A5039703984- Gamma-ray bursts and supernovae
- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Astrophysical Phenomena and Observations
- Stellar, planetary, and galactic studies
- SAS software applications and methods
- Astronomical Observations and Instrumentation
- Astrophysics and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Statistical and numerical algorithms
- Astro and Planetary Science
- Geophysics and Gravity Measurements
- Adaptive optics and wavefront sensing
- Pulsars and Gravitational Waves Research
- Calibration and Measurement Techniques
- Solar and Space Plasma Dynamics
- Astrophysics and Star Formation Studies
- Remote Sensing in Agriculture
- Multidisciplinary Science and Engineering Research
- Advanced Statistical Methods and Models
- Complex Systems and Time Series Analysis
- Advanced Optical Sensing Technologies
- History and Developments in Astronomy
- Satellite Image Processing and Photogrammetry
- Plant Water Relations and Carbon Dynamics
Center for Astrophysics Harvard & Smithsonian
2017-2023
Blackstone (United States)
2021-2023
University of Washington
2008-2019
Harvard University Press
2019
United States Naval Academy
2012-2016
UK Astronomy Technology Centre
2015-2016
University of Edinburgh
2015-2016
Scottish Universities Physics Alliance
2016
Royal Observatory
2016
Institut Català de Ciències del Clima
2012
We model the time variability of ∼9000 spectroscopically confirmed quasars in SDSS Stripe 82 as a damped random walk (DRW). Using 2.7 million photometric measurements collected over 10 yr, we confirm results Kelly et al. and Kozłowski that this can explain quasar light curves at an impressive fidelity level (0.01–0.02 mag). The DRW provides simple, fast (O(N) for N data points), powerful statistical description by characteristic timescale (τ) asymptotic rms on long timescales (SF∞). searched...
We provide a quantitative description and statistical interpretation of the optical continuum variability quasars. The Sloan Digital Sky Survey (SDSS) has obtained repeated imaging in five UV-to-IR photometric bands for 33,881 spectroscopically confirmed About 10,000 quasars have an average 60 observations each band over decade along Stripe 82 (S82), whereas remaining ~25,000 2-3 due to scan overlaps. observed time lags span range from day almost 10 years, constrain quasar at rest-frame up 4...
We present the Data Release 9 Quasar (DR9Q) catalog from Baryon Oscillation Spectroscopic Survey (BOSS) of Sloan Digital Sky III. The includes all BOSS objects that were targeted as quasar candidates during survey, are spectrocopically confirmed quasars via visual inspection, have luminosities Mi[z=2]<-20.5 (in a $\Lambda$CDM cosmology with H0 = 70 km/s/Mpc, $\Omega_{\rm M}$ 0.3, and $\Omega_{\Lambda}$ 0.7) either display at least one emission line full width half maximum (FWHM) larger than...
We present a systematic search for changing-look quasars based on repeat photometry from Sloan Digital Sky Survey (SDSS) and Pan-STARRS1, along with spectra SDSS SDSS-III Baryon Oscillation Spectroscopic Survey. Objects large, |Δg| > 1 mag photometric variations in their light curves are selected as candidates to look changes broad emission line (BEL) features. Out of sample 1011 objects that satisfy our selection criteria have more than one epoch spectroscopy, we find 10 examples variable...
We present the Data Release 14 Quasar catalog (DR14Q) from extended Baryon Oscillation Spectroscopic Survey (eBOSS) of Sloan Digital Sky IV (SDSS-IV). This includes all SDSS-IV/eBOSS objects that were spectroscopically targeted as quasar candidates and are confirmed quasars via a new automated procedure combined with partial visual inspection spectra, have luminosities $M_{\rm i} \left[ z=2 \right] < -20.5$ (in $Λ$CDM cosmology $H_0 = 70 \ {\rm km s^{-1} Mpc ^{-1}}$, $Ω_{\rm M} 0.3$, Λ}...
Measured gravitational waveforms from black hole binary inspiral events directly determine absolute luminosity distances. To use these data for cosmology, it is necessary to independently obtain redshifts the events, which may be difficult those without electromagnetic counterparts. Here demonstrated that certainly in principle, and possibly practice, clustering of galaxies allows extraction redshift information a sample statistically purpose estimating mean cosmological parameters,...
Abstract Active galactic nuclei (AGNs) that show strong rest-frame optical/UV variability in their blue continuum and broad line emission are classified as changing-look AGN, or at higher luminosities, quasars (CLQs). These surprisingly large sometimes rapid transitions challenge accepted models of quasar physics duty cycles, offer several new avenues for study host galaxies, open a wider interpretation the cause differences between narrow-line AGN. To better characterize extreme...
Abstract We present the drastic transformation of X-ray properties active galactic nucleus (AGN) 1ES 1927+654, following a changing-look event. After optical/ultraviolet outburst power-law component, produced in corona, disappeared, and spectrum 1927+65 instead became dominated by blackbody component ( kT ∼ 80–120 eV). This implies that ubiquitously found AGNs, was destroyed Our dense ∼450 days long monitoring shows source is extremely variable band. On timescales varies up to ∼4 dex ∼100...
Abstract Despite their factor of ∼10 8 difference in black hole mass, several lines evidence suggest possible similarities between accretion flows active galactic nuclei (AGN) and Galactic X-ray binaries. However, it is still unclear whether the geometry disk–corona system binaries directly scales up to AGN this analogy holds different states. We test AGN/X-ray binary by comparing observed correlations UV–to–X-ray spectral index ( α OX ) Eddington ratio those predicted from observations...
Abstract Active galactic nuclei (AGN) can vary significantly in their rest-frame optical/UV continuum emission, and with strong associated changes broad line on much shorter timescales than predicted by standard models of accretion disks around supermassive black holes. Most such changing-look or changing-state AGN—and at higher luminosities, quasars (CLQs)—have been found via spectroscopic follow-up known showing photometric variability. The Time Domain Spectroscopic Survey the Sloan...
We conduct a pilot investigation to determine the optimal combination of color and variability information identify quasars in current future multi-epoch optical surveys. use Bayesian quasar selection algorithm 35,820 type 1 candidates 239 field Sloan Digital Sky Survey (SDSS) Stripe 82, using photometry variability. Color analysis is performed on 5-band single- SDSS depth From these data, parameters are calculated by fitting structure function each object band with power-law model 10...
We study the time lags between continuum emission of quasars at different wavelengths, based on more than four years multi-band ($g$, $r$, $i$, $z$) light-curves in Pan-STARRS Medium Deep Fields. As photons from bands emerge radial ranges accretion disk, constrain sizes disks. select 240 with redshifts $z \approx 1$ or 0.3$ that are relatively line free. The light curves sampled day to month timescales, which makes it possible detect scale crossing With code JAVELIN, we typical several days...
We review results from our monitoring observations of several lensed quasars performed in the optical, UV, and X-ray bands. Modeling multi-wavelength light curves provides constraints on extent emission regions. One important analysis is that optical sizes as inferred microlensing are significantly larger than those predicted by theoretical-thin-disk estimate. In a few cases we also constrain slope size-wavelength relation. Our size soft hard regions indicate some objects sample region more...
We develop a method for separating quasars from other variable point sources using Sloan Digital Sky Survey (SDSS) Stripe 82 light-curve data ∼ 10,000 objects. To statistically describe quasar variability, we use damped random walk model parametrized by damping timescale, τ, and an asymptotic amplitude (structure function), SF∞. With the aid of SDSS spectroscopically confirmed sample, demonstrate that variability selection in typical extragalactic fields with low stellar density can deliver...
We analyze the optical, UV, and X-ray microlensing variability of lensed quasar SDSS J0924+0219 using six epochs Chandra data in two energy bands (spanning 0.4–8.0 keV, or 1–20 keV rest frame), 10 F275W (rest-frame 1089 Å) Hubble Space Telescope data, high-cadence R-band 2770 monitoring spanning 11 years. Our joint analysis provides robust constraints on extent continuum emission region projected area accretion disk. The best-fit half-light radius soft is between 1015 cm, we find an upper...
We report the discovery by Palomar Transient Factory (PTF) of transient source PTF11agg, which is distinguished three primary characteristics: (1) bright (Rpeak = 18.3 mag), rapidly fading (ΔR 4 mag in Δt 2 days) optical emission; (2) a faint (R 26.2 ± 0.2 blue (g' − R 0.17 0.29 mag) quiescent counterpart; and (3) an associated year-long, scintillating radio transient. argue that these observed properties are inconsistent with any known class Galactic transients (flare stars, X-ray binaries,...
We discuss 76 large amplitude transients (Delta-m>1.5) occurring in the nuclei of galaxies, nearly all with no previously known Active Galactic Nucleus (AGN). They have been discovered as part Pan-STARRS1 (PS1) 3pi survey, by comparison SDSS photometry a decade earlier, and then monitored Liverpool Telescope, studied spectroscopically William Herschel Telescope (WHT). Based on colours, light curve shape, spectra, these fall into four groups. A few are misclassified stars or objects unknown...
Abstract We study the sudden optical and ultraviolet (UV) brightening of 1ES 1927+654, which until now was known as a narrow-line active galactic nucleus (AGN). 1927+654 part small peculiar class “true Type-2” AGNs that lack broad emission lines line-of-sight obscuration. Our high-cadence spectroscopic monitoring captures appearance blue, featureless continuum, followed several weeks later by Balmer lines. This timescale is generally consistent with expected light travel time between central...
Abstract Extremely variable quasars can also show strong changes in broad-line emission strength and are known as changing-look (CLQs). To study the CLQ transition mechanism, we present a pilot sample of CLQs with X-ray observations both bright faint states. From bright-state archival SDSS spectra (Chandra or XMM-Newton) data, identified five new via optical spectroscopic follow-up then obtained target-of-opportunity Chandra. No absorption is detected either bright- faint-state spectra. The...
We investigate the use of optical photometric variability to select and identify blazars in large-scale time-domain surveys, part aid identification blazar counterparts ~30% gamma-ray sources Fermi 2FGL catalog still lacking reliable associations. Using data from LINEAR asteroid survey, we characterize by fitting a damped random walk model individual light curves with two main parameters, characteristic timescales (tau), driving amplitudes on short (sigma). Imposing cuts minimum tau sigma...
We present 11.2 μm observations of the gravitationally lensed, radio-loud zs = 2.64 quasar MG0414+0534, obtained using Michelle camera on Gemini North. find a flux ratio anomaly A2/A1 0.93 ± 0.02 for images A1 and A2. When combined with 11.7 measurements from Minezaki et al., is nearly 5σ expected model based two visible lens galaxies. The mid-IR can be explained by satellite (substructure), 03 northeast image A2, as detailed very long baseline interferometry (VLBI) structures jet produced...
We report the results of a Sloan Digital Sky Survey-IV eBOSS program to target X-ray sources and mid-infrared-selected WISE AGN candidates in 36.8 deg$^2$ region Stripe 82. About half this survey (15.6 deg$^2$) covers largest contiguous portion 82 survey. This represents spectroscopic selected solely by their colors. combine sample with field identified via other spectroscopy, producing catalog 4847 that is 82% complete $r\sim22$. Based on luminosities or colors, 4730 these are AGN, median...
Abstract We report the discovery of a new “changing-look” active galactic nucleus (CLAGN) event, in quasar SDSS J162829.17+432948.5 at z = 0.2603, identified through repeat spectroscopy from fifth Sloan Digital Sky Survey (SDSS-V). Optical photometry taken during 2020–2021 shows dramatic dimming Δ g ≈ 1 mag, followed by rapid recovery on timescale several months, with ≲2 month period rebrightening captured SDSS-V and Las Cumbres Observatory spectroscopy. This is one fastest CLAGN transitions...
We investigate broad absorption line (BAL) disappearance and emergence using a 470 BAL-quasar sample over < 0.10-5.25 rest-frame years with at least three spectroscopic epochs for each quasar from the Sloan Digital Sky Survey. identify 14 disappearing BALs 1.73-4.62 18 emerging 1.46-3.66 associated CIV 1548,1550 and/or SiIV 1393,1402 doublets, report on their variability behavior. BAL quasars in our dataset exhibit disappearing/emerging rate of 2.3 3.0 per cent, respectively, frequency to...