin, Anca; Aldcroft, Thomas L.; Kalfountzou, Eleni; Sobolewska, Malgosia; Hyde, Ashley K.; Zhou, Hongyan; Kim, Dong-Woo; Haggard, Daryl; Kelly, Brandon C.
Abstract: Striking similarities have been seen between accretion signatures of Galactic X-ray binary (XRB) systems and active galactic nuclei (AGNs). XRB spectral states show a V-shaped correlation between X-ray spectral hardness and Eddington ratio as they vary, and some AGN samples reveal a similar trend, implying analogous processes at vastly larger masses and timescales. To further investigate the analogies, we have matched 617 sources from the Chandra Source Catalog to Sloan Digital Sky Survey spectroscopy, and uniformly measured both X-ray and optical spectral characteristics across a broad range of AGN and galaxy types. We provide useful tabulations of X-ray spectral slope for broad- and narrow-line AGNs, star-forming and passive galaxies, and composite systems, also updating relationships between optical (Ha and [O III]) line emission and X-ray luminosity. We further fit broadband spectral energy distributions with a variety of templates to estimate bolometric luminosity. Our results confirm a significant trend in AGNs between X-ray spectral hardness and Eddington ratio expressed in X-ray luminosity, albeit with significant dispersion. The trend is not significant when expressed in the full bolometric or template-estimated AGN luminosity. We also confirm a relationship between the X-ray/optical spectral slope a_ox and Eddington ratio, but it may not follow the trend predicted by analogy with XRB accretion states.

ID: 113692
Type: article
Authors: Sobolewska, Magorzata A.; Siemiginowska, Aneta; Migliori, G.; Stawarz, L.; Jamrozy, M.; Evans, D.; Cheung, C. C.
Abstract: We present results from a study of nuclear emission from a nearby radio galaxy, 4C+29.30, over a broad 0.5-200 keV X-ray band. This study used new XMM-Newton (~17 ks) and Chandra (~300 ks) data, and archival Swift/BAT data from the 58 month catalog. The hard (>2 keV) X-ray spectrum of 4C+29.30 can be decomposed into an intrinsic hard power law (? ~ 1.56) modified by a cold absorber with an intrinsic column density N _{H, z} ~ 5 × 10²³ cm^-2, and its reflection (|?/2?| ~ 0.3) from a neutral matter including a narrow iron K? emission line at a rest-frame energy ~6.4 keV. The reflected component is less absorbed than the intrinsic one with an upper limit on the absorbing column of N ^refl _{H, z} ²² cm^-2. The X-ray spectrum varied between the XMM-Newton and Chandra observations. We show that a scenario invoking variations of the normalization of the power law is favored over a model with variable intrinsic column density. X-rays in the 0.5-2 keV band are dominated by diffuse emission modeled with a thermal bremsstrahlung component with temperature ~0.7 keV, and contain only a marginal contribution from the scattered power-law component. We hypothesize that 4C+29.30 belongs to a class of "hidden" active galactic nuclei containing a geometrically thick torus. However, unlike the majority of hidden AGNs, 4C+29.30 is radio-loud. Correlations between the scattering fraction and Eddington luminosity ratio, and between black hole mass and stellar velocity dispersion, imply that 4C+29.30 hosts a black hole with ~10⁸ M _? mass.

ID: 99774
Type: article
Authors: Kelly, Brandon C.; Sobolewska, Magorzata A.; Siemiginowska, Aneta
Abstract: In this work, we have developed a new stochastic model for the fluctuations in light curves of accreting black holes. The model is based on a linear combination of stochastic processes and is also the solution to the linear diffusion equation perturbed by a spatially correlated noise field. This allows flexible modeling of the power spectral density (PSD), and we derive the likelihood function for the process, enabling one to estimate the parameters of the process, including break frequencies in the PSD. Our statistical technique is computationally efficient, unbiased by aliasing and red noise leak, and fully accounts for irregular sampling and measurement errors. We show that our stochastic model provides a good approximation to the X-ray light curves of galactic black holes, and the optical and X-ray light curves of active galactic nuclei (AGNs). We use the estimated timescales of our stochastic model to recover the correlation between characteristic timescale of the high-frequency X-ray fluctuations and black hole mass for AGNs, including two new "detections" of the timescale for Fairall 9 and NGC 5548. We find a tight anti-correlation between the black hole mass and the amplitude of the driving noise field, which is proportional to the amplitude of the high-frequency X-ray PSD, and we estimate that this parameter gives black hole mass estimates to within ~0.2 dex precision, potentially the most accurate method for AGNs yet. We also find evidence that ?13% of AGN optical PSDs fall off flatter than 1/f ² and, similar to previous work, find that the optical fluctuations are more suppressed on short timescales compared to the X-rays, but are larger on long timescales, suggesting that the optical fluctuations are not solely due to reprocessing of X-rays.

ID: 108020
Type: article
Authors: Sobolewska, Magorzata A.; Papadakis, I. E.; Done, C.; Malzac, J.
Abstract: We present results on the spectral variability of two Galactic black hole X-ray binaries, GRO J1655-40 and GX 339-4, in the hard state. We confirm a transition in behaviour of the photon index with luminosity, such that the well-known decrease in X-ray photon index with decreasing luminosity only continues down to L_bol~ 0.01L_E. Below this point, the photon index increases again. For Comptonization models, this implies that the ratio of the Compton luminosity to seed photon luminosity, ?_h/?_s, changes with bolometric luminosity, consistent with a scenario where seed photons change from cyclo-synchrotron at the lowest luminosities to those from a truncated disc. Alternatively, the transition could mark the point below which the non-thermal jet starts to dominate, or where reprocessed photons replace the viscous photons in an outflowing corona model.

ID: 101174
Type: article
Authors: Sobolewska, Magorzata A.; Siemiginowska, Aneta; Gierliński, Marek
Abstract: Active galactic nuclei (AGN) and galactic black hole binaries (GBHs) represent two classes of accreting black holes. They both contain an accretion disc emitting a thermal radiation, and a non-thermal X-ray emitting 'corona'. GBHs exhibit state transitions, and the spectral states are characterized by different luminosity levels and shapes of the spectral energy distribution (SED). If AGN transitioned in a similar way, the characteristic time-scales of such transitions would exceed ˜10⁵ yr. Thus the probability to observe an individual AGN transiting between different spectral states is very low. In this paper we follow the spectral evolution of the GBH GRO J1655-40 and then apply its SED evolution pattern to a simulated population of AGN under the reasonable assumption that a large sample of AGN should contain a mixture of sources in different spectral states. We model the X-ray spectra of GRO J1655-40 with the EQPAIR model and then scale the best-fitting models with the black hole mass to simulate the AGN spectra. We compare the simulated and observed AGN SEDs to determine the spectral states of observed Type 1 AGN, LINER and NLS1 populations. We conclude that bright Type 1 AGN and NLS1 galaxies are in a spectral state similar to the soft spectral state of GBHs, while the spectral state of LINERs may correspond to the hard spectral state of GBHs. We find that taking into account the spread of the black hole masses over several orders of magnitude, as they are in the observed AGN samples, leads to a correlation between the X-ray loudness, ?_ox, and the monochromatic luminosity at 2500 Å. We predict that the ?_ox correlates positively with the Eddington luminosity ratio down to the critical value of ?_crit= L/L_E? 0.01, and that this correlation changes its sign for the accretion rates below ?_crit.