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Accretion disk winds launched close to supermassive black holes (SMBHs) are a viable mechanism to provide feedback between the SMBH and the host galaxy. We aim to characterize the X-ray properties of the inner accretion disk wind of the nearby active galactic nucleus (AGN) PG 1126-041, and to study its connection with the ultraviolet (UV)-absorbing wind. We perform spectroscopic analysis of eight XMM-Newton observations of PG 1126-041 taken between 2004 and 2015, using both phenomenological models and the most advanced accretion disk wind models available. For half of the dataset, we can compare the X-ray analysis results with the results of quasi-simultaneous, high-resolution spectroscopic UV observations taken with the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope. The X-ray spectra of PG 1126-041 are complex and absorbed by ionized material which is highly variable on multiple time scales, sometimes as short as 11 days. Accretion disk wind models can account for most of the X-ray spectral complexity of PG 1126-041, with the addition of massive clumps, represented by a partially covering absorber. Variations in column density ($N_H \sim 5-20 \times 10^{22}$ cm$^{-2}$) of the partially covering absorber drive the observed X-ray spectral variability of PG 1126-041. The absorption from the X-ray partially covering gas and from the blueshifted C IV troughs appear to vary in a coordinated way. The line of sight toward PG 1126-041 offers a privileged view through a highly dynamic nuclear wind originating on inner accretion disk scales, making the source a very promising candidate for future detailed studies of the physics of accretion disk winds around SMBHs., Comment: 24 pages, 13 figures, accepted for publication in Astronomy & Astrophysics

We present a new X-ray spectroscopic study of $22$ luminous ($2\times10^{45}\lesssim L_{\rm bol}\rm /erg\,s^{-1} \lesssim 2\times10^{46}$) active galactic nuclei (AGNs) at intermediate-redshift ($0.1 \lesssim z \lesssim 0.4$), as part of the SUpermassive Black hole Winds in the x-rAYS (SUBWAYS) sample, mostly composed of quasars (QSOs) and type\,1 AGN. Here, 17 targets were observed with \textit{XMM-Newton} between 2019--2020 and the remaining 5 are from previous observations. The aim of this large campaign ($1.45\,\rm Ms$ duration) is to characterise the various manifestations of winds in the X-rays driven from supermassive black holes in AGN. In this paper we focus on the search and characterization of ultra-fast outflows (UFOs), which are typically detected through blueshifted absorption troughs in the Fe\,K band ($E>7\,\rm keV$). By following Monte Carlo procedures, we confirm the detection of absorption lines corresponding to highly ionised iron (e.g., Fe\,\textsc{xxv}\,H$\alpha$, Fe\,\textsc{xxvi}\,Ly$\alpha$) in 7/22 sources at the $\gtrsim95\%$ confidence level (for each individual line). The global combined probability of such absorption features in the sample is $>99.9\%$. The SUBWAYS campaign extends at higher luminosity and redshifts than previous local studies on Seyferts, obtained using \xmm and \suzaku observations. We find a UFO detection fraction of $\sim30\%$ on the total sample that is in agreement with the previous findings. This work independently provides further support for the existence of highly-ionised matter propagating at mildly relativistic speed ($\gtrsim0.1c$) in a considerable fraction of AGN over a broad range of luminosities, which is expected to play a key role in the self-regulated AGN feeding-feedback cycle, as also supported by hydrodynamical multiphase simulations., Comment: 30 pages, 10 figures, accepted for publication in A&A

Analyses of absorption from disk winds and atmospheres in accreting compact objects typically treat the central emitting regions in these systems as point sources relative to the absorber. This assumption breaks down if the absorbing gas is located within $few \times 1000\cdot GM/{c}^{2}$, in which case a small component of the absorber's Keplerian motion contributes to the velocity-width of absorption lines. Here, we demonstrate how this velocity-broadening effect can be used to constrain the sizes of central engines in accreting compact objects via a simple geometric relationship, and develop a method for modeling this effect. We apply this method on the Chandra/HETG spectra of three ultra-compact and short period neutron star X-ray binaries in which evidence of gravitationally redshifted absorption, owing to an inner-disk atmosphere, has recently been reported. The significance of the redshift is above $5\sigma$ for XTE J1710$-$281 (this work) and 4U 1916$-$053, and is inconsistent with various estimates of the relative radial velocity of each binary. For our most sensitive spectrum (XTE J1710$-$281), we obtain a 1$\sigma$ upper bound of 310 $\text{km}$ $\text{s}^{-1}$ on the magnitude of this geometric effect and a central engine of size ${R}_{CE} < 60 ~ GM/{c}^{2}$ (or, $< 90 ~ GM/{c}^{2}$ at the $3\sigma$ level). These initial constraints compare favorably to those obtained via microlensing in quasars and approach the sensitivity of constraints via relativistic reflection in neutron stars. This sensitivity will increase with further exposures, as well as the launch of future microcalorimeter and grating missions., Comment: Accepted to ApJ, 32 Pages (3 Appendices), 17 Figures

We present geometric and dynamical modeling of the broad line region for the multi-wavelength reverberation mapping campaign focused on NGC 5548 in 2014. The dataset includes photometric and spectroscopic monitoring in the optical and ultraviolet, covering the H$\beta$, C IV, and Ly$\alpha$ broad emission lines. We find an extended disk-like H$\beta$ BLR with a mixture of near-circular and outflowing gas trajectories, while the C IV and Ly$\alpha$ BLRs are much less extended and resemble shell-like structures. There is clear radial structure in the BLR, with C IV and Ly$\alpha$ emission arising at smaller radii than the H$\beta$ emission. Using the three lines, we make three independent black hole mass measurements, all of which are consistent. Combining these results gives a joint inference of $\log_{10}(M_{\rm BH}/M_\odot) = 7.64^{+0.21}_{-0.18}$. We examine the effect of using the $V$ band instead of the UV continuum light curve on the results and find a size difference that is consistent with the measured UV-optical time lag, but the other structural and kinematic parameters remain unchanged, suggesting that the $V$ band is a suitable proxy for the ionizing continuum when exploring the BLR structure and kinematics. Finally, we compare the H$\beta$ results to similar models of data obtained in 2008 when the AGN was at a lower luminosity state. We find that the size of the emitting region increased during this time period, but the geometry and black hole mass remain unchanged, which confirms that the BLR kinematics suitably gauge the gravitational field of the central black hole., Comment: 26 pages, 19 figures, 1 table, accepted for publication in ApJ

The very small accretion disks in ultra-compact X-ray binaries (UCXBs) are special laboratories in which to study disk accretion and outflows. We report on three sets of new (250 ks total) and archival (50 ks) Chandra/HETG observations of the "dipping" neutron-star X-ray binary 4U 1916$-$053, which has an orbital period of $P\simeq 50$~minutes. We find that the bulk of the absorption in all three spectra originates in a disk atmosphere that is redshifted by $v\simeq 220-290$ $\text{km}$ $\text{s}^{-1}$, corresponding to the gravitational redshift at radius of $R \sim 1200$ $GM/{c}^{2}$. This shift is present in the strongest, most highly ionized lines (Si XIV and Fe XXVI), with a significance of 5$\sigma$. Absorption lines observed during dipping events (typically associated with the outermost disk) instead display no velocity shifts and serve as a local standard of rest, suggesting that the redshift is intrinsic to an inner disk atmosphere and not due to radial motion in the galaxy or a kick. In two spectra, there is also evidence of a more strongly redshifted component that would correspond to a disk atmosphere at $R \sim 70$ $GM/{c}^{2}$; this component is significant at the 3$\sigma$ level. Finally, in one spectrum, we find evidence of disk wind with a blue shift of $v = {-1700}^{+1700}_{-1200}$ $\text{km}$ $\text{s}^{-1}$. If real, this wind would require magnetic driving., Comment: 15 Pages, 6 Figures, Accepted to ApJ Letters

We report on Chandra gratings spectra of the stellar-mass black hole GRS 1915+105 obtained during a novel, highly obscured state. As the source entered this state, a dense, massive accretion disk wind was detected through strong absorption lines. Photionization modeling indicates that it must originate close to the central engine, orders of magnitude from the outer accretion disk. Strong, nearly sinusoidal flux variability in this phase yielded a key insight: the wind is blue-shifted when its column density is relatively low, but red-shifted as it approaches the Compton-thick threshold. At no point does the wind appear to achieve the local escape velocity; in this sense, it is a "failed wind." Later observations suggest that the disk ultimately fails to keep even the central engine clear of gas, leading to heavily obscured and Compton-thick states characterized by very strong Fe K emission lines. Indeed, these later spectra are successfully described using models developed for obscured AGN. We discuss our results in terms the remarkable similarity of GRS 1915+105 deep in its "obscured state" to Seyfert-2 and Compton-thick AGN, and explore how our understanding of accretion and obscuration in massive black holes is impacted by our observations., Comment: Submitted to ApJ

We study the X-ray spectra of a sample of 19 obscured, optically-selected Seyfert galaxies (Sy 1.8, 1.9 and 2) in the local universe ($d \leq 175$~Mpc), drawn from the CfA Seyfert sample. Our analysis is driven by the high sensitivity of NuSTAR in the hard X-rays, coupled with soft X-ray spectra using XMM-Newton, Chandra, Suzaku, and Swift/XRT. We also analyze the optical spectra of these sources in order to obtain accurate mass estimates and Eddington fractions. We employ four different models to analyze the X-ray spectra of these sources, which all result in consistent results. We find that 79-90 % of the sources are heavily obscured with line-of-sight column density $N_{\rm H} > 10^{23}~\rm cm^{-2}$. We also find a Compton-thick ($N_{\rm H} > 10^{24}~\rm cm^{-2}$) fraction of $37-53$ %. These results are consistent with previous estimates based on multi-wavelength analyses. We find that the fraction of reprocessed to intrinsic emission is positively correlated with $N_{\rm H}$ and negatively correlated with the intrinsic, unabsorbed, X-ray luminosity (in agreement with the Iwasawa-Taniguchi effect). Our results support the hypothesis that radiation pressure regulates the distribution of the circumnuclear material., Comment: Accepted for publication in ApJ

In 2014 the NGC 5548 Space Telescope and Optical Reverberation Mapping campaign discovered a two-month anomaly when variations in the absorption and emission lines decorrelated from continuum variations. During this time the soft X-ray part of the intrinsic spectrum had been strongly absorbed by a line-of-sight (LOS) obscurer, which was interpreted as the upper part of a disk wind. Our first paper showed that changes in the LOS obscurer produce the decorrelation between the absorption lines and the continuum. A second study showed that the base of the wind shields the BLR, leading to the emission-line decorrelation. In that study, we proposed the wind is normally transparent with no effect on the spectrum. Changes in the wind properties alter its shielding and affect the SED striking the BLR, producing the observed decorrelations. In this work, we investigate the impact of a translucent wind on the emission lines. We simulate the obscuration using XMM-Newton, NuSTAR, and HST observations to determine the physical characteristics of the wind. We find that a translucent wind can contribute a part of the He II and Fe K? emission. It has a modest optical depth to electron scattering, which explains the fainter far-side emission in the observed velocity delay maps. The wind produces the very broad base seen in the UV emission lines and may also be present in the Fe K? line. Our results highlight the importance of accounting for the effects of such winds in the analysis of the physics of the central engine., Comment: Accepted for publication in ApJ

Chandra obtained two High Energy Transmission Grating (HETG) spectra of the stellar-mass black hole GRO J1655-40 during its 2005 outburst, revealing a rich and complex disk wind. Soon after its launch, the Neil Gehrels Swift Observatory began monitoring the same outburst. Some X-ray Telescope (XRT) observations were obtained in a mode that makes it impossible to remove strong Mn calibration lines, so the Fe K-alpha line region in the spectra was previously neglected. However, these lines enable a precise calibration of the energy scale, facilitating studies of the absorption-dominated disk wind and its velocity shifts. Here, we present fits to 15 Swift/XRT spectra, revealing variability and evolution in the outflow. The data strongly point to a magnetically driven disk wind: both the higher velocity (e.g., v ~ 10^4 km/s) and lower velocity (e.g., v ~ 10^3 km/s) wind components are typically much faster than is possible for thermally driven outflows (v < 200 km/s), and photoionization modeling yields absorption radii that are two orders of magnitude below the Compton radius that defines the typical inner extent of thermal winds. Moreover, correlations between key wind parameters yield an average absorption measure distribution (AMD) that is consistent with magnetohydrodynamic wind models. We discuss our results in terms of recent observational and theoretical studies of black hole accretion disks and outflows, and future prospects., Comment: Accepted for publication in ApJ

We report velocity-delay maps for prominent broad emission lines, Ly_alpha, CIV, HeII and H_beta, in the spectrum of NGC5548. The emission-line responses inhabit the interior of a virial envelope. The velocity-delay maps reveal stratified ionization structure. The HeII response inside 5-10 light-days has a broad single-peaked velocity profile. The Ly_alpha, CIV, and H_beta responses peak inside 10 light-days, extend outside 20 light-days, and exhibit a velocity profile with two peaks separated by 5000 km/s in the 10 to 20 light-day delay range. The velocity-delay maps show that the M-shaped lag vs velocity structure found in previous cross-correlation analysis is the signature of a Keplerian disk with a well-defined outer edge at R=20 light-days. The outer wings of the M arise from the virial envelope, and the U-shaped interior of the M is the lower half of an ellipse in the velocity-delay plane. The far-side response is weaker than that from the near side, so that we see clearly the lower half, but only faintly the upper half, of the velocity--delay ellipse. The delay tau=(R/c)(1-sin(i))=5 light-days at line center is from the near edge of the inclined ring, giving the inclination i=45 deg. A black hole mass of M=7x10^7 Msun is consistent with the velocity-delay structure. A barber-pole pattern with stripes moving from red to blue across the CIV and possibly Ly_alpha line profiles suggests the presence of azimuthal structure rotating around the far side of the broad-line region and may be the signature of precession or orbital motion of structures in the inner disk. Further HST observations of NGC 5548 over a multi-year timespan but with a cadence of perhaps 10 days rather than 1 day could help to clarify the nature of this new AGN phenomenon., Comment: 19 pages, 9 figures, ApJ in press

The mechanisms that drive disk winds are a window into the physical processes that underlie the disk. Stellar-mass black holes are an ideal setting in which to explore these mechanisms, in part because their outbursts span a broad range in mass accretion rate. We performed a spectral analysis of the disk wind found in six Chandra/HETG observations of the black hole candidate 4U~1630$-$472, covering a range of luminosities over two distinct spectral states. We modeled both wind absorption and extended wind re-emission components using PION, a self-consistent photoionized absorption model. In all but one case, two photoionization zones were required in order to obtain acceptable fits. Two independent constraints on launching radii, obtained via the ionization parameter formalism and the dynamical broadening of the re-emission, helped characterize the geometry of the wind. The innermost wind components ($r \simeq {10}^{2-3}$ $GM/{c}^{2}$) tend towards small volume filling factors, high ionization, densities up to $n \simeq {10}^{15-16} {\text{cm}}^{-3}$, and outflow velocities of $\sim 0.003c$. These small launching radii and large densities require magnetic driving, as they are inconsistent with numerical and analytical treatments of thermally driven winds. Outer wind components ($r \simeq {10}^{5}$ $GM/{c}^{2}$) are significantly less ionized and have filling factors near unity. Their larger launching radii, lower densities ($n \simeq {10}^{12} {\text{cm}}^{-3}$), and outflow velocities ($\sim 0.0007c$) are nominally consistent with thermally driven winds. The overall wind structure suggests that these components may also be part of a broader MHD outflow and perhaps better described as magneto-thermal hybrid winds., Comment: 27 pages, 13 figures

We model the ultraviolet spectra of the Seyfert 1 galaxy NGC~5548 obtained with the Hubble Space Telescope during the 6-month reverberation-mapping campaign in 2014. Our model of the emission from NGC 5548 corrects for overlying absorption and deblends the individual emission lines. Using the modeled spectra, we measure the response to continuum variations for the deblended and absorption-corrected individual broad emission lines, the velocity-dependent profiles of Ly$\alpha$ and C IV, and the narrow and broad intrinsic absorption features. We find that the time lags for the corrected emission lines are comparable to those for the original data. The velocity-binned lag profiles of Ly$\alpha$ and C IV have a double-peaked structure indicative of a truncated Keplerian disk. The narrow absorption lines show delayed response to continuum variations corresponding to recombination in gas with a density of $\sim 10^5~\rm cm^{-3}$. The high-ionization narrow absorption lines decorrelate from continuum variations during the same period as the broad emission lines. Analyzing the response of these absorption lines during this period shows that the ionizing flux is diminished in strength relative to the far-ultraviolet continuum. The broad absorption lines associated with the X-ray obscurer decrease in strength during this same time interval. The appearance of X-ray obscuration in $\sim\,2012$ corresponds with an increase in the luminosity of NGC 5548 following an extended low state. We suggest that the obscurer is a disk wind triggered by the brightening of NGC 5548 following the decrease in size of the broad-line region during the preceding low-luminosity state., Comment: 50 pages, 30 figures, uses aastex62.cls. Accepted for publication in ApJ, 07/06/2019. High-level products page in MAST will go live after 7/15/2019. Replaced Figure 4 on 7/12/2019 to be more red/green color-blind friendly

Current measurements show that the observed fraction of Compton-thick (CT) AGN is smaller than the expected values needed to explain the cosmic X-ray background. Prior fits to the X-ray spectrum of the nearby Seyfert-2 galaxy NGC 5347 ($z=0.00792,\, D =35.5 \rm ~Mpc $) have alternately suggested a CT and Compton-thin source. Combining archival data from $Suzaku$, $Chandra$, and - most importantly - new data from $NuSTAR$, and using three distinct families of models, we show that NGC 5347 is an obscured CTAGN ($N_{\rm H} > 2.23\times 10^{24}~\rm cm^{-2}$). Its 2-30~keV spectrum is dominated by reprocessed emission from distant material, characterized by a strong Fe K$\alpha$ line and a Compton hump. We found a large equivalent width of the Fe K$\alpha$ line ($\rm EW = 2.3 \pm 0.3$ keV) and a high intrinsic-to-observed flux ratio ($\sim 100$). All of these observations are typical for bona fide CTAGN. We estimate a bolometric luminosity of $L_{\rm bol} \simeq 0.014 \pm 0.005~L_{\rm Edd.}$. The $Chandra$ image of NGC 5347 reveals the presence of extended emission dominating the soft X-ray spectrum ($E < 2\,\rm keV$), which coincides with the [O III] emission detected in the $Hubble ~Space~ Telescope$ images. Comparison to other CTAGN suggests that NGC 5347 is broadly consistent with the average properties of this source class. We simulated $XRISM$ and $Athena$/X-IFU spectra of the source, showing the potential of these future missions in identifying CTAGN in the soft X-rays., Comment: Accepted for publication in ApJ

Powerful winds driven by supermassive black holes (SMBHs) are likely the main mechanism through which SMBHs regulate their own growth and influence the host galaxy evolution. However, their origin and their capability to impact the large-scale environment are still highly debated. Fundamental results will come from high-energy and spatial resolution X-ray observatories., Comment: Science White Paper Submitted for the Astro2020 Decadal Survey on Astronomy and Astrophysics

Disk and wind signatures are seen in the soft state of Galactic black holes, while the jet is seen in the hard state. Here we study the disk-wind connection in the $\rho$ class of variability in GRS 1915+105 using a joint NuSTAR-Chandra observation. The source shows 50 sec limit cycle oscillations. By including new information provided by the reflection spectrum, and using phase-resolved spectroscopy, we find that the change in the inner disk inferred from the blackbody emission is not matched by reflection measurements. The latter is almost constant, independent of the continuum model. The two radii are comparable only if the disk temperature color correction factor changes, an effect that could be due to the changing opacity of the disk caused by changes in metal abundances. The disk inclination is similar to that inferred from the jet axis, and oscillates by ~10 deg. The simultaneous Chandra data show the presence of two wind components with velocities between 500-5000 km/s, and possibly two more with velocities reaching 20,000 km/s (~0.06 c). The column densities are ~5e22 cm$^{-2}$. An upper limit to the wind response time of 2 sec is measured, implying a launch radius of <6e10 cm. The changes in wind velocity and absorbed flux require the geometry of the wind to change during the oscillations, constraining the wind to be launched from a distance of 290 - 1300 rg from the black hole. Both datasets support fundamental model predictions in which a bulge originates in the inner disk and moves outward as the instability progresses., Comment: Accepted for publication in ApJ

NGC 2617 is a nearby ($z\sim 0.01$) active galaxy that recently switched from being a Seyfert 1.8 to be a Seyfert 1.0. At the same time, it underwent a strong increase of X-ray flux by one order of magnitude with respect to archival measurements. We characterise the X-ray spectral and timing properties of NGC 2617 with the aim of studying the physics of a changing-look active galactic nucleus (AGN). We performed a comprehensive timing and spectral analysis of two XMM-Newton pointed observations spaced by one month, complemented by archival quasi-simultaneous INTEGRAL observations. We found that, to the first order, NGC 2617 looks like a type 1 AGN in the X-ray band and, with the addition of a modest reflection component, its continuum can be modelled well either with a power law plus a phenomenological blackbody, a partially covered power law, or a double Comptonisation model. Independent of the continuum adopted, in all three cases a column density of a few $10^{23}$ cm$^{-2}$ of neutral gas covering 20-40\% of the continuum source is required by the data. Most interestingly, absorption structures due to highly ionised iron have been detected in both observations with a redshift of about $0.1c$ with respect to the systemic redshift of the host galaxy. The redshifted absorber can be ascribed to a failed wind/aborted jets component, to gravitational redshift effects, and/or to matter directly falling towards the central supermassive black hole. In either case, we are probing the innermost accretion flow around the central supermassive black hole of NGC 2617 and might be even watching matter in a direct inflow towards the black hole itself., Comment: Replaced to match the published version

We report on a 120 ks Chandra/HETG spectrum of the black hole GRS 1915+105. The observation was made during an extended and bright soft state in June, 2015. An extremely rich disk wind absorption spectrum is detected, similar to that observed at lower sensitivity in 2007. The very high resolution of the third-order spectrum reveals four components to the disk wind in the Fe K band alone; the fastest has a blue-shift of v = 0.03c. Broadened re-emission from the wind is also detected in the first-order spectrum, giving rise to clear accretion disk P Cygni profiles. Dynamical modeling of the re-emission spectrum gives wind launching radii of r ~ 10^(2-4) GM/c^2. Wind density values of n ~ 10^(13-16) cm^-3 are then required by the ionization parameter formalism. The small launching radii, high density values, and inferred high mass outflow rates signal a role for magnetic driving. With simple, reasonable assumptions, the wind properties constrain the magnitude of the emergent magnetic field to B ~ 10^(3-4) Gauss if the wind is driven via magnetohydrodynamic (MHD) pressure from within the disk, and B ~ 10^(4-5) Gauss if the wind is driven by magnetocentrifugal acceleration. The MHD estimates are below upper limits predicted by the canonical alpha-disk model (Shakura & Sunyaev 1973). We discuss these results in terms of fundamental disk physics and black hole accretion modes., Comment: Accepted for publication in ApJ Letters

We present an analysis of ionized X-ray disk winds observed in the Fe K band of four stellar-mass black holes observed with Chandra, including 4U 1630-47, GRO J1655-40, H 1743-322, and GRS 1915+105. High-resolution photoionization grids were generated in order to model the data. Third-order gratings spectra were used to resolve complex absorption profiles into atomic effects and multiple velocity components. The Fe XXV line is found to be shaped by contributions from the intercombination line (in absorption), and the Fe XXVI line is detected as a spin-orbit doublet. The data require 2-3 absorption zones, depending on the source. The fastest components have velocities approaching or exceeding 0.01c, increasing mass outflow rates and wind kinetic power by orders of magnitude over prior single-zone models. The first-order spectra require re-emission from the wind, broadened by a degree that is loosely consistent with Keplerian orbital velocities at the photoionization radius. This suggests that disk winds are rotating with the orbital velocity of the underlying disk, and provides a new means of estimating launching radii -- crucial to understanding wind driving mechanisms. Some aspects of the wind velocities and radii correspond well to the broad-line region (BLR) in active galactic nuclei, suggesting a physical connection. We discuss these results in terms of prevalent models for disk wind production and disk accretion itself, and implications for massive black holes in active galactic nuclei., Comment: Accepted for publication in ApJ

We report on a Chandra/HETG X-ray spectrum of the black hole candidate MAXI J1305-704. A rich absorption complex is detected in the Fe L band, including density-sensitive lines from Fe XX, XXI, and XXII. Spectral analysis over three bands with photoionization models generally requires a gas density of n > 1 E+17 cm^-3. Assuming a luminosity of L = 1 E+37 erg/s, fits to the 10-14 A band constrain the absorbing gas to lie within r = 3.9(7) E+3 km from the central engine, or about r = 520 +/- 90 (M/5 Msun) r_g, where r_g = GM/c^2. At this distance from the compact object, gas in Keplerian orbits should have a gravitational red-shift of z = v/c ~ 3 +/- 1 E-3 (M/5 Msun), and any tenuous inflowing gas should have a free-fall velocity of v/c ~ 6 +/- 1 E-2 (M/5 Msun)^1/2. The best-fit single-zone photoionization models measure a red-shift of v/c = 2.6-3.2 E-3. Models with two zones provide significantly improved fits; the additional zone is measured to have a red-shift of v/c =4.6-4.9 E-2 (models including two zones suggest slightly different radii and may point to lower densities). Thus, the shifts are broadly consistent with the photoionization radius. The results may be explained in terms of a "failed wind" like those predicted in some numerical simulations. We discuss our results in the context of accretion flows across the mass scale, and the potential role of failed winds in black hole state transitions., Comment: Accepted for publication in ApJ

Understanding the astrophysics of feedback in active galactic nuclei (AGN) is key to understanding the growth and co-evolution of supermassive black holes and galaxies. AGN-driven winds/outflows are potentially the most effective way of transporting energy and momentum from the nuclear scales to the host galaxy, quenching star formation by sweeping away the gas reservoir. Key questions in this field are: 1) how do accretion disks around black holes launch winds/outflows, and how much energy do these carry? 2) How are the energy and metals accelerated in winds/outflows transferred and deposited into the circumgalactic medium? X-ray observations are a unique way to address these questions because they probe the phase of the outflows which carries most of the kinetic energy. We show how a high throughput, high spectral resolution instrument like the X-ray Integral Field Unit (X-IFU) on Athena+ will allow us to address these questions by determining the physical parameters (ionization state, density, temperature, abundances, velocities, geometry, etc.) of the outflows on a dynamical time-scale, in a broad sample of nearby bright AGN. The X-IFU will also allow direct spectral imaging of the impact of these winds on the host galaxy for local AGN, forming a template for understanding AGN at higher redshifts where wind shocks cannot be resolved., Comment: Supporting paper for the science theme "The Hot and Energetic Universe" to be implemented by the Athena+ X-ray observatory (http://www.the-athena-x-ray-observatory.eu). 10 pages, 6 figures

(Abridged) We study stability of gas accretion in Active Galactic Nuclei. Our grid based simulations cover a radial range from 0.1 to 200 pc. Here, as in previous studies by our group, we include gas radiative cooling as well as heating by a sub-Eddington X-ray source near the central supermassive black hole of 10^8 M_{\odot}. Our theoretical estimates and simulations show that for the X-ray luminosity L_X \sim 0.008 L_{Edd}, the gas is thermally and convectivelly unstable within the computational domain. In the simulations, we observe that very tiny fluctuations in an initially smooth, spherically symmetric, accretion flow, grow first linearly and then non-linearly. Consequently, an initially one-phase flow relatively quickly transitions into a two-phase/cold-hot accretion flow. For L_X = 0.015 L_{Edd} or higher, the cold clouds continue to accrete but in some regions of the hot phase, the gas starts to move outward. For L_X < 0.015 L_{Edd}, the cold phase contribution to the total mass accretion rate only moderately dominates over the hot phase contribution. This result might have some consequences for cosmological simulations of the so-called AGN feedback problem. Our simulations confirm the previous results of Barai et al. (2012) who used smoothed particle hydrodynamic simulations to tackle the same problem. However here, because we use a grid based code to solve equations in 1-D and 2-D, we are able to follow the gas dynamics at much higher spacial resolution and for longer time in comparison to the 3-D SPH simulations. One of new features revealed by our simulations is that the cold condensations in the accretion flow initially form long filaments, but at the later times, those filaments may break into smaller clouds advected outwards within the hot outflow. These simulations may serve as an attractive model for the so-called Narrow Line Region in AGN., Comment: Accepted for publication in ApJ, 14 pages, 13 figures, 2 tables

Ultraviolet and X-ray observations show evidence of outflowing gas around many active galactic nuclei. Some of these outflows may be driven off gas infalling towards the central black hole. We perform radiative transfer calculations to compute the gas ionization state and X-ray spectra for two- and three-dimensional (3D) hydrodynamical simulations of this outflow-from-inflow scenario. By comparison with observations, our results can be used to test the theoretical models and guide future numerical simulations. We predict both absorption and emission features, most of which are formed in a polar funnel of outflowing gas. This outflow causes strong absorption for observer orientation angles of < 35 degrees. Particularly in 3D, the strength of this absorption varies significantly for different lines-of-sight owing to the fragmentary structure of the gas flow. Although infalling material occupies a large fraction of the simulation volume, we do not find that it imprints strong absorption features since the ionization state is very high. Thus, an absence of observed inflow absorption features does not exclude the models. The main spectroscopic consequence of the infalling gas is a scattered continuum component that partially re-fills the absorption features caused by the outflowing polar funnel. Fluorescence and scattering in the outflow is predicted to give rise to several emission features for all observer orientations. For the hydrodynamical simulations considered we find both ionization states and column densities for the outflowing gas that are too high to be quantitatively consistent with well-observed X-ray absorption systems. Nevertheless, our results are qualitatively encouraging and further exploration of the model parameter space is warranted. (Abridged.), Comment: 12 pages, 9 figures. Accepted for publication in MNRAS

We perform multi-dimensional radiative transfer simulations to compute spectra for a hydrodynamical simulation of a line-driven accretion disk wind from an active galactic nucleus. The synthetic spectra confirm expectations from parameterized models that a disk wind can imprint a wide variety of spectroscopic signatures including narrow absorption lines, broad emission lines and a Compton hump. The formation of these features is complex with contributions originating from many of the different structures present in the hydrodynamical simulation. In particular, spectral features are shaped both by gas in a successfully launched outflow and in complex flows where material is lifted out of the disk plane but ultimately falls back. We also confirm that the strong Fe Kalpha line can develop a weak, red-skewed line wing as a result of Compton scattering in the outflow. In addition, we demonstrate that X-ray radiation scattered and reprocessed in the flow has a pivotal part in both the spectrum formation and determining the ionization conditions in the wind. We find that scattered radiation is rather effective in ionizing gas which is shielded from direct irradiation from the central source. This effect likely makes the successful launching of a massive disk wind somewhat more challenging and should be considered in future wind simulations., Comment: 14 pages, 8 figures. Accepted for publication by MNRAS

We present the results of hydrodynamical simulations of the disk photosphere irradiated by strong X-rays produced in the inner most part of the disk. As expected, the irradiation heats the photosphere and drives a thermal wind. To apply our results to the well-studied X-ray transient source GRO J1655-40, we adopted the observed mass of its black hole, and the observed properties of its X-ray radiation. To compare the results with the observations, we also computed transmitted X-ray spectra based on the wind solution. Our main finding is: the density of the fast moving part of the wind is more than one order of magnitude lower than that inferred from the observations. Consequently, the model fails to predict spectra with line absorption as strong and as blueshifted as those observed. However, despite the thermal wind being weak and Compton thin, the ratio between the mass-loss rate and the mass accretion rate is about seven. This high ratio is insensitive to the accretion luminosity, in the limit of lower luminosities. Most of the mass is lost from the disk between 0.07 and 0.2 of the Compton radius. We discovered that beyond this range the wind solution is self-similar. In particular, soon after it leaves the disk, the wind flows at a constant angle with respect to the disk. Overall, the thermal winds generated in our comprehensive simulations do not match the wind spectra observed in GRO J1655-40. This supports the conclusion of Miller et al. and Kallman et al. that the wind in GRO J1655-40, and possibly other X-ray transients, may be driven by magnetic processes. This in turn implies that the disk wind carries even more material than our simulations predict and as such has a very significant impact on the accretion disk structure and dynamics., Comment: 23 pages, 7 figures, to appear in ApJ

We find, from high-resolution hydro simulations, that winds from AGN effectively heat the inner parts (~100 pc) of elliptical galaxies, reducing infall to the central SMBH; and radiative (photoionization and X-ray) heating reduces cooling flows at the kpc scale. Including both types of feedback with (peak) efficiencies of 3 10^{-4} < epsilon_mech < 10^{-3} and of epsilon_rad ~10^{-1.3} respectively, produces systems having duty-cycles, central SMBH masses, X-ray luminosities, optical light profiles, and E+A spectra in accord with the broad suite of modern observations of massive elliptical systems. Our main conclusion is that mechanical feedback (including all three of energy, momentum and mass) is necessary but the efficiency, based on several independent arguments must be a factor of 10 lower than is commonly assumed. Bursts are frequent at z>1 and decline in frequency towards the present epoch as energy and metal rich gas are expelled from the galaxies into the surrounding medium. For a representative galaxy of final stellar mass ~3 10^{11} Msun, roughly 3 10^{10} Msun of recycled gas has been added to the ISM since z~2 and, of that, roughly 63% has been expelled from the galaxy, 19% has been converted into new metal rich stars in the central few hundred parsecs, and 2% has been added to the central SMBH, with the remaining 16% in the form hot X-ray emitting ISM. The bursts occupy a total time of ~170 Myr, which is roughly 1.4% of the available time. Of this time, the central SMBH would be seen as an UV or optical source for ~45% and ~71$% of the time, respectively. Restricting to the last 8.5 Gyr, the burst occupy ~44 Myr, corresponding to a fiducial duty-cycle of ~5 10^{-3}., Comment: 41 pages, 11 figures (bitmapped, low-quality), ApJ accepted

We present the first results from a long (496 ks) Chandra High Energy Transmission Grating observation of the intermediate polar EX Hydrae. In addition to the narrow emission lines from the cooling post-shock gas, for the first time we have detected a broad component in some of the X-ray emission lines, namely O VIII 18.97, Mg XII 8.42, Si XIV 6.18, and Fe XVII 16.78. The broad and narrow components have widths of ~ 1600 km s^-1 and ~ 150 km s^-1, respectively. We propose a scenario where the broad component is formed in the pre-shock accretion flow, photoionized by radiation from the post-shock flow. Because the photoionized region has to be close to the radiation source in order to produce strong photoionized emission lines from ions like O VIII, Fe XVII, Mg XII, and Si XIV, our photoionization model constrains the height of the standing shock above the white dwarf surface. Thus, the X-ray spectrum from EX Hya manifests features of both magnetic and non-magnetic cataclysmic variables., Comment: accepted in The Astrophysical Journal

An extraordinary recent development in astrophysics was the discovery of the fossil relationship between central black hole mass and the stellar mass of galactic bulges. The physical process underpinning this relationship has become known as feedback. The Chandra X-ray Observatory was instrumental in realizing the physical basis for feedback, by demonstrating a tight coupling between the energy released by supermassive black holes and the gaseous structures surrounding them. This white paper discusses how a great leap forward in X-ray collecting area and spectral resolution will allow a qualitatively new way of studying how feedback from black holes influenced the growth of structure., Comment: Science white paper submitted to the Astro2010 Decadal Survey

The large scale structure of the present Universe is determined by the growth of dark matter density fluctuations and by the dynamical action of dark energy and dark matter. While much progress has been made in recent years in constraining the cosmological parameters, and in reconstructing the evolution in the large--scale structure of the dark matter distribution, we still lack an understanding of the evolution of the baryonic component of the Universe. Located at nodes of the cosmic web, clusters of galaxies are the largest collapsed structures in the Universe with total masses up to 10$^{15}$ M$_{\sun}$. Over 80% of their mass resides in the form of dark matter. The remaining mass is composed of baryons, most of which (about 85%) is a diffuse, hot plasma that radiates primarily in X-rays. X-ray observations of the evolving cluster population provide a unique opportunity to address such open and fundamental questions as: How do hot diffuse baryons dynamically evolve in dark matter potentials? How and when was the excess energy which we observe in the intergalactic medium generated? What is the cosmic history of heavy-element production and circulation? Our current knowledge comes primarily from detailed studies of clusters in the relatively nearby Universe (z$<$0.5). Major advances will come from high throughput, high spectral and spatial resolution X-ray observations that measure the thermodynamical properties and metal content of the first low mass clusters emerging at z $\sim$ 2 and directly trace their evolution into today's massive clusters., Comment: Science white paper submitted to the Astro2010 Decadal Survey

The importance of the radiative feedback from SMBHs at the centers of elliptical galaxies is not in doubt, given the well established relations among electromagnetic output, black hole mass and galaxy optical luminosity. In addition, feedback due to mechanical and thermal deposition of energy from jets and winds emitted by the accretion disk around the central SMBH is also expected to occur. In this paper we improve and extend the accretion and feedback physics explored in our previous papers to include also a physically motivated mechanical feedback. We study the evolution of an isolated elliptical galaxy with the aid of a high-resolution 1-D hydrodynamical code, where the cooling and heating functions include photoionization and Compton effects, and restricting to models which include only radiative or only mechanical feedback. We confirm that for Eddington ratios above 0.01 both the accretion and radiative output are forced by feedback effects to be in burst mode, so that strong intermittencies are expected at early times, while at low redshift the explored models are characterized by smooth, very sub-Eddington mass accretion rates punctuated by rare outbursts. However, the explored models always fail some observational tests. If we assume the high mechanical efficiency of 10^{-2.3}, we find that most of the gas is ejected from the galaxy, the resulting X-ray luminosity is far less than is typically observed and little SMBH growth occurs. But models with low enough mechanical efficiency to accomodate satisfactory SMBH growth tend to allow too strong cooling flows and leave galaxies at z=0 with E+A spectra more frequently than is observed. We conclude that both types of feedback are required. Models with combined feedback are explored in a forthcoming paper [abridged], Comment: 42 pages, 4 figures (low resolution), ApJ accepted

abridged: We use XSCORT, together with the hydrodynamic accretion disc wind simulation from Proga & Kallman (2004), to calculate the impact that the accretion disk wind has on the X-ray spectrum from a 1E8 solar mass black hole Active Galactic Nuclei (AGN) accreting at 0.5 L/L_Edd. The properties of the resulting spectra depend on viewing angle and clearly reflect the distinct regions apparent in the original hydrodynamic simulation. Very equatorial lines-of-sight (l.o.s) are dominated by Compton scattering and nearly-neutral absorption. Polar l.o.s result in largely featureless spectra. Finally, l.o.s that intersect the transition region between these extremes have a wide range of absorption features imprinted on the spectrum. Both polar and transition region l.o.s produce spectra that show highly-ionized, blue-shifted, Fe absorption features that are qualitatively similar to features observed in the X-ray spectra of a growing number of AGN. The spectra presented here clearly demonstrate that current simulations of line driven AGN accretion disk winds cannot reproduce the smooth soft X-ray excess. Furthermore, they predict that high accretion rate (L/L_Edd) AGN are likely to be strongly affected by obscuration, in sharp contrast to the clean picture that is generally assumed, based on the observed relation between the opening angle of the molecular torus and AGN luminosity., Comment: Accepted for Publication in ApJ (Oct 2008). 27 pages (ApJ preprint style), 5 colour figures, 1 B&W figure, 2 Tables. Minor corrections to table 2 and corresponding text

We have calculated a series of models of outflows from the obscuring torus in active galactic nuclei (AGN). Our modeling assumes that the inner face of a rotationally supported torus is illuminated and heated by the intense X-rays from the inner accretion disk and black hole. As a result of such heating a strong biconical outflow is observed in our simulations. We calculate 3-dimensional hydrodynamical models, assuming axial symmetry, and including the effects of X-ray heating, ionization, and radiation pressure. We discuss the behavior of a large family of these models, their velocity fields, mass fluxes and temperature, as functions of the torus properties and X-ray flux. Synthetic warm absorber spectra are calculated, assuming pure absorption, for sample models at various inclination angles and observing times. We show that these models have mass fluxes and flow speeds which are comparable to those which have been inferred from observations of Seyfert 1 warm absorbers, and that they can produce rich absorption line spectra., Comment: 32 pages, 11 figures Accepted for publication in ApJ

We report on time-dependent axisymmetric simulations of an X-ray excited flow from a parsec-scale, rotating, cold torus around an active galactic nucleus. Our simulations account for radiative heating and cooling and radiation pressure force. The simulations follow the development of a broad bi-conical outflow induced mainly by X-ray heating. We compute synthetic spectra predicted by our simulations. The wind characteristics and the spectra support the hypothesis that a rotationally supported torus can serve as the source of a wind which is responsible for the warm absorber gas observed in the X-ray spectra of many Seyfert galaxies., Comment: ApJ Letters, accepted for publication

Sgr A* is a source of strongly variable emission in several energy bands. It is generally agreed that this emission comes from the material surrounding the black hole which is either falling in or flowing out. The activity must be driven by accretion but the character of accretion flow in this object is an open question. We suggest that the inflow is dominated by the relatively low angular momentum material originating in one of the nearby group of stars. Such material flows in directly towards the black hole up to the distance of order of ten Schwarzschild radii or less, where it hits the angular momentum barrier which leads naturally to a flow variability. We study both the analytical and the numerical solutions for the flow dynamics, and we analyze the radiation spectra in both cases using the Monte Carlo code to simulate the synchrotron, bremsstrahlung and the Compton scattering. Our model roughly reproduces the broad band spectrum of Sgr A* and its variability if we allow for a small fraction of energy to be converted to non-thermal population of electrons. It is also consistent (for a range of viewing angles) with the strong constraints on the amount of circumnuclear material imposed by the measurements of the Faraday rotation., Comment: Proceedings of the Rigtime 9 conference, Opava 2007

We present results from multi-epoch spectral analysis of XMM-Newton and Chandra observations of the mini broad absorption line (BAL) quasar PG 1115+080. This is one of the few X-ray detected mini-BAL quasars to date that is bright enough in the X-ray band, mostly due to large gravitational-lensing magnifications, to allow in-depth spectral analysis. The present XMM-Newton observations of PG 1115+080 have provided the highest signal-to-noise X-ray spectra of a mini-BAL quasar obtained to date. By modeling the spectra of PG 1115+080 we have obtained constraints on the column density and ionization state of its outflowing absorbing gas. A comparison between these constraints over several epochs indicates significant variability in the properties of the outflowing absorbers in PG 1115+080. The depths of the high-energy broad absorption features in PG 1115+080 show a significant decrease between the first two observation epochs separated by a rest-frame timescale of ~ 1 year. This variability supports the intrinsic nature of these absorbers. Assuming the interpretation that the high-energy absorption features arise from highly ionized Fe XXV we constrain the fraction of the total bolometric energy released by quasars PG 1115+080 and APM 08279+5225 into the IGM in the form of kinetic energy to be epsilon_k = 0.64(-0.40,+0.52) (68% confidence), and epsilon_k =0.09(-0.05,+0.07), respectively. According to recent theoretical studies this range of efficiencies is large enough to influence significantly the formation of the host galaxy and to regulate the growth of the central black hole., Comment: 20 pages, includes 5 figures, Accepted for publication in AJ

We present a Chandra-LETGS observation of the Seyfert 1 galaxy Mrk 279. This observation was carried out simultaneously with HST-STIS and FUSE, in the context of a multiwavelength study of this source. The Chandra pointings were spread over ten days for a total exposure time of ~360 ks. The spectrum of Mrk279 shows evidence of broad emission features, especially at the wavelength of the OVII triplet. We quantitatively explore the possibility that this emission is produced in the broad line region (BLR). We modeled the broad UV emission lines seen in the FUSE and HST-STIS spectra following the ``locally optimally emitting cloud" approach. We find that the X-ray lines luminosity derived from the best fit BLR model can match the X-ray features, suggesting that the gas producing the UV lines is sufficient to account also for the X-ray emission. The spectrum is absorbed by ionized gas whose total column density is ~5x10^{20} cm^{-2}. The absorption spectrum can be modeled by two distinct gas components (log xi ~ 0.47 and 2.49, respectively) both showing a significant outflow velocity. However, the data allow also the presence of intermediate ionization components. The distribution of the column densities of such extra components as a function of the ionization parameter is not consistent with a continuous, power law-like, absorber, suggesting a complex structure for the gas outflow for Mrk 279 (abridged)., Comment: 16 pages, 12 figures. To appear in A&A

We explore consequences of a radiation driven disk wind model for mass outflows from active galactic nuclei (AGN). We performed axisymmetric time-dependent hydrodynamic calculations using the same computational technique as Proga, Stone and Kallman (2000). We test the robustness of radiation launching and acceleration of the wind for relatively unfavorable conditions. In particular, we take into account the central engine radiation as a source of ionizing photons but neglect its contribution to the radiation force. Additionally, we account for the attenuation of the X-ray radiation by computing the X-ray optical depth in the radial direction assuming that only electron scattering contributes to the opacity. Our new simulations confirm the main result from our previous work: the disk atmosphere can 'shield' itself from external X-rays so that the local disk radiation can launch gas off the disk photosphere. We also find that the local disk force suffices to accelerate the disk wind to high velocities in the radial direction. This is true provided the wind does not change significantly the geometry of the disk radiation by continuum scattering and absorption processes; we discuss plausibility of this requirement. Synthetic profiles of a typical resonance ultraviolet line predicted by our models are consistent with observations of broad absorption line (BAL) QSOs., Comment: LaTeX, contains color figures, to appear in ApJ

One of the main problems in modeling the ionised outflows in Active Galactic Nuclei is the unknown distance of the outflowing wind to the central source. Only if the density is known this distance can be determined through the ionisation parameter. Here we study density diagnostics based upon O V transitions. O V is known to have metastable levels that are density dependent. We study the population of those levels under photoionisation equilibrium conditions and determine for which parameter range they can have a significant population. We find that resonance line trapping plays an important role in reducing the critical densities above which the metastable population becomes important. We investigate the K-shell absorption lines from these metastable levels. Provided that there is a sufficient population of the metastable levels, the corresponding K-shell absorption lines are detectable and are well separated from the main absorption line originating from the ground state. We then present the Chandra LETGS spectrum of the Seyfert 1 galaxy Mrk 279 that may show for the first time the presence of these metastable level absorption lines. A firm identification is not yet possible due to both uncertainties in the observed wavelength of the strongest line as well as uncertainties in the predicted wavelength. If the line is indeed due to absorption from O V, then we deduce a distance to the central source of one light week to a few light months, depending upon the importance of additional heating processes., Comment: 10 pages, 8 figures, submitted to Astronomy & Astrophysics, main journal

We present results from axisymmetric, time-dependent magnetohydrodynamic (MHD) simulations of the collapsar model for gamma-ray bursts. Our main conclusion is that, within the collapsar model, MHD effects alone are able to launch, accelerate and sustain a strong polar outflow. We also find that the outflow is Poynting flux-dominated, and note that this provides favorable initial conditions for the subsequent production of a baryon-poor fireball., Comment: 4 pages, to appear in proceedings of "2003 GRB Conference" (Santa Fe, NM, September 8-12, 2003), needs aipprocs LaTeX class, movies are available at http://rocinante.colorado.edu/~proga/

We summarize recent developments in modeling of mass outflows from accretion disks in AGN. We illustrate how the hydrodynamical and magnetohydrodynamical wind structures revealed in numerical simulations relate to observations. Important results from the numerical simulations include: no shielding from X-rays is needed to radiatively launch a wind from the inner disk; shielding is needed to accelerate the wind to high velocities. Disk winds launched magnetically seem to be too dense to be accelerated by line driving. It appears that we have an all or nothing situation for radiation-driving: radiation driving has to be responsible for both launching and accelerating the wind or a wind launched by some other mechanism must have a very finely tuned density in order to be accelerated by radiation driving to velocities as high as measured in BAL QSOs., Comment: to appear in the proceedings of "AGN Physics with the SDSS", eds. G. T. Richards and P. B. Hall (San Francisco: ASP) (2004), 6 pages, newpasp.sty

We present results from axisymmetric, time-dependent magnetohydrodynamic (MHD) simulations of the collapsar model for gamma-ray bursts. We begin the simulations after the 1.7 MSUN iron core of a 25 MSUN presupernova star has collapsed and study the ensuing accretion of the 7 MSUN helium envelope onto the central black hole formed by the collapsed iron core. We consider a spherically symmetric progenitor model, but with spherical symmetry broken by the introduction of a small, latitude-dependent angular momentum and a weak radial magnetic field. Our MHD simulations include a realistic equation of state, neutrino cooling, photodisintegration of helium, and resistive heating. Our main conclusion is that, within the collapsar model, MHD effects alone are able to launch, accelerate and sustain a strong polar outflow. We also find that the outflow is Poynting flux-dominated, and note that this provides favorable initial conditions for the subsequent production of a baryon-poor fireball., Comment: submitted in ApJ Letters

We propose a gamma-ray burst scenario involving relativistic jets dominated by Poynting flux with alternating toroidal magnetic fields. Such a structure may arise naturally if the jet is formed and powered by the accretion flow in the core of a collapsar. We conjecture that the polarity of the toroidal magnetic field changes randomly due to hydromagnetic turbulence driven by the magneto-rotational instability (MRI), with the typical reversal time determined by the time scale for amplifying magnetic fields up to a dynamically important level. Poynting flux-dominated jets with reversing B-fields provide a natural and efficient way to dissipate energy via the reconnection process. Gamma-rays are produced at the spatially separated reconnection sites. In this scenario, the emergent synchrotron radiation can be highly polarized and can form both smooth and spiky light curves. We note the possibility that cold and dense filaments can form in the reconnection zones as the result of thermal instability. One could then explain the production of very hard X-ray spectra, as due to bound-free absorption of the synchrotron radiation., Comment: submitted in ApJ Letters

We report on resonance line profiles predicted by radiation driven disk wind models which extend radially one order of magnitude farther out than our previous models. Our main result is that the inclusion of a disk wind at larger radii changes qualitatively and quantitatively the line profiles predicted by the models. Our new models predict line absorption that is significantly stronger than those predicted by old models. Some of the previous line profiles exhibit a doubled-humped structure near the line center which is now replaced by a more plausible single, blueshifted minimum. We emphasize that the improvements in the shape as well as the strength of the absorption were achieved without changing the gross properties of the wind. In particular, our new models do not predict a higher mass-loss rate than the previous models. The main changes in the line profiles are due to the fact that the ratio between the rotational velocity and poloidal velocity of the wind decreases downstream. The new line profiles reproduce well the line absorption of the nova-like variable, IX~Vel, and promise to reproduce observations of other cataclysmic variables. This success of the radiation driven disk wind model provides an important link between outflows in OB stars and outflows in active galactic nuclei., Comment: to appear in ApJ Letter

We report on the second phase of our study of slightly rotating accretion flows onto black holes. We consider magnetohydrodynamical (MHD) accretion flows with a spherically symmetric density distribution at the outer boundary, but with spherical symmetry broken by the introduction of a small, latitude-dependent angular momentum and a weak radial magnetic field. We study accretion flows by means of numerical 2D, axisymmetric, MHD simulations with and without resistive heating. Our main result is that the properties of the accretion flow depend mostly on an equatorial accretion torus which is made of the material that has too much angular momentum to be accreted directly. The torus accretes, however, because of the transport of angular momentum due to the magnetorotational instability (MRI). Initially, accretion is dominated by the polar funnel, as in the hydrodynamic inviscid case, where material has zero or very low angular momentum. At the later phase of the evolution, the torus thickens towards the poles and develops a corona or an outflow or both. Consequently, the mass accretion through the funnel is stopped. The accretion of rotating gas through the torus is significantly reduced compared to the accretion of non-rotating gas (i.e., the Bondi rate). It is also much smaller than the accretion rate in the inviscid, weakly rotating case.Our results do not change if we switch on or off resistive heating. Overall our simulations are very similar to those presented by Stone, Pringle, Hawley and Balbus despite different initial and outer boundary conditions. Thus, we confirm that MRI is very robust and controls the nature of radiatively inefficient accretion flows., Comment: submitted in ApJ

We study the two-dimensional, time-dependent MHD of radiation-driven winds from luminous accretion disks initially threaded by a purely axial magnetic field. The radiation force is mediated primarily by spectral lines. We use ideal MHD to compute the evolution of Keplerian disks, varying the magnetic field strengths and the luminosity of the disk, the central accreting object or both. We find that the magnetic fields very quickly start deviating from purely axial due to the magnetorotational instability. This leads to fast growth of the toroidal magnetic field. As a result the toroidal field dominates over the poloidal field above the disk and the gradient of the former drives a slow and dense disk outflow, which conserves specific angular momentum. Depending on the strength of the magnetic field relative to the system luminosity the disk wind can be radiation- or MHD driven. The pure radiation-driven wind consists of a dense, slow outflow that is bounded on the polar side by a high-velocity stream. The mass-loss rate is mostly due to the fast stream. As the magnetic field strength increases first the slow part of the flow is affected, namely it becomes denser and slightly faster and begins to dominate the mass-loss rate. In very strong magnetic field or pure MHD cases, the wind consists of only a dense, slow outflow without the presence of the distinctive fast stream so typical to pure radiation-driven winds. Our simulations indicate that winds launched by the magnetic fields are likely to remain dominated by the fields downstream because of their relatively high densities., Comment: 30 pages, 4 figure (fig. 1 and fig. 2 in color), to appear in ApJ, "see also http://rocinante.colorado.edu/~proga/"

We report on the first phase of our study of slightly rotating accretion flows onto black holes. We consider inviscid accretion flows with a spherically symmetric density distribution at the outer boundary, but with spherical symmetry broken by the introduction of a small, latitude-dependent angular momentum. We study accretion flows by means of numerical 2D, axisymmetric, hydrodynamical simulations. Our main result is that the properties of the accretion flow do not depend as much on the outer boundary conditions (i.e., the amount as well as distribution of the angular momentum) as on the geometry of the non-accreting matter. The material that has too much angular momentum to be accreted forms a thick torus near the equator. Consequently, the geometry of the polar region, where material is accreted (the funnel), and the mass accretion rate through it are constrained by the size and shape of the torus. Our results show one way in which the mass accretion rate of slightly rotating gas can be significantly reduced compared to the accretion of non-rotating gas (i.e., the Bondi rate), and set the stage for calculations that will take into account the transport of angular momentum and energy., Comment: LaTeX,to appear in ApJ

We present synthetic line profiles as predicted by the models of 2-D line- driven disk winds due to Proga, Stone & Drew. We compare the model line profiles with HST observations of the cataclysmic variable IX Vel. The model wind consists of a slow outflow that is bounded on the polar side by a fast stream. We find that these two components of the wind produce distinct spectral features. The fast stream produces profiles which show features consistent with observations. These include the appearance of the P-Cygni shape for a range of inclinations, the location of the maximum depth of the absorption component at velocities less than the terminal velocity, and the transition from absorption to emission with increasing inclination. However the model profiles have too little absorption or emission equivalent width. This quantitative difference between our models and observations is not a surprise because the line-driven wind models predict a mass loss rate that is lower than the rate required by the observations. We note that the model profiles exhibit a double-humped structure near the line center which is not echoed in observations. We identify this structure with a non-negligible redshifted absorption which is formed in the slow component of the wind where the rotational velocity dominates over expansion velocity. We conclude that the next generation of disk wind models, developed for application to CVs, needs to yield stronger wind driving out to larger disk radii than do the present models., Comment: LaTeX, 19 pages, to appear in ApJ

To confront the predictions of the most recent line-driven disk wind models with observational evidence, we have obtained HST STIS (1180--1700A) echelle spectra of the nova-like variables IX Vel and V3885 Sgr at three epochs. The targets were observed in timetag mode for ~2000sec on each occasion, allowing us to study the spectral time evolution on timescales down to ~10sec. The mean UV spectra are characterised by the wind signature of broad blueshifted absorption in Lya, NV1240, SiIV1398, CIV1549 and HeII1640. There is very little redshifted emission other than in CIV. Narrow blueshifted absorption dips, superposed on the broad absorption at around -900km/s, accompany periods of well-developed wind activity. The continuum level and mean line profiles vary markedly from observation to observation -- with the wind signatures almost disappearing in one epoch of observation of IX Vel. The strong positive correlation between UV brightness and wind activity predicted by line-driven disk wind models is disobeyed by both binaries. The wind signatures in IX Vel's UV spectrum are revealed to be remarkably steady on timescales ranging from ~10 to ~1000sec. More variability is seen in V3885 Sgr, the binary with the lower opacity outflow. But there is only one epoch in which the line profile changes significantly in ~100sec or less. Narrow absorption dips, when present, show only smooth, small changes in velocity., Comment: 19 pages, 14 figures. Accepted for publication in MNRAS