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Ever since the discovery of the first active galactic nuclei (AGN), substantial observational and theoretical effort has been invested into understanding how massive black holes have evolved across cosmic time. Circum-nuclear obscuration is now established as a crucial component, with almost every AGN observed known to display signatures of some level of obscuration in their X-ray spectra. However, despite more than six decades of effort, substantial open questions remain: how does the accretion power impact the structure of the circum-nuclear obscurer? What are the dynamical properties of the obscurer? Can dense circum-nuclear obscuration exist around intrinsically weak AGN? How many intermediate mass black holes occupy the centers of dwarf galaxies? In this paper, we showcase a number of next-generation prospects attainable with the High-Energy X-ray Probe (HEX-P1) to contribute toward solving these questions in the 2030s. The uniquely broad (0.2–80 keV) and strictly simultaneous X-ray passband of HEX-P makes it ideally suited for studying the temporal co-evolution between the central engine and circum-nuclear obscurer. Improved sensitivities and reduced background will enable the development of spectroscopic models complemented by current and future multi-wavelength observations. We show that the angular resolution of HEX-P both below and above 10 keV will enable the discovery and confirmation of accreting massive black holes at both low accretion power and low black hole masses even when concealed by thick obscuration. In combination with other next-generation observations of the dusty hearts of nearby galaxies, HEX-P will be pivotal in paving the way toward a complete picture of black hole growth and galaxy co-evolution.

Since the discovery of the cosmic X-ray background (CXB), astronomers have strived to understand the accreting supermassive black holes (SMBHs) contributing to its peak in the 10–40 keV band. Existing soft X-ray telescopes could study this population up to only 10 keV, and, while NuSTAR (focusing on 3–24 keV) made great progress, it also left significant uncertainties in characterizing the hard X-ray population, crucial for calibrating current population synthesis models. This paper presents an in-depth analysis of simulations of two extragalactic surveys (deep and wide) with the High-Energy X-ray Probe (HEX-P), each observed for 2 Ms. Applying established source detection techniques, we show that HEX-P surveys will reach a flux of ∼10−15 erg s−1 cm−2 in the 10–40 keV band, an order of magnitude fainter than current NuSTAR surveys. With the large sample of new hard X-ray detected sources (∼2000), we showcase HEX-P’s ability to resolve more than 80% of the CXB up to 40 keV into individual sources. The expected precision of HEX-P’s resolved background measurement will allow us to distinguish between population synthesis models of SMBH growth. HEX-P will leverage accurate broadband (0.5–40 keV) spectral analysis and the combination of soft and hard X-ray colors to provide obscuration constraints even for the fainter sources, with the overall objective of measuring the Compton-thick fraction. With unprecedented sensitivity in the 10–40 keV band, HEX-P will explore the hard X-ray emission from AGN to flux limits never reached before, thus expanding the parameter space for serendipitous discoveries. Consequently, it is plausible that new models will be needed to capture the population HEX-P will unveil.

Mrk 817 is a bright and variable Seyfert 1.2 active galactic nucleus (AGN). X-ray monitoring of Mrk 817 with the Neil Gehrels Swift Observatory in 2022 revealed that the source flux had declined to a lower level than recorded at any prior point in the then 19 yr mission. We present an analysis of deep XMM-Newton and NuSTAR observations obtained in this low flux state. The spectra reveal a complex X-ray wind consisting of neutral and ionized absorption zones. Three separate velocity components are detected as part of a structured ultrafast outflow (UFO), with $v/c={0.043}_{-0.003}^{+0.007}$ , $v/c={0.079}_{-0.0008}^{+0.003}$ , and $v/c={0.074}_{-0.005}^{+0.004}$ . These projected velocities suggest that the wind likely arises at radii that are much smaller than the optical broad-line region. In order for each component of the outflow to contribute significant feedback, the volume filling factors must be greater than f ≃ 0.009, f ≃ 0.003, and f ≃ 0.3, respectively. For plausible, data-driven volume filling factors, these limits are passed, and the total outflow likely delivers the fierce feedback required to reshape its host environment, despite a modest radiative Eddington fraction of λ ≃ 0.008–0.016 (this range reflects plausible masses). UFOs are often detected at or above the Eddington limit; this result signals that black hole accretion has the potential to shape host galaxies even at modest Eddington fractions and over a larger fraction of a typical AGN lifetime. We discuss our findings in terms of models for disk winds and black hole feedback in this and other AGN.

We present a velocity-resolved reverberation mapping analysis of the hypervariable quasar RM160 (SDSS J141041.25+531849.0) at z = 0.359 with 153 spectroscopic epochs of data representing a 10 yr baseline (2013–2023). We split the baseline into two regimes based on the 3× flux increase in the light curve: a “low state” phase during the years 2013–2019 and a “high state” phase during the years 2022–2023. The velocity-resolved lag profiles (VRLPs) indicate that gas with different kinematics dominates the line emission in different states. The H β VRLP begins with a signature of inflow onto the broad-line region (BLR) in the low state, while in the high state it is flatter with less signature of inflow. The H α VRLP begins consistent with a virialized BLR in the low state, while in the high state shows a signature of inflow. The differences in the kinematics between the Balmer lines and between the low state and the high state suggests complex BLR dynamics. We find that the BLR radius and velocity (both FWHM and σ ) do not obey a constant virial product throughout the monitoring period. We find that the BLR lags and continuum luminosity are correlated, consistent with rapid response of the BLR gas to the illuminating continuum. The BLR kinematic profile changes in unpredictable ways that are not related to continuum changes and reverberation lag. Our observations indicate that nonvirial kinematics can significantly contribute to observed line profiles, suggesting caution for black hole mass estimation in luminous and highly varying quasars like RM160.

The structure of the jet in Cen A is likely better revealed in X-rays than in the radio band, which is usually used to investigate jet proper motions. In this paper, we analyze Chandra Advanced CCD Imaging Spectrometer observations of Cen A from 2000 to 2022 and develop an algorithm for systematically fitting the proper motions of its X-ray jet knots. Most of the knots had an apparent proper motion below the detection limit. However, one knot at a transverse distance of 520 pc had an apparent superluminal proper motion of 2.7 ± 0.4 c . This constrains the inclination of the jet to be i < 41° ± 6° and the velocity of this knot to be β > 0.94 ± 0.02. This agrees well with the inclination measured in the inner jet by the Event Horizon Telescope but contradicts previous estimates based on jet and counterjet brightness. It also disagrees with the proper motion of the corresponding radio knot, of 0.8 ± 0.1 c , which further indicates that the X-ray and radio bands trace distinct structures in the jet. There are four prominent X-ray jet knots closer to the nucleus, but only one of these is inconsistent with being stationary. A few jet knots also have a significant proper-motion component in the nonradial direction. This component is typically larger closer to the center of the jet. We also detect brightness and morphology variations at a transverse distance of 100 pc from the nucleus.

High-quality Extragalactic Legacy-field Monitoring (HELM) is a long-term observing program that photometrically monitors several well-studied extragalactic legacy fields with the Dark Energy Camera (DECam) imager on the CTIO 4 m Blanco telescope. Since 2019 February, HELM has been monitoring regions within COSMOS, XMM-LSS, CDF-S, S-CVZ, ELAIS-S1, and SDSS Stripe 82 with few-day cadences in the ( u ) gri ( z ) bands, over a collective sky area of ∼38 deg ^2 . The main science goal of HELM is to provide high-quality optical light curves for a large sample of active galactic nuclei (AGNs), and to build decades-long time baselines when combining past and future optical light curves in these legacy fields. These optical images and light curves will facilitate the measurements of AGN reverberation mapping lags, as well as studies of AGN variability and its dependencies on accretion properties. In addition, the time-resolved and coadded DECam photometry will enable a broad range of science applications from galaxy evolution to time-domain science. We describe the design and implementation of the program and present the first data release that includes source catalogs and the first ∼3.5 yr of light curves during 2019A–2022A.

The supermassive black holes ( M _BH ∼ 10 ^6 –10 ^10 M _⊙ ) that power luminous active galactic nuclei (AGNs), i.e., quasars, generally show a correlation between thermal disk emission in the ultraviolet (UV) and coronal emission in hard X-rays. In contrast, some “massive” black holes (mBHs; M _BH ∼ 10 ^5 –10 ^6 M _⊙ ) in low-mass galaxies present curious X-ray properties with coronal radiative output up to 100× weaker than expected. To examine this issue, we present a pilot study incorporating Very Large Array radio observations of a sample of 18 high-accretion-rate (Eddington ratios L _bol / L _Edd > 0.1), mBH-powered AGNs ( M _BH ∼ 10 ^6 M _⊙ ) with Chandra X-ray coverage. Empirical correlations previously revealed in samples of radio-quiet, high-Eddington AGNs indicate that the radio–X-ray luminosity ratio, L _R / L _X , is approximately constant. Through multiwavelength analysis, we instead find that the X-ray-weaker mBHs in our sample tend toward larger values of L _R / L _X even though they remain radio-quiet per their optical–UV properties. This trend results in a tentative but highly intriguing correlation between L _R / L _X and X-ray weakness, which we argue is consistent with a scenario in which X-rays may be preferentially obscured from our line of sight by a “slim” accretion disk. We compare this observation to weak emission-line quasars (AGNs with exceptionally weak broad-line emission and a significant X-ray-weak fraction) and conclude by suggesting that our results may offer a new observational signature for finding high-accretion-rate AGNs.

We present a focused X-ray and multiwavelength study of the ultraluminous weak-line quasar (WLQ) SDSS J1521+5202, one of the few X-ray weak WLQs that is amenable to basic X-ray spectral and variability investigations. J1521+5202 shows striking X-ray variability during 2006–2023, by up to a factor of ≈32 in 0.5–2 keV flux, and our new 2023 Chandra observation caught it in its brightest X-ray flux state to date. Concurrent infrared/optical observations show only mild variability. The 2023 Chandra spectrum can be acceptably described by a power law with intrinsic X-ray absorption, and it reveals a nominal intrinsic level of X-ray emission relative to its optical/ultraviolet emission. In contrast, an earlier Chandra spectrum from 2013 shows apparent spectral complexity that is not well fit by a variety of models, including ionized absorption or standard Compton-reflection models. Overall, the observations are consistent with the thick-disk plus outflow model previously advanced for WLQs, where a nominal level of underlying X-ray emission plus variable absorption leads to the remarkable observed X-ray variability. In the case of J1521+5202, it appears likely that the outflow, and not the thick disk itself, lies along our line of sight and causes the X-ray absorption.

We present near-infrared spectroscopy of 10 weak emission-line quasars (WLQs) at redshifts of z ∼ 2, obtained with the Palomar 200 inch Hale Telescope. WLQs are an exceptional population of type 1 quasars that exhibit weak or no broad emission lines in the ultraviolet (e.g., the C iv λ 1549 line), and they display remarkable X-ray properties. We derive H β -based single-epoch virial black hole masses (median value 1.7 × 10 ^9 M _⊙ ) and Eddington ratios (median value 0.5) for our sources. We confirm the previous finding that WLQ H β lines, as a major low-ionization line, are not significantly weak compared to typical quasars. The most prominent feature of the WLQ optical spectra is the universally weak/absent [O iii ] λ 5007 emission. They also display stronger optical Fe ii emission than typical quasars. Our results favor the super-Eddington accretion scenario for WLQs, where the weak lines are a result of a soft ionizing continuum; the geometrically thick inner accretion disk and/or its associated outflow is responsible for obscuring the nuclear high-energy radiation and producing the soft ionizing continuum. We also report candidate extreme [O iii ] outflows (blueshifts of ≈500 and 4900 km s ^−1 ) in one object.

We present a catalog of hard X-ray serendipitous sources detected in the first 80 months of observations by the Nuclear Spectroscopic Telescope Array (NuSTAR). The NuSTAR serendipitous survey 80 month (NSS80) catalog has an unprecedented ∼62 Ms of effective exposure time over 894 unique fields (a factor of 3 increase over the 40 month catalog, NSS40), with an areal coverage of ∼36 deg ^2 , larger than all NuSTAR extragalactic surveys. NSS80 provides 1274 hard X-ray sources in the 3−24 keV band (822 new detections compared to the previous NSS40). Approximately 76% of the NuSTAR sources have lower-energy (

We present the rest-frame ultraviolet−optical spectral properties of 65 broad absorption line (BAL) quasars from the Gemini Near Infrared Spectrograph−Distant Quasar Survey (GNIRS-DQS). These properties are compared with those of 195 non-BAL quasars from GNIRS-DQS in order to identify the drivers for the appearance of BALs in quasar spectra. In particular, we compare equivalent widths and velocity widths, as well as velocity offsets from systemic redshifts, of principal emission lines. In spite of the differences between their rest-frame ultraviolet spectra, we find that luminous BAL quasars are generally indistinguishable from their non-BAL counterparts in the rest-frame optical band at redshifts 1.55 ≲ z ≲ 3.50. We do not find any correlation between BAL trough properties and the H β -based supermassive black hole masses and normalized accretion rates in our sample. Considering the Sloan Digital Sky Survey quasar sample, which includes the GNIRS-DQS sample, we find that a monochromatic luminosity at rest-frame 2500 Å of ≳10 ^45 erg s ^−1 is a necessary condition for launching BAL outflows in quasars. We compare our findings with other BAL quasar samples and discuss the roles that accretion rate and orientation play in the appearance of BAL troughs in quasar spectra.

We present the results of an investigation of a highly variable C iv broad absorption line (BAL) feature in spectra of the quasar SBS 1408+544 ( z = 2.337) that shows a significant shift in velocity over time. This source was observed as a part of the Sloan Digital Sky Survey (SDSS) Reverberation Mapping project and the SDSS-V Black Hole Mapper Reverberation Mapping project, and has been included in two previous studies, both of which identified significant variability in a high-velocity C iv BAL on timescales of just a few days in the quasar rest frame. Using ∼130 spectra acquired over 8 yr of spectroscopic monitoring with SDSS, we have determined that this BAL is not only varying in strength, but is also systematically shifting to higher velocities. Using cross-correlation methods, we measure the velocity shifts (and corresponding acceleration) of the BAL over a wide range of timescales, measuring an overall velocity shift of ${\rm{\Delta }}v=-{683}_{-84}^{+89}$ km s ^−1 over the 8 yr monitoring period. This corresponds to an average rest-frame acceleration of a = 1.04 ${}_{-0.13}^{+0.14}$ cm s ^−2 , though the magnitude of the acceleration on shorter timescales is not constant throughout. We place our measurements in the context of BAL-acceleration models and examine various possible causes of the observed velocity shift.

We present the final data from the Sloan Digital Sky Survey (SDSS) Reverberation Mapping (RM) project, a precursor to the SDSS-V Black Hole Mapper RM program. This data set includes 11 yr photometric and 7 yr spectroscopic light curves for 849 broad-line quasars over a redshift range of 0.1 < z < 4.5 and a luminosity range of L _bol = 10 ^44−47.5 erg s ^−1 , along with spectral and variability measurements. We report 23, 81, 125, and 110 RM lags (relative to optical continuum variability) for broad H α , H β , Mg ii , and C iv using the SDSS-RM sample, spanning much of the luminosity and redshift ranges of the sample. Using 30 low-redshift RM active galactic nuclei with dynamical-modeling black hole masses, we derive a new estimate of the average virial factor of $\left\langle \mathrm{log}f\right\rangle =0.62\pm 0.07$ for the line dispersion measured from the rms spectrum. The intrinsic scatter of individual virial factors is 0.31 ± 0.07 dex, indicating a factor of 2 systematic uncertainty in RM black hole masses. Our lag measurements reveal significant R – L relations for H β and Mg ii at high redshift, consistent with the latest measurements based on heterogeneous samples. While we are unable to robustly constrain the slope of the R – L relation for C iv given the limited dynamic range in luminosity, we found substantially larger scatter in C iv lags at fixed L _1350 . Using the SDSS-RM lag sample, we derive improved single-epoch (SE) mass recipes for H β , Mg ii , and C iv , which are consistent with their respective RM masses as well as between the SE recipes from two different lines, over the luminosity range probed by our sample. The new H β and Mg ii recipes are approximately unbiased estimators at given RM masses, but there are systematic biases in the C iv recipe. The intrinsic scatter of SE masses around RM masses is ∼0.45 dex for H β and Mg ii , increasing to ∼0.58 dex for C iv .

“Changing-look” active galactic nuclei (CL-AGNs) challenge our basic ideas about the physics of accretion flows and circumnuclear gas around supermassive black holes. Using first-year Sloan Digital Sky Survey V (SDSS-V) repeated spectroscopy of nearly 29,000 previously known active galactic nuclei (AGNs), combined with dedicated follow-up spectroscopy, and publicly available optical light curves, we have identified 116 CL-AGNs where (at least) one broad emission line has essentially (dis-)appeared, as well as 88 other extremely variable systems. Our CL-AGN sample, with 107 newly identified cases, is the largest reported to date, and includes ∼0.4% of the AGNs reobserved in first-year SDSS-V operations. Among our CL-AGNs, 67% exhibit dimming while 33% exhibit brightening. Our sample probes extreme AGN spectral variability on months to decades timescales, including some cases of recurring transitions on surprisingly short timescales (≲2 months in the rest frame). We find that CL events are preferentially found in lower-Eddington-ratio ( f _Edd ) systems: Our CL-AGNs have a f _Edd distribution that significantly differs from that of a carefully constructed, redshift- and luminosity-matched control sample (Anderson–Darling test yielding p _AD ≈ 6 × 10 ^−5 ; median f _Edd ≈ 0.025 versus 0.043). This preference for low f _Edd strengthens previous findings of higher CL-AGN incidence at lower f _Edd , found in smaller samples. Finally, we show that the broad Mg ii emission line in our CL-AGN sample tends to vary significantly less than the broad H β emission line. Our large CL-AGN sample demonstrates the advantages and challenges in using multi-epoch spectroscopy from large surveys to study extreme AGN variability and physics.

We report on a study of the narrow Fe K α line and reflection spectrum in the well-known Seyfert-2 active galactic nucleus (AGN), NGC 4388. X-ray spectra summed from two extensive NICER monitoring campaigns, separated by years, show strong evidence of variation in the direct continuum and reflected emission, but only small variations in the obscuring gas. Fits to the spectra from individual NICER observations find a strong, positive correlation between the power-law photon index, Γ, and direct flux that is commonly observed in unobscured AGN. A search for a reverberation lag between the direct and reflected spectra—dominated by the narrow Fe K α emission line—measures a timescale of $t={16.37}_{-0.38}^{+0.46}$ days, or a characteristic radius of $r={1.374}_{-0.032}^{+0.039}\,\times {10}^{-2}$ pc $={\,3.4}_{-0.1}^{+0.1}\times {10}^{4}\,{GM}/{c}^{2}$ . Only one cycle of this tentative lag is observed, but it is driven by a particularly sharp drop in the direct continuum that leads to the subsequent disappearance of the otherwise prominent Fe K α line. Physically motivated fits to high-resolution Chandra spectra of NGC 4388 measure a line production radius of $r={2.9}_{-0.7}^{+1.2}\,\times {10}^{4}\,{GM}/{c}^{2}$ , formally consistent with the tentative lag. The line profile also prefers a Compton-thick reflector, indicating an origin in the disk and/or thick clumps within a wind. We discuss the strengths and weaknesses of our analysis and methods for testing our results in future observations, and we note the potential for X-ray reverberation lags to constrain black hole masses in obscured Seyferts wherein the optical broad line region is not visible.

We present an observational study of wind acceleration based on four low-ionization broad absorption line (BAL) quasars (J0136, J1238, J1259, and J1344). J0136 and J1344 (group 1) are radio-quiet and show large BAL-velocity shifts as opposed to stable line-locking associated absorption lines (AALs). Notably, J1344 displays a linear relation between BAL-velocity shift and time interval over three consecutive epochs, characteristic of compelling evidence for BAL acceleration. J1238 and J1259 (group 2) exhibit small BAL-velocity shifts along with steep-spectrum, weak radio emission at 3.0 and 1.4 GHz. All four quasars have spectral energy distributions (SEDs) with a peak at λ _rest ∼ 10 μ m, suggesting a link between the BAL acceleration and hot dust emission. The group-2 quasars are redder than group-1 quasars and have a steeper rise at 1 μ m < λ _rest < 3 μ m in their SEDs. All but J1238 exhibit a steep rise followed by a plateau-like time evolution in BAL-velocity shift. Our investigations, combined with previous studies of BAL acceleration, indicate that (1) the coupling process between the BALs and the interstellar medium (ISM) is one of the major avenues for the origin of quasar reddening and patchy obscuration, (2) AAL outflows are ubiquitous and likely signify large-scale remnants of BAL winds coupled to the ISM, and (3) wind deceleration that is closely linked to the BAL–ISM coupling process may produce weak radio emission in otherwise radio-quiet quasars.

Periodic signatures in time-domain observations of quasars have been used to search for binary supermassive black holes (SMBHs). These searches, across existing time-domain surveys, have produced several hundred candidates. The general stochastic variability of quasars, however, can masquerade as a false-positive periodic signal, especially when monitoring cadence and duration are limited. In this work, we predict the detectability of binary SMBHs in the upcoming Rubin Observatory Legacy Survey of Space and Time (LSST). We apply computationally inexpensive sinusoidal curve fits to millions of simulated LSST Deep Drilling Field light curves of both single, isolated quasars and binary quasars. The period and phase of simulated binary signals can generally be disentangled from quasar variability. Binary amplitude is overestimated and poorly recovered for two-thirds of potential binaries due to quasar accretion variability. Quasars with strong intrinsic variability can obscure a binary signal too much for recovery. We also find that the most luminous quasars mimic current binary candidate light curves and their properties: The false-positive rates are 60% for these quasars. The reliable recovery of binary period and phase for a wide range of input binary LSST light curves is promising for multi-messenger characterization of binary SMBHs. However, pure electromagnetic detections of binaries using photometric periodicity with amplitude greater than 0.1 mag will result in samples that are overwhelmed by false positives. This paper represents an important and computationally inexpensive way forward for understanding the true and false-positive rates for binary candidates identified by Rubin.

The growth of supermassive black holes is strongly linked to their galaxies. It has been shown that the population mean black hole accretion rate ( $\overline{\mathrm{BHAR}}$ ) primarily correlates with the galaxy stellar mass ( M _⋆ ) and redshift for the general galaxy population. This work aims to provide the best measurements of $\overline{\mathrm{BHAR}}$ as a function of M _⋆ and redshift over ranges of 10 ^9.5 < M _⋆ < 10 ^12 M _⊙ and z < 4. We compile an unprecedentedly large sample with 8000 active galactic nuclei (AGNs) and 1.3 million normal galaxies from nine high-quality survey fields following a wedding cake design. We further develop a semiparametric Bayesian method that can reasonably estimate $\overline{\mathrm{BHAR}}$ and the corresponding uncertainties, even for sparsely populated regions in the parameter space. $\overline{\mathrm{BHAR}}$ is constrained by X-ray surveys sampling the AGN accretion power and UV-to-infrared multiwavelength surveys sampling the galaxy population. Our results can independently predict the X-ray luminosity function (XLF) from the galaxy stellar mass function (SMF), and the prediction is consistent with the observed XLF. We also try adding external constraints from the observed SMF and XLF. We further measure $\overline{\mathrm{BHAR}}$ for star-forming and quiescent galaxies and show that star-forming $\overline{\mathrm{BHAR}}$ is generally larger than or at least comparable to the quiescent $\overline{\mathrm{BHAR}}$ .

A fundamental question in galaxy and black hole evolution remains how galaxies and their supermassive black holes have evolved together over cosmic time. Specifically, it is still unclear how the position of X-ray active galactic nucleus (AGN) host galaxies with respect to the star-forming main sequence (MS) may change with the X-ray luminosity ( L _X ) of the AGN or the stellar mass ( M _⋆ ) of the host galaxy. We use data from the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) to probe this issue. XMM-SERVS is covered by the largest medium-depth X-ray survey (with superb supporting multiwavelength data) and thus contains the largest sample to date for study. To ensure consistency, we locally derive the MS from a large reference galaxy sample. In our analysis, we demonstrate that the turnover of the galaxy MS does not allow reliable conclusions to be drawn for high-mass AGNs, and we establish a robust safe regime where the results do not depend upon the choice of MS definition. Under this framework, our results indicate that less massive AGN host galaxies ( $\mathrm{log}{M}_{\star }\sim 9.5\mbox{--}10.5\,{M}_{\odot }$ ) generally possess enhanced star formation rates compared to their normal-galaxy counterparts while the more massive AGN host galaxies ( $\mathrm{log}{M}_{\star }\sim 10.5\mbox{--}11.5\,{M}_{\odot }$ ) lie on or below the star-forming MS. Further, we propose an empirical model for how the placement of an AGN with respect to the MS (SFR _norm ) evolves as a function of both M _⋆ and L _X .

Cen A hosts the closest active galactic nucleus to the Milky Way, which makes it an ideal target for investigating the dynamical processes in the vicinity of accreting supermassive black holes. In this paper, we present 14 Chandra HETGS spectra of the nucleus of Cen A that were observed throughout 2022. We compared them with each other, and contrasted them against the two previous Chandra HETGS spectra from 2001. This enabled an investigation into the spectral changes occurring on timescales of months and 21 years. All Chandra spectra could be well fitted by an absorbed power law with a strong and narrow Fe K α line, a leaked power-law feature at low energies, and Si and S K α lines that could not be associated with the central engine. The flux of the continuum varied by a factor of 2.74 ± 0.05 over the course of the observations, whereas the Fe line only varied by 18.8% ± 8.8%. The photon index increased over 21 years, and the hydrogen column density varied significantly within a few months as well. The Fe K α line was found at a lower energy than expected from the Cen A redshift, amounting to an excess velocity of ${326}_{-94}^{+84}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ relative to Cen A. We investigated warped accretion disks, bulk motion, and outflows as possible explanations of this shift. The spectra also featured ionized absorption lines from Fe xxv and Fe xxvi , describing a variable inflow.

This work studies the relationship between accretion-disk size and quasar properties, using a sample of 95 quasars from the Sloan Digital Sky Survey Reverberation Mapping Project with measured lags between the g and i photometric bands. Our sample includes disk lags that are both longer and shorter than predicted by the Shakura and Sunyaev model, requiring explanations that satisfy both cases. Although our quasars each have one lag measurement, we explore the wavelength-dependent effects of diffuse broad-line region (BLR) contamination through our sample’s broad redshift range, 0.1 < z < 1.2. We do not find significant evidence of variable diffuse Fe ii and Balmer nebular emission in the rms spectra, nor from Anderson–Darling tests of quasars in redshift ranges with and without diffuse nebular emission falling in the observed-frame filters. Contrary to previous work, we do not detect a significant correlation between the measured continuum and BLR lags in our luminous quasar sample, similarly suggesting that our continuum lags are not dominated by diffuse nebular emission. Similar to other studies, we find that quasars with larger-than-expected continuum lags have lower 3000 Å luminosities, and we additionally find longer continuum lags with lower X-ray luminosities and black hole masses. Our lack of evidence for diffuse BLR contribution to the lags indicates that the anticorrelation between continuum lag and luminosity is not likely to be due to the Baldwin effect. Instead, these anticorrelations favor models in which the continuum lag increases in lower-luminosity active galactic nuclei, including scenarios featuring magnetic coupling between the accretion disk and X-ray corona, and/or ripples or rims in the disk.

Fourteen sulfide-linked 3,4,5-trimethoxyphenyl-thiosemicarbazide/triazole hybrid derivatives containing a variety of structural modifications on the thiosemicarbazide moiety were synthesized. Structure-activity correlations were investigated to determine the influence of structural variations on the antioxidant, antiglycation and DNA cleavage activities. Antioxidant activity was determined using the DPPH radical scavenging and CUPRAC assays. The majority of the derivatives displayed moderate to weak DPPH radical scavenging activity (IC50 = 20.96 to 106.7 μM) compared to ascorbic acid (IC50 = 13.72 μM), with derivatives having π-donating substituents being the most effective. A similar trend was observed for the CUPRAC assay. All derivatives containing electron-donating substituents were more effective than Trolox at reducing copper(II) ion, with Trolox Equivalent Antioxidant Capacity (TEAC) values ranging from 1.44 to 2.45. However, only the nitro derivative was found to be a promising antiglycation agent, inhibiting the formation of advanced glycation end products (AGEs) by 75 % compared to 27 % for the aminoguanidine control. In addition, the majority of the derivatives cleaved pBR322 plasmid DNA in the presence of copper(II) acetate. The interaction of the derivatives with DNA was confirmed by molecular docking studies, which revealed that all of the derivatives bind favorably in the minor groove of DNA.

We report XMM-Newton observations of two examples of an unclassified type of X-ray weak quasars from the Pu et al. survey of X-ray weak quasars in the Chandra archive, SDSS J083116.62+321329.6 at z = 1.797 and SDSS J142339.87+042041.1 at z = 1.702. They do not belong to the known populations of X-ray weak quasars that show broad absorption lines, weak ultraviolet (UV) broad emission lines, or red optical/UV continua. Instead, they display typical quasar UV spectra and spectral energy distributions. In the XMM-Newton observations, both quasars show nominal levels of X-ray emission with typical quasar X-ray spectral shapes (power-law photon indices of ${1.99}_{-0.23}^{+0.27}$ and ${1.86}_{-0.14}^{+0.15}$ ), displaying strong X-ray variability compared to the archival Chandra data (variability factors of ${4.0}_{-1.4}^{+1.6}$ and ${9.0}_{-3.8}^{+7.4}$ in terms of the 2 keV flux density). Simultaneous optical (rest-frame UV) spectra indicate no strong variability compared to the archival spectra. Long-term optical/UV and infrared light curves do not show any substantial variability either. We consider that the X-ray weakness observed in the Chandra data is due to X-ray obscuration from a small-scale dust-free absorber, likely related to accretion-disk winds. Such X-ray weak/absorbed states are probably rare in typical quasars, and thus both targets recovered to X-ray nominal-strength states in the XMM-Newton observations.

We explore reprocessing models for a sample of 17 hypervariable quasars, taken from the Sloan Digital Sky Survey Reverberation Mapping project, which all show coordinated optical luminosity hypervariability with amplitudes of factors ≳2 between 2014 and 2020. We develop and apply reprocessing models for quasar light curves in simple geometries that are likely to be representative of quasar inner environments. In addition to the commonly investigated thin-disk model, we include the thick-disk and hemisphere geometries. The thick-disk geometry could, for instance, represent a magnetically elevated disk, whereas the hemisphere model can be interpreted as a first-order approximation for any optically thick out-of-plane material caused by outflows/winds, warped/tilted disks, and so on. Of the 17 quasars in our sample, 11 are best-fitted by a hemisphere geometry, five are classified as thick disks, and both models fail for just one object. We highlight the successes and shortcomings of our thermal reprocessing models in case studies of four quasars that are representative of the sample. While reprocessing is unlikely to explain all of the variability that we observe in quasars, we present our classification scheme as a starting point for revealing the likely geometries of reprocessing for quasars in our sample and hypervariable quasars in general.

The most reliable single-epoch supermassive black hole mass ( M _BH ) estimates in quasars are obtained by using the velocity widths of low-ionization emission lines, typically the H β λ 4861 line. Unfortunately, this line is redshifted out of the optical band at z ≈ 1, leaving M _BH estimates to rely on proxy rest-frame ultraviolet (UV) emission lines, such as C iv λ 1549 or Mg ii λ 2800, which contain intrinsic challenges when measuring, resulting in uncertain M _BH estimates. In this work, we aim at correcting M _BH estimates derived from the C iv and Mg ii emission lines based on estimates derived from the H β emission line. We find that employing the equivalent width of C iv in deriving M _BH estimates based on Mg ii and C iv provides values that are closest to those obtained from H β . We also provide prescriptions to estimate M _BH values when only C iv , only Mg ii , and both C iv and Mg ii are measurable. We find that utilizing both emission lines, where available, reduces the scatter of UV-based M _BH estimates by ∼15% when compared to previous studies. Lastly, we discuss the potential of our prescriptions to provide more accurate and precise estimates of M _BH given a much larger sample of quasars at 3.20 ≲ z ≲ 3.50, where both Mg ii and H β can be measured in the same near-infrared spectrum.

Quasars at z ≳ 1 most often have redshifts measured from rest-frame ultraviolet emission lines. One of the most common such lines, C iv λ 1549, shows blueshifts up to ≈5000 km s ^−1 and in rare cases even higher. This blueshifting results in highly uncertain redshifts when compared to redshift determinations from rest-frame optical emission lines, e.g., from the narrow [O iii ] λ 5007 feature. We present spectroscopic measurements for 260 sources at 1.55 ≲ z ≲ 3.50 having −28.0 ≲ M _i ≲ − 30.0 mag from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS) catalog, augmenting the previous iteration, which contained 226 of the 260 sources whose measurements are improved upon in this work. We obtain reliable systemic redshifts based on [O iii ] λ 5007 for a subset of 121 sources, which we use to calibrate prescriptions for correcting UV-based redshifts. These prescriptions are based on a regression analysis involving C iv full-width-at-half-maximum intensity and equivalent width, along with the UV continuum luminosity at a rest-frame wavelength of 1350 Å. Applying these corrections can improve the accuracy and the precision in the C iv -based redshift by up to ∼850 km s ^−1 and ∼150 km s ^−1 , respectively, which correspond to ∼8.5 and ∼1.5 Mpc in comoving distance at z = 2.5. Our prescriptions also improve the accuracy of the best available multifeature redshift determination algorithm by ∼100 km s ^−1 , indicating that the spectroscopic properties of the C iv emission line can provide robust redshift estimates for high-redshift quasars. We discuss the prospects of our prescriptions for cosmological and quasar studies utilizing upcoming large spectroscopic surveys.

We report strong and rapid X-ray variability found from the super-Eddington accreting quasar SDSS J081456.10+532533.5 at z = 0.1197. It has a black hole mass of 2.7 × 10 ^7 M _⊙ and a dimensionless accretion rate of ≈4 measured from reverberation-mapping observations. It showed weak X-ray emission in the 2021 February Chandra observation, with the 2 keV flux density being ${9.6}_{-4.6}^{+11.6}$ times lower compared to an archival Swift observation. The 2 keV flux density is also ${11.7}_{-6.3}^{+9.6}$ times weaker compared to the expectation from its optical/UV emission. In a follow-up XMM-Newton observation 32 days later, the 2 keV flux density increased by a factor of ${5.3}_{-2.4}^{+6.4}$ , and the spectra are best described by a power law modified with partial-covering absorption; the absorption-corrected intrinsic continuum is at a nominal flux level. Nearly simultaneous optical spectra reveal no variability, and there is only mild long-term optical/infrared variability from archival data (with a maximum variability amplitude of ≈50%). We interpret the X-ray variability with an obscuration scenario, where the intrinsic X-ray continuum does not vary but the absorber has a variable column density and covering factor along the line of sight. The absorber is likely the small-scale clumpy accretion wind that has been proposed to be responsible for similar X-ray variability in other super-Eddington accreting quasars.

We investigate the extreme X-ray variability of a z = 1.608 active galactic nucleus in the 7 Ms Chandra Deep Field-South (XID 403), which showed two significant X-ray brightening events. In the first event, XID 403 brightened by a factor of >2.5 in ≲6.1 rest-frame days in the observed-frame 0.5–5 keV band. The event lasted for ≈5.0–7.3 days, and then XID 403 dimmed by a factor of >6.0 in ≲6.1 days. After ≈1.1–2.5 yr in the rest frame (including long observational gaps), it brightened again, with the 0.5–5 keV flux increasing by a factor of >12.6. The second event lasted over 251 days, and the source remained bright until the end of the 7 Ms exposure. The spectrum is a steep power law (photon index Γ = 2.8 ± 0.3) without obscuration during the second outburst, and the rest-frame 2–10 keV luminosity reaches ${1.5}_{-0.5}^{+0.8}\times {10}^{43}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ ; there is no significant spectral evolution within this epoch. The infrared-to-UV spectral energy distribution of XID 403 is dominated by the host galaxy. There is no significant optical/UV variability and R -band (rest-frame ≈2500 Å) brightening contemporaneous with the X-ray brightening. The extreme X-ray variability is likely due to two X-ray unveiling events, where the line of sight to the corona is no longer shielded by high-density gas clumps in a small-scale dust-free absorber. XID 403 is probably a high-redshift analog of local narrow-line Seyfert 1 galaxies, and the X-ray absorber is a powerful accretion disk wind. On the other hand, we cannot exclude the possibility that XID 403 is an unusual candidate for tidal disruption events.

We present a high-cadence multiepoch analysis of dramatic variability of three broad emission lines (Mg ii , H β , and H α ) in the spectra of the luminous quasar ( λ L _λ (5100 Å) = 4.7 × 10 ^44 erg s ^−1 ) SDSS J141041.25+531849.0 at z = 0.359 with 127 spectroscopic epochs over nine years of monitoring (2013–2022). We observe anticorrelations between the broad emission-line widths and flux in all three emission lines, indicating that all three broad emission lines “breathe” in response to stochastic continuum variations. We also observe dramatic radial velocity shifts in all three broad emission lines, ranging from Δ v ∼ 400 km s ^−1 to ∼800 km s ^−1 , that vary over the course of the monitoring period. Our preferred explanation for the broad-line variability is complex kinematics in the gas in the broad-line region. We suggest a model for the broad-line variability that includes a combination of gas inflow with a radial gradient, an azimuthal asymmetry (e.g., a hot spot), superimposed on the stochastic flux-driven changes to the optimal emission region (“line breathing”). Similar instances of line-profile variability due to complex gas kinematics around quasars are likely to represent an important source of false positives in radial velocity searches for binary black holes, which typically lack the kind of high-cadence data we analyze here. The long-duration, wide-field, and many-epoch spectroscopic monitoring of SDSS-V BHM-RM provides an excellent opportunity for identifying and characterizing broad emission-line variability, and the inferred nature of the inner gas environment, of luminous quasars.

We present a multiwavelength analysis of the dwarf Seyfert 2 galaxy J144013+024744, a candidate obscured active galactic nucleus (AGN) thought to be powered by an intermediate-mass black hole (IMBH, M _• ≈ 10 ^4 −10 ^6 M _⊙ ) of mass M _• ∼ 10 ^5.2 M _⊙ . To study its X-ray properties, we targeted J144013+024744 with NuSTAR for ≈100 ks. The X-ray spectrum was fitted with an absorbed power law, Pexmon, and a physical model (RXTorus). A Bayesian X-ray analysis was performed to estimate the posteriors. The phenomenological and the physical models suggest the AGN to be heavily obscured by a column density of N _H = (3.4–7.0) × 10 ^23 cm ^−2 . In particular, the RXTorus model with a subsolar metallicity suggests the obscuring column to be almost Compton-thick. We compared the 2–10 keV intrinsic X-ray luminosity with the inferred X-ray luminosities based on empirical scaling relations for unobscured AGNs using L _[O _iv _] 25.89 _ μ _m , L _[O _iii _] _λ _5007 , and L _6 _μ _m and found that the high-excitation [O iv ] line provides a better estimate of the intrinsic 2–10 keV X-ray luminosity ( ${L}_{2\mbox{--}10}^{\mathrm{int}}\sim {10}^{41.41}$ erg s ^−1 ). Our results suggest that J144013+024744 is the first type 2 dwarf galaxy that shows X-ray spectroscopic evidence for obscuration. The column density that we estimated is among the highest measured to date for IMBH-powered AGNs, implying that a typical AGN torus geometry might extend to the low-mass end. This work has implications for constraining the BH occupation fraction in dwarf galaxies using X-ray observations.

Sustainable and integrated pest management often involves insect parasitoids. However, the effectiveness of parasitoids biocontrol has often failed, frequently for obscure reasons. A parasitoid's success is partly due to its behavioral response to pest density, i.e. its consumer functional response. For many years in New Zealand, a braconid parasitoid, Microctonus hyperodae successfully suppressed a severe ryegrass weevil pest, Listronotus bonariensis. However, there is now evidence that this has severely declined, but that the extent of decline can depend on the pasture species. Here, we tested whether the current functional responses of M. hyperodae to L. bonarensis in two of the most common New Zealand pasture grasses (Lolium multiflorum and L. perenne) reflect observed differences in field parasitism and whether this functional response has changed over time. Our analysis involved data from 1993 and 2018. We found a type I functional response in L. multiflorum in both years, but the slope of the relationship declined over time. There was no evidence for any type of functional response in L. perenne. This lack of response in L. perenne coincided with consistently found lower parasitism rates on this host plant than in L. multiflorum; both in the field and laboratory. Here, we found that apparently declining searching efficiency was correlated with the decline in parasitism. This observation supports the hypothesis that parasitism decline could be the result of evolution of resistance based on enhanced evasive behavior by L. bonariensis.