Gordon Richards

Aims We aim to reveal the sizes of the continuum and broad emission line (BEL) emitting regions in the gravitationally lensed quasar SDSS J1004+4112 by analyzing the unique signatures of microlensing in this system. Through a comprehensive analysis of 20 spectroscopic observations acquired between 2003 and 2018, we studied the striking deformations of various BEL profiles and determined the sizes of their respective emitting regions.Methods Our approach involves a detailed analysis of the magnitude differences in the BEL wings and their adjacent continua, and the implementation of a statistical model to quantify the distribution and impact of microlensing magnifications. To ensure a reliable baseline for no microlensing, we used the emission line cores as a reference. We then applied a Bayesian estimate to derive the size lower limits of the Lyα, Si IV, C IV, C III], and Mg II emitting regions, as well as the …

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 . We do not find any correlation between BAL trough properties and the H-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 A of erg s 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.

The origin of radio emission in different populations of radio-quiet quasars is relatively unknown, but recent work has uncovered various drivers of increased radio-detection fraction. In this work, we pull together three known factors: optical colour (g − i), C iv distance (a proxy for L/LEdd), and whether or not the quasar contains broad absorption lines (BALQSOs) which signify an outflow. We use SDSS (Sloan Digital Sky Survey) DR14 spectra along with the LOFAR Two Metre Sky Survey Data Release 2 and find that each of these properties have an independent effect. BALQSOs are marginally more likely to be radio-detected than non-BALQSOs at similar colours and L/LEdd, moderate reddening significantly increases the radio-detection fraction and the radio detection increases with L/LEdd above a threshold for all populations. We test a widely used simple model for radio wind shock emission and calculate …

We present the optical-near infrared spectral energy distributions (SED) and near infrared variability properties of 30 low-redshift iron low-ionization Broad Absorption Line quasars (FeLoBALQs) and matched samples of LoBALQs and unabsorbed quasars. Significant correlations between the SED properties and accretion rate indicators found among the unabsorbed comparison sample objects suggest an intrinsic origin for SED differences. A range of reddening likely mutes these correlations among the FeLoBAL quasars. The restframe optical-band reddening is correlated with the location of the outflow, suggesting a link between the outflows and the presence of dust. We analyzed WISE variability and provide a correction for photometry uncertainties in an appendix. We found an anticorrelation between the variability amplitude and inferred continuum emission region size, and suggest that as the origin of the anticorrelation between variability amplitude and luminosity typically observed in quasars. We found that the LoBALQ optical emission line and other parameters are more similar to those of the unabsorbed continuum sample objects than the FeLoBALQs. Thus, FeLoBAL quasars are a special population of objects. We interpret the results using an accretion-rate scenario for FeLoBAL quasars. The high accretion rate FeLoBAL quasars are radiating powerfully enough to drive a thick, high-velocity outflow. Quasars with intermediate accretion rates may have an outflow, but it is not sufficiently thick to include FeII absorption. Low accretion rate FeLoBAL outflows originate in absorption in a failing torus, no longer optically thick enough to …

J1004+4112 is a lensed quasar for which the first broad emission line profile deformations due to microlensing were identified. Detailed interpretations of these features have nevertheless remained controversial. Based on 15 spectra obtained from 2003 to 2018, in this work, we revisit the microlensing effect that distorts the C IV broad emission line profile in J1004+4112. We take advantage of recent measurements of the image macro-magnification ratios, along with the fact that at one epoch, image B was not microlensed, thus constituting a reference spectrum to unambiguously characterize the microlensing effect observed in image A. After disentangling the microlensing in images A and B, we show that the microlensing-induced line profile distortions in image A, although variable, are remarkably similar over a period of 15 years. We find they are characterized by a strong magnification of the blue part of the line …

Development of the Rubin Observatory Legacy Survey of Space and Time (LSST) includes a series of Data Challenges (DCs) arranged by various LSST Scientific Collaborations that are taking place during the project's preoperational phase. The AGN Science Collaboration Data Challenge (AGNSC-DC) is a partial prototype of the expected LSST data on active galactic nuclei (AGNs), aimed at validating machine learning approaches for AGN selection and characterization in large surveys like LSST. The AGNSC-DC took place in 2021, focusing on accuracy, robustness, and scalability. The training and the blinded data sets were constructed to mimic the future LSST release catalogs using the data from the Sloan Digital Sky Survey Stripe 82 region and the XMM-Newton Large Scale Structure Survey region. Data features were divided into astrometry, photometry, color, morphology, redshift, and class label with the …

The ground-based gamma-ray observatory Very Energetic Radiation Imaging Telescope Array System (VERITAS, https://veritas.sao.arizona.edu/) is sensitive to photons of astrophysical origin with energies in the range between ≈85 GeV and ≈30 TeV. The instrument consists of four 12 m diameter imaging Cherenkov telescopes operating at the Fred Lawrence Whipple Observatory in southern Arizona. VERITAS started four-telescope operations in 2007 and collects about 1100 hr of good-weather data per year. The VERITAS collaboration has published over 100 journal articles since 2008 reporting on gamma-ray observations of a large variety of objects: Galactic sources like supernova remnants, pulsar wind nebulae, and binary systems; extragalactic sources like star-forming galaxies, dwarf-spheroidal galaxies, and highly variable active galactic nuclei. This note presents VTSCat: the catalog of high-level …

Using ≈190 000 spectra from the 17th data release of the Sloan Digital Sky Survey (SDSS), we investigate the ultraviolet emission line properties in z ≈ 2 quasars. Specifically, we quantify how the shape of C iv λ1549 and the equivalent width (EW) of He ii λ1640 depend on the black hole mass and Eddington ratio inferred from Mg ii λ2800. Above L/LEdd ≳ 0.2, there is a strong mass dependence in both C iv blueshift and He ii EW. Large C iv blueshifts are observed only in regions with both high mass and high accretion rate. Including X-ray measurements for a subsample of 5000 objects, we interpret our observations in the context of AGN accretion and outflow mechanisms. The observed trends in He ii and 2 keV strength are broadly consistent with theoretical qsosed models of AGN spectral energy distributions (SEDs) for low spin black holes, where the ionizing SED depends on the accretion …

Blueshifts – or, more accurately, blue asymmetries – in broad emission lines such as C iv λ1550 are common in luminous quasars and correlate with fundamental properties such as Eddington ratio and broad absorption line (BAL) characteristics. However, the formation of these blueshifts is still not understood, and neither is their physical connection to the BAL phenomenon or accretion disc. In this work, we present Monte Carlo radiative transfer and photoionization simulations using parametrized biconical disc-wind models. We take advantage of the azimuthal symmetry of a quasar and show that we can reproduce C iv blueshifts provided that (i) the disc-mid-plane is optically thick out to radii beyond the line formation region, so that the receding wind bicone is obscured; and (ii) the system is viewed from relatively low (that is, more face-on) inclinations (≲40°). We show that C iv emission-line blueshifts and …

We reanalyze the UV spectra of over 200 archival HST spectra of luminous quasars. The spectra are reconstructed using the Mean-Field Independent Component Analysis templates of Rankine et al.(2021). By using this suite of templates, we are able to determine robust and uniformly measured properties of the CIV emission line, including equivalent width and blueshift. These measurements are combined into a non-linear metric, the CIV" distance"(Rivera et al. 2022; Richards et al. 2021), which we show to be a robust indicator of L/LEdd and of the presence of accretion disk winds. Using this CIV-based diagnostic tool, we find that high optical/UV luminosity is a necessary, but insufficient condition for accretion disk winds.

Quasars at z≳ 1 most often have redshifts measured from rest-frame ultraviolet emission lines. One of the most common such lines, C iv λ1549, 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, eg, from the narrow [O iii] λ5007 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] λ5007 for a subset of 121 sources, which we use to calibrate prescriptions for correcting UV-based redshifts. These prescriptions are based on a …

We analyse the rest-frame ultraviolet (UV) spectra of 2531 high-redshift (3.5 < z < 4.0) quasars from the Sloan Digital Sky Survey DR16Q catalogue. In combination with previous work, we study the redshift evolution of the rest-frame UV line properties across the entire redshift range, 1.5 < z < 4.0. We improve the systemic redshift estimates at z > 3.5 using a cross-correlation algorithm that employs high signal-to-noise template spectra spanning the full range in UV emission line properties. We then quantify the evolution of C iv and He ii emission line properties with redshift. The increase in C iv blueshifts with cosmological redshift can be fully explained by the higher luminosities of quasars observed at high redshifts. We recover broadly similar trends between the He ii equivalent width and C iv blueshift at both 1.5 < z < 2.65 and 3.5 < z < 4.0 suggesting that the blueshift depends systematically on the spectral energy …

We present preliminary results of our X-ray analysis of SDSS quasars new to DR16, with the goal of combining X-ray data and optical/UV indicators of Eddington ratio (L/L Edd). Using Bayesian statistical methods and stacked archival Chandra observations, we measure spectral properties such as the X-ray photon index (Γ) and the optical-to-X-ray flux ratio (α ox) for several thousand sources. For objects with existing UV spectral coverage, we aim to leverage these X-ray measurements with C IV emission line parameters such as C IV distance (eg, Rivera et al. 2022) to better predict X-ray exposure times that are needed to achieve sufficient counts for accurate spectral analysis. Our methods will produce improved spectral measurements for faint and/or X-ray weak sources in particular as well as provide tighter constraints on the intrinsic distribution of spectral properties related to accretion.

Weak emission-line quasars (WLQs) are a subset of type 1 quasars that exhibit extremely weak Lyα+ N v λ1240 and/or C iv λ1549 emission lines. We investigate the relationship between emission-line properties and accretion rate for a sample of 230" ordinary" type 1 quasars and 18 WLQs at z< 0.5 and 1.5< z< 3.5 that have rest-frame ultraviolet and optical spectral measurements. We apply a correction to the Hβ-based black hole mass (M BH) estimates of these quasars using the strength of the optical Fe ii emission. We confirm previous findings that WLQs' M BH values are overestimated by up to an order of magnitude using the traditional broad-emission-line region size–luminosity relation. With this M BH correction, we find a significant correlation between Hβ-based Eddington luminosity ratios and a combination of the rest-frame C iv equivalent width and C iv blueshift with respect to the systemic redshift. This …

We present the analysis of the rest frame ultraviolet and optical spectra of 30 bright blue quasars at z ∼ 3, selected to examine the suitability of active galactic nuclei as cosmological probes. In our previous works, based on pointed XMM-Newton observations, we found an unexpectedly high fraction (≈25%) of X-ray weak quasars in the sample. The latter sources also display a flatter UV continuum and a broader and fainter C IV profile in the archival UV data with respect to their X-ray normal counterparts. Here we present new observations with the Large Binocular Telescope in both the zJ (covering the rest frame ≃2300–3100 Å) and the KS (≃4750–5350 Å) bands. We estimated black hole masses (MBH) and Eddington ratios (λEdd) from the available rest frame optical and UV emission lines (Hβ, Mg II), finding that our z ∼ 3 quasars are on average highly accreting (⟨λEdd⟩≃1.2 and ⟨MBH⟩≃109.7 M⊙ …

I will present new high-resolution 6-GHz VLA observations of a homogeneous, volume-complete sample of radio-quiet QSOs at z~ 0.25. These high-resolution images, as well as comparison of flux densities from earlier lower-resolution observations at the same frequency, yield brand new information about the sub-galactic radio morphology in radio-quiet QSOs and their host galaxies. While a compact central component (presumably from the super-massive black hole) is typically responsible for over half of the radio emission, significant sub-galactic-scale radio emission is present in nearly 3/4 of the population. One QSO shows striking symmetric, double-lobed morphology and appears to be the first radio-quiet QSO with FRII type morphology on an arcsec scale, while several others have morphology suggestive of kpc-scale radio jets. These results support the growing notion that radio-quiet QSOs are not a …

The census of obscured quasar populations is incomplete and remains a major unsolved problem, especially at higher redshifts, where we expect a greater density of galaxy formation and quasar activity. We present Gemini GNIRS near-infrared spectroscopy of 24 luminous obscured quasar candidates from the Sloan Digital Sky Survey’s Stripe 82 region. The targets were photometrically selected using a WISE/W4 selection technique that is optimized to identify IR-bright and heavily reddened/optically obscured targets at z > 1. We detect emission lines of Hα, Hβ, and/or [O iii] in 23 sources allowing us to measure spectroscopic redshifts in the range 1 < z < 3 with bolometric luminosities spanning L = 1046.3–1047.3 erg s−1. We observe broad 103–104 km s−1 Balmer emissions with large Hα/Hβ ratios, and we directly observe a heavily reddened rest-frame optical continuum in several sources, suggesting high …

Broad absorption line quasars are actively accreting supermassive black holes that have strong outflows characterized by broad absorption lines in their rest-UV spectra. Variability in these absorption lines occurs over months to years depending on the source. WPVS 007, a low-redshift, low-luminosity narrow-line Seyfert 1 (NLS1) shows strong variability over shorter timescales, providing a unique opportunity to study the driving mechanism behind this variability that may mimic longer-scale variability in much more massive quasars. We present the first variability study using the spectral synthesis code SimBAL, which provides velocity-resolved changes in physical conditions of the gas using constraints from multiple absorption lines. Overall, we find WPVS 007 to have a highly ionized outflow with a large mass-loss rate and kinetic luminosity. We determine the primary cause of the absorption-line variability in WPVS …

Quasi-stellar objects (QSOs) are nominally divided into two categories, radio-loud and radio-quiet. Typically, radio-loud QSOs are identified by their high radio luminosities, up to orders of magnitude greater than can be explained by underlying starlight, as well as the presence of jets that may extend far beyond the QSO host galaxy. Radio-quiet QSOs instead have radio luminosities either on par with or orders of magnitude below that expected from the host, and their radio emission is confined to within host-galaxy dimensions. Decades of research have been devoted to revealing two distinct origins of radio emission in these objects, but recent research suggests there is substantial overlap between the two populations, with radio-quiet QSOs consisting of a mixture of mainly jet-powered and starburst-powered host galaxies. I will present sub-galactic-scale VLA images of both radio-loud and radio-quiet QSOs, and …

We present ultraviolet spectroscopy covering the Lyα+ N v complex of six candidate low-redshift (0.9< z< 1.5) weak emission-line quasars (WLQs) based on observations with the Hubble Space Telescope. The original systematic searches for these puzzling Type 1 quasars with intrinsically weak broad emission lines revealed an N≈ 100 WLQ population from optical spectroscopy of high-redshift (z> 3) quasars, defined by a Lyα+ N v rest-frame equivalent width (EW) threshold< 15.4 Å. Identification of lower-redshift (z< 3) WLQ candidates, however, has relied primarily on optical spectroscopy of weak broad emission lines at longer rest-frame wavelengths. With these new observations expanding existing optical coverage into the ultraviolet, we explore unifying the low-and high-z WLQ populations via EW [Lyα+ N v]. Two objects in the sample unify with high-z WLQs, three others appear consistent with the intermediate …

We examine the UV/X-ray properties of 1378 quasars in order to link empirical correlations to theoretical models of the physical mechanisms dominating quasars as a function of mass and accretion rate. The clarity of these correlations is improved when (1) using C iv broad emission line equivalent width (EQW) and blueshift (relative to systemic) values calculated from high signal-to-noise ratio reconstructions of optical/UV spectra and (2) removing quasars expected to be absorbed based on their UV/X-ray spectral slopes. In addition to using the traditional C iv parameter space measures of C iv EQW and blueshift, we define a" C iv∥ distance" along a best-fit polynomial curve that incorporates information from both C iv parameters. We find that the C iv∥ distance is linearly correlated with both the optical-to-X-ray slope, α ox, and broad-line He ii EQW, which are known spectral energy distribution indicators, but does …

We aim to uncover the structure of the continuum and broad emission line (BEL) emitting regions in the gravitationally lensed quasar SDSS J1004+4112 through unique microlensing signatures. Analyzing 20 spectroscopic observations from 2003 to 2018, we study the striking deformations of various BEL profiles and determine the sizes of their respective emitting regions. We use the emission line cores as a baseline for no microlensing and then apply Bayesian methods to derive the sizes of the Lyα, Si IV, C IV, C III], and Mg II emitting regions, as well as of the underlying continuum-emitting sources. We find that the sizes of the emitting regions for the BELs are a few light-days across, notably smaller than in typical lensed quasars. The asymmetric distortions observed in the BELs suggest that the broad-line region lacks spherical symmetry and is likely confined to a plane. The inferred continuum emitting region …

The Cherenkov Telescope Array (CTA) observatory is the next generation of ground-based imaging atmospheric Cherenkov telescopes (IACTs). Building on the strengths of current IACTs, CTA is designed to achieve an order of magnitude improvement in sensitivity, with unprecedented angular and energy resolution. CTA will also increase the energy reach of IACTs, observing photons in the energy range from 20 GeV to beyond 100 TeV. These advances in performance will see CTA heralding in a new era for high-energy astrophysics, with the emphasis shifting from source discovery, to population studies and precision measurements. In this talk we discuss CTA’s ability to conduct source population studies of γ-ray bright active galactic nuclei and how this ability will enhance our understanding on the redshift evolution of this dominant γ-ray source class.

Characterizing the peak of the spectral energy distribution of unobscured broad-line active galactic nuclei (BLAGN) in the extreme UV is key to understand accretion onto supermassive black holes, and to calculate the budget of ionizing photons produced by BLAGN over cosmic time. While theory predicts that the peak and shape of this so-called Big Blue Bump should change with black hole mass and luminosity, existing UV composite spectra of BLAGN are either based on simplistic aggregates of archival data or just on luminous quasars. We propose the first dedicated spectroscopic survey to study the Big Blue Bump of low-luminosity BLAGN with HST/COS. Limited archival data on five mostly serendipitously observed objects reveal typical BLAGN UV continua, one of which is truncated by Lyman continuum absorption of neutral gas in the host environment. This may support limited indications from photometry …

Both sets of observations were performed in the radio astronomy" C-band," which comprises the frequency range 4-8 GHz. The 2010-2011 observations were performed during the commissioning and verification phase of the upgrade from the legacy Very Large Array (VLA) hardware and software to the new Karl G. Jansky VLA. As only 2GHz of bandwidth was available for C-band observations at that time, the original set of observations covered the frequency range 5-7GHz. The 2019 observations used the full 4-8GHz range of the C-band receiver by utilizing two pairs of the VLA's 3bit samplers in each antenna.

We observed these targets in the Very Large Array (VLA) C configuration and in the S band (~ 2-4GHz).

Risaliti & Lusso (2015) have developed a method for using quasars to constrain cosmological parameters. Their method depends on the non-linear relationship between X-ray and optical/UV flux (α ox) and reducing possible sources of scatter in that relationship. Scatter could come in the form of dust reddening or gas absorption and/or variability between the optical and X-ray epochs. We find that there is potential for applying a CIV emission-line-based correction in addition to (or instead of) cutting absorbed objects—even after accounting for the trend in X-ray and optical/UV flux with luminosity (Δα ox). It would appear that a simple multi-dimensional linear fit to Δα ox as a function of both X-ray photon index (Gamma) and CIV emission-line properties could be used to make corrections to α ox for individual objects in a way that would further reduce the scatter in the (corrected) α ox distribution. Doing so could enable …

We present damped harmonic oscillator (DHO) light-curve modeling for a sample of 12,714 spectroscopically confirmed quasars in the Sloan Digital Sky Survey Stripe 82 region. DHO is a second-order continuous-time autoregressive moving-average process, which can be fully described using four independent parameters: a natural oscillation frequency (ω 0), a damping ratio (ξ), a characteristic perturbation timescale (τ perturb), and an amplitude for the perturbing white noise (σ epsilon). The asymptotic variability amplitude of a DHO process is quantified by σ DHO—a function of ω 0, ξ, τ perturb, and σ epsilon. We find that both τ perturb and σ epsilon follow different dependencies with rest-frame wavelength (λ RF) on either side of 2500 Å, whereas σ DHO follows a single power-law relation with λ RF. After correcting for wavelength dependence, σ DHO exhibits anticorrelations with both the Eddington ratio and the …

We define a quasar as any object listed in the SDSS catalog of spectroscopically confirmed quasars (the" DR7 Quasar Catalog;" Schneider+ 2010, VII/260).

Using a sample of 438 1.6< z< 2.2 quasars from the SDSS, we explore the use of broad CIV emission to constrain the origins of radio emission in radio-quiet quasars. Accurate placement of the quasar sample in CIV equivalent width (EW)-blueshift space enables the creation of a new emission-line metric, the" CIV distance," which isolates quasars with excess radio emission at either extreme of the CIV parameter space. We find that quasars with small CIV distance (high EW, small blueshift) have high radio detection fractions that are likely the result of small-scale jets or radio-active coronae, while quasars with high CIV distance (low EW, high blueshift) show radio excess that is due either to star formation or shocks from strong quasar winds; quasars with intermediate CIV distance (low EW, low blueshift) show no such excess. These results suggest more than one underlying process, although more dedicated pointed …

We present analysis of a homogeneous, optically selected, volume-limited (0.2< z< 0.3) sample of 128 radio-quiet quasi-stellar objects (QSOs) recently observed at 6 GHz with the Very Large Array (VLA) in A configuration (∼ 0 farcs 33 resolution). We compare these new results to earlier (2010–2011) 6 GHz observations with the VLA in C configuration (∼ 3 farcs 5). While all of these radio-quiet QSOs (RQQs) were unresolved on a 3 farcs 5 scale (∼ 14 kpc at z= 0.25), we resolve notable complex subgalactic structures in about half of the RQQs at 0 farcs 33 resolution (∼ 1.3 kpc at z= 0.25). By comparison of flux density measurements between the two sets of observations, we demonstrate that significant sub-galactic-scale radio structure is present in at least 70% of the RQQ population and that the central component accounts for an average of≈ 65% of the total detected radio power. One RQQ, J0935+ 4819 …

Very-high Energy (VHE) gamma-ray astroparticle physics is a relatively young field, and observations over the past decade have surprisingly revealed almost two hundred VHE emitters which appear to act as cosmic particle accelerators. These sources are an important component of the Universe, influencing the evolution of stars and galaxies. At the same time, they also act as a probe of physics in the most extreme environments known-such as in supernova explosions, and around or after the merging of black holes and neutron stars. However, the existing experiments have provided exciting glimpses, but often falling short of supplying the full answer. A deeper understanding of the TeV sky requires a significant improvement in sensitivity at TeV energies, a wider energy coverage from tens of GeV to hundreds of TeV and a much better angular and energy resolution with respect to the currently running facilities. The next generation gamma-ray observatory, the Cherenkov Telescope Array Observatory (CTAO), is the answer to this need. In this talk I will present this upcoming observatory from its design to the construction, and its potential science exploitation. CTAO will allow the entire astronomical community to explore a new discovery space that will likely lead to paradigm-changing breakthroughs. In particular, CTA has an unprecedented sensitivity to short (sub-minute) timescale phenomena, placing it as a key instrument in the future of multi-messenger and multi-wavelength time domain astronomy.

Current estimates of the normalized accretion rates of quasars (L/L Edd) rely on measuring the velocity widths of broad optical-UV emission lines (eg, Hβ and Mg ii λ2800). However, such lines tend to be weak or inaccessible in the most distant quasars, leading to increasing uncertainty in L/L Edd estimates at z> 6. Utilizing a carefully selected sample of 53 radio-quiet quasars that have Hβ and C iv λ1549 spectroscopy as well as Chandra coverage, we searched for a robust accretion-rate indicator for quasars, particularly at the highest-accessible redshifts (z∼ 6–7). Our analysis explored relationships between the Hβ-based L/L Edd, the equivalent width (EW) of C iv, and the optical-to-X-ray spectral slope (α ox). Our results show that EW (C iv) is the strongest indicator of the Hβ-based L/L Edd parameter, consistent with previous studies, although significant scatter persists particularly for sources with weak C iv lines …

This repository hosts the dataset used in the LSSTC AGN Data Challenge (DC) 2021 (PI: Gordon Richards). More information about the data challenge can be found in the DC GitHub repository @ https://github.com/RichardsGroup/AGN_DataChallenge. Dataset Versions: 1.0: The initial dataset used in the DC, as well as the blinded dataset (ObjectTable_Blinded.parquet) that was used to evaluate submissions. Note that the image cutouts are not included here due to the large size, but the script used to generate those cutouts using SDSS archive services is included in the DC GitHub repository. 1.1: The same dataset as in v1.0 but with the following updates: Uncovered the true coordinates of each source in the dataset Added E(B-V) for every source using the SFD1998 dust map Added spectrum source information (i.e., SDSS fiberid, plate, mjd) if available. Caveat: The optical (grizY) and NIR photometry of sources in the XMM-LSS field is a product of the HSC/VISTA pixel-level joint processing initiative led by Raphael Shirley and Manda Banerji. Thus, it is an early prototype dataset and is still subject to testing and characterization. Citation: The DC dataset released here is a compilation of data from various sources. If you find the DC dataset useful for your research and would like to acknowledge it, please also reference the original sources of the data. Below is a list of publications that you should consider citing. X-ray in XMM-LSS (XMM-SERVS): 2018MNRAS.478.2132C UV Photometry (GALEX): 2017ApJS..230...24B Optical Photometry (in the object/source tables): DES: 2021ApJS..255...20A SDSS Stripe 82 Coadd: 2014ApJ...794..120A HSC …

The SDSS-RM field is a single 7.2 field that coincides with the PS1 Medium Deep Field (MDF) MD07 (RAJ2000= 213.704, DEJ2000=+ 53.083), which lies within the CFHT-LS W3 field. The SDSS-RM sample contains 849 broad-line quasars over a redshift range of 0.1< z< 4.5. Most of the SDSS-RM quasars were previously spectroscopically confirmed quasars in SDSS-I-III.

Broad absorption line quasars (BALQs) exhibit clear evidence for powerful outflows from central supermassive black holes in their rest-UV spectra. FeLoBALQs are a rare type of BALQs that show higher column density outflows with absorption lines from low-ionization ions including FeII. They may represent a short-lived step in quasar evolution where the quasar expels its cocoon of gas and dust. We analyzed 53 FeLoBALQs, measuring the outflow gas properties and estimating the outflow strengths (kinetic luminosities) for all identified BAL outflows using the forward-modeling spectral fitting software SimBAL. We found a large range of physical properties (ionization parameter, density and column density). Notably, the absorbers in the outflows are found from parsecs to kiloparsecs from the central quasar, spanning four orders of magnitude. Patterns and trends among physical conditions and velocity profiles as a …

Abstract The Schwarzschild-Couder Telescope (SCT) is a telescope concept proposed for the Cherenkov Telescope Array. It employs a dual-mirror optical design to remove comatic aberrations over an 8∘ field of view, and a high-density silicon photomultiplier camera (with a pixel resolution of 4 arcmin) to record Cherenkov emission from cosmic ray and gamma-ray initiated particle cascades in the atmosphere. The prototype SCT (pSCT), comprising a 9.7 m diameter primary mirror and a partially instrumented camera with 1536 pixels, has been constructed at the Fred Lawrence Whipple Observatory. The telescope was inaugurated in January 2019, with commissioning continuing throughout 2019. We describe the first campaign of observations with the pSCT, conducted in January and February of 2020, and demonstrate the detection of gamma-ray emission from the Crab Nebula with a statistical significance of 8.6 σ.

The Galactic Center (GC) region hosts a variety of powerful astronomical sources and rare astrophysical processes that emit a large flux of nonthermal radiation. The inner 375 pc× 600 pc region, called the Central Molecular Zone, is home to the supermassive black hole Sagittarius A*, massive cloud complexes, and particle accelerators such as supernova remnants (SNRs). We present the results of our improved analysis of the very-high-energy gamma-ray emission above 2 TeV from the GC using 125 hr of data taken with the Very Energetic Radiation Imaging Telescope Array System imaging-atmospheric Cerenkov telescope between 2010 and 2018. The central source VER J1745–290, consistent with the position of Sagittarius A*, is detected at a significance of 38 standard deviations above the background level (38σ), and we report its spectrum and light curve. Its differential spectrum is consistent with a power law …

We request 190 ks on a uniform sample of 12 optically-selected, low-z, radio-quiet SDSS quasars. The range of L/LEdd complement the~ 60well-studied, but potentially biased (in terms of L/LEdd)``reverberationmapped''(RM) quasars. With both SDSS and HST spectroscopy, we are ableto estimate L/Ledd from 3 optical/UV-based estimators. X-ray data fromChandra enables a 4th L/LEdd estimator (alpha_ox) for the full sample of25 objects. The 12 proposed targets lack sufficient Chandra counts toinvestigate the robustness of the hard X-ray spectral index, Gamma, asan indicator of L/LEdd. Our observations will enable intercomparisonof 5 optical/UV and X-ray estimators of L/LEdd for a well-defined sampleof quasars.

With their emission mainly coming from a relativistic jet pointing toward us, blazars are fundamental sources for studying extragalactic jets and their central engines, consisting of supermassive black holes fed by accretion disks. They are also candidate sources of high-energy neutrinos and cosmic rays. Because of the jet orientation, the nonthermal blazar emission is Doppler beamed; its variability is unpredictable, and it occurs on timescales from less than 1 hr to years. Comprehension of the diverse mechanisms producing the flux and spectral changes requires well-sampled multiband light curves over long time periods. In particular, outbursts are the best test bench for shedding light on the underlying physics, especially when studied in a multiwavelength context. The Vera C. Rubin Legacy Survey of Space and Time (Rubin-LSST) will monitor the southern sky for 10 yr in six photometric bands, offering a …

We use both multi-epoch spectroscopy and multi-wavelength data to develop our understanding of black hole accretion physics. We use the multi-epoch quasar spectra to determine how accurately single-epoch spectroscopy can locate quasars in emission-line parameter space to inform investigations where time-resolved spectroscopy is not available. We explore the improvements in the calculation of emission-line measurements that arise from using non-parametric information from many lines, utilizing reconstructions based on an independent component analysis applied to data from the Sloan Digital Sky Survey Reverberation Mapping project. We further examine multi-wavelength (particularly UV/X-ray) properties of 1378 quasars in order to link correlations in observed parameters to theoretical models of the physical mechanisms dominating quasars as a function of mass and accretion rate. The clarity of …

Using data from SDSS, UKIDSS, and WISE, we investigate the properties of the high-frequency cutoff to the infrared emission in ≃5000 carefully selected luminous (Lbol ∼ 1047) type 1 quasars. The strength of ≃2 μm emission, corresponding to emission from the hottest () dust in the sublimation zone surrounding the central continuum source, is observed to correlate with the blueshift of the C iv λ1550 emission line. We therefore find that objects with stronger signatures of nuclear outflows tend to have a larger covering fraction of sublimation-temperature dust. When controlling for the observed outflow strength, the hot dust covering fraction does not vary significantly across our sample as a function of luminosity, black hole mass, or Eddington fraction. The correlation between the hot dust and the C iv line blueshifts, together with the lack of correlation between the hot dust and other parameters …

We present radio follow-up observations of 101 extremely red quasars (ERQs) with VLA which we combine with detections in the FIRST survey. The observations were carried out using the VLA B configuration in the C band (~ 4-8GHz; Program 16A-108, PI: Zakamska), which provides a resolution of 1.3-arcsec, or~ 10kpc at z= 2.5.

We analyse the properties of the high-ionisation C IVλ1549 broad emission line in connection with the X-ray emission of 30 bright, optically selected quasars at z ≃ 3.0−3.3 with pointed XMM-Newton observations, which were selected to test the suitability of active galactic nuclei as cosmological tools. In our previous work, we found that a large fraction (≈25%) of the quasars in this sample are X-ray under-luminous by factors of > 3−10. As absorbing columns of ≳1023 cm−2 can be safely ruled out, their weakness is most likely intrinsic. Here we explore possible correlations between the UV and X-ray features of these sources to investigate the origin of X-ray weakness with respect to X-ray-normal quasars at similar redshifts. We fit the UV spectra from the Sloan Digital Sky Survey of the quasars in our sample and analyse their C IV properties – for example equivalent width (EW) and line peak velocity (υpeak) – as a …

Vera C. Rubin Observatory is a ground-based astronomical facility under construction, a joint project of the National Science Foundation and the US Department of Energy, designed to conduct a multipurpose 10 yr optical survey of the Southern Hemisphere sky: the Legacy Survey of Space and Time. Significant flexibility in survey strategy remains within the constraints imposed by the core science goals of probing dark energy and dark matter, cataloging the solar system, exploring the transient optical sky, and mapping the Milky Way. The survey's massive data throughput will be transformational for many other astrophysics domains and Rubin's data access policy sets the stage for a huge community of potential users. To ensure that the survey science potential is maximized while serving as broad a community as possible, Rubin Observatory has involved the scientific community at large in the process of setting …

Continuous-time autoregressive moving average (CARMA) processes have became increasingly popular in recent years owing to their success at modeling irregularly-spaced, time-series data and our growing capability of collecting/storing time-domain information. CARMA modeling has been employed in many scientific disciplines; in astronomy, its application is often found in AGN variability analysis. In fact, the extensively studied Damped Random Walk (DRW) model is the lowest order CARMA model—CARMA (1, 0). However, the application of higher-order CARMA models to large data sets has been very limited mostly because of the high computational cost. Here, we introduce a new tool that can significantly speed up the process of fitting CARMA models to time series by utilizing'celerite', a fast gaussian process (GP) modeling library that can compute the likelihood for a certain class of GPs in O (NJ 2 …

The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will observe several Deep Drilling Fields (DDFs) to a greater depth and with a more rapid cadence than the main survey. In this paper, we describe the ‘DeepDrill’ survey, which used the Spitzer Space Telescope Infrared Array Camera (IRAC) to observe three of the four currently defined DDFs in two bands, centred on 3.6 and 4.5 μm. These observations expand the area that was covered by an earlier set of observations in these three fields by the Spitzer Extragalactic Representative Volume Survey (SERVS). The combined DeepDrill and SERVS data cover the footprints of the LSST DDFs in the Extended Chandra Deep Field–South (ECDFS) field, the ELAIS-S1 field (ES1), and the XMM-Large-Scale Structure Survey field (XMM-LSS). The observations reach an approximate 5σ point-source depth of 2 μJy (corresponding to an AB magnitude of …

In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass∼ 6.5× 109Me. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss …

We report on the search for very-high-energy gamma-ray emission from the regions around three nearby supersonic pulsars (PSR B0355+ 54, PSR J0357+ 3205, and PSR J1740+ 1000) that exhibit long X-ray tails. To date there is no clear detection of TeV emission from any pulsar tail that is prominent in X-ray or radio. We provide upper limits on the TeV flux, and luminosity, and also compare these limits with other pulsar wind nebulae detected in X-rays and the tail emission model predictions. We find that at least one of the three tails is likely to be detected in observations that are a factor of 2–3 more sensitive. The analysis presented here also has implications for deriving the properties of pulsar tails, for those pulsars whose tails could be detected in TeV.

We discuss a probe of the contribution of wind-related shocks to the radio emission in otherwise radio-quiet quasars. Given (1) the nonlinear correlation between UV and X-ray luminosity in quasars,(2) that such a correlation leads to higher likelihood of radiation-line-driven winds in more luminous quasars, and (3) that luminous quasars are more abundant at high redshift, deep radio observations of high-redshift quasars are needed to probe potential contributions from accretion disk winds. We target a sample of 50 z≃ 1.65 color-selected quasars that span the range of expected accretion disk wind properties as traced by broad C iv emission. 3 GHz observations with the Very Large Array to an rms of≈ 10 μJy beam− 1 probe to star formation rates of∼ 400 M⊙ yr− 1, leading to 22 detections. Supplementing these pointed observations are survey data of 388 sources from the LOFAR Two-meter Sky Survey Data …

Black hole-galaxy feedback is an established ingredient in cosmological structure formation simulations, but the contribution of quasars to feedback is not observationally determined. Among the candidates for quasar-mode feedback are broad absorption line (BAL) outflows and ionized emission-line outflows. These phenomena are found at similar distances from the central engine (parsecs to kiloparsecs), and they are both powered by photoionization of gas with similar physical conditions. It is conceivable that they are manifestations of the same outflowing gas, with the difference being that BAL quasar outflows are observed in the line of sight to the continuum source.

We present spectroscopic measurements for 226 sources from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS). Being the largest uniform, homogeneous survey of its kind, it represents a flux-limited sample (m i≲ 19.0 mag, H≲ 16.5 mag) of Sloan Digital Sky Survey (SDSS) quasars at 1.5≲ z≲ 3.5 with a monochromatic luminosity (

We have obtained NIR (~ 0.8-2.5 um) spectra of 272 quasars at high redshift using the Gemini Near-Infrared Spectrograph (GNIRS), at the Gemini North Observatory, with a Gemini Large and Long Program. Our Distant Quasar Survey (GNIRS-DQS) was designed to produce spectra that, at a minimum, encompass the essential Hβ and [OIII] region in each source.

In this paper, we present an analysis of the observations of the high-synchrotron-peaked BL Lac (HBL) 1ES 1215+ 303 between 2008 and 2017 from radio to VHE gamma-ray energies.

The Kepler satellite potentially provides the highest precision photometry of active galactic nuclei (AGNs) available to investigate short-timescale optical variability. We targeted quasars from the Sloan Digital Sky Survey that lie in the fields of view of the Kepler/K2 campaigns. Based on those observations, we report the discovery and properties of a previously unidentified instrumental signature in K2. Systematic errors in K2, beyond those due to the motion of the detector, plague our AGNs and other faint-target, guest observer science proposals. Weakly illuminated pixels are dominated by low-frequency trends that are both nonastrophysical and correlated from object to object. The instrumental signature lags in time as a function of radius from the center of the detector, crossing channel boundaries. Thus, systematics documented in this investigation are unlikely to be due to Moiré noise, rolling band, or pointing jitter …

Broad absorption line (BAL) features in quasar spectra reveal unambiguous signatures of energetic outflows from central supermassive black holes. BAL quasars are thus prime targets for investigating the potential mechanism of luminous quasar feedback on galaxies. We have developed a powerful forward-modeling spectral synthesis tool, SimBAL, that allows us to extract the physical properties of these outflows from high signal-to-noise-ratio spectra. We have the greatest success from broad-band spectra with absorption lines from ions with a range of ionization and excitation energies. A notable recent result from SimBAL analysis is the discovery of an extreme outflow from the overlapping-trough iron low-ionization BAL quasar, SDSS J1352+ 4239, with a measured kinetic luminosity of 10 erg/s. Further analysis of this population of BAL quasars holds promise for understanding the upper range of kinetic power …

We present an investigation of the low-frequency radio and ultraviolet properties of a sample of ≃10 500 quasars from the Sloan Digital Sky Survey Data Release 14, observed as part of the first data release of the Low-Frequency-Array Two-metre Sky Survey. The quasars have redshifts 1.5 < z < 3.5 and luminosities . We employ ultraviolet spectral reconstructions based on an independent component analysis to parametrize the C iv λ1549-emission line that is used to infer the strength of accretion disc winds, and the He ii λ1640 line, an indicator of the soft X-ray flux. We find that radio-detected quasars are found in the same region of C iv blueshift versus equivalent-width space as radio-undetected quasars, but that the loudest, most luminous and largest radio sources exist preferentially at low C iv blueshifts. Additionally, the radio-detection fraction increases with blueshift …

The orientation of the disk of material accreting onto supermassive black holes that power quasars is one of most important quantities that are needed to understand quasars—both individually and in the ensemble average. We present a hypothesis for determining comparatively edge-on orientation in a subset of quasars (both radio loud and radio quiet). If confirmed, this orientation indicator could be applicable to individual quasars without reference to radio or X-ray data and could identify some 10%–20% of quasars as being more edge-on than average, based only on moderate resolution and signal-to-noise spectroscopy covering the C iv λ 1549 Å emission feature. We present a test of said hypothesis using X-ray observations and identify additional data that are needed to confirm this hypothesis and calibrate the metric.

Recent observations of the gamma-ray source HAWC J2227+610 by Tibet AS+MD and LHAASO confirm the special interest of this source as a galactic PeVatron candidate in the northern hemisphere. HAWC J2227+610 emits Very High Energy (VHE) gamma-rays up to 500 TeV, from a region coincident with molecular clouds and significantly displaced from the nearby pulsar J2229+6114. Even if this morphology favours an hadronic origin, both leptonic or hadronic models can describe the current VHE gamma-ray emission. The morphology of the source is not well constrained by the present measurements and a better characterisation would greatly help the understanding of the underlying particle acceleration mechanisms. The Cherenkov Telescope Array (CTA) will be the future most sensitive Imaging Atmospheric Cherenkov Telescope and, thanks to its unprecedented angular resolution, could contribute to better constrain the nature of this source. The present work investigates the potentiality of CTA to study the morphology and the spectrum of HAWC J2227+610. For this aim, the source is simulated assuming the hadronic model proposed by the Tibet AS+MD collaboration, recently fitted on multi-wavelength data, and two spatial templates associated to the source nearby molecular clouds. Different CTA layouts and observation times are considered. A 3D map based analysis shows that CTA is able to significantly detect the extension of the source and to attribute higher detection significance to the simulated molecular cloud template compared to the alternative one. CTA data does not allow to disentangle the hadronic and the leptonic emission …

High angular resolution observations at optical wavelengths provide valuable insights into stellar astrophysics,, and enable direct measurements of fundamental stellar parameters, and the probing of stellar atmospheres, circumstellar disks, the elongation of rapidly rotating stars and the pulsations of Cepheid variable stars. The angular size of most stars is of the order of one milliarcsecond or less, and to spatially resolve stellar disks and features at this scale requires an optical interferometer using an array of telescopes with baselines on the order of hundreds of metres. We report on the implementation of a stellar intensity interferometry system developed for the four VERITAS imaging atmospheric Cherenkov telescopes. The system was used to measure the angular diameter of the two sub-milliarcsecond stars β Canis Majoris and ϵ Orionis with a precision of greater than 5%. The system uses an offline approach in …

We present a study of γ-ray emission from the core-collapse supernova remnant Cas A in the energy range from 0.1 GeV to 10 TeV. We used 65 hr of the Very Energetic Radiation Imaging Telescope Array System (VERITAS) data to cover 200 GeV–10 TeV, and 10.8 yr of Fermi-Large Area Telescope (LAT) data to cover 0.1–500 GeV. The spectral analysis of Fermi-LAT data shows a significant spectral curvature around 1.3±0.4 stat GeV that is consistent with the expected spectrum from pion decay. Above this energy, the joint spectrum from Fermi-LAT and VERITAS deviates significantly from a simple power law, and it is best described by a power law with a spectral index of 2.17±0.02 stat and a cutoff energy of 2.3±0.5 stat TeV. These results, along with radio, X-ray, and γ-ray data, are interpreted in the context of leptonic and hadronic models. Assuming a one-zone model, we exclude a purely leptonic scenario and …

Blazars are a subclass of radio-loud active galactic nuclei (AGNs) with jets of relativistic material beamed nearly along the line of sight (Blandford & Rees 1978; Urry & Padovani 1995) whose nonthermal radiation is observed across the entire spectrum, from radio to γ-rays. Due to Doppler beaming, the bolometric luminosity of blazars can be dominated by very high energy (VHE;> 100 GeV) γ-rays. At a redshift of z= 0.031, Mrk 421 is the closest known BL Lac object (de Vaucouleurs et al. 1995) and the first extragalactic object to be detected in VHE γ-rays (Punch et al. 1992). Blazars now comprise the majority source class of VHE extragalactic γ-ray emitters (Wakely & Horan 2008), and while there is much we have learned from multiwavelength data taken over the past 40 years on Mrk 421 and other blazars, there remain many unanswered questions. Indeed, there is still no general agreement on the particle …

We present the results of our attempts to identify a robust accretion-rate indicator for quasars based on a unique quasar sample. We selected 48 quasars from the Chandra X-ray Observatory archive that are radio quiet, do not have broad absorption lines, and have high-quality data in the C IV and Hβ spectral bands. Among the various spectral properties that we investigated, our results show that the equivalent width (EW) of C IV is the strongest indicator of the Hβ-based Eddington ratio. We do not find evidence for broad-band optical-X-ray emission (ie, α ox) improving predictions of the latter parameter. Since about half of our sources have optical-band monochromatic luminosities above 10 45.5 erg/s, a potential explanation of this result could be that a strong correlation between EW (C IV) and α ox is only observed above a certain luminosity threshold above which strong quasar winds may form. Shallow Chandra …

We propose to perform a Chandra archival investigation of SDSS quasars that have been sub-classed based on their UV emission-line features in a novel manner using Independent Component Analysis. This analysis captures the full covariance of the UV emission features (both weak and strong) in a way that maximizes our knowledge of the diversity of intrinsic quasar properties. We will investigate how evidence for accretion disk winds changes as a function of their combined UV and X-ray properties, including alpha_ox, Gamma, and X-ray weak/normal fraction using both detected objects and stacking analysis. A preliminary query of the Chandra Source Catalog reveals that there is sufficient data to carry out the project and to test the archive for potential aggregated target-selection biases.

Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multiwavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+ 303 (z= 0.130), with a focus on its gamma-ray emission from 100 MeV to 30 TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline, and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by Very Long …

In this paper, we provide updated constraints on the bolometric quasar luminosity function (QLF) from z = 0 to z = 7. The constraints are based on an observational compilation that includes observations in the rest-frame IR, B band, UV, soft, and hard X-ray in past decades. Our method follows Hopkins et al. with an updated quasar SED model and bolometric and extinction corrections. The new best-fitting bolometric quasar luminosity function behaves qualitatively different from the old Hopkins model at high redshift. Compared with the old model, the number density normalization decreases towards higher redshift and the bright-end slope is steeper at z ≳ 2. Due to the paucity of measurements at the faint end, the faint end slope at z ≳ 5 is quite uncertain. We present two models, one featuring a progressively steeper faint-end slope at higher redshift and the other featuring a shallow faint-end slope at z ≳ 5 …

The Very Large Array Sky Survey (VLASS) is a synoptic, all-sky radio sky survey with a unique combination of high angular resolution (≈ 2 farcs 5), sensitivity (a 1σ goal of 70 μJy/beam in the coadded data), full linear Stokes polarimetry, time domain coverage, and wide bandwidth (2–4 GHz). The first observations began in 2017 September, and observing for the survey will finish in 2024. VLASS will use approximately 5500 hr of time on the Karl G. Jansky Very Large Array (VLA) to cover the whole sky visible to the VLA (decl.>− 40), a total of 33 885 deg . The data will be taken in three epochs to allow the discovery of variable and transient radio sources. The survey is designed to engage radio astronomy experts, multi-wavelength astronomers, and citizen scientists alike. By utilizing an" on the fly" interferometry mode, the observing overheads are much reduced compared to a conventional pointed survey. In this …

We use multiepoch quasar spectroscopy to determine how accurately single-epoch spectroscopy can locate quasars in emission-line parameter space in order to inform investigations where time-resolved spectroscopy is not available. We explore the improvements in emission-line characterization that result from using nonparametric information from many lines as opposed to a small number of parameters for a single line, utilizing reconstructions based on an independent component analysis applied to the data from the Sloan Digital Sky Survey Reverberation Mapping project. We find that most of the quasars are well described by just two components, while more components signal a quasar likely to yield a successful reverberation mapping analysis. In single-epoch spectroscopy the apparent variability of equivalent width is exaggerated because it is dependent on the continuum. Multiepoch spectroscopy …

Broad absorption-line (BAL) features in quasar spectra reveal an unambiguous signature of energetic outflows from central supermassive black holes, and thus, BAL quasars are prime targets for investigating the potential process of luminous quasar feedback on galaxies. We analyzed the rest-UV spectrum of an" overlapping trough" iron low-ionization broad absorption-line quasar (FeLoBAL) SDSS J135246. 37+ 423923.5 using the novel spectral synthesis code SimBAL and discovered an extraordinarily fast and energetic BAL outflow. Our analysis revealed outflow velocities reaching

With 8 h of observations, VERITAS confirms the detection of two very high energy gamma-ray sources. The gamma-ray binary LS 5039 is detected with a statistical significance of 8.8 σ. The measured flux above 1 TeV is (2.5±0.4)× 10− 12 cm− 2 s− 1 near inferior conjunction and (7.8±2.8)× 10− 13 cm− 2 s− 1 near superior conjunction. The pulsar wind nebula HESS J1825-137 is detected with a statistical significance of 6.7σ and a measured flux above 1 TeV of (3.9±0.8)× 10− 12 cm− 2 s− 1.

HESS J0632+ 057 is a gamma-ray binary composed of a compact object orbiting a Be star with a period of about 315 days. Extensive X-ray and TeV gamma-ray observations have revealed a peculiar light curve containing two peaks, separated by a dip. We present the results of simultaneous observations in hard X-rays with NuSTAR and in TeV gamma-rays with VERITAS, performed in 2017 November and December. These observations correspond to the orbital phases ϕ≈ 0.22 and 0.3, where the fluxes are rising toward the first light-curve peak. A significant variation of the spectral index from 1.77±0.05 to 1.56±0.05 is observed in the X-ray data. The multiwavelength spectral energy distributions (SED) derived from the observations are interpreted in terms of a leptonic model, in which the compact object is assumed to be a pulsar and nonthermal radiation is emitted by high-energy electrons accelerated at the …

The radio source 3C 264, hosted by the giant elliptical galaxy NGC 3862, was observed with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) between 2017 February and 2019 May. These deep observations resulted in the discovery of very high energy (VHE; E> 100 GeV) γ-ray emission from this active galaxy. An analysis of∼ 57 hr of quality-selected live time yields a detection at the position of the source, corresponding to a statistical significance of 7.8 standard deviations above background. The observed VHE flux is variable on monthly timescales, with an elevated flux seen in 2018 observations. The VHE emission during this elevated state is well characterized by a power-law spectrum with a photon index Γ= 2.20±0.27 and flux F (> 315 GeV)=(

We present by far the largest sample of spectroscopically confirmed binary quasars with proper transverse separations of 17.0<= R<= 36.2 h-1 kpc. Our sample, which is~ 6x larger than any previous homogeneously selected sample on these proper scales, is derived from SDSS imaging over an area corresponding to SDSS DR6. Our quasars are targeted using a KDE technique, and confirmed using long-slit spectroscopy on a range of facilities. We derive a statistically complete subsample of 47 binary quasars with g< 20.85, which extends across angular scales of 2.9-arcsec<{DELTA} θ< 6.3-arcsec and redshifts of 0.43< z< 2.26.

At high-redshift CIV EQW and blueshift capture most of the diversity of the broad emission-line properties of quasars. It has been posited that the relationships between these two properties suggest a two-component (disk-wind) model of the broad-emission-line region (BELR) where the component that dominates is a function of L/L Edd. In order to correctly classify quasars and further investigate physical models we must first know how accurately single-epoch spectroscopy can locate quasars in emission line parameter space when multi-epoch spectroscopy is not available. We aim to ascertain the true distribution of quasars in CIV parameter space and how variability (as well as noise) may result in the movement of an individual object in the parameter space over time. We investigate the diversity of SDSSRM quasars using independent component analysis (ICA); a computational technique which is able to …

Clustering measurements of obscured and unobscured quasars show that obscured quasars reside in more massive dark matter halos than their unobscured counterparts. These results are inconsistent with simple unified (torus) scenarios but might be explained by models in which the distribution of obscuring material depends on Eddington ratio or galaxy stellar mass. We test these possibilities by constructing simple physical models to compare to observed active galactic nucleus populations. We find that previously observed relationships between obscuration and Eddington ratio or stellar mass are not sufficient to reproduce the observed quasar clustering results (

We investigate how measurements of differential chromatic refraction might influence choices for survey strategy in the Legacy Survey of Space and Time.

There is a well-known correlation between the mass of the supermassive black hole at the center of a galaxy and the mass of that galaxy's spheroidal component. However, the sphere of gravitational influence for the supermassive black hole is small relative to the size of the galaxy. This means that there must be some method of feedback between the supermassive black hole and its host. A promising potential avenue for such feedback is quasar outflows. Quasar outflows manifest themselves unambiguously through blue-shifted absorption lines in Broad Absorption Line Quasars (BALQs). The rarest subclass of BALQs with the most morphologically diverse spectra are known as FeLoBALs. These objects are named for the presence of absorption lines from Fe+, observed in the rest frame UV. The presence of thousands of observable Fe+ transitions allows for excellent constraints on the physical conditions of the …

Using a sample of ≃144 000 quasars from the Sloan Digital Sky Survey Data Release 14, we investigate the outflow properties, evident in both absorption and emission, of high-ionization broad absorption line (BAL) and non-BAL quasars with redshifts 1.6 ≲ ≤ 3.5 and luminosities 45.3 erg s−1 < log10(Lbol) < 48.2 erg s−1. Key to the investigation is a continuum and emission-line reconstruction scheme, based on mean-field independent component analysis, that allows the kinematic properties of the C iv λ1550 emission line to be compared directly for both non-BAL and BAL quasars. C iv emission blueshift and equivalent width (EW) measurements are thus available for both populations. Comparisons of the emission-line and BAL trough properties reveal strong systematic correlations between the emission and absorption properties. The dependence of quantitative outflow indicators on physical …

The optical/UV emission-line properties of quasars are highly correlated, yet analyses of quasar spectra typically throw away most of the information available by measuring just a few line parameters of a few of the emission lines. While principal component analysis (PCA) can capture more information, the components are mathematical constructs with orthogonality constraints that may not accurately describe the physics underlying the correlated behavior. We show that using instead Mean Field Independent Component Analysis (MFICA) has the potential for revealing more meaningful ties between empirical observations and the physics that underlies the data. Not only are emission-line properties correlated, but MFICA also reveals correlations between emission and absorption (including both NALs and BALs), X-ray and radio properties of quasars. We further explore how MFICA can help to improve the signal-to …