Cosmic dust plays a crucial role in the evolution of galaxies, significantly influencing star formation and the interstellar medium. However, in active galactic nuclei (AGN), the role and origin of dust remain poorly understood. High-resolution X-ray spectroscopy is a powerful tool for probing the properties of dust in AGN. NGC 6860, an X-ray bright type-1 quasar, is an ideal target for investigating the connection between dust and winds in AGN. It exhibits reddening and X-ray absorption by both dust and winds. By modeling high-resolution X-ray spectra from XMM-Newton and Chandra observations, we determine the properties of dust and outflows in this AGN. Our analysis finds four photoionized components, outflowing with velocities of 50-300 km/s. The first two are relatively highly ionized with logxi = 3.4 and logxi = 2.9. The results of our photoionization modeling suggest that these two components are thermally unstable. The third component is ionized, with logxi = 2.3 and is located further away from the central black hole. The fourth component is less ionized, and is possibly located in the host galaxy. The application of dust models enables us to probe the abundance and location of the dust in NGC 6860. Our findings suggest that dust absorption and reddening originates from the extended narrow-line region and its host galaxy.

We reanalyse the Chandra/HETGS observations of NGC 3783 from the campaign in the year 2001 and identify significant spectral variations in the Fe unresolved transition array (UTA) over timescales of weeks to months. These changes correlate with a 1.4- to two-fold increase in the ionising continuum and exceed 10 sigma significance. The variations primarily originate from a low-ionisation state (log xi = 1.65) component of the warm absorber. Time-dependent photoionisation modelling confirmed the sensitivity of this low-ionisation component to continuum variations within the Fe UTA band. Local fitting indicated a lower density limit of > 10(12.3) m(-3) at a 3 sigma statistical uncertainty, with the component located within 0.27 pc. Our findings suggest that this low-ionisation component is a potential failed wind candidate.

We present the result from the 2024 April observation of the low-mass X-ray binary GX 13+1 with the Imaging X-ray Polarimetry Explorer (IXPE), together with Neutron Star Interior Composition Explorer and Swift- X-Ray Telescope coordinated observations. Two light-curve dips were observed; during them, the harder Comptonized spectral component was dominant and the polarization degree (PD) higher than in the softer, off-dip intervals. Through a joint analysis of the three IXPE observations, which also included the dip from the first observation, we demonstrate that the polarization properties varied in response to the intensity and spectral hardness changes associated with the dips. The PD attained values up to ∼4%. The polarization angle (PA) showed a swing of ∼70 ∘ across the dip and off-dip states, comparable to the continuous rotation seen during the first IXPE observation. We discuss these results in the context of models for polarized emission from the accretion disk and the boundary/spreading layer on the neutron star surface. We also draw attention to the role that an extended accretion disk corona or disk wind can play in generating high PDs and, possibly, swings of the PA.

We observed the Seyfert 1 galaxy Mrk 817 during an intensive multiwavelength reverberation mapping campaign for 16 months. Here, we examine the behavior of narrow UV absorption lines seen in the Hubble Space Telescope/Cosmic Origins Spectrograph spectra, both during the campaign and in other epochs extending over 14 yr. We conclude that, while the narrow absorption outflow system (at -3750 km s(-1) with FWHM = 177 km s(-1)) responds to the variations of the UV continuum as modified by the X-ray obscurer, its total column density (log N-H = 19.5 (+0.61)(-0.13) cm(-2)) did not change across all epochs. The adjusted ionization parameter (scaled with respect to the variations in the hydrogen-ionizing continuum flux) is log U-H = -1.0(-0.3)(+0.1) . The outflow is located at a distance smaller than 38 pc from the central source, which implies a hydrogen density of n(H) > 3000 cm(-3). The absorption outflow system only covers the continuum emission source and not the broad emission line region, which suggests that its transverse size is small (< 10(16) cm), with potential cloud geometries ranging from spherical to elongated along the line of sight.

We present the results of the XMM-Newton and NuSTAR observations taken as part of the ongoing, intensive multiwavelength monitoring program of the Seyfert 1 galaxy Mrk 817 by the AGN Space Telescope and Optical Reverberation Mapping 2 (AGN STORM 2) Project. The campaign revealed an unexpected and transient obscuring outflow, never before seen in this source. Of our four XMM-Newton/NuSTAR epochs, one fortuitously taken during a bright X-ray state has strong narrow absorption lines in the high-resolution grating spectra. From these absorption features, we determine that the obscurer is in fact a multiphase ionized wind with an outflow velocity of similar to 5200 km s-1, and for the first time find evidence for a lower ionization component with the same velocity observed in absorption features in the contemporaneous Hubble Space Telescope spectra. This indicates that the UV absorption troughs may be due to dense clumps embedded in diffuse, higher ionization gas responsible for the X-ray absorption lines of the same velocity. We observe variability in the shape of the absorption lines on timescales of hours, placing the variable component at roughly 1000 R g if attributed to transverse motion along the line of sight. This estimate aligns with independent UV measurements of the distance to the obscurer suggesting an accretion disk wind at the inner broad line region. We estimate that it takes roughly 200 days for the outflow to travel from the disk to our line of sight, consistent with the timescale of the outflow's column density variations throughout the campaign.

Context. Ultra-fast outflows (UFOs) have been revealed in a large number of active galactic nuclei (AGN) in the past two decades. Their extreme velocities and high ionization states make them a promising candidate for AGN feedback on the evolution of the host galaxy. However, their exact underlying driving mechanism is not yet fully understood. Aims. Given that the variability of UFOs may be used to distinguish among different launching mechanisms, we aim to search for and characterize the responses of the UFO properties to the variable irradiating luminosity. Methods. We perform a high-resolution time- and flux-resolved spectroscopy of archival XMM-Newton observations on six highly accreting narrow-line Seyfert 1 (NLS1) galaxies, selected by UFO detection and sufficient exposure times. The state-of-the-art methods of the blind Gaussian line scan and photoionization model scan are used to identify UFO solutions. We search for ionized winds and investigate the structure of ionized winds and their responses to the luminosity variations. The location, density, and kinetic energy of UFOs are estimated as well. Results. The powerful photoionization model scan reveals three previously unreported UFOs in RE J1034+396, PG 1244+026 and I ZW 1 with a detection significance above 3 sigma, and two new warm absorbers (WAs) in RE J1034+396. Five out of six (83%) AGN in our sample host multi-phase ionized winds, where outflows in I ZW 1 are energy-conserved. The relatively low-ionization entrained UFOs are discovered in four (66%) AGN of our sample, supporting the shocked outflow interpretation for ionized winds in AGN. We notice that two out of seven (28%) UFOs in our sample seem to respond to the radiation field and three (43%) UFOs hint at a radiatively accelerated nature, requiring further observations. Combined with published works, we do not find any correlations between UFO responses and AGN properties except for a tentative (similar to 1.8 sigma) anti-correlation between the UFO acceleration and the Eddington ratio, to be confirmed by further observations and an enlarged sample. The kinetic energy of UFOs, mostly detected in soft X-rays, is found to have a large uncertainty. We, therefore, cannot conclude whether soft X-ray UFOs have sufficient energy to drive the AGN feedback, although they are very promising based on some reasonable assumptions. The primary UFO in I ZW 1 (detected in the hard X-ray) is the only case in our sample to possess conclusively sufficient energy to affect the host galaxy.

Weakly magnetized neutron stars in X-ray binaries show a complex phenomenology with several spectral components that can be associated with the accretion disk, the boundary, and/or a spreading layer, a corona, and a wind. Spectroscopic information alone, however, is not enough to distinguish these components. The analysis of the timing data revealed that most of the variability, and in particular, kilohertz quasi-period oscillations, are associated with the high-energy component that corresponds to the boundary and/or spreading layer. Additional information about the nature of the spectral components, and in particular, about the geometry of the emission region, can be provided by X-ray polarimetry. One of the objects of the class, a bright, persistent, and rather peculiar galactic Type I X-ray burster was observed with the Imaging X-ray Polarimetry Explorer (IXPE) and the X-ray Multi-Mirror Mission Newton ( Using the data, we obtained the best-fit values for the continuum spectral parameters and detected strong absorption lines associated with the accretion disk wind. IXPE data showed the source to be significantly polarized in the 2--8 keV energy band, with an overall polarization degree (PD) of $1.4 at a polarization angle (PA) of $-2 (errors at the 68 confidence level). During the two-day long observation, we detected rotation of the PA by about 70 with the corresponding changes in the PD from 2 to nondetectable and then up to 5. These variations in polarization properties are not accompanied by visible spectral state changes of the source. The energy-resolved polarimetric analysis showed a significant change in polarization, from being strongly dependent on energy at the beginning of the observation to being almost constant with energy in the later parts of the observation. As a possible interpretation, we suggest a constant polarization component, strong wind scattering, or a different polarization of the two main spectral components with an individually peculiar behavior. The rotation of the PA suggests a misalignment of the neutron star spin from the orbital axis.

This white paper discusses the breadth of science related to active galactic nuclei (AGN) and associated phenomena to be enabled by a mission with microcalorimeter energy resolution in the soft X-ray band, a large collecting area, and wide-field imaging. Such a mission, the Line Emission Mapper (LEM), has been proposed to NASA's 2023 Astrophysics Probe Explorer call. While the science pillars of the PI-led part of the mission focus on galaxy evolution, the PI-led LEM All-Sky Survey (LASS) and General Observer/Investigator opportunities will enable vital discoveries for AGN science in the critical soft X-ray band.

Multiwavelength spectroscopy of NGC 5548 revealed remarkable changes due to the presence of an obscuring wind from the accretion disk. This broadened our understanding of obscuration and outflows in active galactic nuclei. Swift monitoring of NGC 5548 shows that over the last 10 yr, the obscuration has gradually declined. This provides a valuable opportunity for analyses that have not been feasible before because of too much obscuration. The lowered obscuration, together with the high-energy spectral coverage of Chandra HETG, facilitates the first study of X-ray absorption lines in the obscured state. The comparison of the lines (Mg xi, Mg xii, Si xiii, and Si xiv) between the new and historical spectra reveals interesting changes, most notably the He-like absorption being significantly diminished in 2022. Our study finds that the changes are caused by an increase in both the ionization parameter and the column density of the warm-absorber outflow in the obscured state. This is contrary to the shielding scenario that is evident in the appearance of the UV lines, where the inner obscuring wind shields outflows that are farther out, thus lowering their ionization. The X-ray absorption lines in the HETG spectra appear to be unaffected by the obscuration. The results suggest that the shielding is complex because various components of the ionized outflow are affected differently. We explore various possibilities for the variability behavior of the X-ray absorption lines and find that the orbital motion of a clumpy ionized outflow traversing our line of sight is the most likely explanation.

The radiation from accreting X-ray pulsars was expected to be highly polarized, with some estimates for the polarization degree of up to 80%. However, phase-resolved and energy-resolved polarimetry of X-ray pulsars is required in order to test different models and to shed light on the emission processes and the geometry of the emission region. Here we present the first results of the observations of the accreting X-ray pulsar Vela X-1 performed with the Imaging X-ray Polarimetry Explorer. Vela X-1 is considered to be the archetypal example of a wind-accreting, high-mass X-ray binary system, consisting of a highly magnetized neutron star accreting matter from its supergiant stellar companion. The spectropolarimetric analysis of the phase-averaged data for Vela X-1 reveals a polarization degree (PD) of 2.3% ± 0.4% at the polarization angle (PA) of −47.°3 ± 5.°4. A low PD is consistent with the results obtained for other X-ray pulsars and is likely related to the inverse temperature structure of the neutron star atmosphere. The energy-resolved analysis shows the PD above 5 keV reaching 6%–10% and a ∼90° difference in the PA compared to the data in the 2–3 keV range. The phase-resolved spectropolarimetric analysis finds a PD in the range 0%–9% with the PA varying between −80° and 40°.

We present the IXPE observation of GRB 221009A, which includes upper limits on the linear polarization degree of both prompt and afterglow emission in the soft X-ray energy band. GRB 221009A is an exceptionally bright gamma-ray burst (GRB) that reached Earth on 2022 October 9 after traveling through the dust of the Milky Way. The Imaging X-ray Polarimetry Explorer (IXPE) pointed at GRB 221009A on October 11 to observe, for the first time, the 2–8 keV X-ray polarization of a GRB afterglow. We set an upper limit to the polarization degree of the afterglow emission of 13.8% at a 99% confidence level. This result provides constraints on the jet opening angle and the viewing angle of the GRB, or alternatively, other properties of the emission region. Additionally, IXPE captured halo-rings of dust-scattered photons that are echoes of the GRB prompt emission. The 99% confidence level upper limit to the prompt polarization degree depends on the background model assumption, and it ranges between ∼55% and ∼82%. This single IXPE pointing provides both the first assessment of X-ray polarization of a GRB afterglow and the first GRB study with polarization observations of both the prompt and afterglow phases.

We present the first results from a 100-day Swift, NICER and ground-based X-ray/UV/optical reverberation mapping campaign of the Narrow-Line Seyfert 1 Mrk 335, when it was in an unprecedented low X-ray flux state. Despite dramatic suppression of the X-ray variability, we still observe UV/optical lags as expected from disk reverberation. Moreover, the UV/optical lags are consistent with archival observations when the X-ray luminosity was >10 times higher. Interestingly, both low- and high-flux states reveal UV/optical lags that are 6-11 times longer than expected from a thin disk. These long lags are often interpreted as due to contamination from the broad line region, however the u band excess lag (containing the Balmer jump from the diffuse continuum) is less prevalent than in other AGN. The Swift campaign showed a low X-ray-to-optical correlation (similar to previous campaigns), but NICER and ground-based monitoring continued for another two weeks, during which the optical rose to the highest level of the campaign, followed 10 days later by a sharp rise in X-rays. While the low X-ray countrate and relatively large systematic uncertainties in the NICER background make this measurement challenging, if the optical does lead X-rays in this flare, this indicates a departure from the zeroth-order reprocessing picture. If the optical flare is due to an increase in mass accretion rate, this occurs on much shorter than the viscous timescale. Alternatively, the optical could be responding to an intrinsic rise in X-rays that is initially hidden from our line-of-sight.

We present reverberation mapping measurements for the prominent ultraviolet broad emission lines of the active galactic nucleus Mrk 817 using 165 spectra obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. Our ultraviolet observations are accompanied by X-ray, optical, and near-infrared observations as part of the AGN Space Telescope and Optical Reverberation Mapping Program 2 (AGN STORM 2). Using the cross-correlation lag analysis method, we find significant correlated variations in the continuum and emission-line light curves. We measure rest-frame delayed responses between the far-ultraviolet continuum at 1180 Å and Ly α λ 1215 Å ( 10.4 − 1.4 + 1.6 days), N v λ 1240 Å ( 15.5 − 4.8 + 1.0 days), Si iv + ]O iv λ 1397 Å ( 8.2 − 1.4 + 1.4 days), C iv λ 1549 Å ( 11.8 − 2.8 + 3.0 days), and He ii λ 1640 Å ( 9.0 − 1.9 + 4.5 days) using segments of the emission-line profile that are unaffected by absorption and blending, which results in sampling different velocity ranges for each line. However, we find that the emission-line responses to continuum variations are more complex than a simple smoothed, shifted, and scaled version of the continuum light curve. We also measure velocity-resolved lags for the Ly α and C iv emission lines. The lag profile in the blue wing of Ly α is consistent with virial motion, with longer lags dominating at lower velocities, and shorter lags at higher velocities. The C iv lag profile shows the signature of a thick rotating disk, with the shortest lags in the wings, local peaks at ±1500 km s −1 , and a local minimum at the line center. The other emission lines are dominated by broad absorption lines and blending with adjacent emission lines. These require detailed models, and will be presented in future work.

The AGN STORM 2 campaign is a large, multiwavelength reverberation mapping project designed to trace out the structure of Mrk 817 from the inner accretion disk to the broad emission line region and out to the dusty torus. As part of this campaign, Swift performed daily monitoring of Mrk 817 for approximately 15 months, obtaining observations in X-rays and six UV/optical filters. The X-ray monitoring shows that Mrk 817 was in a significantly fainter state than in previous observations, with only a brief flare where it reached prior flux levels. The X-ray spectrum is heavily obscured. The UV/optical light curves show significant variability throughout the campaign and are well correlated with one another, but uncorrelated with the X-rays. Combining the Swift UV/optical light curves with Hubble Space Telescope UV continuum light curves, we measure interband continuum lags, τ ( λ ), that increase with increasing wavelength roughly following τ ( λ ) ∝ λ 4/3 , the dependence expected for a geometrically thin, optically thick, centrally illuminated disk. Modeling of the light curves reveals a period at the beginning of the campaign where the response of the continuum is suppressed compared to later in the light curve—the light curves are not simple shifted and scaled versions of each other. The interval of suppressed response corresponds to a period of high UV line and X-ray absorption, and reduced emission line variability amplitudes. We suggest that this indicates a significant contribution to the continuum from the broad-line region gas that sees an absorbed ionizing continuum.

We present an investigation into the spectroscopic properties of non-equilibrium photoionization processes operating in a time-evolving mode. Through a quantitative comparison between equilibrium and time-evolving models, we find that the time-evolving model exhibits a broader distribution of charge states compared to the equilibrium model, accompanied by a slight shift in the peak ionization state depending on the source variability and gas density. The time-evolving code, tpho in SPEX, has been successfully employed to analyze the spectral properties of warm absorbers in the Seyfert galaxy NGC 3783. The incorporation of variability in the tpho model improves the fits of the time-integrated spectra, providing more accurate descriptions to the average charge states of several elements, in particular for Fe which is peaked around Fe XIX. The inferred densities and distances of the relevant X-ray absorber components are estimated to be approximately a few 1E11 per cubic meter and less than 1 pc, respectively. Furthermore, the updated fit suggests a potential scenario in which the observed absorbers are being expelled from the central AGN at the escape velocities. This implies that these absorbers might not play a significant role in the AGN feedback mechanism.

Ultra-fast outflows (UFOs) have been revealed in a large number of active galactic nuclei (AGN) and are regarded as promising candidates for AGN feedback on the host galaxy. The nature and launching mechanism of UFOs are not yet fully understood. Here we perform a time- and flux-resolved X-ray spectroscopy on four XMM-Newton observations of a highly accreting narrow-line Seyfert 1 (NLS1) galaxy, Mrk 1044, to study the dependence of the outflow properties on the source luminosity. We find that the UFO in Mrk 1044 responds to the source variability quickly and its velocity increases with the X-ray flux, suggesting a high-density ($10^{9}-4.5\times10^{12}\,\mathrm{cm}^{-3}$) and radiatively driven outflow, launched from the region within a distance of $98-6600\, R_\mathrm{g}$ from the black hole. The kinetic energy of the UFO is conservatively estimated ($L_\mathrm{UFO}\sim4.4\%L_\mathrm{Edd}$), reaching the theoretical criterion to affect the evolution of the host galaxy. We also find emission lines, from a large-scale region, have a blueshift of $2700-4500$ km/s in the spectra of Mrk 1044, which is rarely observed in AGN. By comparing with other sources, we propose a correlation between the blueshift of emission lines and the source accretion rate, which can be verified by a future sample study.

The AGN STORM 2 Collaboration targeted the Seyfert 1 galaxy Mrk 817 for a year-long multiwavelength, coordinated reverberation mapping campaign including Hubble Space Telescope, Swift, XMM-Newton, NICER, and ground-based observatories. Early observations with NICER and XMM revealed an X-ray state 10 times fainter than historical observations, consistent with the presence of a new dust-free, ionized obscurer. The following analysis of NICER spectra attributes variability in the observed X-ray flux to changes in both the column density of the obscurer by at least one order of magnitude ( N H ranges from 2.85 − 0.33 + 0.48 × 10 22 cm − 2 to 25.6 − 3.5 + 3.0 × 10 22 cm − 2 ) and the intrinsic continuum brightness (the unobscured flux ranges from 10 −11.8 to 10 −10.5 erg s −1 cm −2 ). While the X-ray flux generally remains in a faint state, there is one large flare during which Mrk 817 returns to its historical mean flux. The obscuring gas is still present at lower column density during the flare, but it also becomes highly ionized, increasing its transparency. Correlation between the column density of the X-ray obscurer and the strength of UV broad absorption lines suggests that the X-ray and UV continua are both affected by the same obscuration, consistent with a clumpy disk wind launched from the inner broad-line region.

Outflows in active galactic nuclei (AGN) are considered a promising candidate for driving AGN feedback at large scales. However, without information on the density of these outflows, we cannot determine how much kinetic power they are imparting to the surrounding medium. Monitoring the response of the ionisation state of the absorbing outflows to changes in the ionising continuum provides the recombination timescale of the outflow, which is a function of the electron density. We have developed a new self-consistent time-dependent photoionisation model, TPHO, enabling the measurement of the plasma density through time-resolved X-ray spectroscopy. The algorithm solves the full-time-dependent energy and ionisation balance equations in a self-consistent fashion for all the ionic species. The model can therefore reproduce the time-dependent absorption spectrum of ionized outflows responding to changes in the ionizing radiation of the AGN. We find that when the ionised gas is in a non-equilibrium state its transmitted spectra are not accurately reproduced by standard photoionisation models. Our simulations with the current X-ray grating observations show that the spectral features identified as a multiple-components warm absorber, might be in fact features of a time-changing warm absorber and not distinctive components. The TPHO model facilitates accurate photoionisation modelling in the presence of a variable ionising source, thus providing constraints on the density and in turn the location of the AGN outflows. Ascertaining these two parameters will provide important insight into the role and impact of ionised outflows in AGN feedback.

Knowledge of the dust content in interstellar matter is important to our understanding of the composition and evolution of the interstellar medium. The Chandra High Energy Transmission Grating (HETG) Spectrometer provides a unique opportunity to measure X-ray absorption of interstellar dust and its compositions through the X-ray edge absorption structure. We measure gas and dust optical depths at Si K toward nine bright low-mass x-ray binaries in the Galactic Bulge with very high-precision and pileup-free spectra. We include a likely instrumental feature affecting the Si K edge structure in our analysis. While gas optical depths grow consistently with broadband hydrogen-equivalent columns, the dust optical depths do not. Calculations including dust self-shielding show that the observed dust optical depths can be explained by variations in dust grain columns between various lines of sight. At least three grain column regimes can be identified toward the Galactic Bulge. While grain sizes define the self-shielding effect, variations in grain size distributions do not seem relevant. This shows that the gas-to-dust optical depth ratio toward sources in the Galactic Bulge is not homogeneous. The dust optical depths also roughly correlate with molecular hydrogen columns. Lowly ionized Si K contributions toward the Galactic Bulge were detected but are very small. We also find Si xiii absorption with velocity widths of 800–1100 km s −1 , which we attribute to the circumbinary medium.

We present measurements of the polarization of X-rays in the 2-8 keV band from the pulsar in the ultracompact low-mass X-ray binary 4U 1626-67 using data from the Imaging X-Ray Polarimetry Explorer (IXPE). The 7.66 s pulsations were clearly detected throughout the IXPE observations as well as in the NICER soft X-ray observations, which we used as the basis for our timing analysis and to constrain the spectral shape over the 0.4-10 keV energy band. Chandra HETGS high-resolution X-ray spectra were also obtained near the times of the IXPE observations for firm spectral modeling. We found an upper limit on the pulse-averaged linear polarization of <4% (at 95% confidence). Similarly, there was no significant detection of polarized flux in pulse phase intervals when subdividing the bandpass by energy. However, spectropolarimetric modeling over the full bandpass in pulse phase intervals provided a marginal detection of polarization of the power-law spectral component at the 4.8% +/- 2.3% level (90% confidence). We discuss the implications concerning the accretion geometry onto the pulsar, favoring two-component models of the pulsed emission.