CV & Publications

2013
Chakravorty S, Lee JC, Neilsen J. The effects of thermodynamic stability on wind properties in different low mass black hole binary states. MNRAS [Internet]. 2013;436 :560-569. Weblink: ADSAbstract
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. Accepted for publication to MNRAS 2013 January 8. Received 2013 January 7; in original form 2012 August 20. 31 MNRAS pages [Internet]. 2013. Publisher's VersionAbstract

We present results from a coordinated IR-to-X-ray spectral campaign of the QSO IRAS 13349+2438. Optical spectra reveal extreme Eigenvector-1 characteristics, but the H-beta line width argues against a NLS1 classification; we refine z=0.10853 based on [O III]. We estimate a BH mass=10^9 Msun using 2 independent methods (H-beta line width & SED fits). Blue-shifted absorption (-950km/s & -75km/s) is seen for the 1st time in STIS UV spectra from Ly-alpha, NV, & CIV. The higher velocity UV lines are coincident with the lower-ionisation (xi~1.6) X-ray warm absorber lines. A dusty multiple ionization absorber blueshifted by 700-900km/s is required to fit the X-ray data. Theoretical models comparing different ionising SEDs reveal that a UV-inclusive (i.e., the accretion disc) ionising continuum strongly impacts conclusions for the thermodynamic stability of the warm absorber. Specific to IRAS13349, an Xray-UV ionising SED favors a continuous distribution of ionisation states in a smooth flow (this paper), versus discrete clouds in pressure equilibrium (work by others where UV is omitted). Direct dust detections are seen in both the IR: PAH emission at (7.7 & 11.3)micron which may also be blended with forsterite, and (10 & 18)micron silicate emission, and X-rays: iron dust with a dust-to-gas ratio > 90%. We develop a geometrical model whereby the QSO nuclear region is viewed through the upper atmosphere of an obscuring torus. This sight line is obscured by dust that blocks a direct view of the UV/optical emission region but is largely transparent in X-rays since the gas is ionised. In our model, 20% of the intrinsic UV/optical continuum is scattered into our sight line by the far wall of an obscuring torus. An additional 2.4% 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}. \apj. 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. }

{Evans} D  A, {Summers} A  C, {Hardcastle} M  J, {Kraft} R  P, {Gandhi} P, {Croston} J  H, {Lee} J  C. {The Suzaku View of the Disk-Jet Connection in the Low-excitation Radio Galaxy NGC 6251}. \apjl. 2011;741 :L4.Abstract

{We present results from an 87 ks Suzaku observation of the canonical low-excitation radio galaxy (LERG) NGC 6251. We have previously suggested that LERGs violate conventional active galactic nucleus unification schemes: they may lack an obscuring torus and are likely to accrete in a radiatively inefficient manner, with almost all of the energy released by the accretion process being channeled into powerful jets. We model the 0.5-20 keV Suzaku spectrum with a single power law of photon index {$\Gamma$} = 1.82$^{+0.04}$ $_{- 0.05}$, together with two collisionally ionized plasma models whose parameters are consistent with the known galaxy- and group-scale thermal emission. Our observations confirm that there are no signatures of obscured, accretion-related X-ray emission in NGC 6251, and we show that the luminosity of any such component must be substantially sub-Eddington in nature. }

{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. }

2010
{Lal} D  V, {Kraft} R  P, {Forman} W  R, {Hardcastle} M  J, {Jones} C, {Nulsen} P  E  J, {Evans} D  A, {Croston} J  H, {Lee} J  C. {A Chandra Observation of 3C 288{\mdash}Reheating the Cool Core of a 3 keV Cluster from a Nuclear Outburst at z = 0.246}. \apj. 2010;722 :1735-1743.Abstract

{We present results from a 42 ks Chandra/ACIS-S observation of the transitional FR I/FR II radio galaxy 3C 288 at z = 0.246. We detect \~{}3 keV gas extending to a radius of \~{}0.5 Mpc with a 0.5-2.0 keV luminosity of 6.6 {\times} 10$^{43}$ erg s$^{-1}$, implying that 3C 288 lies at the center of a poor cluster. We find multiple surface brightness discontinuities in the gas indicative of either a shock driven by the inflation of the radio lobes or a recent merger event. The temperature across the discontinuities is roughly constant with no signature of a cool core, thus disfavoring either the merger cold front or sloshing scenarios. We argue therefore that the discontinuities are shocks due to the supersonic inflation of the radio lobes. If they are shocks, the energy of the outburst is \~{}10$^{60}$ erg, or roughly 30% of the thermal energy of the gas within the radius of the shock, assuming that the shocks are part of a front produced by a single outburst. The cooling time of the gas is \~{}10⁸ yr, so that the energy deposited by the nuclear outburst could have reheated and efficiently disrupted a cool core. }

{Evans} D  A, {Reeves} J  N, {Hardcastle} M  J, {Kraft} R  P, {Lee} J  C, {Virani} S  N. {The Hard X-ray View of Reflection, Absorption, and the Disk-Jet Connection in the Radio-loud AGN 3C 33}. \apj. 2010;710 :859-868.Abstract

{We present results from Suzaku and Swift observations of the nearby radio galaxy 3C 33, and investigate the nature of absorption, reflection, and jet production in this source. We model the 0.5-100 keV nuclear continuum with a power law that is transmitted either through one or more layers of pc-scale neutral material, or through a modestly ionized pc-scale obscurer. The standard signatures of reflection from a neutral accretion disk are absent in 3C 33: there is no evidence of a relativistically blurred Fe K{$\alpha$} emission line, and no Compton reflection hump above 10 keV. We find the upper limit to the neutral reflection fraction is R łt} 0.41 for an e-folding energy of 1 GeV. We observe a narrow, neutral Fe K{$\alpha$} line, which is likely to originate at least 2000 R $_{s}$ from the black hole. We show that the weakness of reflection features in 3C 33 is consistent with two interpretations: either the inner accretion flow is highly ionized, or the black-hole spin configuration is retrograde with respect to the accreting material. }

{Lee} J  C. {X-ray Spectroscopy of Astrophysical Dust. A High Spectral Resolution (Re)View and Look to the Future}. 2010;157 :93-101.Abstract

{High spectral resolution X-ray instruments on powerful X-ray satellites (e.g. Chandra, XMM-Newton) pointed through dust and gas at bright black holes and neutron stars can be used to study dust and intervening material in unique ways. With the new subfield of Condensed Matter Astrophysics as its goal, I will discuss current efforts to combine techniques and knowledge from condensed matter physics and astrophysics to determine the species-specific quantity and composition of interstellar gas and dust in the ISM and ionized environments. Prospects for improving on this work in future X-ray missions with higher throughput and spectral resolution are also presented in the context of spectral resolution goals for gratings and calorimeters. }

{Lee} J  C. {X-ray Spectroscopy of Astrophysical Dust. A High Spectral Resolution (Re)View and Look to the Future}. 2010;157 :93-101.Abstract

{High spectral resolution X-ray instruments on powerful X-ray satellites (e.g. Chandra, XMM-Newton) pointed through dust and gas at bright black holes and neutron stars can be used to study dust and intervening material in unique ways. With the new subfield of Condensed Matter Astrophysics as its goal, I will discuss current efforts to combine techniques and knowledge from condensed matter physics and astrophysics to determine the species-specific quantity and composition of interstellar gas and dust in the ISM and ionized environments. Prospects for improving on this work in future X-ray missions with higher throughput and spectral resolution are also presented in the context of spectral resolution goals for gratings and calorimeters. }

2009
{Hanke} M, {Wilms} J, {Nowak} M  A, {Pottschmidt} K, {Schulz} N  S, {Lee} J  C. {Chandra X-Ray Spectroscopy of the Focused Wind in the Cygnus X-1 System. I. The Nondip Spectrum in the Low/Hard State}. \apj. 2009;690 :330-346.Abstract

{We present analyses of a 50 ks observation of the supergiant X-ray binary system Cygnus X-1 (Cyg X-1)/HDE226868 taken with the Chandra High Energy Transmission Grating Spectrometer (HETGS). Cyg X-1 was in its spectrally hard state and the observation was performed during superior conjunction of the black hole, allowing for the spectroscopic analysis of the accreted stellar wind along the line of sight. A significant part of the observation covers X-ray dips as commonly observed for Cyg X-1 at this orbital phase, however, here we analyze only the high count rate nondip spectrum. The full 0.5-10 keV continuum can be described by a single model consisting of a disk, a narrow and a relativistically broadened Fe K{$\alpha$} line, and a power-law component, which is consistent with simultaneous Rossi X-Ray Timing Explorer broadband data. We detect absorption edges from overabundant neutral O, Ne, and Fe, and absorption line series from highly ionized ions and infer column densities and Doppler shifts. With emission lines of He-like Mg XI, we detect two plasma components with velocities and densities consistent with the base of the spherical wind and a focused wind. A simple simulation of the photoionization zone suggests that large parts of the spherical wind outside of the focused stream are completely ionized, which is consistent with the low velocities (łt}200 km s$^{-1}$) observed in the absorption lines, as the position of absorbers in a spherical wind at low projected velocity is well constrained. Our observations provide input for models that couple the wind activity of HDE 226868 to the properties of the accretion flow onto the black hole. }

{Neilsen} J, {Lee} J  C. {Accretion disk winds as the jet suppression mechanism in the microquasar GRS 1915+105}. \nat. 2009;458 :481-484.Abstract

{Stellar-mass black holes with relativistic jets, also known as microquasars, mimic the behaviour of quasars and active galactic nuclei. Because timescales around stellar-mass black holes are orders of magnitude smaller than those around more distant supermassive black holes, microquasars are ideal nearby `laboratories' for studying the evolution of accretion disks and jet formation in black-hole systems. Whereas studies of black holes have revealed a complex array of accretion activity, the mechanisms that trigger and suppress jet formation remain a mystery. Here we report the presence of a broad emission line in the faint, hard states and narrow absorption lines in the bright, soft states of the microquasar GRS 1915+105. (`Hard' and `soft' denote the character of the emitted X-rays.) Because the hard states exhibit prominent radio jets, we argue that the broad emission line arises when the jet illuminates the inner accretion disk. The jet is weak or absent during the soft states, and we show that the absorption lines originate when the powerful radiation field around the black hole drives a hot wind off the accretion disk. Our analysis shows that this wind carries enough mass away from the disk to halt the flow of matter into the radio jet. }

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