# CV & Publications

2018
Danehkar A, Nowak MA, Lee JC, Smith RK. MPI_XSTAR: MPI-based Parallelization of the XSTAR Photoionization Program. PASP [Internet]. 2018;130 (984) :024501. Publisher's VersionAbstract
We describe a program for the parallel implementation of multiple runs of XSTAR, a photoionization code that is used to predict the physical properties of an ionized gas from its emission and/or absorption lines. The parallelization program, called MPI_XSTAR, has been developed and implemented in the C++ language by using the Message Passing Interface (MPI) protocol, a conventional standard of parallel computing. We have benchmarked parallel multiprocessing executions of XSTAR, using MPI_XSTAR, against a serial execution of XSTAR, in terms of the parallelization speedup and the computing resource efficiency. Our experience indicates that the parallel execution runs significantly faster than the serial execution, however, the efficiency in terms of the computing resource usage decreases with increasing the number of processors used in the parallel computing.
Kriss GA, Lee JC, Danehkar A, Nowak MA, Fang T, Hardcastle MJ;, Neilsen J, Young A. Discovery of an Ultraviolet Counterpart to an Ultrafast X-Ray Outflow in the Quasar PG 1211+143. The Astrophysical Journal [Internet]. 2018;853 (2) :166. Publisher's VersionAbstract
We observed the quasar PG 1211+143 using the Cosmic Origins Spectrograph on the Hubble Space Telescope in 2015 April as part of a joint campaign with the Chandra X-ray Observatory and the Jansky Very Large Array. Our ultraviolet spectra cover the wavelength range 912–2100 Å. We find a broad absorption feature (∼ 1080 {km} {{{s}}}-1) at an observed wavelength of 1240 Å. Interpreting this as H I Lyα, in the rest frame of PG 1211+143 (z = 0.0809), this corresponds to an outflow velocity of ‑16,980 {km} {{{s}}}-1 (outflow redshift {z}{out}∼ -0.0551), matching the moderate ionization X-ray absorption system detected in our Chandra observation and reported previously by Pounds et al. With a minimum H I column density of {log} {N}{{H}{{I}}}> 14.5, and no absorption in other UV resonance lines, this Lyα absorber is consistent with arising in the same ultrafast outflow as the X-ray absorbing gas. The Lyα feature is weak or absent in archival ultraviolet spectra of PG 1211+143, strongly suggesting that this absorption is transient, and intrinsic to PG 1211+143. Such a simultaneous detection in two independent wavebands for the first time gives strong confirmation of the reality of an ultrafast outflow in an active galactic nucleus.
Danehkar A, Nowak MA, Lee JC, Kriss GA, Young AJ, Hardcastle MJ, Chakravorty S, Fang T, Neilsen J, Rahoui F, et al. The Ultra-fast Outflow of the Quasar PG 1211+143 as Viewed by Time-averaged Chandra Grating Spectroscopy. The Astrophysical Journal [Internet]. 2018;853 :165. Publisher's VersionAbstract
We present a detailed X-ray spectral study of the quasar PG 1211+143 based on Chandra High Energy Transmission Grating Spectrometer (HETGS) observations collected in a multi-wavelength campaign with UV data using the Hubble Space Telescope Cosmic Origins Spectrograph (HST-COS) and radio bands using the Jansky Very Large Array (VLA). We constructed a multi-wavelength ionizing spectral energy distribution using these observations and archival infrared data to create XSTAR photoionization models specific to the PG 1211+143 flux behavior during the epoch of our observations. Our analysis of the Chandra-HETGS spectra yields complex absorption lines from H-like and He-like ions of Ne, Mg, and Si, which confirm the presence of an ultra-fast outflow (UFO) with a velocity of approximately ‑17,300 km s‑1 (outflow redshift zout ∼ ‑0.0561) in the rest frame of PG 1211+143. This absorber is well described by an ionization parameter {log}ξ ∼ 2.9 {erg} {{{s}}}-1 {cm} and column density {log}{N}{{H}}∼ 21.5 {{cm}}-2. This corresponds to a stable region of the absorber’s thermal stability curve, and furthermore its implied neutral hydrogen column is broadly consistent with a broad Lyα absorption line at a mean outflow velocity of approximately ‑16,980 km s‑1 detected by our HST-COS observations. Our findings represent the first simultaneous detection of a UFO in both X-ray and UV observations. Our VLA observations provide evidence for an active jet in PG 1211+143, which may be connected to the X-ray and UV outflows; this possibility can be evaluated using very-long-baseline interferometric observations.
2016
Miškovičová I, Hell N, Hanke M, Nowak MA, Pottschmidt K, Schulz NS, Grinberg V, Duro R, Madej OK, Lohfink AM, et al. Chandra X-ray spectroscopy of focused wind in the Cygnus X-1 system. II. The non-dip spectrum in the low/hard state - modulations with orbital phase. Astronomy & Astrophysics [Internet]. 2016;590 (590) :A114. Publisher's VersionAbstract
Accretion onto the black hole in the system HDE 226868/Cygnus X-1 is powered by the strong line-driven stellar wind of the O-type donor star. We study the X-ray properties of the stellar wind in the hard state of Cyg X-1, as determined using data from the Chandra High Energy Transmission Gratings. Large density and temperature inhomogeneities are present in the wind, with a fraction of the wind consisting of clumps of matter with higher density and lower temperature embedded in a photoionized gas. Absorption dips observed in the light curve are believed to be caused by these clumps. This work concentrates on the non-dip spectra as a function of orbital phase. The spectra show lines of H-like and He-like ions of S, Si, Na, Mg, Al, and highly ionized Fe (Fe xvii–Fe xxiv). We measure velocity shifts, column densities, and thermal broadening of the line series. The excellent quality of these five observations allows us to investigate the orbital phase-dependence of these parameters. We show that the absorber is located close to the black hole. Doppler shifted lines point at a complex wind structure in this region, while emission lines seen in some observations are from a denser medium than the absorber. The observed line profiles are phase-dependent. Their shapes vary from pure, symmetric absorption at the superior conjunction to P Cygni profiles at the inferior conjunction of the black hole
2014
Brenneman LW, Reynolds CS, Fabian AC, Nowak MA, Reis RC, Lohfink A, Miller JM, Iwasawa K, Mushotzky R, Volonteri M, et al. A Survey of Spin and Relativistic Phenomena in AGN, in Suzaku-MAXI 2014: Expanding the Frontiers of the X-ray Universe. ; 2014 :285. Publisher's VersionAbstract
Relativistically broadened spectral features have now been seen in the X-ray spectra of many active galactic nuclei (AGN) and Galactic Black Hole Binaries (GBHBs). Investigations of these features allow us to probe the physics of the innermost accretion flow, the geometry of the still-mysterious hard X-ray source, and the spacetime metric of the black hole itself. We conducted a Suzaku Key Project (AO4-AO6) that, through very deep observations, has enabled detailed studies of strong gravitational physics in five AGN. This has been the first observational census of supermassive black hole (SMBH) spin ever conducted, and acts as a crucial pathfinder study for one of the principal scientific goals of the Astro-H and ATHENA missions. In addition to elucidating the role of black hole spin as an energy source in astrophysics, these data have given us our first glimpse at the spin distribution of the local SMBH population. Our deep Suzaku observations have yielded spin constraints for three of the five AGN studied, all of which show medium-to-high prograde spin values.
Eikmann W, Wilms J, Smith RK, Lee JC. X-ray transmission and reflection through a Compton-thick medium via Monte-Carlo simulations, in Acta Polytechnica. Vol 54. ; 2014 :177-182. Publisher's VersionAbstract
The spectral shape of an X-ray source strongly depends on the amount and distribution of the surrounding material. The spectrum of a primary source which is located in an optically thin medium with respect to Compton scattering is mainly modified by photo absorption in the lower energy range and is almost unaltered above ~ 10 keV. This picture changes when the source is obscured by gas exceeding hydrogen column densities of ~ 1024cm−2. At this degree of absorption it is likely that photons are scattered at least twice before leaving the medium. The multiple scatterings lead to a lack of photons in the high energy range of the resulting spectrum as well as to an accumulation of photons at moderate energies forming the so-called Compton-bump. The shape of the fluorescent lines also changes since scattered line photons form several Compton-shoulders which are very prominent especially for Compton-thick sources. Using a Monte Carlo method, we demonstrate the importance of Compton scattering for high column densities. For that purpose, we compare our results with existing absorption models that do not consider Compton scattering. These calculations will be implemented in a prospective version of the tbabs absorption model including an analytic evaluation of the strength of the fluorescent lines.
Rahoui F, Coriat M, Lee JC. Optical and near-infrared spectroscopy of the black hole GX 339-4 - II. The spectroscopic content in the low/hard and high/soft states. Monthly Notices of the Royal Astronomical Society. 2014;442 (2) :1610-1618.Abstract
As a complement to our optical and near-infrared study of the continuum properties of GX 339−4 in the two hard and one soft state observations made by the ESO/Very Large Telescope (VLT), FOcal Reducer and Spectrograph #2 (FORS2) and infrared spectrometer and array camera (ISAAC) in early 2010, we report here on the results of our spectral line analysis for the same observations. In the soft state, the presence of strong Balmer, Paschen and Brackett emission lines points to the optical and near-infrared spectra stemming from the irradiated chromosphere of the optically thick and geometrically thin accretion disc. Most of these H I features are still detected in emission in both hard states but are veiled by the compact jets continuum. We also confirm the presence of a broad Hβ absorption feature, prominent in the soft state and shallower in the first hard state, which we argue forms in the deep layers of the optically thick accretion disc. However, this trough is absent in the second hard state, a likely consequence of the formation of a geometrically thick extended envelope that arises above the disc plane and eventually enshrouds the region where the Hβ absorption feature forms. We detect this envelope through the presence of a broad Paβ emission line, which is constant during the first hard state but correlates with the underlying continuum during the second hard state, pointing to changing physical properties. We consider that this behaviour may be consistent with the launch of a thermally driven accretion disc wind during the second hard state.
Neilsen J, Coriat M;, Fender R, Lee JC, Ponti G, Tzioumis AK, Edwards PG, Broderick JW. A Link between X-Ray Emission Lines and Radio Jets in 4U 1630-47?. The Astrophysical Journal Letters [Internet]. 2014;784 (1) :L5. Publisher's VersionAbstract
Recently, Díaz Trigo et al. reported an XMM-Newton detection of relativistically Doppler-shifted emission lines associated with steep-spectrum radio emission in the stellar-mass black hole candidate 4U 1630-47 during its 2012 outburst. They interpreted these lines as indicative of a baryonic jet launched by the accretion disk. Here we present a search for the same lines earlier in the same outburst using high-resolution X-ray spectra from the Chandra HETGS. While our observations (eight months prior to the XMM-Newton campaign) also coincide with detections of steep spectrum radio emission by the Australia Telescope Compact Array, we find no evidence for any relativistic X-ray emission lines. Indeed, despite ~5 × brighter radio emission, our Chandra spectra allow us to place an upper limit on the flux in the blueshifted Fe XXVI line that is  20 × weaker than the line observed by Díaz Trigo et al. We explore several scenarios that could explain our differing results, including variations in the geometry of the jet or a mass-loading process or jet baryon content that evolves with the accretion state of the black hole. We also consider the possibility that the radio emission arises in an interaction between a jet and the nearby interstellar medium, in which case the X-ray emission lines might be unrelated to the radio emission.
2013
Chakravorty S, Lee JC, Neilsen J. The effects of thermodynamic stability on wind properties in different low mass black hole binary states. Monthly Notices of the Royal Astronomical Society [Internet]. 2013;436 :560-569. Publisher's VersionAbstract
We present a systematic theory-motivated study of the thermodynamic stability condition as an explanation for the observed accretion disk wind signatures in different states of low mass black hole binaries (BHB). The variability in observed ions is conventionally explained either by variations in the driving mechanisms or the changes in the ionizing flux or due to density effects, whilst thermodynamic stability considerations have been largely ignored. It would appear that the observability of particular ions in different BHB states can be accounted for through simple thermodynamic considerations in the static limit. Our calculations predict that in the disk dominated soft thermal and intermediate states, the wind should be thermodynamically stable and hence observable. On the other hand, in the powerlaw dominated spectrally hard state the wind is found to be thermodynamically unstable for a certain range of 3.55 <= log \xi <= 4.20. In the spectrally hard state, a large number of the He-like and H-like ions (including e.g. Fe XXV, Ar XVIII and S XV) have peak ion fractions in the unstable ionization parameter (\xi) range, making these ions undetectable. Our theoretical predictions have clear corroboration in the literature reporting differences in wind ion observability as the BHBs transition through the accretion states Lee et al. 2002; Miller et al. 2008; Neilsen & Lee 2009; Blum et al. 2010; Ponti et al. 2012; Neilsen & Homan 2012). While this effect may not be the only one responsible for the observed gradient in the wind properties as a function of the accretion state in BHBs, it is clear that its inclusion in the calculations is crucial to understanding the link between the environment of the compact object and its accretion
Lee JC, Kriss G, Chakravorty S, Rahoui F, Young AJ, Brandt WN, Hines DC, Ogle PM, Reynolds CS. The Ionized Absorber and Nuclear Environment of IRAS 13349+2438: Multi-wavelength insights from coordinated Chandra HETGS, HST STIS, HET, and Spitzer IRS. Monthly Notices of the Royal Astronomical Society [Internet]. 2013;430 (4) :2650–2679. Publisher's VersionAbstract

We present results from a multi-wavelength infrared (IR)-to-X-ray campaign of the infrared bright (but highly optical-ultraviolet extincted) quasi-stellar object (QSO) IRAS 13349+2438 obtained with the Chandra High Energy Transmission Grating Spectrometer (HETGS), the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS), the Hobby–Eberly Telescope (HET) 8 m and the Spitzer Infrared Spectrometer (IRS). Based on HET optical spectra of [O III], we refine the redshift of IRAS 13349 to be z = 0.108 53. The weakness of the [O III] in combination with strong Fe II in the HET spectra reveals extreme Eigenvector-1 characteristics in IRAS 13349, but the 2468 km s−1 width of the Hβ line argues against a narrow-line Seyfert 1 classification; on average, IR, optical and optical-ultraviolet (UV) spectra show IRAS 13349 to be a typical QSO. Independent estimates based on the Hβ line width and fits to the IRAS 13349 spectral energy distribution (SED) both give a black hole mass of MBH = 109  M. The heavily reddened STIS UV spectra reveal for the first time blueshifted absorption from Ly Α, N V and C IV, with components at systemic velocities of −950km/s and −75km/s. The higher velocity UV lines are coincident with the lower ionization (ξ ∼ 1.6) WA-1 warm absorber lines seen in the X-rays with the HETGS. In addition, a ξ ∼ 3.4 WA-2 is also required by the data, while a ξ ∼ 3 WA-3 is predicted by theory and seen at less significance; all detected X-ray absorption lines are blueshifted by ∼ 700-900 km s−1 . Theoretical models comparing different ionizing SEDs reveal that including the UV (i.e. the accretion disc) as part of the ionizing continuum has strong implications for the conclusions one would draw about the thermodynamic stability of the warm absorber. Specific to IRAS 13349, we find that an X-ray–UV ionizing SED favours a continuous distribution of ionization states in a smooth flow (this paper) versus discrete clouds in pressure equilibrium (previous work by other authors). Direct detections of dust are seen in both the IR and X-rays. We see weak polycyclic aromatic hydrocarbon (PAH) emission at 7.7 μm and 11.3 μm which may also be blended with forsterite, and 10 μm and 18 μm silicate emission, as well as an Fe L edge at 700 eV indicative of iron-based dust with a dust-to-gas ratio >90 per cent. We develop a geometrical model in which we view the nuclear regions of the QSO along a line of sight that passes through the upper atmosphere of an obscuring torus. This sight line is largely transparent in X-rays since the gas is ionized, but it is completely obscured by dust that blocks a direct view of the UV/optical emission region. In the context of our model, 20 per cent of the intrinsic UV/optical continuum is scattered into our sight line by the far wall of an obscuring torus. An additional 2.4 per cent of the direct light, which likely dominates the UV emission, is Thomson-scattered into our line of sight by another off-plane component of highly ionized gas.

2012
{Neilsen} J, {Petschek} A J, {Lee} J C. {Accretion disc wind variability in the states of the microquasar GRS 1915+105}. MNRAS. 2012;421 :502-511.Abstract

{Continuing our study of the role and evolution of accretion disc winds in the microquasar GRS 1915+105, we present high-resolution spectral variability analysis of the {$\beta$} and {$\gamma$} states with the Chandra High-Energy Transmission Grating Spectrometer. By tracking changes in the absorption lines from the accretion disc wind, we find new evidence that radiation links the inner and outer accretion discs on a range of time-scales. As the central X-ray flux rises during the high-luminosity {$\gamma$} state, we observe the progressive overionization of the wind. In the {$\beta$} state, we argue that changes in the inner disc leading to the ejection of a transient 'baby jet' also quench the highly ionized wind from the outer disc. Our analysis reveals how the state, structure and X-ray luminosity of the inner accretion disc all conspire to drive the formation and variability of highly ionized accretion disc winds. }

Neilsen J, Remillard R  A, Lee J  C. Radiation Pressure and Mass Ejection in rho-like States of GRS 1915+105. Astrophysical Journal. 2012;750 :71.Abstract

{We present a unifying scenario to address the physical origin of the diversity of X-ray light curves within the {$\rho$} variability class of the microquasar GRS 1915+105. This ''heartbeat'' state is characterized by a bright flare that recurs every \~{}50-100 s, but the profile and duration of the flares vary significantly from observation to observation. Based on a comprehensive, phase-resolved study of heartbeats in the Rossi X-ray Timing Explorer archive, we demonstrate that very different X-ray light curves do not require origins in different accretion processes. Indeed, our detailed comparison of the phase-resolved spectra of a double-peaked oscillation and a single-peaked oscillation shows that different cycles can have basically similar X-ray spectral evolution. We argue that all heartbeat oscillations can be understood as the result of a combination of a thermal-viscous radiation pressure instability, a local Eddington limit in the disk, and a sudden, radiation-pressure-driven evaporation or ejection event in the inner accretion disk. This ejection appears to be a universal, fundamental part of the {$\rho$} state, and is largely responsible for a hard X-ray pulse seen in the light curve of all cycles. We suggest that the detailed shape of oscillations in the mass accretion rate through the disk is responsible for the phenomenological differences between different {$\rho$}-type light curves, and we discuss how future time-dependent simulations of disk instabilities may provide new insights into the role of radiation pressure in the accretion flow. }

{Anderson} G E, {Gaensler} B M, {Slane} P O, {Rea} N, {Kaplan} D L, {Posselt} B, {Levin} L, {Johnston} S, {Murray} S S, {Brogan} C L, et al. {Multi-wavelength Observations of the Radio Magnetar PSR J1622-4950 and Discovery of Its Possibly Associated Supernova Remnant}. The Astrophysical Journal. 2012;751 :53.Abstract

{We present multi-wavelength observations of the radio magnetar PSR J1622-4950 and its environment. Observations of PSR J1622-4950 with Chandra (in 2007 and 2009) and XMM (in 2011) show that the X-ray flux of PSR J1622-4950 has decreased by a factor of \~{}50 over 3.7 years, decaying exponentially with a characteristic time of {$\tau$} = 360 {\plusmn} 11 days. This behavior identifies PSR J1622-4950 as a possible addition to the small class of transient magnetars. The X-ray decay likely indicates that PSR J1622-4950 is recovering from an X-ray outburst that occurred earlier in 2007, before the 2007 Chandra observations. Observations with the Australia Telescope Compact Array show strong radio variability, including a possible radio flaring event at least one and a half years after the 2007 X-ray outburst that may be a direct result of this X-ray event. Radio observations with the Molonglo Observatory Synthesis Telescope reveal that PSR J1622-4950 is 8' southeast of a diffuse radio arc, G333.9+0.0, which appears non-thermal in nature and which could possibly be a previously undiscovered supernova remnant (SNR). If G333.9+0.0 is an SNR then the estimates of its size and age, combined with the close proximity and reasonable implied velocity of PSR J1622-4950, suggest that these two objects could be physically associated. }

{Rahoui} F, {Coriat} M, {Corbel} S, {Cadolle Bel} M, {Tomsick} J  A, {Lee} J  C, {Rodriguez} J, {Russell} D  M, {Migliari} S. {Optical and near-infrared spectroscopy of the black hole GX 339-4 - I. A focus on the continuum in the low/hard and high/soft states}. \mnras. 2012;422 :2202-2212.Abstract

{The microquasar GX 339-4, known to exhibit powerful compact jets that dominate its radio to near-infrared emission, entered an outburst in 2010 for the fifth time in about 15 yr. An extensive radio to X-ray multiwavelength campaign was immediately triggered, and we report here on European Southern Observatory/FORS2+ISAAC optical and near-infrared spectroscopic observations, supported by Australia Telescope Compact Array radio and Rossi X-ray Timing Experiment/Swift X-ray quasi-simultaneous data. GX 339-4 was observed at three different epochs, once in the soft state and twice in the hard state. In the soft state, the optical and near-infrared continuum is largely consistent with the Raleigh-Jeans tail of a thermal process. As an explanation, we favour irradiation of the outer accretion disc by its inner regions, enhanced by disc warping. An excess is also present at low frequencies, likely due to an M subgiant companion star. During the first hard state, the optical/near-infrared continuum is well described by the optically thin synchrotron emission of the compact jet combined with disc irradiation and perhaps another component peaking in the ultraviolet. The spectral break where the jet transits from the optically thick to thin regimes, located below 1.20 {\times} 10$^{14}$ Hz, is not detected and the extension of the optically thin synchrotron is consistent with the 3-50 keV spectrum. In contrast, the emission during the second hard state is more difficult to understand and points towards a more complex jet continuum. In both cases, the near-infrared continuum is found to be variable at time-scales at least as short as 20 s, although these variabilities are smoothed out beyond a few hundred seconds. This implies rapid variations - in flux and frequency - of the location of the spectral break, i.e. dramatic short time-scale changes of the physical conditions at the base of the jet, such as the magnetic field and/or the base radius. $^{ a }$ Same as DISKBB. }

2011
{Anderson} G  E, {Gaensler} B  M, {Kaplan} D  L, {Posselt} B, {Slane} P  O, {Murray} S  S, {Mauerhan} J  C, {Benjamin} R  A, {Brogan} C  L, {Chakrabarty} D, et al. {Identification of a Population of X-ray-emitting Massive Stars in the Galactic Plane}. \apj. 2011;727 :105.Abstract

{We present X-ray, infrared, optical, and radio observations of four previously unidentified Galactic plane X-ray sources: AX J163252-4746, AX J184738-0156, AX J144701-5919, and AX J144547-5931. Detection of each source with the Chandra X-ray Observatory has provided sub-arcsecond localizations, which we use to identify bright infrared counterparts to all four objects. Infrared and optical spectroscopy of these counterparts demonstrate that all four X-ray sources are extremely massive stars, with spectral classifications: Ofpe/WN9 (AX J163252-4746), WN7 (AX J184738-0156 = WR121a), WN7-8h (AX J144701-5919), and OIf$^{+}$ (AX J144547-5931). AX J163252-4746 and AX J184738-0156 are both luminous, hard, X-ray emitters with strong Fe XXV emission lines in their X-ray spectra at \~{}6.7 keV. The multi-wavelength properties of AX J163252-4746 and AX J184738-0156 are not consistent with isolated massive stars or accretion onto a compact companion; we conclude that their X-ray emission is most likely generated in a colliding-wind binary (CWB) system. For both AX J144701-5919 and AX J144547-5931, the X-ray emission is an order of magnitude less luminous and with a softer spectrum. These properties are consistent with a CWB interpretation for these two sources also, but other mechanisms for the generation of X-rays cannot be excluded. There are many other as yet unidentified X-ray sources in the Galactic plane, with X-ray properties similar to those seen for AX J163252-4746, AX J184738-0156, AX J144701-5919, and AX J144547-5931. This may indicate a substantial population of X-ray-emitting massive stars and CWBs in the Milky Way. }

{Mocz} P, {Lee} J  C, {Iwasawa} K, {Canizares} C  R. {A Detection of an X-ray Wind and an Ionized Disk in the Chandra HETGS Observation of the Seyfert 2 Galaxy IRAS 18325-5926}. \apj. 2011;729 :30.Abstract

{We analyze the Chandra High Energy Transmission Grating Spectrometer observation of the Seyfert 2 AGN IRAS 18325-5926. We detect a v = -360$^{+41}$ $_{-66}$ km s$^{-1}$ blueshifted ionized absorber in the X-ray spectrum, with photoionization parameter log {$\xi$} = 2.0$^{+0.1}$ $_{-0.1}$ and hydrogen column density N $_{H}$ = 1.55$^{+0.75}$ $_{-0.38}$ {\times} 10$^{21}$ cm$^{-2}$. The absorber may be a photoionized wind originating in the obscuring torus/global covering around the black hole or outer edge of the accretion disk. The estimated mass outflow rate suggests that the supermassive black hole in IRAS 18325-5926 may significantly affect the large-scale environment of the host galaxy, unless the solid angle subtended by the outflow or the gas filling factor is small. A second warm absorber may be needed to explain the absorption features in the vicinity of the iron K edge, although insufficient counts in the data beyond 7.0 keV make it difficult to assess the nature of the second absorber. Most plausible is a high ionization (log {$\xi$} \~{} 2.3 to 2.6), high column density (N $_{H}$ \~{} 10$^{23}$ cm$^{-2}$) absorber with v \~{} -3000 to 0 km s$^{-1}$, although these parameters are not well constrained. We also examine the broad Fe K emission line in the spectrum, which is likely due to Fe XXV in a highly ionized accretion disk inclined at 25{\deg}, consistent with the XMM-Newton EPIC observations of the emission line. Because we are able to view both the obscuring gas and the accretion disk of IRAS 18325-5926, the surrounding gas of IRAS 18325-5926 may be patchy or we are viewing the system at an angle just grazing the obscuring torus. }

{Rahoui} F, {Lee} J  C, {Heinz} S, {Hines} D  C, {Pottschmidt} K, {Wilms} J, {Grinberg} V. {A Multiwavelength Study of Cygnus X-1: The First Mid-infrared Spectroscopic Detection of Compact Jets}. \apj. 2011;736 :63.Abstract

{We report on a Spitzer/InfraRed Spectrograph (mid-infrared), RXTE/PCA+HEXTE (X-ray), and Ryle (radio) simultaneous multiwavelength study of the microquasar Cygnus X-1, which aimed at an investigation of the origin of its mid-infrared emission. Compact jets were present in two out of three observations, and we show that they strongly contribute to the mid-infrared continuum. During the first observation, we detect the spectral break{\mdash}where the transition from the optically thick to the optically thin regime takes place{\mdash}at about 2.9 {\times} 10$^{13}$ Hz. We then show that the jet's optically thin synchrotron emission accounts for Cygnus X-1's emission beyond 400 keV, although it cannot alone explain its 3-200 keV continuum. A compact jet was also present during the second observation, but we do not detect the break, since it has likely shifted to higher frequencies. In contrast, the compact jet was absent during the last observation, and we show that the 5-30 {$μ$}m mid-infrared continuum of Cygnus X-1 stems from the blue supergiant companion star HD 226868. Indeed, the emission can then be understood as the combination of the photospheric Rayleigh-Jeans tail and the bremsstrahlung from the expanding stellar wind. Moreover, the stellar wind is found to be clumpy, with a filling factor f $_{∞}$ {\ap} 0.09-0.10. Its bremsstrahlung emission is likely anti-correlated to the soft X-ray emission, suggesting an anti-correlation between the mass-loss and mass-accretion rates. Nevertheless, we do not detect any mid-infrared spectroscopic evidence of interaction between the jets and Cygnus X-1's environment and/or the companion star's stellar wind. }

{Neilsen} J, {Remillard} R  A, {Lee} J  C. {The Physics of the ''Heartbeat'' State of GRS 1915+105}. \apj. 2011;737 :69.Abstract

{We present the first detailed phase-resolved spectral analysis of a joint Chandra High-Energy Transmission Grating Spectrometer and Rossi X-ray Timing Explorer observation of the {$\rho$} variability class in the microquasar GRS 1915+105. The {$\rho$} cycle displays a high-amplitude, double-peaked flare that recurs roughly every 50 s and is sometimes referred to as the ''heartbeat'' oscillation. The spectral and timing properties of the oscillation are consistent with the radiation pressure instability and the evolution of a local Eddington limit in the inner disk. We exploit strong variations in the X-ray continuum, iron emission lines, and the accretion disk wind to probe the accretion geometry over nearly six orders of magnitude in distance from the black hole. At small scales (1-10 R $_{g}$), we detect a burst of bremsstrahlung emission that appears to occur when a portion of the inner accretion disk evaporates due to radiation pressure. Jet activity, as inferred from the appearance of a short X-ray hard state, seems to be limited to times near minimum luminosity, with a duty cycle of \~{}10%. On larger scales (10⁵-10⁶ R $_{g}$), we use detailed photoionization arguments to track the relationship between the fast X-ray variability and the accretion disk wind. For the first time, we are able to show that changes in the broadband X-ray spectrum produce changes in the structure and density of the accretion disk wind on timescales as short as 5 s. These results clearly establish a causal link between the X-ray oscillations and the disk wind and therefore support the existence of a disk-jet-wind connection. Furthermore, our analysis shows that the mass-loss rate in the wind may be sufficient to cause long-term oscillations in the accretion rate, leading to state transitions in GRS 1915+105. }

{Brenneman} L  W, {Reynolds} C  S, {Nowak} M  A, {Reis} R  C, {Trippe} M, {Fabian} A  C, {Iwasawa} K, {Lee} J  C, {Miller} J  M, {Mushotzky} R  F, et al. {The Spin of the Supermassive Black Hole in NGC 3783}. \apj. 2011;736 :103.Abstract

{The Suzaku AGN Spin Survey is designed to determine the supermassive black hole spin in six nearby active galactic nuclei (AGNs) via deep Suzaku stares, thereby giving us our first glimpse of the local black hole spin distribution. Here, we present an analysis of the first target to be studied under the auspices of this Key Project, the Seyfert galaxy NGC 3783. Despite complexity in the spectrum arising from a multi-component warm absorber, we detect and study relativistic reflection from the inner accretion disk. Assuming that the X-ray reflection is from the surface of a flat disk around a Kerr black hole, and that no X-ray reflection occurs within the general relativistic radius of marginal stability, we determine a lower limit on the black hole spin of a {\gt}= 0.88 (99% confidence). We examine the robustness of this result to the assumption of the analysis and present a brief discussion of spin-related selection biases that might affect flux-limited samples of AGNs. }

{Xiang} J, {Lee} J  C, {Nowak} M  A, {Wilms} J. {Using the X-Ray Dust Scattering Halo of Cygnus X-1 to Determine Distance and Dust Distributions}. \apj. 2011;738 :78.Abstract

{We present a detailed study of the X-ray dust scattering halo of the black hole candidate Cygnus X-1 based on two Chandra High Energy Transmission Gratings Spectrometer observations. Using 18 different dust models, including one modified by us (eponymously dubbed XLNW), we probe the interstellar medium between us and this source. A consistent description of the cloud properties along the line of sight (LOS) that describes at the same time the halo radial profile, the halo light curves, and the column density from source spectroscopy is best achieved with a small subset of these models. Combining the studies of the halo radial profile and the halo light curves, we favor a geometric distance to Cygnus X-1 of d = 1.81 {\plusmn} 0.09 kpc. Our study also shows that there is a dense cloud, which contributes \~{}50% of the dust grains along the LOS to Cygnus X-1, located at \~{}1.6 kpc from us. The remainder of the dust along the LOS is close to the black hole binary. }