Author: "Chelsea L. MacLeod" - Searchworks@Jio Institute Digital Library Search Results

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73 results on '"Chelsea L. MacLeod"'

1. Erratum: 'Changing-Look Quasar Candidates: First Results from Follow-up Spectroscopy of Highly Optically Variable Quasars' (2019, ApJ, 874, 8)

Author: Chelsea L. MacLeod, Paul J. Green, Scott F. Anderson, Alastair Bruce, Michael Eracleous, Matthew Graham, David Homan, Andy Lawrence, Amy LeBleu, Nicolas P. Ross, John J. Ruan, Jessie Runnoe, Daniel Stern, William Burgett, Kenneth C. Chambers, Nick Kaiser, Eugene Magnier, and Nigel Metcalfe
Subjects: Astrophysics, QB460-466
Published: 2023
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2. Probing the Origin of Changing-look Quasar Transitions with Chandra

Author: Qian Yang, Paul J. Green, Chelsea L. MacLeod, Richard M. Plotkin, Scott F. Anderson, Allyson Bieryla, Francesca Civano, Michael Eracleous, Matthew Graham, John J. Ruan, Jessie Runnoe, and Xiurui Zhao
Subjects: Accretion, Quasars, Active galactic nuclei, Variable radiation sources, Catalogs, Astrophysics, QB460-466
Abstract: Extremely variable quasars can also show strong changes in broad-line emission strength and are known as changing-look quasars (CLQs). To study the CLQ transition mechanism, we present a pilot sample of CLQs with X-ray observations in both the bright and faint states. From a sample of quasars with bright-state archival SDSS spectra and (Chandra or XMM-Newton) X-ray data, we identified five new CLQs via optical spectroscopic follow-up and then obtained new target-of-opportunity X-ray observations with Chandra. No strong absorption is detected in either the bright- or the faint-state X-ray spectra. The intrinsic X-ray flux generally changes along with the optical variability, and the X-ray power-law slope becomes harder in the faint state. Large-amplitude mid-infrared variability is detected in all five CLQs, and it echoes the variability in the optical with a time lag expected from the light-crossing time of the dusty torus for CLQs with robust lag measurements. The changing-obscuration model is not consistent with the observed X-ray spectra and spectral energy distribution changes seen in these CLQs. It is highly likely that the observed changes are due to the changing accretion rate of the supermassive black hole, so the multiwavelength emission varies accordingly, with promising analogies to the accretion states of X-ray binaries.
Published: 2023
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3. The ‘Big Dipper’: the nature of the extreme variability of the AGN SDSS J2232−0806

Author: Daniel Kynoch, Martin J Ward, Andy Lawrence, Alastair G Bruce, Hermine Landt, and Chelsea L MacLeod
Published: 2019
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4. The Time Domain Spectroscopic Survey: Changing-look Quasar Candidates from Multi-epoch Spectroscopy in SDSS-IV

Author: Paul J. Green, Lina Pulgarin-Duque, Scott F. Anderson, Chelsea L. MacLeod, Michael Eracleous, John J. Ruan, Jessie Runnoe, Matthew Graham, Benjamin R. Roulston, Donald P. Schneider, Austin Ahlf, Dmitry Bizyaev, Joel R. Brownstein, Sonia Joesephine del Casal, Sierra A. Dodd, Daniel Hoover, Cayenne Matt, Andrea Merloni, Kaike Pan, Arnulfo Ramirez, Margaret Ridder, and Serena Moseley
Published: 2022
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5. Behaviour of the Mg ii 2798 Å line over the full range of AGN variability

Author: Alastair Bruce, Andy Lawrence, Nicholas P. Ross, D. Homan, and Chelsea L. MacLeod
Subjects: Physics, Continuum (measurement), Population sample, 010308 nuclear & particles physics, Baldwin effect, astro-ph.GA, media_common.quotation_subject, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics - Astrophysics of Galaxies, 01 natural sciences, Asymmetry, Line width, symbols.namesake, Space and Planetary Science, Skewness, Astrophysics of Galaxies (astro-ph.GA), 0103 physical sciences, symbols, Emission spectrum, 010303 astronomy & astrophysics, media_common
Abstract: We investigate the responsiveness of the 2798AA Mg II broad emission line in AGN on timescales of several years. Our study is based on a sample of extremely variable AGN as well as a broad population sample. The observed response of the line in previous studies has been mixed. By focussing on extreme variability ($|\Delta g|>$ 1) we find that Mg II clearly does respond to the continuum. However, the degree of responsiveness varies strikingly from one object to another; we see cases of Mg II changing by as much as the continuum, more than the continuum, or very little at all. In 74% of the highly variable sample the behaviour of Mg II corresponds with that of H$\beta$, with 30% of the objects showing large variations in both lines. We do not detect any change in the line width that would correspond to Broad Line Region `breathing', in accordance with results from literature. Some of the objects in our highly variable sample show a clear asymmetry in the Mg II profile. This skewness can be both to the blue and the red of the line centre. Results from our broad population sample show that highly variable quasars have lower Eddington ratios. This result holds for the variability of the continuum, but the correlation is significantly reduced for the variability of the Mg II line. For the first time, we present an overview of the value of the intrinsic Baldwin Effect for Mg II in a large sample., Comment: 22 pages, 21 figures
Published: 2020

6. Probing the disk-corona systems and broad line regions of changing-look quasars with X-ray and optical observations

Author: Anh Doan, Daryl Haggard, Marie Joëlle Gingras, Xiangyu Jin, Paul J. Green, Jessie C. Runnoe, Michael Eracleous, Joseph Hountalas, Chelsea L. MacLeod, Scott F. Anderson, and John J. Ruan
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Active galactic nucleus, 010504 meteorology & atmospheric sciences, Accretion (meteorology), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Type (model theory), Lambda, 01 natural sciences, Corona, Astrophysics - Astrophysics of Galaxies, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), 0103 physical sciences, Emission spectrum, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Line (formation)
Abstract: "Changing-look" quasars are a new class of highly variable active galactic nuclei that have changed their spectral type over surprisingly short timescales of just a few years. The origin of this phenomenon is debated, but is likely to reflect some change in the accretion flow. To investigate the disk-corona systems in these objects, we measure optical/UV-X-ray spectral indices ($\alpha_{\rm OX}$) and Eddington ratios ($\lambda_{\rm Edd}$) of ten previously-discovered changing-look quasars at two or more epochs. By comparing these data with simulated results based on the behavior of X-ray binaries, we find possible similarities in spectral indices below 1% Eddington ratio. We further investigate the Eddington ratios of changing-look quasars before and after their spectral type changes, and find that changing-look quasars cross the 1% Eddington ratio boundary when their broad emission lines disappear/emerge. This is consistent with the disk-wind model as the origin of broad emission lines., Comment: 31 pages, 9 figures, accepted for publication in ApJ
Published: 2021

7. Improving Damped Random Walk parameters for SDSS Stripe 82 Quasars with Pan-STARRS1

Author: Krzysztof Suberlak, Željko Ivezić, and Chelsea L. MacLeod
Subjects: Brightness, Active galactic nucleus, 010504 meteorology & atmospheric sciences, media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Luminosity, 0103 physical sciences, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, media_common, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Quasar, Light curve, Astrophysics - Astrophysics of Galaxies, Redshift, Black hole, 13. Climate action, Space and Planetary Science, Sky, Astrophysics of Galaxies (astro-ph.GA), Astrophysics - High Energy Astrophysical Phenomena
Abstract: We use the Panoramic Survey Telescope and Rapid Response System 1 Survey (Pan-STARRS1, PS1) data to extend the Sloan Digital Sky Survey (SDSS) Stripe 82 quasar light curves. Combining PS1 and SDSS light curves provides a 15 yr baseline for 9248 quasars - 5 yr longer than prior studies that used only SDSS. We fit the light curves with the damped random walk (DRW) model model - a statistical description of their variability. We correlate the resulting DRW model parameters: asymptotic variability amplitude SF$_{\infty}$, and characteristic timescale $\tau$, with quasar physical properties - black hole mass, bolometric luminosity, and redshift. Using simulated light curves, we find that a longer baseline allows us to better constrain the DRW parameters. After adding PS1 data, the variability amplitude is a stronger function of the black hole mass, and has a weaker dependence on quasar luminosity. In addition, the characteristic timescale $\tau$ dependence on quasar luminosity is marginally weaker. We also make predictions for the fidelity of DRW model parameter retrieval when light curves will be further extended with Zwicky Transient Facility (ZTF) and the Rubin Observatory Legacy Survey of Space and Time (LSST) data. Finally, we show how updated DRW parameters offer an independent method of discovering changing-look quasar candidates (CLQSOs). The candidates are outliers in terms of differences in magnitude and scatter between SDSS and PS1 segments. We identify 40 objects (35 newly reported) with tenfold increase in variability timescale between SDSS and SDSS--PS1 data, which is due to a large change in brightness (over 0.5 mag) - characteristic for CLQSOs., Comment: 34 pages, 26 figures
Published: 2020

8. The 16th Data Release of the Sloan Digital Sky Surveys : First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra

Author: Romina Ahumada, Carlos Allende Prieto, Andrés Almeida, Friedrich Anders, Scott F. Anderson, Brett H. Andrews, Borja Anguiano, Riccardo Arcodia, Eric Armengaud, Marie Aubert, Santiago Avila, Vladimir Avila-Reese, Carles Badenes, Christophe Balland, Kat Barger, Jorge K. Barrera-Ballesteros, Sarbani Basu, Julian Bautista, Rachael L. Beaton, Timothy C. Beers, B. Izamar T. Benavides, Chad F. Bender, Mariangela Bernardi, Matthew Bershady, Florian Beutler, Christian Moni Bidin, Jonathan Bird, Dmitry Bizyaev, Guillermo A. Blanc, Michael R. Blanton, Médéric Boquien, Jura Borissova, Jo Bovy, W. N. Brandt, Jonathan Brinkmann, Joel R. Brownstein, Kevin Bundy, Martin Bureau, Adam Burgasser, Etienne Burtin, Mariana Cano-Díaz, Raffaella Capasso, Michele Cappellari, Ricardo Carrera, Solène Chabanier, William Chaplin, Michael Chapman, Brian Cherinka, Cristina Chiappini, Peter Doohyun Choi, S. Drew Chojnowski, Haeun Chung, Nicolas Clerc, Damien Coffey, Julia M. Comerford, Johan Comparat, Luiz da Costa, Marie-Claude Cousinou, Kevin Covey, Jeffrey D. Crane, Katia Cunha, Gabriele da Silva Ilha, Yu Sophia Dai, Sanna B. Damsted, Jeremy Darling, James W. Davidson, Roger Davies, Kyle Dawson, Nikhil De, Axel de la Macorra, Nathan De Lee, Anna Bárbara de Andrade Queiroz, Alice Deconto Machado, Sylvain de la Torre, Flavia Dell’Agli, Hélion du Mas des Bourboux, Aleksandar M. Diamond-Stanic, Sean Dillon, John Donor, Niv Drory, Chris Duckworth, Tom Dwelly, Garrett Ebelke, Sarah Eftekharzadeh, Arthur Davis Eigenbrot, Yvonne P. Elsworth, Mike Eracleous, Ghazaleh Erfanianfar, Stephanie Escoffier, Xiaohui Fan, Emily Farr, José G. Fernández-Trincado, Diane Feuillet, Alexis Finoguenov, Patricia Fofie, Amelia Fraser-McKelvie, Peter M. Frinchaboy, Sebastien Fromenteau, Hai Fu, Lluís Galbany, Rafael A. Garcia, D. A. García-Hernández, Luis Alberto Garma Oehmichen, Junqiang Ge, Marcio Antonio Geimba Maia, Doug Geisler, Joseph Gelfand, Julian Goddy, Violeta Gonzalez-Perez, Kathleen Grabowski, Paul Green, Catherine J. Grier, Hong Guo, Julien Guy, Paul Harding, Sten Hasselquist, Adam James Hawken, Christian R. Hayes, Fred Hearty, S. Hekker, David W. Hogg, Jon A. Holtzman, Danny Horta, Jiamin Hou, Bau-Ching Hsieh, Daniel Huber, Jason A. S. Hunt, J. Ider Chitham, Julie Imig, Mariana Jaber, Camilo Eduardo Jimenez Angel, Jennifer A. Johnson, Amy M. Jones, Henrik Jönsson, Eric Jullo, Yerim Kim, Karen Kinemuchi, Charles C. Kirkpatrick IV, George W. Kite, Mark Klaene, Jean-Paul Kneib, Juna A. Kollmeier, Hui Kong, Marina Kounkel, Dhanesh Krishnarao, Ivan Lacerna, Ting-Wen Lan, Richard R. Lane, David R. Law, Jean-Marc Le Goff, Henry W. Leung, Hannah Lewis, Cheng Li, Jianhui Lian, Lihwai Lin, Dan Long, Penélope Longa-Peña, Britt Lundgren, Brad W. Lyke, J. Ted Mackereth, Chelsea L. MacLeod, Steven R. Majewski, Arturo Manchado, Claudia Maraston, Paul Martini, Thomas Masseron, Karen L. Masters, Savita Mathur, Richard M. McDermid, Andrea Merloni, Michael Merrifield, Szabolcs Mészáros, Andrea Miglio, Dante Minniti, Rebecca Minsley, Takamitsu Miyaji, Faizan Gohar Mohammad, Benoit Mosser, Eva-Maria Mueller, Demitri Muna, Andrea Muñoz-Gutiérrez, Adam D. Myers, Seshadri Nadathur, Preethi Nair, Kirpal Nandra, Janaina Correa do Nascimento, Rebecca Jean Nevin, Jeffrey A. Newman, David L. Nidever, Christian Nitschelm, Pasquier Noterdaeme, Julia E. O’Connell, Matthew D. Olmstead, Daniel Oravetz, Audrey Oravetz, Yeisson Osorio, Zachary J. Pace, Nelson Padilla, Nathalie Palanque-Delabrouille, Pedro A. Palicio, Hsi-An Pan, Kaike Pan, James Parker, Romain Paviot, Sebastien Peirani, Karla Peña Ramŕez, Samantha Penny, Will J. Percival, Ismael Perez-Fournon, Ignasi Pérez-Ràfols, Patrick Petitjean, Matthew M. Pieri, Marc Pinsonneault, Vijith Jacob Poovelil, Joshua Tyler Povick, Abhishek Prakash, Adrian M. Price-Whelan, M. Jordan Raddick, Anand Raichoor, Amy Ray, Sandro Barboza Rembold, Mehdi Rezaie, Rogemar A. Riffel, Rogério Riffel, Hans-Walter Rix, Annie C. Robin, A. Roman-Lopes, Carlos Román-Zúñiga, Benjamin Rose, Ashley J. Ross, Graziano Rossi, Kate Rowlands, Kate H. R. Rubin, Mara Salvato, Ariel G. Sánchez, Laura Sánchez-Menguiano, José R. Sánchez-Gallego, Conor Sayres, Adam Schaefer, Ricardo P. Schiavon, Jaderson S. Schimoia, Edward Schlafly, David Schlegel, Donald P. Schneider, Mathias Schultheis, Axel Schwope, Hee-Jong Seo, Aldo Serenelli, Arman Shafieloo, Shoaib Jamal Shamsi, Zhengyi Shao, Shiyin Shen, Matthew Shetrone, Raphael Shirley, Víctor Silva Aguirre, Joshua D. Simon, M. F. Skrutskie, Anže Slosar, Rebecca Smethurst, Jennifer Sobeck, Bernardo Cervantes Sodi, Diogo Souto, David V. Stark, Keivan G. Stassun, Matthias Steinmetz, Dennis Stello, Julianna Stermer, Thaisa Storchi-Bergmann, Alina Streblyanska, Guy S. Stringfellow, Amelia Stutz, Genaro Suárez, Jing Sun, Manuchehr Taghizadeh-Popp, Michael S. Talbot, Jamie Tayar, Aniruddha R. Thakar, Riley Theriault, Daniel Thomas, Zak C. Thomas, Jeremy Tinker, Rita Tojeiro, Hector Hernandez Toledo, Christy A. Tremonti, Nicholas W. Troup, Sarah Tuttle, Eduardo Unda-Sanzana, Marica Valentini, Jaime Vargas-González, Mariana Vargas-Magaña, Jose Antonio Vázquez-Mata, M. Vivek, David Wake, Yuting Wang, Benjamin Alan Weaver, Anne-Marie Weijmans, Vivienne Wild, John C. Wilson, Robert F. Wilson, Nathan Wolthuis, W. M. Wood-Vasey, Renbin Yan, Meng Yang, Christophe Yèche, Olga Zamora, Pauline Zarrouk, Gail Zasowski, Kai Zhang, Cheng Zhao, Gongbo Zhao, Zheng Zheng, Guangtun Zhu, Hu Zou, Department of Physics, Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015 - 2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Instituto de Astrofisica de Canarias (IAC), Institut de Recherches sur les lois Fondamentales de l'Univers (IRFU), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, Centre de Physique des Particules de Marseille (CPPM), Aix Marseille Université (AMU)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Universidad Nacional Autónoma de México (UNAM), Department of Astrophysical Sciences [Princeton], Princeton University, Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE (UMR_7585)), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Department of Astronomy, Yale University [New Haven], University of Notre Dame [Indiana] (UND), Department of Physics and Astronomy [Philadelphia], University of Pennsylvania [Philadelphia], University of Wisconsin-Madison, Texas Tech University Health Sciences Center, Texas Tech University [Lubbock] (TTU), Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), California Institute of Technology (CALTECH), Sub-department of Astrophysics [Oxford], Department of Physics [Oxford], University of Oxford [Oxford]-University of Oxford [Oxford], Center for Astrophysics and Space Sciences [La Jolla] (CASS), University of California [San Diego] (UC San Diego), University of California-University of California, Department of Psychology, St John's University, Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Departamento de FisicaTeorica e IFT-UAM/CSIC, Universidad Autonoma de Madrid (UAM), Lowell Observatory [Flagstaff], Observatorio Nacional [Rio de Janeiro], Vernalis (R&D) Ltd, Special Care Dentistry, UCLH Eastman Dental Hospital, University of Utah, Laboratoire d'Astrophysique de Marseille (LAM), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Universidad de La Laguna [Tenerife - SP] (ULL), University of Virginia [Charlottesville], University of Wyoming (UW), School of Physics and Astronomy, University of Birmingham [Birmingham], Max Planck Institute for Extraterrestrial Physics (MPE), Max-Planck-Gesellschaft, Arizona State University [Tempe] (ASU), Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213) (UTINAM), Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Max-Planck-Institut für Astronomie (MPIA), Texas Christian University (TCU), Department of Physics and Astronomy [Irvine], University of California [Irvine] (UCI), Department of Physics and Astronomy [Pittsburgh], University of Pittsburgh (PITT), Pennsylvania Commonwealth System of Higher Education (PCSHE)-Pennsylvania Commonwealth System of Higher Education (PCSHE), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), New York University [New York] (NYU), NYU System (NYU), Research Institute of Forest Resource Information Techniques, Chinese Academy of Forestry, New Mexico State University, Pennsylvania State University (Penn State), Penn State System, Princess Margaret Hospital, University of Toronto, Cognition, Langues, Langage, Ergonomie (CLLE-ERSS), École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Toulouse - Jean Jaurès (UT2J)-Université Bordeaux Montaigne-Centre National de la Recherche Scientifique (CNRS), J. A. Baker Institute, Cornell University [New York], Institute of Infection, Immunity & Inflammation, University of Glasgow, Sainsbury Laboratory Cambridge University (SLCU), University of Cambridge [UK] (CAM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Carnegie Observatories, Carnegie Institution for Science [Washington], Institute of Science and Technology [Austria] (IST Austria), Universidad de Atacama, Department of Chemical and Biomolecular Engineering, Universidad de Antofagasta, Harvard-Smithsonian Center for Astrophysics (CfA), Smithsonian Institution-Harvard University [Cambridge], Institute of cosmology and gravitation, University of Portsmouth, Institut d'Astronomie et d'Astrophysique [Bruxelles] (IAA), Université libre de Bruxelles (ULB), Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée (DAPNIA), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Max-Planck-Institut für Astrophysik (MPA), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Département des Sciences et Gestion de l'Environnement/Océanologie [Liège], Université de Liège, Universidad Andrés Bello [Santiago] (UNAB), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Montana State University (MSU), Institut d'Astrophysique de Paris (IAP), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Department of Astronomy (Ohio State University), Ohio State University [Columbus] (OSU), Institut Lagrange de Paris, Sorbonne Université (SU), The Wellcome Trust Centre for Human Genetics [Oxford], University of Oxford [Oxford], Liverpool John Moores University (LJMU), Lawrence Berkeley National Laboratory [Berkeley] (LBNL), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institute of Space Sciences [Barcelona] (ICE-CSIC), Spanish National Research Council [Madrid] (CSIC), Chinese Academy of Sciences [Beijing] (CAS), McDonald Observatory, University of Texas at Austin [Austin], Astronomy Centre, University of Sussex, Department of Physics and Astronomy [Aarhus], Aarhus University [Aarhus], University of Washington [Seattle], Vanderbilt University [Nashville], Stellar Astrophysics Centre [Aarhus] (SAC), University of Colorado [Boulder], Laboratoire de Biochimie Médicale (LBM), CHU Rouen, Normandie Université (NU)-Normandie Université (NU), University of St Andrews [Scotland], Instituto de Astronomıa, universidad catolica del Norte, Institut d'Astrophysique et de Géophysique [Liège], Laboratoire de Physique des Solides (LPS), Centre National de la Recherche Scientifique (CNRS)-Université Paris-Sud - Paris 11 (UP11), Department of Computer Science and Engineering [Minneapolis], University of Minnesota [Twin Cities] (UMN), University of Minnesota System-University of Minnesota System, Dunlap Institute for Astronomy and Astrophysics [Toronto], World Bank, State Key Laboratory in Computer Science [Beijing] (SKLCS), Institute of Software Chinese Academy of Sciences [Beijing], Nanjing University of Information Science and Technology (NUIST), Laboratoire de Chimie - UMR5182 (LC), Centre National de la Recherche Scientifique (CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École normale supérieure - Lyon (ENS Lyon)-Institut de Chimie du CNRS (INC), Johns Hopkins University (JHU), Universidad Nacional Autónoma de México = National Autonomous University of Mexico (UNAM), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), University of Pennsylvania, Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), University of Oxford-University of Oxford, University of California (UC)-University of California (UC), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Universidad Autónoma de Madrid (UAM), University of Virginia, Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC), University of California [Irvine] (UC Irvine), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Toulouse - Jean Jaurès (UT2J), Université de Toulouse (UT)-Université de Toulouse (UT)-Université Bordeaux Montaigne (UBM)-Centre National de la Recherche Scientifique (CNRS), Carnegie Institution for Science, Institute of Science and Technology [Klosterneuburg, Austria] (IST Austria), Harvard University-Smithsonian Institution, Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), University of Oxford, Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Centre National d'Études Spatiales [Toulouse] (CNES), Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Ahumada R., Prieto C.A., Almeida A., Anders F., Anderson S.F., Andrews B.H., Anguiano B., Arcodia R., Armengaud E., Aubert M., Avila S., Avila-Reese V., Badenes C., Balland C., Barger K., Barrera-Ballesteros J.K., Basu S., Bautista J., Beaton R.L., Beers T.C., Benavides B.I.T., Bender C.F., Bernardi M., Bershady M., Beutler F., Bidin C.M., Bird J., Bizyaev D., Blanc G.A., Blanton M.R., Boquien M., Borissova J., Bovy J., Brandt W.N., Brinkmann J., Brownstein J.R., Bundy K., Bureau M., Burgasser A., Burtin E., Cano-Diaz M., Capasso R., Cappellari M., Carrera R., Chabanier S., Chaplin W., Chapman M., Cherinka B., Chiappini C., Doohyun Choi P., Chojnowski S.D., Chung H., Clerc N., Coffey D., Comerford J.M., Comparat J., Da Costa L., Cousinou M.-C., Covey K., Crane J.D., Cunha K., Ilha G.D.S., Dai Y.S., Damsted S.B., Darling J., Davidson J.W., Davies R., Dawson K., De N., De La Macorra A., De Lee N., Queiroz A.B.D.A., Deconto Machado A., De La Torre S., Dell'Agli F., Du Mas Des Bourboux H., Diamond-Stanic A.M., Dillon S., Donor J., Drory N., Duckworth C., Dwelly T., Ebelke G., Eftekharzadeh S., Davis Eigenbrot A., Elsworth Y.P., Eracleous M., Erfanianfar G., Escoffier S., Fan X., Farr E., Fernandez-Trincado J.G., Feuillet D., Finoguenov A., Fofie P., Fraser-Mckelvie A., Frinchaboy P.M., Fromenteau S., Fu H., Galbany L., Garcia R.A., Garcia-Hernandez D.A., Oehmichen L.A.G., Ge J., Maia M.A.G., Geisler D., Gelfand J., Goddy J., Gonzalez-Perez V., Grabowski K., Green P., Grier C.J., Guo H., Guy J., Harding P., Hasselquist S., Hawken A.J., Hayes C.R., Hearty F., Hekker S., Hogg D.W., Holtzman J.A., Horta D., Hou J., Hsieh B.-C., Huber D., Hunt J.A.S., Chitham J.I., Imig J., Jaber M., Angel C.E.J., Johnson J.A., Jones A.M., Jonsson H., Jullo E., Kim Y., Kinemuchi K., Kirkpatrick Iv C.C., Kite G.W., Klaene M., Kneib J.-P., Kollmeier J.A., Kong H., Kounkel M., Krishnarao D., Lacerna I., Lan T.-W., Lane R.R., Law D.R., Le Goff J.-M., Leung H.W., Lewis H., Li C., Lian J., Lin L., Long D., Longa-Peña P., Lundgren B., Lyke B.W., Ted Mackereth J., Macleod C.L., Majewski S.R., Manchado A., Maraston C., Martini P., Masseron T., Masters K.L., Mathur S., McDermid R.M., Merloni A., Merrifield M., Meszaros S., Miglio A., Minniti D., Minsley R., Miyaji T., Mohammad F.G., Mosser B., Mueller E.-M., Muna D., Muñoz-Gutierrez A., Myers A.D., Nadathur S., Nair P., Nandra K., Do Nascimento J.C., Nevin R.J., Newman J.A., Nidever D.L., Nitschelm C., Noterdaeme P., O'Connell J.E., Olmstead M.D., Oravetz D., Oravetz A., Osorio Y., Pace Z.J., Padilla N., Palanque-Delabrouille N., Palicio P.A., Pan H.-A., Pan K., Parker J., Paviot R., Peirani S., Ramrez K.P., Penny S., Percival W.J., Perez-Fournon I., Perez-Rafols I., Petitjean P., Pieri M.M., Pinsonneault M., Poovelil V.J., Povick J.T., Prakash A., Price-Whelan A.M., Raddick M.J., Raichoor A., Ray A., Rembold S.B., Rezaie M., Riffel R.A., Riffel R., Rix H.-W., Robin A.C., Roman-Lopes A., Roman-Zuñiga C., Rose B., Ross A.J., Rossi G., Rowlands K., Rubin K.H.R., Salvato M., Sanchez A.G., Sanchez-Menguiano L., Sanchez-Gallego J.R., Sayres C., Schaefer A., Schiavon R.P., Schimoia J.S., Schlafly E., Schlegel D., Schneider D.P., Schultheis M., Schwope A., Seo H.-J., Serenelli A., Shafieloo A., Shamsi S.J., Shao Z., Shen S., Shetrone M., Shirley R., Aguirre V.S., Simon J.D., Skrutskie M.F., Slosar A., Smethurst R., Sobeck J., Sodi B.C., Souto D., Stark D.V., Stassun K.G., Steinmetz M., Stello D., Stermer J., Storchi-Bergmann T., Streblyanska A., Stringfellow G.S., Stutz A., Suarez G., Sun J., Taghizadeh-Popp M., Talbot M.S., Tayar J., Thakar A.R., Theriault R., Thomas D., Thomas Z.C., Tinker J., Tojeiro R., Toledo H.H., Tremonti C.A., Troup N.W., Tuttle S., Unda-Sanzana E., Valentini M., Vargas-Gonzalez J., Vargas-Magaña M., Vazquez-Mata J.A., Vivek M., Wake D., Wang Y., Weaver B.A., Weijmans A.-M., Wild V., Wilson J.C., Wilson R.F., Wolthuis N., Wood-Vasey W.M., Yan R., Yang M., Yeche C., Zamora O., Zarrouk P., Zasowski G., Zhang K., Zhao C., Zhao G., Zheng Z., Zhu G., Zou H., Alfred P. Sloan Foundation, and Department of Energy (US)
Subjects: Optical telescopes, SAMPLE, Astrophysics, 01 natural sciences, Astronomi, astrofysik och kosmologi, Infrared astronomy, Observatory, Astronomy, Astrophysics and Cosmology, Astrophysics::Solar and Stellar Astrophysics, REDSHIFT 0.8, redshift surveys, stellar spectral lines, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, media_common, Astronomy databases, Redshift surveys, Physics, Astrophysics::Instrumentation and Methods for Astrophysics, stellar properties, CATALOG, astro-ph.CO, astronomy databases, Data release, [PHYS.ASTR.IM]Physics [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM], infrared astonomy, TELESCOPE, astro-ph.GA, media_common.quotation_subject, Astrophysics::Cosmology and Extragalactic Astrophysics, MASS, [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Galactic abundances, Stellar properties, 0103 physical sciences, Astrophysics::Galaxy Astrophysics, DISTANCES, Stellar spectral lines, 010308 nuclear & particles physics, Astronomy and Astrophysics, optical telescopes, 115 Astronomy, Space science, Galaxy, GALAXY, [PHYS.ASTR.GA]Physics [physics]/Astrophysics [astro-ph]/Galactic Astrophysics [astro-ph.GA], STELLAR, 13. Climate action, Space and Planetary Science, Sky, [SDU]Sciences of the Universe [physics], galactic abundances, MILKY, astro-ph.IM, SDSS-IV MANGA
Abstract: This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the Southern Hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey and new data from the SPectroscopic IDentification of ERosita Survey programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17)., Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS website is www.sdss.org.
Published: 2020

9. The broad-band SEDs of four ‘hypervariable’ AGN

Author: Suvi Gezari, Chris Done, Alastair Bruce, Andy Lawrence, Philip J. Marshall, James S. Collinson, Chelsea L. MacLeod, Martin Elvis, and Martin Ward
Subjects: Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, media_common.quotation_subject, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Gravitational microlensing, 01 natural sciences, Luminosity, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Emission spectrum, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, media_common, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Accretion (meteorology), 010308 nuclear & particles physics, Astronomy, Astronomy and Astrophysics, Black hole, Space and Planetary Science, Sky, Spectral energy distribution, Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present an optical to X-ray spectral analysis of four 'hypervariable' AGN (HVAs) discovered by comparing Pan-STARRS data to that from SDSS over a 10 year baseline (Lawrence et al 2016). There is some evidence that these objects are X-ray loud for their corresponding UV luminosities, but given that we measured them in a historic high state, it is not clear whether to take the high-state or low-state as typical of the properties of these HVAs. We estimate black hole masses based on MgII and H$\alpha$ emission line profiles, and either the high and low state luminosities, finding mass ranges $\log(M_{\rm BH}/M_{\odot}) = 8.2-8.8$ and $\log(M_{\rm BH}/M_{\odot}) = 7.9-8.3$ respectively. We then fit energy conserving models to the SEDs, obtaining strong constraints on the bolometric luminosity and $\alpha_{\rm OX}$. We compare the SED properties with a larger, X-ray selected AGN sample for both of these scenarios, and observe distinct groupings in spectral shape versus luminosity parameter space. In general, the SED properties are closer to normal if we assume that the low-state is representative. This supports the idea that the large slow outbursts may be due to extrinsic effects (for example microlensing) as opposed to accretion rate changes, but a larger sample of HVAs is needed to be confident of this conclusion., Comment: 11 pages, 7 figures, 5 tables; accepted for publication in MNRAS
Published: 2017

10. The 450 Day X-Ray Monitoring of the Changing-look AGN 1ES 1927+654

Author: Keith C. Gendreau, A. C. Fabian, R. Remillard, Erin Kara, James F. Steiner, D. Pasham, Claudio Ricci, Chelsea L. MacLeod, P. Kosec, C.-H. Chan, Poshak Gandhi, Iair Arcavi, Diego Altamirano, Luis C. Ho, Edward M. Cackett, Zaven Arzoumanian, M. Loewenstein, Benny Trakhtenbrot, and Ruancun Li
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Supermassive black hole, Active galactic nucleus, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), X-ray, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: 1ES 1927+654 is a nearby active galactic nucleus (AGN) which underwent a changing-look event in early 2018, developing prominent broad Balmer lines which were absent in previous observations. We have followed up this object in the X-rays with an ongoing campaign that started in May 2018, and that includes 265 NICER (for a total of 678ks) and 14 Swift/XRT (26ks) observations, as well as three simultaneous XMM-Newton/NuSTAR (158/169 ks) exposures. In the X-rays, 1ES 1927+654 shows a behaviour unlike any previously known AGN. The source is extremely variable both in spectral shape and flux, and does not show any correlation between X-ray and UV flux on timescales of hours or weeks/months. After the outburst the power-law component almost completely disappeared, and the source showed an extremely soft continuum dominated by a blackbody component. The temperature of the blackbody increases with the luminosity, going from $kT\sim 80$eV (for a 0.3--2keV luminosity of $L_{0.3-2}\sim 10^{41.5}\rm\,erg\,s^{-1}$) to $\sim 200$eV (for $L_{0.3-2}\sim 10^{44}\rm\,erg\,s^{-1}$). The spectra show evidence of ionized outflows, and of a prominent feature at $\sim 1$keV, which can be reproduced by a broad emission line. The unique characteristics of 1ES 1927+654 in the X-ray band suggest that it belongs to a new type of changing-look AGN. Future X-ray surveys might detect several more objects with similar properties., Comment: Accepted for publication in ApJS, 56 pages. The complete 114-pages manuscript will be available upon publication
Published: 2021

11. Solving the puzzle of discrepant quasar variability on monthly time-scales implied by SDSS and CRTS data sets

Author: Matthew J. Graham, Branimir Sesar, Krzysztof Suberlak, Željko Ivezić, and Chelsea L. MacLeod
Subjects: media_common.quotation_subject, Continuum (design consultancy), FOS: Physical sciences, Image processing, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, CRTS, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, media_common, Physics, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, Astronomy and Astrophysics, Quasar, Light curve, Astrophysics - Astrophysics of Galaxies, Data set, Stars, Space and Planetary Science, Sky, Astrophysics of Galaxies (astro-ph.GA)
Abstract: We present an improved photometric error analysis for the 7,100 CRTS (Catalina Real-Time Transient Survey) optical light curves for quasars from the SDSS (Sloan Digital Sky Survey) Stripe 82 catalogue. The SDSS imaging survey has provided a time-resolved photometric data set which greatly improved our understanding of the quasar optical continuum variability: Data for monthly and longer time-scales are consistent with a damped random walk (DRW). Recently, newer data obtained by CRTS provided puzzling evidence for enhanced variability, compared to SDSS results, on monthly time-scales. Quantitatively, SDSS results predict about 0.06 mag root-mean-square (rms) variability for monthly time-scales, while CRTS data show about a factor of 2 larger rms, for spectroscopically confirmed SDSS quasars. Our analysis has successfully resolved this discrepancy as due to slightly underestimated photometric uncertainties from the CRTS image processing pipelines. As a result, the correction for observational noise is too small and the implied quasar variability is too large. The CRTS photometric error correction factors, derived from detailed analysis of non-variable SDSS standard stars that were re-observed by CRTS, are about 20-30%, and result in reconciling quasar variability behaviour implied by the CRTS data with earlier SDSS results. An additional analysis based on independent light curve data for the same objects obtained by the Palomar Transient Factory provides further support for this conclusion. In summary, the quasar variability constraints on weekly and monthly time-scales from SDSS, CRTS and PTF surveys are mutually compatible, as well as consistent with DRW model., 9 pages, 8 figures, published in MNRAS https://doi.org/10.1093/mnras/stx2310
Published: 2017

12. Changing-look Quasar Candidates: First Results from Follow-up Spectroscopy of Highly Optically Variable Quasars

Author: Amy Lebleu, Matthew J. Graham, Paul J. Green, Nicholas P. Ross, Daniel Stern, Eugene A. Magnier, Nigel Metcalfe, Jessie C. Runnoe, Nick Kaiser, Alastair Bruce, Chelsea L. MacLeod, John J. Ruan, Andy Lawrence, Michael Eracleous, Scott F. Anderson, K. C. Chambers, William S. Burgett, D. Homan, Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University [Cambridge]-Smithsonian Institution, Department of Astronomy [Seattle], University of Washington [Seattle], Institute for Astronomy [Edinburgh] (IfA), University of Edinburgh, Cahill Center for Astronomy and Astrophysics, California Institute of Technology (CALTECH), University of Central Florida [Orlando] (UCF), McGill University = Université McGill [Montréal, Canada], Department of Astronomy, University of Michigan, University of Michigan [Ann Arbor], University of Michigan System-University of Michigan System, Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Institute for Astronomy, University of Hawai'i at Manoa, Astrophysique, Laboratoire de physique de l'ENS - ENS Paris (LPENS (UMR_8023)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Université Paris Diderot - Paris 7 (UPD7)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Université Paris Diderot - Paris 7 (UPD7), Smithsonian Institution-Harvard University [Cambridge], University of Central Florida [Orlando], McGill University, Fédération de recherche du Département de physique de l'Ecole Normale Supérieure - ENS Paris (FRDPENS), Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Fédération de recherche du Département de physique de l'Ecole Normale Supérieure - ENS Paris (FRDPENS), and Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Active galactic nucleus, 010504 meteorology & atmospheric sciences, astro-ph.GA, media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, Population, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Spectral line, Photometry (optics), 0103 physical sciences, education, Spectroscopy, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, media_common, Physics, education.field_of_study, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Quasar, Astrophysics - Astrophysics of Galaxies, Galaxy, [PHYS.ASTR.GA]Physics [physics]/Astrophysics [astro-ph]/Galactic Astrophysics [astro-ph.GA], Space and Planetary Science, Sky, Astrophysics of Galaxies (astro-ph.GA)
Abstract: Active galactic nuclei (AGN) 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 changing look quasars (CLQs). These surprisingly large and sometimes rapid transitions challenge accepted models of quasar physics and duty cycles, offer several new avenues for study of quasar host galaxies, and open a wider interpretation of the cause of differences between broad and narrow line AGN. To better characterize extreme quasar variability, we present follow-up spectroscopy as part of a comprehensive search for CLQs across the full SDSS footprint using spectroscopically confirmed quasars from the SDSS DR7 catalog. Our primary selection requires large-amplitude (|\Delta g|>1 mag, |\Delta r|>0.5 mag) variability over any of the available time baselines probed by the SDSS and Pan-STARRS 1 surveys. We employ photometry from the Catalina Sky Survey to verify variability behavior in CLQ candidates where available, and confirm CLQs using optical spectroscopy from the William Herschel, MMT, Magellan, and Palomar telescopes. For our adopted S/N threshold on variability of broad H\beta emission, we find 17 new CLQs, yielding a confirmation rate of >~ 20%. These candidates are at lower Eddington ratio relative to the overall quasar population which supports a disk-wind model for the broad line region. Based on our sample, the CLQ fraction increases from 10% to roughly half as the continuum flux ratio between repeat spectra at 3420 Angstroms increases from 1.5 to 6. We release a catalog of over 200 highly variable candidates to facilitate future CLQ searches., Comment: 26 pages, 9 Figures, 3 Tables. Replaced with accepted version
Published: 2019

13. The 'Big Dipper': The nature of the extreme variability of the AGN SDSS J2232-0806

Author: Daniel Kynoch, Hermine Landt, Alastair G Bruce, Andy Lawrence, Chelsea L. MacLeod, and Martin Ward
Subjects: Physics, Brightness, Active galactic nucleus, 010308 nuclear & particles physics, Infrared, astro-ph.GA, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Astrophysics - Astrophysics of Galaxies, Galaxy, Optical spectra, Accretion disc, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, sense organs, 010303 astronomy & astrophysics, Big Dipper, Astrophysics::Galaxy Astrophysics
Abstract: SDSS J2232-0806 (the 'Big Dipper') has been identified as a 'slow-blue nuclear hypervariable': a galaxy with no previously known active nucleus, blue colours and large-amplitude brightness evolution occurring on a timescale of years. Subsequent observations have shown that this source does indeed contain an active galactic nucleus (AGN). Our optical photometric and spectroscopic monitoring campaign has recorded one major dimming event (and subsequent rise) over a period of around four years; there is also evidence of previous events consistent with this in archival data recorded over the last twenty years. Here we report an analysis of the eleven optical spectra obtained to date and we assemble a multiwavelength data set including infrared, ultraviolet and X-ray observations. We find that an intrinsic change in the luminosity is the most favoured explanation of the observations, based on a comparison of continuum and line variability and the apparent lagged response of the hot dust. This source, along with several other recently-discovered 'changing-look' objects, demonstrate that AGN can exhibit large-amplitude luminosity changes on timescales much shorter than those predicted by standard thin accretion disc models., 17 pages, 8 figures and 7 tables. Accepted by MNRAS
Published: 2019

14. The Analogous Structure of Accretion Flows in Supermassive and Stellar Mass Black Holes: New Insights from Faded Changing-Look Quasars

Author: Scott F. Anderson, Daryl Haggard, Michael Eracleous, Chelsea L. MacLeod, Paul J. Green, Jessie C. Runnoe, Malgosia Sobolewska, and John J. Ruan
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Supermassive black hole, Spectral index, Active galactic nucleus, 010504 meteorology & atmospheric sciences, Stellar mass, Astrophysics::High Energy Astrophysical Phenomena, X-ray binary, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Accretion (astrophysics), Black hole, Space and Planetary Science, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences
Abstract: Despite their factor of ~10^8 difference in black hole mass, several lines of evidence suggest possible similarities between black hole accretion flows in active galactic nuclei (AGN) and Galactic X-ray binaries. However, it is still unclear whether the geometry of the disk-corona system in X-ray binaries directly scale up to AGN, and whether this analogy still holds in different accretion states. We test this AGN/X-ray binary analogy, by comparing the observed correlations between the UV-to-X-ray spectral index (alpha_OX) and Eddington ratio in AGN to those predicted from observations of X-ray binary outbursts. This approach probes the geometry of their disk-corona systems as they transition between different accretion states. We use new Chandra X-ray and ground-based rest-UV observations of faded 'changing-look' quasars to extend this comparison to lower Eddington ratios of, 26 pages, 12 figures, published in ApJ, 883, 76
Published: 2019
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15. SDSS-IV eBOSS Spectroscopy of X-ray and WISE AGN in Stripe 82X: Overview of the Demographics of X-ray and Mid-Infrared Selected Active Galactic Nuclei

Author: Tonima Tasnim Ananna, Mara Salvato, Stephanie M. LaMassa, C. Meg Urry, M. Vivek, Antonis Georgakakis, Chelsea L. MacLeod, and Nicholas P. Ross
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Active galactic nucleus, Demographics, Astrophysics::High Energy Astrophysical Phenomena, X-ray, Mid infrared, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics - Astrophysics of Galaxies, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics - High Energy Astrophysical Phenomena, Spectroscopy, Astrophysics::Galaxy Astrophysics
Abstract: 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 a 36.8 deg$^2$ region of Stripe 82. About half this survey (15.6 deg$^2$) covers the largest contiguous portion of the Stripe 82 X-ray survey. This program represents the largest spectroscopic survey of AGN candidates selected solely by their WISE colors. We combine this sample with X-ray and WISE AGN in the field identified via other sources of spectroscopy, producing a catalog of 4847 sources that is 82% complete to $r\sim22$. Based on X-ray luminosities or WISE colors, 4730 of these sources are AGN, with a median sample redshift of $z\sim1$. About 30% of the AGN are optically obscured (i.e., lack broad lines in their optical spectra). BPT analysis, however, indicates that 50% of the WISE AGN at $z 10^{44}$ erg s$^{-1}$), indicating that MIR selection misses a sizable fraction of the highest luminosity AGN, as well as lower luminosity sources where AGN heated dust is not dominating the MIR emission. Conversely, $\sim$58% of WISE AGN are undetected by X-rays, though we do not find that they are preferentially redder than the X-ray detected WISE AGN., resubmitted to AAS Journals after addressing referee's comments. 21 pages, 17 figures, 5 Tables. Tables 4 & 5 summarize the demographics of the sample. Figures 15 & 16 compare AGN populations from X-ray and MIR selection. The catalog (in fits format) can be downloaded at http://doi.org/10.5281/zenodo.2577357
Published: 2019
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16. Gravitational lensing size scales for quasars

Author: Jeffrey A. Blackburne, Xinyu Dai, Ana M. Mosquera, Chelsea L. MacLeod, Carter Rhea, Christopher S. Kochanek, Christopher W. Morgan, Bin Chen, and George Chartas
Subjects: Physics, Astrophysics::High Energy Astrophysical Phenomena, Magnification, Astronomy and Astrophysics, Quasar, Astrophysics::Cosmology and Extragalactic Astrophysics, Radius, Astrophysics, Light curve, Gravitational microlensing, 01 natural sciences, Gravitational lens, Space and Planetary Science, 0103 physical sciences, Astrophysics::Earth and Planetary Astrophysics, Caustic (optics), 010306 general physics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Line (formation)
Abstract: We review results from our monitoring observations of several lensed quasars performed in the optical, UV, and X-ray bands. Modeling of the multi-wavelength light curves provides constraints on the extent of the optical, UV, and X-ray emission regions. One of the important results of our analysis is that the optical sizes as inferred from the microlensing analysis are significantly larger than those predicted by the theoretical-thin-disk estimate. In a few cases we also constrain the slope of the size-wavelength relation. Our size constraints of the soft and hard X-ray emission regions of quasars indicate that in some objects of our sample the hard X-ray emission region is more compact than the soft and in others the soft emission region is smaller. This difference may be the result of the relative strengths of the disk-reflected (harder and extended) versus corona-direct (softer and compact) components in the quasars of our sample. Finally, we present the analysis of several strong microlensing events where we detect an evolution of the relativistic Fe line profile as the magnification caustic traverses the accretion disk. These caustic crossings are used to provide constraints on the innermost stable circular orbit (ISCO) radius and the accretion disk inclination angle of the black hole in quasar RX J1131-1231.
Published: 2016

17. The Destruction and Recreation of the X-Ray Corona in a Changing-look Active Galactic Nucleus

Author: Andrew C. Fabian, Keith C. Gendreau, Michael Loewenstein, Luis C. Ho, Benny Trakhtenbrot, Poshak Gandhi, Ruancun Li, Ron Remillard, Diego Altamirano, Zaven Arzoumanian, Claudio Ricci, Erin Kara, Edward M. Cackett, James F. Steiner, P. Kosec, Dheeraj R. Pasham, Chelsea L. MacLeod, C.-H. Chan, and Iair Arcavi
Subjects: Active galactic nucleus, 010504 meteorology & atmospheric sciences, High-energy astronomy, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, Luminosity, Corona (optical phenomenon), 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Supermassive black hole, Accretion (meteorology), Astronomy and Astrophysics, Quasar, Astrophysics - Astrophysics of Galaxies, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics - High Energy Astrophysical Phenomena, Event (particle physics)
Abstract: We present the drastic transformation of the X-ray properties of the active galactic nucleus 1ES 1927+654, following a changing-look event. After the optical/UV outburst the power-law component, produced in the X-ray corona, disappeared, and the spectrum of 1ES 1927+65 instead became dominated by a blackbody component ($kT\sim 80-120$ eV). This implies that the X-ray corona, ubiquitously found in AGN, was destroyed in the event. Our dense $\sim 450$ day long X-ray monitoring shows that the source is extremely variable in the X-ray band. On long time scales the source varies up to $\sim 4$ dex in $\sim 100$ days, while on short timescales up to $\sim2$ dex in $\sim 8$ hours. The luminosity of the source is found to first show a strong dip down to $\sim 10^{40}\rm\,erg\,s^{-1}$, and then a constant increase in luminosity to levels exceeding the pre-outburst level $\gtrsim $300 days after the optical event detection, rising up asymptotically to $\sim 2\times10^{44}\rm\,erg\,s^{-1}$. As the X-ray luminosity of the source increases, the X-ray corona is recreated, and a very steep power-law component ($\Gamma\simeq 3$) reappears, and dominates the emission for 0.3-2 keV luminosities $\gtrsim 10^{43.7}\rm\,erg\,s^{-1}$, $\sim 300$ days after the beginning of the event. We discuss possible origins of this event, and speculate that our observations could be explained by the interaction between the accretion flow and debris from a tidally disrupted star. Our results show that changing-look events can be associated with dramatic and rapid transformations of the innermost regions of accreting SMBHs., Comment: ApJL in press
Published: 2020

18. The Time-Domain Spectroscopic Survey: Radial Velocity Variability in Dwarf Carbon Stars

Author: Benjamin R. Roulston, Keivan G. Stassun, Chelsea L. MacLeod, John J. Ruan, Joel R. Brownstein, Donald P. Schneider, Carles Badenes, Paul J. Green, and Scott F. Anderson
Subjects: Physics, Proper motion, 010504 meteorology & atmospheric sciences, Binary number, White dwarf, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Carbon star, Radial velocity, Stars, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Spectroscopy, 010303 astronomy & astrophysics, Main sequence, Astrophysics::Galaxy Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), 0105 earth and related environmental sciences
Abstract: Dwarf carbon (dC) stars, main sequence stars showing carbon molecular bands, were initially thought to be an oxymoron since only AGB stars dredge carbon into their atmospheres. Mass transfer from a former AGB companion that has since faded to a white dwarf seems the most likely explanation. Indeed, a few types of giants known to show anomalous abundances --- notably, the CH, Ba and CEMP-s stars --- are known to have a high binary frequency. The dC stars may be the enhanced-abundance progenitors of most, if not all, of these systems, but this requires demonstrating a high binary frequency for dCs. Here, for a sample of 240 dC stars targeted for repeat spectroscopy by the SDSS-IV's Time Domain Spectroscopic Survey, we analyze radial velocity variability to constrain the binary frequency and orbital properties. A handful of dC systems show large velocity variability ($>$100 km s$^{-1}$). We compare the dCs to a control sample with a similar distribution of magnitude, color, proper motion, and parallax. Using MCMC methods, we use the measured $\Delta$RV distribution to estimate the binary fraction and the separation distribution assuming both a unimodal and bimodal distribution. We find the dC stars have an enhanced binary fraction of 95\%, consistent with them being products of mass transfer. These models result in mean separations of less than 1 AU corresponding to periods on the order of 1 year. Our results support the conclusion that dC stars form from close binary systems via mass transfer., Comment: 13 pages, 11 figures. Accepted to ApJ April 15, 2019
Published: 2018
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19. The Sloan Digital Sky Survey Quasar Catalog: Fourteenth data release

Author: Anne-Marie Weijmans, Vivek Mariappan, Graziano Rossi, Jean-Paul Kneib, Kyle S. Dawson, Christophe Yèche, Julian E. Bautista, Eric Armengaud, Scott F. Anderson, Rita Tojeiro, Chelsea L. MacLeod, Nathalie Palanque-Delabrouille, Sylvain de la Torre, Michael R. Blanton, Etienne Burtin, Adam D. Myers, Hee-Jong Seo, Joel R. Brownstein, Benjamin A. Weaver, Héctor Gil-Marín, Stephanie M. LaMassa, Ian D. McGreer, W. N. Brandt, Patrick Petitjean, Ashley J. Ross, Jonathan Brinkmann, Will J. Percival, Paul J. Green, Andrea Merloni, Pauline Zarrouk, Patrick B. Hall, Éric Aubourg, Isabelle Pâris, Pasquier Noterdaeme, Jean Marc Le Goff, Brad W. Lyke, Michael Blomqvist, Donald P. Schneider, Antonis Georgakakis, Alina Streblyanska, Gong-Bo Zhao, Laboratoire d'Astrophysique de Marseille (LAM), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Institut d'Astrophysique de Paris (IAP), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), AstroParticule et Cosmologie (APC (UMR_7164)), Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherches sur les lois Fondamentales de l'Univers (IRFU), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, Institut Lagrange de Paris, Sorbonne Universités, Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE (UMR_7585)), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), SDSS, Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), ANR-16-CE31-0021,eBOSS,Sondes cosmologiques de la gravitation et de l'énergie noire(2016), The Leverhulme Trust, University of St Andrews. School of Physics and Astronomy, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Sorbonne Université (SU), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Centre National d'Études Spatiales [Toulouse] (CNES), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Observatoire de Paris, and PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), media_common.quotation_subject, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Surveys, 01 natural sciences, Cosmology, Spectral line, Photometry (optics), surveys, quasars: general, 0103 physical sciences, QB Astronomy, Emission spectrum, Spectral resolution, 010303 astronomy & astrophysics, QC, Astrophysics::Galaxy Astrophysics, media_common, QB, Physics, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Quasar, general [Quasars], DAS, Astrophysics - Astrophysics of Galaxies, Redshift, QC Physics, 13. Climate action, Space and Planetary Science, Sky, Astrophysics of Galaxies (astro-ph.GA), Catalogs, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], catalogs, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present the Data Release 14 Quasar catalog (DR14Q) from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) of the Sloan Digital Sky Survey IV (SDSS-IV). This catalog includes all SDSS-IV/eBOSS objects that were spectroscopically targeted as quasar candidates and that are confirmed as quasars via a new automated procedure combined with a partial visual inspection of spectra, have luminosities $M_{\rm i} \left[ z=2 \right] < -20.5$ (in a $\Lambda$CDM cosmology with $H_0 = 70 \ {\rm km \ s^{-1} \ Mpc ^{-1}}$, $\Omega_{\rm M} = 0.3$, and $\Omega_{\rm \Lambda} = 0.7$), and either display at least one emission line with a full width at half maximum (FWHM) larger than $500 \ {\rm km \ s^{-1}}$ or, if not, have interesting/complex absorption features. The catalog also includes previously spectroscopically-confirmed quasars from SDSS-I, II and III. The catalog contains 526,356 quasars 144,046 are new discoveries since the beginning of SDSS-IV) detected over 9,376 deg$^2$ (2,044 deg$^2$ having new spectroscopic data available) with robust identification and redshift measured by a combination of principal component eigenspectra. The catalog is estimated to have about 0.5% contamination. The catalog identifies 21,877 broad absorption line quasars and lists their characteristics. For each object, the catalog presents SDSS five-band CCD-based photometry with typical accuracy of 0.03 mag. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys., Comment: Accepted for publication in A&A. The catalog is available at https://data.sdss.org/sas/dr14/eboss/qso/DR14Q/DR14Q_v4_4.fits
Published: 2018

20. The Time-Domain Spectroscopic Survey: Target Selection for Repeat Spectroscopy

Author: John J. Ruan, W. N. Brandt, Nurten Filiz Ak, Kyle S. Dawson, Suzanne L. Hawley, Michael R. Blanton, Jessie C. Runnoe, Sarah J. Schmidt, Amy Lebleu, Chelsea L. MacLeod, Eugene A. Magnier, Jeremy L. Tinker, Daniel Hoover, Michael Eracleous, Jenny E. Greene, Keivan G. Stassun, Rachael Amaro, C. Z. Waters, Eric Morganson, K. C. Chambers, R. P. Kudritzki, José G. Fernández-Trincado, Matthew A. Bershady, Sean McGraw, Nigel Metcalfe, Carles Badenes, Adam D. Myers, Hee-Jong Seo, Axel Schwope, Scott F. Anderson, Vivek Mariappan, Yue Shen, Catherine J. Grier, Isabelle Pâris, Patrick B. Hall, Donald P. Schneider, Paul J. Green, Nick Kaiser, Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules ( UTINAM ), Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ) -Université de Franche-Comté ( UFC ), Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213) (UTINAM), Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), and Université de Franche-Comté (UFC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), [ PHYS.ASTR ] Physics [physics]/Astrophysics [astro-ph], Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, RR Lyrae variable, 01 natural sciences, surveys, quasars: general, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Emission spectrum, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, Physics, Supermassive black hole, 010308 nuclear & particles physics, White dwarf, Astronomy and Astrophysics, Quasar, Astrophysics - Astrophysics of Galaxies, Carbon star, stars: variables: general, Stars, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics::Earth and Planetary Astrophysics, Variable star, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: As astronomers increasingly exploit the information available in the time domain, spectroscopic variability in particular opens broad new channels of investigation. Here we describe the selection algorithms for all targets intended for repeat spectroscopy in the Time Domain Spectroscopic Survey (TDSS), part of the extended Baryon Oscillation Spectroscopic Survey within the Sloan Digital Sky Survey-IV. Also discussed are the scientific rationale and technical constraints leading to these target selections. The TDSS includes a large "Repeat Quasar Spectroscopy" (RQS) program delivering ~13,000 repeat spectra of confirmed SDSS quasars, and several smaller "Few-Epoch Spectroscopy" (FES) programs targeting specific classes of quasars as well as stars. The RQS program aims to provide a large and diverse quasar data set for studying variations in quasar spectra on timescales of years, a comparison sample for the FES quasar programs, and opportunity for discovering rare, serendipitous events. The FES programs cover a wide variety of phenomena in both quasars and stars. Quasar FES programs target broad absorption line quasars, high signal-to-noise ratio normal broad line quasars, quasars with double-peaked or very asymmetric broad emission line profiles, binary supermassive black hole candidates, and the most photometrically variable quasars. Strongly variable stars are also targeted for repeat spectroscopy, encompassing many types of eclipsing binary systems, and classical pulsators like RR Lyrae. Other stellar FES programs allow spectroscopic variability studies of active ultracool dwarf stars, dwarf carbon stars, and white dwarf/M dwarf spectroscopic binaries. We present example TDSS spectra and describe anticipated sample sizes and results., 26 pages, 11 figures, replaced with accepted version to AJ
Published: 2017

21. Spectral analysis of four 'hypervariable' AGN: a microneedle in the haystack?

Author: Andy Lawrence, Rubina Kotak, Alastair Bruce, Philip J. Marshall, James S. Collinson, Chelsea L. MacLeod, R. P. Kudritzki, Marco C. Lam, Martin Ward, Christopher Waters, Suvi Gezari, Martin Elvis, Eugene A. Magnier, J. Polshaw, Cosimo Inserra, and Nick Kaiser
Subjects: ACTIVE GALACTIC NUCLEI, Active galactic nucleus, Stellar mass, DATA RELEASE, PROBABILITY-DISTRIBUTIONS, QUASAR ACCRETION DISKS, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Gravitational microlensing, 01 natural sciences, accretion, H-BETA, 0103 physical sciences, William Herschel Telescope, 010303 astronomy & astrophysics, MICROLENSING LIGHT CURVES, absorption lines-quasars, QC, Astrophysics::Galaxy Astrophysics, QB, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Astronomy, CENTRAL BLACK-HOLE, Astronomy and Astrophysics, active galaxies, Radius, Light curve, Astrophysics - Astrophysics of Galaxies, Galaxy, Redshift, VARIABILITY, Space and Planetary Science, NGC 5548, Astrophysics of Galaxies (astro-ph.GA), micro-galaxies, DIGITAL SKY SURVEY, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, emission lines, accretion discs-gravitational lensing, nuclei-quasars
Abstract: We analyze four extreme active galactic nuclei (AGN) transients to explore the possibility that they are caused by rare, high-amplitude microlensing events. These previously unknown type-I AGN are located in the redshift range 0.6-1.1 and show changes of > 1.5 mag in the g-band on a time-scale of ~years. Multi-epoch optical spectroscopy, from the William Herschel Telescope, shows clear differential variability in the broad line fluxes with respect to the continuum changes and also evolution in the line profiles. In two cases, a simple point-source, point-lens microlensing model provides an excellent match to the long-term variability seen in these objects. For both models, the parameter constraints are consistent with the microlensing being due to an intervening stellar mass object but as yet there is no confirmation of the presence of an intervening galaxy. The models predict a peak amplification of 10.3/13.5 and an Einstein time-scale of 7.5/10.8 yr, respectively. In one case, the data also allow constraints on the size of the CIII] emitting region, with some simplifying assumptions, to to be ~1.0-6.5 light-days and a lower limit on the size of the MgII emitting region to be > 9 light-days (half-light radii). This CIII] radius is perhaps surprisingly small. In the remaining two objects, there is spectroscopic evidence for an intervening absorber but the extra structure seen in the light curves requires a more complex lensing scenario to adequately explain., 23 pages, 17 figures; matches version published in MNRAS
Published: 2017

22. Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe

Author: Michael R. Blanton, Matthew A. Bershady, Bela Abolfathi, Franco D. Albareti, Carlos Allende Prieto, Andres Almeida, Javier Alonso-García, Friedrich Anders, Scott F. Anderson, Brett Andrews, Erik Aquino-Ortíz, Alfonso Aragón-Salamanca, Maria Argudo-Fernández, Eric Armengaud, Eric Aubourg, Vladimir Avila-Reese, Carles Badenes, Stephen Bailey, Kathleen A. Barger, Jorge Barrera-Ballesteros, Curtis Bartosz, Dominic Bates, Falk Baumgarten, Julian Bautista, Rachael Beaton, Timothy C. Beers, Francesco Belfiore, Chad F. Bender, Andreas A. Berlind, Mariangela Bernardi, Florian Beutler, Jonathan C. Bird, Dmitry Bizyaev, Guillermo A. Blanc, Michael Blomqvist, Adam S. Bolton, Médéric Boquien, Jura Borissova, Remco van den Bosch, Jo Bovy, William N. Brandt, Jonathan Brinkmann, Joel R. Brownstein, Kevin Bundy, Adam J. Burgasser, Etienne Burtin, Nicolás G. Busca, Michele Cappellari, Maria Leticia Delgado Carigi, Joleen K. Carlberg, Aurelio Carnero Rosell, Ricardo Carrera, Nancy J. Chanover, Brian Cherinka, Edmond Cheung, Yilen Gómez Maqueo Chew, Cristina Chiappini, Peter Doohyun Choi, Drew Chojnowski, Chia-Hsun Chuang, Haeun Chung, Rafael Fernando Cirolini, Nicolas Clerc, Roger E. Cohen, Johan Comparat, Luiz da Costa, Marie-Claude Cousinou, Kevin Covey, Jeffrey D. Crane, Rupert A. C. Croft, Irene Cruz-Gonzalez, Daniel Garrido Cuadra, Katia Cunha, Guillermo J. Damke, Jeremy Darling, Roger Davies, Kyle Dawson, Axel de la Macorra, Flavia Dell’Agli, Nathan De Lee, Timothée Delubac, Francesco Di Mille, Aleks Diamond-Stanic, Mariana Cano-Díaz, John Donor, Juan José Downes, Niv Drory, Hélion du Mas des Bourboux, Christopher J. Duckworth, Tom Dwelly, Jamie Dyer, Garrett Ebelke, Arthur D. Eigenbrot, Daniel J. Eisenstein, Eric Emsellem, Mike Eracleous, Stephanie Escoffier, Michael L. Evans, Xiaohui Fan, Emma Fernández-Alvar, J. G. Fernandez-Trincado, Diane K. Feuillet, Alexis Finoguenov, Scott W. Fleming, Andreu Font-Ribera, Alexander Fredrickson, Gordon Freischlad, Peter M. Frinchaboy, Carla E. Fuentes, Lluís Galbany, R. Garcia-Dias, D. A. García-Hernández, Patrick Gaulme, Doug Geisler, Joseph D. Gelfand, Héctor Gil-Marín, Bruce A. Gillespie, Daniel Goddard, Violeta Gonzalez-Perez, Kathleen Grabowski, Paul J. Green, Catherine J. Grier, James E. Gunn, Hong Guo, Julien Guy, Alex Hagen, ChangHoon Hahn, Matthew Hall, Paul Harding, Sten Hasselquist, Suzanne L. Hawley, Fred Hearty, Jonay I. Gonzalez Hernández, Shirley Ho, David W. Hogg, Kelly Holley-Bockelmann, Jon A. Holtzman, Parker H. Holzer, Joseph Huehnerhoff, Timothy A. Hutchinson, Ho Seong Hwang, Héctor J. Ibarra-Medel, Gabriele da Silva Ilha, Inese I. Ivans, KeShawn Ivory, Kelly Jackson, Trey W. Jensen, Jennifer A. Johnson, Amy Jones, Henrik Jönsson, Eric Jullo, Vikrant Kamble, Karen Kinemuchi, David Kirkby, Francisco-Shu Kitaura, Mark Klaene, Gillian R. Knapp, Jean-Paul Kneib, Juna A. Kollmeier, Ivan Lacerna, Richard R. Lane, Dustin Lang, David R. Law, Daniel Lazarz, Youngbae Lee, Jean-Marc Le Goff, Fu-Heng Liang, Cheng Li, Hongyu Li, Jianhui Lian, Marcos Lima, Lihwai Lin, Yen-Ting Lin, Sara Bertran de Lis, Chao Liu, Miguel Angel C. de Icaza Lizaola, Dan Long, Sara Lucatello, Britt Lundgren, Nicholas K. MacDonald, Alice Deconto Machado, Chelsea L. MacLeod, Suvrath Mahadevan, Marcio Antonio Geimba Maia, Roberto Maiolino, Steven R. Majewski, Elena Malanushenko, Viktor Malanushenko, Arturo Manchado, Shude Mao, Claudia Maraston, Rui Marques-Chaves, Thomas Masseron, Karen L. Masters, Cameron K. McBride, Richard M. McDermid, Brianne McGrath, Ian D. McGreer, Nicolás Medina Peña, Matthew Melendez, Andrea Merloni, Michael R. Merrifield, Szabolcs Meszaros, Andres Meza, Ivan Minchev, Dante Minniti, Takamitsu Miyaji, Surhud More, John Mulchaey, Francisco Müller-Sánchez, Demitri Muna, Ricardo R. Munoz, Adam D. Myers, Preethi Nair, Kirpal Nandra, Janaina Correa do Nascimento, Alenka Negrete, Melissa Ness, Jeffrey A. Newman, Robert C. Nichol, David L. Nidever, Christian Nitschelm, Pierros Ntelis, Julia E. O’Connell, Ryan J. Oelkers, Audrey Oravetz, Daniel Oravetz, Zach Pace, Nelson Padilla, Nathalie Palanque-Delabrouille, Pedro Alonso Palicio, Kaike Pan, John K. Parejko, Taniya Parikh, Isabelle Pâris, Changbom Park, Alim Y. Patten, Sebastien Peirani, Marcos Pellejero-Ibanez, Samantha Penny, Will J. Percival, Ismael Perez-Fournon, Patrick Petitjean, Matthew M. Pieri, Marc Pinsonneault, Alice Pisani, Radosław Poleski, Francisco Prada, Abhishek Prakash, Anna Bárbara de Andrade Queiroz, M. Jordan Raddick, Anand Raichoor, Sandro Barboza Rembold, Hannah Richstein, Rogemar A. Riffel, Rogério Riffel, Hans-Walter Rix, Annie C. Robin, Constance M. Rockosi, Sergio Rodríguez-Torres, A. Roman-Lopes, Carlos Román-Zúñiga, Margarita Rosado, Ashley J. Ross, Graziano Rossi, John Ruan, Rossana Ruggeri, Eli S. Rykoff, Salvador Salazar-Albornoz, Mara Salvato, Ariel G. Sánchez, D. S. Aguado, José R. Sánchez-Gallego, Felipe A. Santana, Basílio Xavier Santiago, Conor Sayres, Ricardo P. Schiavon, Jaderson da Silva Schimoia, Edward F. Schlafly, David J. Schlegel, Donald P. Schneider, Mathias Schultheis, William J. Schuster, Axel Schwope, Hee-Jong Seo, Zhengyi Shao, Shiyin Shen, Matthew Shetrone, Michael Shull, Joshua D. Simon, Danielle Skinner, M. F. Skrutskie, Anže Slosar, Verne V. Smith, Jennifer S. Sobeck, Flavia Sobreira, Garrett Somers, Diogo Souto, David V. Stark, Keivan Stassun, Fritz Stauffer, Matthias Steinmetz, Thaisa Storchi-Bergmann, Alina Streblyanska, Guy S. Stringfellow, Genaro Suárez, Jing Sun, Nao Suzuki, Laszlo Szigeti, Manuchehr Taghizadeh-Popp, Baitian Tang, Charling Tao, Jamie Tayar, Mita Tembe, Johanna Teske, Aniruddha R. Thakar, Daniel Thomas, Benjamin A. Thompson, Jeremy L. Tinker, Patricia Tissera, Rita Tojeiro, Hector Hernandez Toledo, Sylvain de la Torre, Christy Tremonti, Nicholas W. Troup, Octavio Valenzuela, Inma Martinez Valpuesta, Jaime Vargas-González, Mariana Vargas-Magaña, Jose Alberto Vazquez, Sandro Villanova, M. Vivek, Nicole Vogt, David Wake, Rene Walterbos, Yuting Wang, Benjamin Alan Weaver, Anne-Marie Weijmans, David H. Weinberg, Kyle B. Westfall, David G. Whelan, Vivienne Wild, John Wilson, W. M. Wood-Vasey, Dominika Wylezalek, Ting Xiao, Renbin Yan, Meng Yang, Jason E. Ybarra, Christophe Yèche, Nadia Zakamska, Olga Zamora, Pauline Zarrouk, Gail Zasowski, Kai Zhang, Gong-Bo Zhao, Zheng Zheng, Xu Zhou, Zhi-Min Zhou, Guangtun B. Zhu, Manuela Zoccali, Hu Zou, The Leverhulme Trust, University of St Andrews. School of Physics and Astronomy, Institut de Recherches sur les lois Fondamentales de l'Univers (IRFU), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, APC - Cosmologie, AstroParticule et Cosmologie (APC (UMR_7164)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Astrophysique de Marseille (LAM), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Centre de Physique des Particules de Marseille (CPPM), Aix Marseille Université (AMU)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213) (UTINAM), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC), Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Institut d'Astrophysique de Paris (IAP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Centre National d'Études Spatiales [Toulouse] (CNES), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Pierre et Marie Curie - Paris 6 (UPMC), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Collège de France (CdF)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-AstroParticule et Cosmologie (APC (UMR_7164)), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Aix Marseille Université (AMU), Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS), PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Claude Bernard Lyon 1 (UCBL), and Université de Lyon-Université de Lyon-École normale supérieure - Lyon (ENS Lyon)
Subjects: Astrophysics and Astronomy, Milky Way, astro-ph.GA, FOS: Physical sciences, Espectros astronômicos, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Surveys, 01 natural sciences, law.invention, Telescope, Redshift-space distortions, surveys, Observatory, law, 0103 physical sciences, QB Astronomy, Astrophysics::Solar and Stellar Astrophysics, spectrographs [Instrumentation], observations [Cosmology], Galaxy: general, stars: general, 010303 astronomy & astrophysics, general [Galaxy], QC, Astrophysics::Galaxy Astrophysics, instrumentation: spectrographs, QB, Mapeamentos astronômicos, Physics, general [Stars], 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Quasar, general [Galaxies], DAS, galaxies: general, Astrophysics - Astrophysics of Galaxies, Galaxy, Redshift, QC Physics, Space and Planetary Science, cosmology: observations, Astrophysics of Galaxies (astro-ph.GA), Catalogos astronomicos, Baryon acoustic oscillations, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: We describe the Sloan Digital Sky Survey IV (SDSS-IV), a project encompassing three major spectroscopic programs. The Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) is observing hundreds of thousands of Milky Way stars at high resolution and high signal-to-noise ratio in the near-infrared. The Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey is obtaining spatially-resolved spectroscopy for thousands of nearby galaxies (median redshift of z = 0.03). The extended Baryon Oscillation Spectroscopic Survey (eBOSS) is mapping the galaxy, quasar, and neutral gas distributions between redshifts z = 0.6 and 3.5 to constrain cosmology using baryon acoustic oscillations, redshift space distortions, and the shape of the power spectrum. Within eBOSS, we are conducting two major subprograms: the SPectroscopic IDentification of eROSITA Sources (SPIDERS), investigating X-ray AGN and galaxies in X-ray clusters, and the Time Domain Spectroscopic Survey (TDSS), obtaining spectra of variable sources. All programs use the 2.5-meter Sloan Foundation Telescope at Apache Point Observatory; observations there began in Summer 2014. APOGEE-2 also operates a second near-infrared spectrograph at the 2.5-meter du Pont Telescope at Las Campanas Observatory, with observations beginning in early 2017. Observations at both facilities are scheduled to continue through 2020. In keeping with previous SDSS policy, SDSS-IV provides regularly scheduled public data releases; the first one, Data Release 13, was made available in July 2016., Published in Astronomical Journal
Published: 2017

23. Broad Absorption Line Disappearance And Emergence Using Multiple-Epoch Spectroscopy From The Sloan Digital Sky Survey

Author: Timothy A. Hutchinson, Scott F. Anderson, Catherine J. Grier, W. N. Brandt, Patrick B. Hall, Paul J. Green, Chelsea L. MacLeod, M. Vivek, N. Filiz Ak, Donald P. Schneider, and Sean McGraw
Subjects: Physics, 010308 nuclear & particles physics, Epoch (reference date), media_common.quotation_subject, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, respiratory system, Astrophysics - Astrophysics of Galaxies, 01 natural sciences, Spectral line, respiratory tract diseases, Space and Planetary Science, Sky, Astrophysics of Galaxies (astro-ph.GA), 0103 physical sciences, Outflow, Spectroscopy, 010303 astronomy & astrophysics, media_common
Abstract: 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. We identify 14 disappearing BALs over < 1.73-4.62 rest-frame years and 18 emerging BALs over < 1.46-3.66 rest-frame years associated with the CIV 1548,1550 and/or SiIV 1393,1402 doublets, and report on their variability behavior. BAL quasars in our dataset exhibit disappearing/emerging CIV BALs at a rate of 2.3 and 3.0 per cent, respectively, and the frequency for BAL to non-BAL quasar transitions is 1.7 per cent. We detect four re-emerging BALs over < 3.88 rest-frame years on average and three re-disappearing BALs over < 4.15 rest-frame years on average, the first reported cases of these types. We infer BAL lifetimes along the line of sight to be nominally < 100-1000 yr using disappearing CIV BALs in our sample. Interpretations of (re-)emerging and (re-)disappearing BALs reveal evidence that collectively supports both transverse-motion and ionization-change scenarios to explain BAL variations. We constrain a nominal CIV/SiIV BAL outflow location of < 100 pc from the central source and a radial size of > 1x10^-7 pc (0.02 au) using the ionization-change scenario, and constrain a nominal outflow location of < 0.5 pc and a transverse size of ~0.01 pc using the transverse-motion scenario. Our findings are consistent with previous work, and provide evidence in support of BALs tracing compact flow geometries with small filling factors., 25 pages, 9 figures, 5 tables, accepted to MNRAS, please visit MNRAS or contact W.N. Brandt to access supplementary material
Published: 2017

24. The 13th Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-IV Survey Mapping Nearby Galaxies at Apache Point Observatory

Author: Franco D. Albareti, Carlos Allende Prieto, Andres Almeida, Friedrich Anders, Scott Anderson, Brett H. Andrews, Alfonso Aragón-Salamanca, Maria Argudo-Fernández, Eric Armengaud, Eric Aubourg, Vladimir Avila-Reese, Carles Badenes, Stephen Bailey, Beatriz Barbuy, Kat Barger, Jorge Barrera-Ballesteros, Curtis Bartosz, Sarbani Basu, Dominic Bates, Giuseppina Battaglia, Falk Baumgarten, Julien Baur, Julian Bautista, Timothy C. Beers, Francesco Belfiore, Matthew Bershady, Sara Bertran de Lis, Jonathan C. Bird, Dmitry Bizyaev, Guillermo A. Blanc, Michael Blanton, Michael Blomqvist, Adam S. Bolton, J. Borissova, Jo Bovy, William Nielsen Brandt, Jonathan Brinkmann, Joel R. Brownstein, Kevin Bundy, Etienne Burtin, Nicolás G. Busca, Hugo Orlando Camacho Chavez, M. Cano Díaz, Michele Cappellari, Ricardo Carrera, Yanping Chen, Brian Cherinka, Edmond Cheung, Cristina Chiappini, Drew Chojnowski, Chia-Hsun Chuang, Haeun Chung, Rafael Fernando Cirolini, Nicolas Clerc, Roger E. Cohen, Julia M. Comerford, Johan Comparat, Janaina Correa do Nascimento, Marie-Claude Cousinou, Kevin Covey, Jeffrey D. Crane, Rupert Croft, Katia Cunha, Jeremy Darling, James W. Davidson, Kyle Dawson, Luiz Da Costa, Gabriele Da Silva Ilha, Alice Deconto Machado, Timothée Delubac, Nathan De Lee, Axel De la Macorra, Sylvain De la Torre, Aleksandar M. Diamond-Stanic, John Donor, Juan Jose Downes, Niv Drory, Cheng Du, Hélion Du Mas des Bourboux, Tom Dwelly, Garrett Ebelke, Arthur Eigenbrot, Daniel J. Eisenstein, Yvonne P. Elsworth, Eric Emsellem, Michael Eracleous, Stephanie Escoffier, Michael L. Evans, Jesús Falcón-Barroso, Xiaohui Fan, Ginevra Favole, Emma Fernandez-Alvar, J. G. Fernandez-Trincado, Diane Feuillet, Scott W. Fleming, Andreu Font-Ribera, Gordon Freischlad, Peter Frinchaboy, Hai Fu, Yang Gao, Rafael A. Garcia, R. Garcia-Dias, D. A. Garcia-Hernández, Ana E. Garcia Pérez, Patrick Gaulme, Junqiang Ge, Douglas Geisler, Bruce Gillespie, Hector Gil Marin, Léo Girardi, Daniel Goddard, Yilen Gomez Maqueo Chew, Violeta Gonzalez-Perez, Kathleen Grabowski, Paul Green, Catherine J. Grier, Thomas Grier, Hong Guo, Julien Guy, Alex Hagen, Matt Hall, Paul Harding, R. E. Harley, Sten Hasselquist, Suzanne Hawley, Christian R. Hayes, Fred Hearty, Saskia Hekker, Hector Hernandez Toledo, Shirley Ho, David W. Hogg, Kelly Holley-Bockelmann, Jon A. Holtzman, Parker H. Holzer, Jian Hu, Daniel Huber, Timothy Alan Hutchinson, Ho Seong Hwang, Héctor J. Ibarra-Medel, Inese I. Ivans, KeShawn Ivory, Kurt Jaehnig, Trey W. Jensen, Jennifer A. Johnson, Amy Jones, Eric Jullo, T. Kallinger, Karen Kinemuchi, David Kirkby, Mark Klaene, Jean-Paul Kneib, Juna A. Kollmeier, Ivan Lacerna, Richard R. Lane, Dustin Lang, Pierre Laurent, David R. Law, Alexie Leauthaud, Jean-Marc Le Goff, Chen Li, Cheng Li, Niu Li, Ran Li, Fu-Heng Liang, Yu Liang, Marcos Lima, Lihwai Lin, Lin Lin, Yen-Ting Lin, Chao Liu, Dan Long, Sara Lucatello, Nicholas MacDonald, Chelsea L. MacLeod, J. Ted Mackereth, Suvrath Mahadevan, Marcio Antonio Geimba Maia, Roberto Maiolino, Steven R. Majewski, Olena Malanushenko, Viktor Malanushenko, Nícolas Dullius Mallmann, Arturo Manchado, Claudia Maraston, Rui Marques-Chaves, Inma Martinez Valpuesta, Karen L. Masters, Savita Mathur, Ian D. McGreer, Andrea Merloni, Michael R. Merrifield, Szabolcs Meszáros, Andres Meza, Andrea Miglio, Ivan Minchev, Karan Molaverdikhani, Antonio D. Montero-Dorta, Benoit Mosser, Demitri Muna, Adam Myers, Preethi Nair, Kirpal Nandra, Melissa Ness, Jeffrey A. Newman, Robert C. Nichol, David L. Nidever, Christian Nitschelm, Julia O’Connell, Audrey Oravetz, Daniel J. Oravetz, Zachary Pace, Nelson Padilla, Nathalie Palanque-Delabrouille, Kaike Pan, John Parejko, Isabelle Paris, Changbom Park, John A. Peacock, Sebastien Peirani, Marcos Pellejero-Ibanez, Samantha Penny, Will J. Percival, Jeffrey W. Percival, Ismael Perez-Fournon, Patrick Petitjean, Matthew Pieri, Marc H. Pinsonneault, Alice Pisani, Francisco Prada, Abhishek Prakash, Natalie Price-Jones, M. Jordan Raddick, Mubdi Rahman, Anand Raichoor, Sandro Barboza Rembold, A. M. Reyna, James Rich, Hannah Richstein, Jethro Ridl, Rogemar A. Riffel, Rogério Riffel, Hans-Walter Rix, Annie C. Robin, Constance M. Rockosi, Sergio Rodríguez-Torres, Thaíse S. Rodrigues, Natalie Roe, A. Roman Lopes, Carlos Román-Zúñiga, Ashley J. Ross, Graziano Rossi, John Ruan, Rossana Ruggeri, Jessie C. Runnoe, Salvador Salazar-Albornoz, Mara Salvato, Sebastian F. Sanchez, Ariel G. Sanchez, José R. Sanchez-Gallego, Basílio Xavier Santiago, Ricardo Schiavon, Jaderson S. Schimoia, Eddie Schlafly, David J. Schlegel, Donald P. Schneider, Ralph Schönrich, Mathias Schultheis, Axel Schwope, Hee-Jong Seo, Aldo Serenelli, Branimir Sesar, Zhengyi Shao, Matthew Shetrone, Michael Shull, Victor Silva Aguirre, M. F. Skrutskie, Anže Slosar, Michael Smith, Verne V. Smith, Jennifer Sobeck, Garrett Somers, Diogo Souto, David V. Stark, Keivan G. Stassun, Matthias Steinmetz, Dennis Stello, Thaisa Storchi Bergmann, Michael A. Strauss, Alina Streblyanska, Guy S. Stringfellow, Genaro Suarez, Jing Sun, Manuchehr Taghizadeh-Popp, Baitian Tang, Charling Tao, Jamie Tayar, Mita Tembe, Daniel Thomas, Jeremy Tinker, Rita Tojeiro, Christy Tremonti, Nicholas Troup, Jonathan R. Trump, Eduardo Unda-Sanzana, O. Valenzuela, Remco Van den Bosch, Mariana Vargas-Magaña, Jose Alberto Vazquez, Sandro Villanova, M. Vivek, Nicole Vogt, David Wake, Rene Walterbos, Yuting Wang, Enci Wang, Benjamin Alan Weaver, Anne-Marie Weijmans, David H. Weinberg, Kyle B. Westfall, David G. Whelan, Eric Wilcots, Vivienne Wild, Rob A. Williams, John Wilson, W. M. Wood-Vasey, Dominika Wylezalek, Ting Xiao, Renbin Yan, Meng Yang, Jason E. Ybarra, Christophe Yeche, Fang-Ting Yuan, Nadia Zakamska, Olga Zamora, Gail Zasowski, Kai Zhang, Cheng Zhao, Gong-Bo Zhao, Zheng Zheng, Zhi-Min Zhou, Guangtun Zhu, Joel C. Zinn, Hu Zou, Institut de Recherches sur les lois Fondamentales de l'Univers (IRFU), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, AstroParticule et Cosmologie (APC (UMR_7164)), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7), Laboratoire d'Astrophysique de Marseille (LAM), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Centre National d'Études Spatiales [Toulouse] (CNES), Centre de Physique des Particules de Marseille (CPPM), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Aix Marseille Université (AMU), Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'astrophysique de l'observatoire de Besançon (LAOB), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), Institut d'Astrophysique de Paris (IAP), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE (UMR_7585)), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), SDSS, Maiolino, Roberto [0000-0002-4985-3819], Apollo - University of Cambridge Repository, Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Aix Marseille Université (AMU)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Laboratoire d'astrophysique de l'observatoire de Besançon (UMR 6091) (LAOB), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), University of St Andrews. School of Physics and Astronomy, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École normale supérieure - Lyon (ENS Lyon), Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherches sur les lois Fondamentales de l'Univers ( IRFU ), Commissariat à l'énergie atomique et aux énergies alternatives ( CEA ) -Université Paris-Saclay, AstroParticule et Cosmologie ( APC - UMR 7164 ), Centre National de la Recherche Scientifique ( CNRS ) -Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -Observatoire de Paris-Université Paris Diderot - Paris 7 ( UPD7 ) -Commissariat à l'énergie atomique et aux énergies alternatives ( CEA ), Laboratoire d'Astrophysique de Marseille ( LAM ), Aix Marseille Université ( AMU ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National d'Etudes Spatiales ( CNES ) -Centre National de la Recherche Scientifique ( CNRS ), Centre de Physique des Particules de Marseille ( CPPM ), Centre National de la Recherche Scientifique ( CNRS ) -Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -Aix Marseille Université ( AMU ), Centre de Recherche Astrophysique de Lyon ( CRAL ), École normale supérieure - Lyon ( ENS Lyon ) -Université Claude Bernard Lyon 1 ( UCBL ), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ), Laboratoire d'astrophysique de l'observatoire de Besançon ( LAOB ), Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ) -Université de Franche-Comté ( UFC ), Laboratoire AIM, Université Paris Diderot - Paris 7 ( UPD7 ) -Centre d'Etudes de Saclay, Institut d'Astrophysique de Paris ( IAP ), Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ), Laboratoire de Physique Nucléaire et de Hautes Énergies ( LPNHE ), Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -Université Paris Diderot - Paris 7 ( UPD7 ) -Centre National de la Recherche Scientifique ( CNRS ), Laboratoire d'études spatiales et d'instrumentation en astrophysique ( LESIA ), Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Observatoire de Paris-Université Paris Diderot - Paris 7 ( UPD7 ) -Centre National de la Recherche Scientifique ( CNRS ), Joseph Louis LAGRANGE ( LAGRANGE ), Université Nice Sophia Antipolis ( UNS ), Université Côte d'Azur ( UCA ) -Université Côte d'Azur ( UCA ) -Observatoire de la Côte d'Azur, and Université Côte d'Azur ( UCA ) -Centre National de la Recherche Scientifique ( CNRS )
Subjects: [ PHYS.ASTR ] Physics [physics]/Astrophysics [astro-ph], media_common.quotation_subject, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Surveys, 01 natural sciences, Set (abstract data type), surveys, Observatory, 0103 physical sciences, QB Astronomy, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, QC, Astrophysics::Galaxy Astrophysics, QB, media_common, Physics, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, Atlases, DAS, Astronomy and Astrophysics, Quasar, GALÁXIAS, Galaxy, Redshift, atlases, QC Physics, Data access, Space and Planetary Science, Sky, Catalogs, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], catalogs, Data reduction
Abstract: The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) began observations in July 2014. It pursues three core programs: APOGEE-2,MaNGA, and eBOSS. In addition, eBOSS contains two major subprograms: TDSS and SPIDERS. This paper describes the first data release from SDSS-IV, Data Release 13 (DR13), which contains new data, reanalysis of existing data sets and, like all SDSS data releases, is inclusive of previously released data. DR13 makes publicly available 1390 spatially resolved integral field unit observations of nearby galaxies from MaNGA,the first data released from this survey. It includes new observations from eBOSS, completing SEQUELS. In addition to targeting galaxies and quasars, SEQUELS also targeted variability-selected objects from TDSS and X-ray selected objects from SPIDERS. DR13 includes new reductions ofthe SDSS-III BOSS data, improving the spectrophotometric calibration and redshift classification. DR13 releases new reductions of the APOGEE-1data from SDSS-III, with abundances of elements not previously included and improved stellar parameters for dwarf stars and cooler stars. For the SDSS imaging data, DR13 provides new, more robust and precise photometric calibrations. Several value-added catalogs are being released in tandem with DR13, in particular target catalogs relevant for eBOSS, TDSS, and SPIDERS, and an updated red-clump catalog for APOGEE.This paper describes the location and format of the data now publicly available, as well as providing references to the important technical papers that describe the targeting, observing, and data reduction. The SDSS website, http://www.sdss.org, provides links to the data, tutorials and examples of data access, and extensive documentation of the reduction and analysis procedures. DR13 is the first of a scheduled set that will contain new data and analyses from the planned ~6-year operations of SDSS-IV. Postprint
Published: 2017

25. 1ES 1927+654: An AGN Caught Changing Look on a Timescale of Months

Author: Erin Kara, D. Andrew Howell, Iair Arcavi, Benny Trakhtenbrot, J. L. Prieto, D. Bersier, Michael Loewenstein, Melissa L. Graham, Griffin Hosseinzadeh, Daniel Stern, Thomas G. Brink, Ruancun Li, WeiKang Zheng, Chelsea L. MacLeod, Alexei V. Filippenko, Benjamin J. Shappee, Daichi Hiramatsu, Thomas W.-S. Holoien, Fiona A. Harrison, Jamison Burke, Stephen J. Smartt, Ronald A. Remillard, Armin Rest, and Claudio Ricci
Subjects: Active galactic nucleus, 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, nuclei [galaxies], FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, medicine.disease_cause, 01 natural sciences, symbols.namesake, individual (1ES 1927+654) [galaxies], emission lines [quasars], 0103 physical sciences, medicine, Astrophysics::Solar and Stellar Astrophysics, Emission spectrum, Spectroscopy, 010303 astronomy & astrophysics, QC, Astrophysics::Galaxy Astrophysics, QB, 0105 earth and related environmental sciences, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, general [quasars], Spectral properties, Balmer series, Astronomy and Astrophysics, Astrophysics - Astrophysics of Galaxies, Galaxy, Travel time, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), active [galaxies], symbols, Astrophysics - High Energy Astrophysical Phenomena, Ultraviolet
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). 1ES 1927+654 was part of the small and peculiar class of "true Type-2" AGN, which lack broad emission lines and line-of-sight obscuration. Our high-cadence spectroscopic monitoring captures the appearance of a blue, featureless continuum, followed several weeks later by the appearance of broad Balmer emission lines. This timescale is generally consistent with the expected light travel time between the central engine and the broad-line emission region in (persistent) broad-line AGN. Hubble Space Telescope spectroscopy reveals no evidence for broad UV emission lines (e.g., CIV1549, CIII]1909, MgII2798), probably owing to dust in the broad-line emission region. To the best of our knowledge, this is the first case where the lag between the change in continuum and in broad-line emission of a "changing-look" AGN has been temporally resolved. The nature and timescales of the photometric and spectral evolution disfavor both a change in line-of-sight obscuration and a change of the overall rate of gas inflow as driving the drastic spectral transformations seen in this AGN. Although the peak luminosity and timescales are consistent with those of tidal disruption events seen in inactive galaxies, the spectral properties are not. The X-ray emission displays a markedly different behavior, with frequent flares on timescales of hours to days, and will be presented in a companion publication., accepted for publication in ApJ
Published: 2019

26. Gemini Imaging of the Host Galaxies of Changing-look Quasars

Author: John J. Ruan, Scott F. Anderson, Daryl Haggard, Chelsea L. MacLeod, Jessie C. Runnoe, Paul J. L. Charlton, and Michael Eracleous
Subjects: Active galactic nucleus, 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, Doubly ionized oxygen, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Galaxy merger, 01 natural sciences, Luminosity, 0103 physical sciences, Surface brightness, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Astronomy and Astrophysics, Quasar, Astrophysics - Astrophysics of Galaxies, Galaxy, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Sersic profile
Abstract: Changing-look quasars are a newly-discovered class of luminous active galactic nuclei that undergo rapid ($\lesssim$10 year) transitions between Type 1 and Type 1.9/2, with an associated change in their continuum emission. We characterize the host galaxies of four faded changing-look quasars using broadband optical imaging. We use \textit{gri} images obtained with the Gemini Multi Object Spectrograph (GMOS) on Gemini North to characterize the surface brightness profiles of the quasar hosts and search for [O III] $\lambda4959,\lambda5007$ emission from spatially extended regions, or voorwerpjes, with the goal of using them to examine past luminosity history. Although we do not detect, voorwerpjes surrounding the four quasar host galaxies, we take advantage of the dim nuclear emission to characterize the colors and morphologies of the host galaxies. Three of the four galaxies show morphological evidence of merger activity or tidal features in their residuals. The three galaxies which are not highly distorted are fit with a single S\'ersic profile to characterize their overall surface brightness profiles. The single-S\'ersic fits give intermediate S\'ersic indices between the $n=1$ of disk galaxies and the $n=4$ of ellipticals. On a color-magnitude diagram, our changing-look quasar host galaxies reside in the blue cloud, with other AGN host galaxies and star-forming galaxies. On a color-S\'ersic index diagram the changing-look quasar hosts reside with other AGN hosts in the "green valley". Our analysis suggests that the hosts of changing-look quasars are predominantly disrupted or merging galaxies that resemble AGN hosts, rather than inactive galaxies., Comment: 20 pages, 5 figures
Published: 2019

27. The time-domain spectroscopic survey: Understanding the optically variable sky with sequels in SDSS-III

Author: Matthew A. Bershady, Donald P. Schneider, Chelsea L. MacLeod, W. N. Brandt, Jean-Paul Kneib, Kyle S. Dawson, Timothy M. Heckman, Jedidah Isler, Nicholas P. Ross, Scott F. Anderson, Carles Badenes, Donald G. York, Keivan G. Stassun, James R. A. Davenport, H. Flewelling, Paula Szkody, Edward F. Schlafly, Jessie C. Runnoe, Eric Morganson, Michael Eracleous, Isabelle Paris, Yue Shen, John J. Ruan, C. Z. Waters, Adam D. Myers, K. C. Chambers, Axel Schwope, Paul J. Green, Nick Kaiser, Sarah J. Schmidt, Department of Astrophysical Sciences [Princeton], Princeton University, Department of Physics and Astronomy [UCLA Los Angeles], University of California [Los Angeles] (UCLA), University of California-University of California, Department of Physics and Astronomy [Baltimore], Johns Hopkins University (JHU), Laboratoire d'Astrophysique de Marseille (LAM), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Centre National d'Études Spatiales [Toulouse] (CNES), Universidad de Chile = University of Chile [Santiago] (UCHILE), University of California (UC)-University of California (UC), and Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), astro-ph.SR, media_common.quotation_subject, astro-ph.GA, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, RR Lyrae variable, Astronomy & Astrophysics, 01 natural sciences, Atomic, Physical Chemistry, Spectral line, Particle and Plasma Physics, surveys, quasars: general, 0103 physical sciences, Binary star, Astrophysics::Solar and Stellar Astrophysics, Nuclear, Time domain, Blazar, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, media_common, Physics, general [quasars], 010308 nuclear & particles physics, Molecular, Astronomy and Astrophysics, Quasar, Astrophysics - Astrophysics of Galaxies, Redshift, stars: variables: general, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Sky, variables: general [stars], Astrophysics of Galaxies (astro-ph.GA), astro-ph.CO, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astronomical and Space Sciences, Astrophysics - Cosmology and Nongalactic Astrophysics, Physical Chemistry (incl. Structural)
Abstract: The Time-Domain Spectroscopic Survey (TDSS) is an SDSS-IV eBOSS subproject primarily aimed at obtaining identification spectra of ~220,000 optically-variable objects systematically selected from SDSS/Pan-STARRS1 multi-epoch imaging. We present a preview of the science enabled by TDSS, based on TDSS spectra taken over ~320 deg^2 of sky as part of the SEQUELS survey in SDSS-III, which is in part a pilot survey for eBOSS in SDSS-IV. Using the 15,746 TDSS-selected single-epoch spectra of photometrically variable objects in SEQUELS, we determine the demographics of our variability-selected sample, and investigate the unique spectral characteristics inherent in samples selected by variability. We show that variability-based selection of quasars complements color-based selection by selecting additional redder quasars, and mitigates redshift biases to produce a smooth quasar redshift distribution over a wide range of redshifts. The resulting quasar sample contains systematically higher fractions of blazars and broad absorption line quasars than from color-selected samples. Similarly, we show that M-dwarfs in the TDSS-selected stellar sample have systematically higher chromospheric active fractions than the underlying M-dwarf population, based on their H-alpha emission. TDSS also contains a large number of RR Lyrae and eclipsing binary stars with main-sequence colors, including a few composite-spectrum binaries. Finally, our visual inspection of TDSS spectra uncovers a significant number of peculiar spectra, and we highlight a few cases of these interesting objects. With a factor of ~15 more spectra, the main TDSS survey in SDSS-IV will leverage the lessons learned from these early results for a variety of time-domain science applications., 17 pages, 14 figures, submitted to ApJ
Published: 2016

28. A systematic search for changing-look quasars in SDSS

Author: E. A. Magnier, Richard J. Wainscoat, K. C. Chambers, William S. Burgett, Nick Kaiser, Klaus W. Hodapp, Keith Horne, Andy Lawrence, Christopher Waters, H. Flewelling, Chelsea L. MacLeod, Nicholas P. Ross, M. R. Goad, Science & Technology Facilities Council, and University of St Andrews. School of Physics and Astronomy
Subjects: ACTIVE GALACTIC NUCLEI, active [Galaxies], Astrophysics::High Energy Astrophysical Phenomena, NDAS, Library science, FOS: Physical sciences, BROAD-LINE REGION, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, AGN DUSTY TORI, OSCILLATION SPECTROSCOPIC SURVEY, emission lines [Quasars], 7TH DATA RELEASE, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, QB Astronomy, 010303 astronomy & astrophysics, RELATIVISTIC IRON LINE, BLACK-HOLES, Astrophysics::Galaxy Astrophysics, QC, QB, Physics, 010308 nuclear & particles physics, Astronomy, Astronomy and Astrophysics, general [Quasars], Astrophysics - Astrophysics of Galaxies, QC Physics, Accretion, accretion discs, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), X-RAY, SPECTRAL VARIABILITY, DIGITAL SKY SURVEY, Astrophysics::Earth and Planetary Astrophysics, Systematic search
Abstract: We present a systematic search for changing-look quasars based on repeat photometry from SDSS and Pan-STARRS1, along with repeat spectra from SDSS and SDSS-III BOSS. Objects with large, |\Delta g|>1 mag photometric variations in their light curves are selected as candidates to look for changes in broad emission line (BEL) features. Out of a sample of 1011 objects that satisfy our selection criteria and have more than one epoch of spectroscopy, we find 10 examples of quasars that have variable and/or "changing-look" BEL features. Four of our objects have emerging BELs; five have disappearing BELs, and one object shows tentative evidence for having both emerging and disappearing BELs. With redshifts in the range 0.20 < z < 0.63, this sample includes the highest-redshift changing-look quasars discovered to date. We highlight the quasar J102152.34+464515.6 at z = 0.204. Here, not only have the Balmer emission lines strongly diminished in prominence, including H$\beta$ all but disappearing, but the blue continuum $f_{\nu} \propto \nu^{1/3}$ typical of an AGN is also significantly diminished in the second epoch of spectroscopy. Using our selection criteria, we estimate that >15% of strongly variable luminous quasars display changing-look BEL features on rest-frame timescales of 8 to 10 years. Plausible timescales for variable dust extinction are factors of 2-10 too long to explain the dimming and brightening in these sources, and simple dust reddening models cannot reproduce the BEL changes. On the other hand, an advancement such as disk reprocessing is needed if the observed variations are due to accretion rate changes., Comment: 15 pages, 8 Figures, 3 Tables, replaced with version accepted to MNRAS
Published: 2016

29. Slow blue nuclear hypervariables in PanSTARRS-1

Author: Chelsea L. MacLeod, William S. Burgett, Richard J. Wainscoat, K. W. Smith, Darryl Wright, Martin Elvis, Andy Lawrence, Paul A. Price, T. W. Chen, Suvi Gezari, Nigel Metcalfe, John L. Tonry, K. C. Chambers, Nick Kaiser, Alexander Mead, Stefano Valenti, Rubina Kotak, Alastair Bruce, Alicia M. Soderberg, Cosimo Inserra, Martin Ward, Christopher Waters, P. Marshall, Eugene A. Magnier, Stephen J. Smartt, Morgan Fraser, and Apollo - University of Cambridge Repository
Subjects: Active galactic nucleus, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, galaxies: active, nuclei [galaxies], FOS: Physical sciences, Astrophysics, gravitational lensing: micro, Astrophysics::Cosmology and Extragalactic Astrophysics, Gravitational microlensing, 01 natural sciences, accretion, quasars: general, 0103 physical sciences, William Herschel Telescope, Astrophysics::Solar and Stellar Astrophysics, 010306 general physics, Blazar, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), general [quasars], Astronomy, Astronomy and Astrophysics, Quasar, accretion discs, Astrophysics - Astrophysics of Galaxies, Galaxy, Stars, Supernova, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), active [galaxies], micro [gravitational lensing], accretion, accretion discs, Astrophysics::Earth and Planetary Astrophysics, galaxies: nuclei, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw1963, 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 of the Pan-STARRS1 (PS1) 3$\pi$ survey, by comparison with Sloan Digital Sky Survey (SDSS) photometry a decade earlier, and then monitored with the Liverpool Telescope, and studied spectroscopically with the William Herschel Telescope (WHT). Based on colours, light-curve shape, and spectra, these transients fall into four groups. A few are misclassified stars or objects of unknown type. Some are red/fast transients and are known or likely nuclear supernovae. A few are either radio sources or erratic variables and so likely blazars. However the majority (~66 per cent) are blue and evolve slowly, on a time-scale of years. Spectroscopy shows them to be AGN at $z$ ~ 0.3 − 1.4, which must have brightened since the SDSS photometry by around an order of magnitude. It is likely that these objects were in fact AGN a decade ago, but too weak to be recognized by SDSS; they could then be classed as ‘hypervariable’ AGN. By searching the SDSS Stripe 82 quasar database, we find 15 similar objects. We discuss several possible explanations for these slow-blue hypervariables – (i) unusually luminous tidal disruption events; (ii) extinction events; (iii) changes in accretion state; and (iv) large amplitude microlensing by stars in foreground galaxies. A mixture of explanations (iii) and (iv) seems most likely. Both hold promise of considerable new insight into the AGN phenomenon.
Published: 2016
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30. The nature of the cataclysmic variable PT Per

Author: J. P. Osborne, Chelsea L. MacLeod, Alastair Bruce, Axel Schwope, and M. G. Watson
Subjects: 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, Cataclysmic variable star, FOS: Physical sciences, Astrophysics, 01 natural sciences, symbols.namesake, Intermediate polar, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Spectroscopy, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), 0105 earth and related environmental sciences, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Zeeman effect, White dwarf, Astronomy, Astronomy and Astrophysics, Accretion (astrophysics), Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, symbols, Polar, Astrophysics - High Energy Astrophysical Phenomena, Visible spectrum
Abstract: We present a study of the cataclysmic variable star PT Per based on archival XMM-Newton X-ray data and new optical spectroscopy from the WHT with ISIS. The X-ray data show deep minima which recur at a period of 82 minutes and a hard, unabsorbed X-ray spectrum. The optical spectra of PT Per show a relatively featureless blue continuum. From an analysis of the X-ray and optical data we conclude that PT Per is likely to be a magnetic cataclysmic variable of the polar class in which the minima correspond to those phase intervals when the accretion column rotates out of the field of view of the observer. We suggest that the optical spectrum, obtained around 4 years after the X-ray coverage, is dominated by the white dwarf in the system, implying that PT Per was in a low accretion state at the time of the observations. An analysis of the likely system parameters for PT Per suggests a distance of $\approx90$ pc and a very low-mass secondary, consistent with the idea that PT Per is a "period-bounce" binary., LAST UPDATED VERSION with modified discussion of WD field estimation etc. Accepted for publication in MNRAS
Published: 2015

31. The Type I Superluminous Supernova PS16aqv: Lightcurve Complexity and Deep Limits on Radioactive Ejecta in a Fast Event

Author: Ryan Chornock, Edo Berger, P. K. Blanchard, Chelsea L. MacLeod, Kornpob Bhirombhakdi, Wen-fai Fong, Matt Nicholl, Dan Milisavljevic, and Raffaella Margutti
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Absolute magnitude, Physics, 010308 nuclear & particles physics, Star formation, Metallicity, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Type (model theory), Magnetar, 01 natural sciences, Galaxy, Supernova, Astrophysics - Solar and Stellar Astrophysics, 13. Climate action, Space and Planetary Science, 0103 physical sciences, Continuum (set theory), Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR)
Abstract: [Abridged] We present UV/optical observations of PS16aqv (SN 2016ard), a Type I superluminous supernova (SLSN-I) classified as part of our search for low-$z$ SLSNe. PS16aqv is a fast evolving SLSNe-I that reached a peak absolute magnitude of $M_{r} \approx -22.1$. The lightcurves exhibit a significant undulation at 30 rest-frame days after peak, with a behavior similar to undulations seen in the slowly fading SLSN-I SN 2015bn. This similarity strengthens the case that fast and slow SLSNe-I form a continuum with a common origin. At $\approx\!80$ days after peak, the lightcurves exhibit a transition to a slow decline, followed by significant subsequent steepening, indicative of a plateau phase or a second significant undulation. Deep limits at $\approx280$ days after peak imply a tight constraint on the nickel mass, $M_{\rm Ni} \lesssim 0.35$ M$_{\odot}$ (lower than for previous SLSNe-I), and indicate that some SLSNe-I do not produce significantly more nickel than normal Type Ic SNe. Using MOSFiT, we model the lightcurve with a magnetar central engine model and find $P_{\rm spin} \approx 0.9$ ms, $B \approx 1.5 \times 10^{14}$ G, and $M_{\rm ej} \approx 16$ M$_{\odot}$. The implied rapid spin-down time and large reservoir of available energy coupled with the high ejecta mass may account for the fast evolving lightcurve and slow spectroscopic evolution. We also study the location of PS16aqv in its host galaxy and find that it occurred at an offset of $2.46 \pm 0.21$ kpc from the central star-forming region. We find the host galaxy exhibits low metallicity and spatially varying extinction and star formation rate, with the explosion site exhibiting lower values than the central region. The complexity seen in the lightcurves of PS16aqv and other events highlights the importance of obtaining well-sampled lightcurves for exploring deviations from a uniform decline., Comment: 16 pages, 10 figures, submitted to ApJ
Published: 2018

32. Multiwavelength observations of radio-quiet quasars with weak emission lines

Author: W. N. Brandt, Xiaohui Fan, Donald P. Schneider, Chelsea L. MacLeod, Aleksandar M. Diamond-Stanic, Richard M. Plotkin, Scott F. Anderson, Ohad Shemmer, and High Energy Astrophys. & Astropart. Phys (API, FNWI)
Subjects: Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Active galactic nucleus, media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Flux, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Light curve, Galaxy, Stars, Space and Planetary Science, Sky, Emission spectrum, Astrophysics::Galaxy Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics, media_common
Abstract: We present radio and X-ray observations, as well as optical light curves, for a subset of 26 BL Lac candidates from the Sloan Digital Sky Survey (SDSS) lacking strong radio emission and with z, 15 pages, 4 figures, 5 tables. Accepted for publication in ApJ
Published: 2010

33. Quasar Classification Using Color and Variability

Author: Gordon T. Richards, Chelsea L. MacLeod, Christina M. Peters, Željko Ivezić, Nicholas P. Ross, Ryan Riegel, Kasper B. Schmidt, Michael A. Strauss, and Adam D. Myers
Subjects: Physics, media_common.quotation_subject, Astrophysics::Instrumentation and Methods for Astrophysics, Color analysis, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics - Astrophysics of Galaxies, Spectral line, Photometry (optics), Stars, Space and Planetary Science, Sky, Astrophysics of Galaxies (astro-ph.GA), Magnitude (astronomy), Astrophysics::Solar and Stellar Astrophysics, Luminosity function, Astrophysics::Galaxy Astrophysics, media_common
Abstract: We conduct a pilot investigation to determine the optimal combination of color and variability information to identify quasars in current and future multi-epoch optical surveys. We use a Bayesian quasar selection algorithm (Richards et al. 2004) to identify 35,820 type 1 quasar candidates in a 239 square degree field of the Sloan Digital Sky Survey (SDSS) Stripe 82, using a combination of optical photometry and variability. Color analysis is performed on 5-band single- and multi-epoch SDSS optical photometry to a depth of r ~22.4. From these data, variability parameters are calculated by fitting the structure function of each object in each band with a power law model using 10 to >100 observations over timescales from ~1 day to ~8 years. Selection was based on a training sample of 13,221 spectroscopically-confirmed type-1 quasars, largely from the SDSS. Using variability alone, colors alone, and combining variability and colors we achieve 91%, 93%, and 97% quasar completeness and 98%, 98%, and 97% efficiency respectively, with particular improvement in the selection of quasars at 2.7, Comment: 32 pages, 23 figures. Accepted for publication in ApJS. Data file is available at http://oberon.physics.drexel.edu/~tinapeters/quasarclassification/Peters2015Catalog_30042015.fit.bz2
Published: 2015

34. SDSSJ14584479+3720215: A Benchmark JHK Blazar Light Curve from the 2MASS Calibration Scans

Author: Chelsea L. MacLeod, Andrew C. Becker, James R. A. Davenport, John J. Ruan, and Roc M. Cutri
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Active galactic nucleus, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Young stellar object, Astrophysics::High Energy Astrophysical Phenomena, Flux, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Light curve, Space and Planetary Science, Ophiuchus, Astrophysics::Solar and Stellar Astrophysics, Blazar, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics::Galaxy Astrophysics, Fermi Gamma-ray Space Telescope, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Active galactic nuclei (AGNs) are well-known to exhibit flux variability across a wide range of wavelength regimes, but the precise origin of the variability at different wavelengths remains unclear. To investigate the relatively unexplored near-IR variability of the most luminous AGNs, we conduct a search for variability using well sampled JHKs-band light curves from the 2MASS survey calibration fields. Our sample includes 27 known quasars with an average of 924 epochs of observation over three years, as well as one spectroscopically confirmed blazar (SDSSJ14584479+3720215) with 1972 epochs of data. This is the best-sampled NIR photometric blazar light curve to date, and it exhibits correlated, stochastic variability that we characterize with continuous auto-regressive moving average (CARMA) models. None of the other 26 known quasars had detectable variability in the 2MASS bands above the photometric uncertainty. A blind search of the 2MASS calibration field light curves for AGN candidates based on fitting CARMA(1,0) models (damped-random walk) uncovered only 7 candidates. All 7 were young stellar objects within the {\rho} Ophiuchus star forming region, five with previous X-ray detections. A significant {\gamma}-ray detection (5{\sigma}) for the known blazar using 4.5 years of Fermi photon data is also found. We suggest that strong NIR variability of blazars, such as seen for SDSSJ14584479+3720215, can be used as an efficient method of identifying previously-unidentified {\gamma}-ray blazars, with low contamination from other AGN., Comment: 6 pages, 3 figures, ApJ Accepted
Published: 2015
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35. Detection of Time Lags between Quasar Continuum Emission Bands Based On Pan-STARRS Light Curves

Author: John J. Ruan, Jenny E. Greene, W. N. Brandt, William S. Burgett, Caroline Scott, Pavlos Protopapas, Catherine J. Grier, Chelsea L. MacLeod, Anna Pancoast, R. P. Kudritzki, J. T. Tonry, Christopher Waters, Yan-Fei Jiang, Richard J. Wainscoat, Nick Kaiser, Nigel Metcalfe, Eugene A. Magnier, Eric Morganson, H.-W. Rix, Yue Shen, Scott F. Anderson, Paul J. Green, Klaus W. Hodapp, and Mark E. Huber
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Metallicity, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Gravitational microlensing, Light curve, 01 natural sciences, Redshift, Accretion (astrophysics), Galaxy, Thin disk, Space and Planetary Science, 0103 physical sciences, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics
Abstract: We study the time lags between the continuum emission of quasars at different wavelengths, based on more than four years of multi-band ($g$, $r$, $i$, $z$) light-curves in the Pan-STARRS Medium Deep Fields. As photons from different bands emerge from different radial ranges in the accretion disk, the lags constrain the sizes of the accretion disks. We select 240 quasars with redshifts $z \approx 1$ or $z \approx 0.3$ that are relatively emission line free. The light curves are sampled from day to month timescales, which makes it possible to detect lags on the scale of the light crossing time of the accretion disks. With the code JAVELIN, we detect typical lags of several days in the rest frame between the $g$ band and the $riz$ bands. The detected lags are $\sim 2-3$ times larger than the light crossing time estimated from the standard thin disk model, consistent with the recently measured lag in NGC5548 and micro-lensing measurements of quasars. The lags in our sample are found to increase with increasing luminosity. Furthermore, the increase in lags going from $g-r$ to $g-i$ and then to $g-z$ is slower than predicted in the thin disk model, particularly for high luminosity quasars. The radial temperature profile in the disk must be different from what is assumed. We also find evidence that the lags decrease with increasing line ratios between ultraviolet FeII lines and MgII, which may point to changes in the accretion disk structure at higher metallicity., 18 pages, 17 Figures, 3 Tables, submitted to ApJ
Published: 2017

36. Optical variability of quasars: a damped random walk

Author: Chelsea L. MacLeod and Željko Ivezić
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Covariance matrix, Stochastic process, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Random walk, Astrophysics - Astrophysics of Galaxies, Redshift, Luminosity, Black hole, Amplitude, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics - High Energy Astrophysical Phenomena
Abstract: A damped random walk is a stochastic process, defined by an exponential covariance matrix that behaves as a random walk for short time scales and asymptotically achieves a finite variability amplitude at long time scales. Over the last few years, it has been demonstrated, mostly but not exclusively using SDSS data, that a damped random walk model provides a satisfactory statistical description of observed quasar variability in the optical wavelength range, for rest-frame timescales from 5 days to 2000 days. The best-fit characteristic timescale and asymptotic variability amplitude scale with the luminosity, black hole mass, and rest wavelength, and appear independent of redshift. In addition to providing insights into the physics of quasar variability, the best-fit model parameters can be used to efficiently separate quasars from stars in imaging surveys with adequate long-term multi-epoch data, such as expected from LSST., 4 pages, 1 figure, presented at the IAU Symposium #304
Published: 2013

37. A photometric redshift of z = 6.39 ± 0.12 for GRB 050904

Author: Alicia M. Soderberg, C. M. Zdarowicz, Mansi M. Kasliwal, Chelsea L. MacLeod, D. Bersier, A. Alvarez, Shrinivas R. Kulkarni, A. de Ugarte Postigo, James E. Rhoads, Fiona A. Harrison, A. S. Fruchter, J. W. Bartelme, Avishay Gal-Yam, S. Klose, D. Maturana, René Hudec, Melissa C. Nysewander, Matt J. Jarvis, Brian P. Schmidt, D. Q. Lamb, C. E. Mack, N. Gehrels, P. A. Price, Robert S. Priddey, J. A. Crain, G. Grant Williams, A. Foster, R. Canterna, H-S Park, Petr Kubánek, Sergei Guziy, A. J. Castro-Tirado, Scott Barthelmy, Nial R. Tanvir, D. B. Fox, A. A. Henden, David N. Burrows, Francisco Prada, A. J.M. Fernandez, Charles R. Evans, S. Pizarro, J. Kirschbrown, Dieter H. Hartmann, J. C. Clemens, Javier Gorosabel, P. T. O'Brien, P. Ugarte, Chryssa Kouveliotou, Andrew J. Levan, Martin Jelínek, Josh Haislip, James R. Graham, Ralph A. M. J. Wijers, Mariano Moles, Evert Rol, Matthew B. Bayliss, E. Alfaro, Stanislav Vítek, E. Figueredo, Eduardo S. Cypriano, Robert Chapman, Daniel E. Reichart, Stephen Bradley Cenko, N. D. Kumar, Aaron P. LaCluyze, K. M. Ivarsen, and Dae-Sik Moon
Subjects: Physics, Multidisciplinary, Star formation, Metallicity, media_common.quotation_subject, Astronomy, Astrophysics, Redshift, Universe, Afterglow, Gamma-ray burst, Reionization, Photometric redshift, media_common
Abstract: Gamma-ray bursts (GRBs) and their afterglows are the most brilliant transient events in the Universe. Both the bursts themselves and their afterglows have been predicted to be visible out to redshifts of z approximately 20, and therefore to be powerful probes of the early Universe. The burst GRB 000131, at z = 4.50, was hitherto the most distant such event identified3. Here we report the discovery of the bright near-infrared afterglow of GRB 050904 (ref. 4). From our measurements of the near-infrared afterglow, and our failure to detect the optical afterglow, we determine the photometric redshift of the burst to be z = 6.29^(+0.11)_(-0.12) (refs 5–7). Subsequently, it was measured spectroscopically to be z = 6.29 ± 0.01, in agreement with our photometric estimate. These results demonstrate that GRBs can be used to trace the star formation, metallicity, and reionization histories of the early Universe.
Published: 2006

38. Time Delay and Accretion Disk Size Measurements in the Lensed Quasar SBS 0909+532 from Multiwavelength Microlensing Analysis

Author: Emilio E. Falco, Chelsea L. MacLeod, Trudy Tilleman, Laura J. Hainline, Zachary D. Landaal, Christopher S. Kochanek, Vyacheslav N. Shalyapin, Luis J. Goicoechea, Hugh C. Harris, Christopher W. Morgan, and Universidad de Cantabria
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), individual (SBS 0909+532) [Quasars], Gravitational lensing: strong, Dark matter, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Gravitational microlensing, strong [Gravitational lensing], 01 natural sciences, Gravitational lensing: micro, micro [Gravitational lensing], Photometry (optics), 0103 physical sciences, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, Quasars: individual (SBS 0909+532), 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Quasar, Astrometry, Accretion, accretion disks, Galaxy, Robotic telescope, Thin disk, Space and Planetary Science, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present three complete seasons and two half-seasons of SDSS r-band photometry of the gravitationally lensed quasar SBS 0909+532 from the U.S. Naval Observatory, as well as two seasons each of SDSS g-band and r-band monitoring from the Liverpool Robotic Telescope. Using Monte Carlo simulations to simultaneously measure the system's time delay and model the r-band microlensing variability, we confirm and significantly refine the precision of the system's time delay to \Delta t_{AB} = 50^{+2}_{-4} days, where the stated uncertainties represent the bounds of the formal 1\sigma\ confidence interval. There may be a conflict between the time delay measurement and a lens consisting of a single galaxy. While models based on the Hubble Space Telescope astrometry and a relatively compact stellar distribution can reproduce the observed delay, the models have somewhat less dark matter than we would typically expect. We also carry out a joint analysis of the microlensing variability in the r- and g-bands to constrain the size of the quasar's continuum source at these wavelengths, obtaining log[(r_{s,r}/cm) [cos{i}/0.5]^{1/2}] = 15.3 \pm 0.3 and log[(r_{s,g}/cm) [cos{i}/0.5]^{1/2}] = 14.8 \pm 0.9, respectively. Our current results do not formally constrain the temperature profile of the accretion disk but are consistent with the expectations of standard thin disk theory., Comment: 10 pages, 5 figures, 3 tables, accepted for publication in ApJ
Published: 2013

39. Optical selection of quasars: SDSS and LSST

Author: W. Niel Brandt, Chelsea L. MacLeod, Peter Yoachim, Xiaohui Fan, Željko Ivezić, and Gordon T. Richards
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Computer science, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics::Cosmology and Extragalactic Astrophysics, Redshift, Optical imaging, Space and Planetary Science, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Instrumentation and Methods for Astrophysics (astro-ph.IM), Selection (genetic algorithm), Astrophysics::Galaxy Astrophysics
Abstract: Over the last decade, quasar sample sizes have increased from several thousand to several hundred thousand, thanks mostly to SDSS imaging and spectroscopic surveys. LSST, the next-generation optical imaging survey, will provide hundreds of detections per object for a sample of more than ten million quasars with redshifts of up to about seven. We briefly review optical quasar selection techniques, with emphasis on methods based on colors, variability properties and astrometric behavior., Comment: 7 pages, 3 figures, presented at the IAU Symposium #304
Published: 2013
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40. The Sloan Digital Sky Survey quasar catalog: ninth data release

Author: Ismael Perez-Fournon, Nao Suzuki, Claudia Maraston, Richard G. McMahon, Jordi Miralda-Escudé, Jian Ge, Eduard Arnau, Michael A. Strauss, Kyle S. Dawson, Andreu Font-Ribera, Khee-Gan Lee, Daniel J. Eisenstein, Scott F. Anderson, Adam S. Bolton, Nicholas P. Ross, Hayley Finley, Benjamin A. Weaver, Yue Shen, Kaike Pan, Matthew M. Pieri, Julian E. Bautista, Jeremy L. Tinker, Jo Bovy, Patrick B. Hall, Pasquier Noterdaeme, Martin White, David J. Schlegel, Jean-Marc Le Goff, Isabelle Pâris, Anze Slosar, Garrett Ebelke, Gordon T. Richards, Zeljko Ivezic, Éric Aubourg, D. Kirkby, Howard Brewington, Nathalie Palanque-Delabrouille, Donald P. Schneider, Joseph F. Hennawi, Robert R. Gibson, Demitri Muna, Amy Kimball, Xiaohui Fan, Ian D. McGreer, Viktor Malanushenko, Shirley Ho, Erin S. Sheldon, Britt Lundgren, Audrey Simmons, Emmanuel Rollinde, Stephen Bailey, Elena Malanushenko, Jessica A. Kirkpatrick, Alaina Shelden, Matteo Viel, Timothée Delubac, David H. Weinberg, W. Michael Wood-Vasey, William Carithers, W. N. Brandt, Chelsea L. MacLeod, Patrick Petitjean, Nur Filiz Ak, Daniel M. Capellupo, Dmitry Bizyaev, Fred Hamann, David W. Hogg, Rupert A. C. Croft, Joel R. Brownstein, Stephanie A. Snedden, Nicolás G. Busca, Adam D. Myers, Christophe Yèche, Daniel Oravetz, Linhua Jiang, Philip Engelke, AstroParticule et Cosmologie (APC (UMR_7164)), Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3), SDSS-III, APC - Cosmologie, Physique Corpusculaire et Cosmologie - Collège de France (PCC), Collège de France (CdF)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Collège de France (CdF)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-AstroParticule et Cosmologie (APC (UMR_7164)), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), [SDU.ASTR.CO]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astronomy & Astrophysics, 01 natural sciences, Spectral line, Photometry (optics), [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Settore FIS/05 - Astronomia e Astrofisica, surveys, quasars: general, 0103 physical sciences, Emission spectrum, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, media_common, Physics, [PHYS]Physics [physics], general [quasars], 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Quasar, Redshift, Boss, Space and Planetary Science, Sky, astro-ph.CO, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Data release, Astronomical and Space Sciences, catalogs, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present the Data Release 9 Quasar (DR9Q) catalog from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. The catalog includes all BOSS objects that were targeted as quasar candidates during the survey, are spectrocopically confirmed as quasars via visual inspection, have luminosities Mi[z=2]2.15$ (61,931) is ~2.8 times larger than the number of z>2.15 quasars previously known. Redshifts and FWHMs are provided for the strongest emission lines (CIV, CIII], MgII). The catalog identifies 7,533 broad absorption line quasars and gives their characteristics. For each object the catalog presents five-band (u,g,r,i,z) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys., Comment: Accepted for publication in A&A, Catalog available online at http://www.sdss3.org/dr9/algorithms/qso_catalog.php
Published: 2012

41. Characterizing the Optical Variability of Bright Blazars: Variability-based Selection of Fermi Active Galactic Nuclei

Author: John J. Ruan, T. H. Burnett, Scott F. Anderson, Chelsea L. MacLeod, Zeljko Ivezic, Andrew C. Becker, Christopher S. Kochanek, Branimir Sesar, J. Scott Stuart, James R. A. Davenport, Richard M. Plotkin, and High Energy Astrophys. & Astropart. Phys (API, FNWI)
Subjects: Physics, Astrophysics::High Energy Astrophysical Phenomena, Flux, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Light curve, 01 natural sciences, Amplitude, Relativistic beaming, 13. Climate action, Space and Planetary Science, Asteroid, 0103 physical sciences, 010306 general physics, Blazar, 010303 astronomy & astrophysics, Fermi Gamma-ray Space Telescope
Abstract: We investigate the use of optical photometric variability to select and identify blazars in large-scale time-domain surveys, in part to aid in the identification of blazar counterparts to the ~30% of γ-ray sources in the Fermi 2FGL catalog still lacking reliable associations. Using data from the optical LINEAR asteroid survey, we characterize the optical variability of blazars by fitting a damped random walk model to individual light curves with two main model parameters, the characteristic timescales of variability τ, and driving amplitudes on short timescales $\hat{\sigma }$. Imposing cuts on minimum τ and $\hat{\sigma }$ allows for blazar selection with high efficiency E and completeness C. To test the efficacy of this approach, we apply this method to optically variable LINEAR objects that fall within the several-arcminute error ellipses of γ-ray sources in the Fermi 2FGL catalog. Despite the extreme stellar contamination at the shallow depth of the LINEAR survey, we are able to recover previously associated optical counterparts to Fermi active galactic nuclei with E ≥ 88% and C = 88% in Fermi 95% confidence error ellipses having semimajor axis r < 8'. We find that the suggested radio counterpart to Fermi source 2FGL J1649.6+5238 has optical variability consistent with other γ-ray blazars and is likely to be the γ-ray source. Our results suggest that the variability of the non-thermal jet emission in blazars is stochastic in nature, with unique variability properties due to the effects of relativistic beaming. After correcting for beaming, we estimate that the characteristic timescale of blazar variability is ~3 years in the rest frame of the jet, in contrast with the ~320 day disk flux timescale observed in quasars. The variability-based selection method presented will be useful for blazar identification in time-domain optical surveys and is also a probe of jet physics.
Published: 2012

42. Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk

Author: Željko Ivezić, Brandon C. Kelly, S. Kozłowski, Amy Kimball, Andrew C. Becker, Chelsea L. MacLeod, W. H. de Vries, Christopher S. Kochanek, E. Bullock, Robert R. Gibson, K. Brooks, Branimir Sesar, and David Westman
Subjects: Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Light curve, Random walk, 01 natural sciences, Power law, Redshift, Luminosity, Black hole, Amplitude, Space and Planetary Science, 0103 physical sciences, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We model the time variability of ~9,000 spectroscopically confirmed quasars in SDSS Stripe 82 as a damped random walk. Using 2.7 million photometric measurements collected over 10 years, we confirm the results of Kelly et al. (2009) and Koz{\l}owski et al. (2010) that this model can explain quasar light curves at an impressive fidelity level (0.01-0.02 mag). The damped random walk model provides a simple, fast [O(N) for N data points], and powerful statistical description of quasar light curves by a characteristic time scale (tau) and an asymptotic rms variability on long time scales (SF_inf). We searched for correlations between these two variability parameters and physical parameters such as luminosity and black hole mass, and rest-frame wavelength. We find that tau increases with increasing wavelength with a power law index of 0.17, remains nearly constant with redshift and luminosity, and increases with increasing black hole mass with power law index of 0.21+/-0.07. The amplitude of variability is anti-correlated with the Eddington ratio, which suggests a scenario where optical fluctuations are tied to variations in the accretion rate. The radio-loudest quasars have systematically larger variability amplitudes by about 30%, when corrected for the other observed trends, while the distribution of their characteristic time scale is indistinguishable from that of the full sample. We do not detect any statistically robust differences in the characteristic time scale and variability amplitude between the full sample and the small subsample of quasars detected by ROSAT. Our results provide a simple quantitative framework for generating mock quasar light curves, such as currently used in LSST image simulations. (abridged), Comment: 39 pages, accepted to ApJ
Published: 2010
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43. Detection of a Companion Lens Galaxy using the Mid-infrared Flux Ratios of the Gravitationally Lensed Quasar H1413+117

Author: Christopher S. Kochanek, Eric Agol, and Chelsea L. MacLeod
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Extinction (astronomy), FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Gravitational microlensing, 01 natural sciences, law.invention, law, 0103 physical sciences, 010306 general physics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, Astronomy and Astrophysics, Quasar, Astrometry, Astrophysics - Astrophysics of Galaxies, Galaxy, Lens (optics), Gravitational lens, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics::Earth and Planetary Astrophysics, Anomaly (physics), Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present the first resolved mid-IR (11 micron) observations of the four-image quasar lens H1413+117 using the Michelle camera on Gemini North. All previous observations (optical, near-IR, and radio) of this lens show a "flux anomaly," where the image flux ratios cannot be explained by a simple, central lens galaxy. We attempt to reproduce the mid-IR flux ratios, which are insensitive to extinction and microlensing, by modeling the main lens as a singular isothermal ellipsoid. This model fails to reproduce the flux ratios. However, we can explain the flux ratios simply by adding to the model a nearby galaxy detected in the H-band by HST/NICMOS-NIC2. This perturbing galaxy lies 4.0" from the main lens and it has a critical radius of 0.63" +/- 0.02" which is similar to that of the main lens, as expected from their similar H-band fluxes. More remarkably, this galaxy is not required to obtain a good fit to the system astrometry, so this represents the first clear detection of an object through its effect on the image fluxes of a gravitational lens. This is a parallel to the detections of visible satellites from astrometric anomalies, and provides a proof of the concept of searching for substructure in galaxies using anomalous flux ratios., 11 pages, 4 figures, 4 tables, Submitted to ApJ. v4: Figure 1 corrected
Published: 2009

44. Precision of Hubble constant derived using black hole binary absolute distances and statistical redshift information

Author: Craig J. Hogan and Chelsea L. MacLeod
Subjects: Physics, Nuclear and High Energy Physics, Astrophysics (astro-ph), Order (ring theory), Astronomy, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Redshift survey, Galaxy, Redshift, Luminosity, Black hole, symbols.namesake, Observational cosmology, symbols, Hubble's law
Abstract: 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 for the events, which may be difficult for those without electromagnetic counterparts. Here it is demonstrated that certainly in principle, and possibly in practice, clustering of galaxies allows extraction of the redshift information from a sample statistically for the purpose of estimating mean cosmological parameters, without identification of host galaxies for individual events. We extract mock galaxy samples from the 6th Data Release of the Sloan Digital Sky Survey resembling those that would be associated with inspiral events of stellar mass black holes falling into massive black holes at redshift z ~ 0.1 to 0.5. A simple statistical procedure is described to estimate a likelihood function for the Hubble constant H_0: each galaxy in a LISA error volume contributes linearly to the log likelihood for the source redshift, and the log likelihood for each source contributes linearly to that of H_0. This procedure is shown to provide an accurate and unbiased estimator of H_0. It is estimated that a precision better than one percent in H_0 may be possible if the rate of such events is sufficiently high, on the order of 20 to z = 0.5., Comment: 9 pages, 4 figures, submitted to Phys. Rev. D; new references added
Published: 2007
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45. Size Measurements of the Quasar X-Ray Continuum Emission Region by Analysis of Microlensing in Chandra Imagery

Author: Chelsea L. MacLeod and Christopher W. Morgan
Subjects: Physics, Accretion (meteorology), Accretion disc, Space and Planetary Science, Continuum (design consultancy), X-ray, Astronomy, Astronomy and Astrophysics, Quasar, Astrophysics, Gravitational microlensing, OVV quasar, Redshift
Abstract: Microlensing offers a unique way to constrain the physical extent of different emission regions in a lensed quasar, putting to test various accretion and continuum emission models. We perform a microlensing analysis using six Chandra observations (spanning six years) of the lensed quasar SDSS 0924+0219 (redshift zs=1.52), in which X-ray microlensing variability is detected with high confidence. The system exhibits pronounced microlensing variability in the X-rays compared to the optical, indicating a comparatively small extent of r1/24 cm (95% confidence) for the X-ray continuum emitting region, near the inner edge of the accretion disk.
Published: 2013

46. ERRATUM: 'A DESCRIPTION OF QUASAR VARIABILITY MEASURED USING REPEATED SDSS AND POSS IMAGING' (2012, ApJ, 753, 106)

Author: Donald P. Schneider, Gordon T. Richards, Scott F. Anderson, Chelsea L. MacLeod, Željko Ivezić, Brandon C. Kelly, Wim de Vries, Robert H. Lupton, Patrick B. Hall, Branimir Sesar, Christopher S. Kochanek, and Andrew C. Becker
Subjects: Physics, Space and Planetary Science, Astronomy, Astronomy and Astrophysics, Quasar, Astrophysics
Published: 2014

47. VARIABILITY-BASED ACTIVE GALACTIC NUCLEUS SELECTION USING IMAGE SUBTRACTION IN THE SDSS AND LSST ERA

Author: Andrew C. Becker, Robert R. Gibson, John J. Ruan, Andrew J. Connolly, Scott F. Anderson, Yumi Choi, Chelsea L. MacLeod, and Željko Ivezić
Subjects: Physics, QSOS, Infrared, Astrophysics::High Energy Astrophysical Phenomena, media_common.quotation_subject, Astronomy and Astrophysics, Image subtraction, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Light curve, Image differencing, Amplitude, Space and Planetary Science, Sky, Blazar, Astrophysics::Galaxy Astrophysics, media_common
Abstract: With upcoming all sky surveys such as LSST poised to generate a deep digital movie of the optical sky, variability-based AGN selection will enable the construction of highly-complete catalogs with minimum contamination. In this study, we generate $g$-band difference images and construct light curves for QSO/AGN candidates listed in SDSS Stripe 82 public catalogs compiled from different methods, including spectroscopy, optical colors, variability, and X-ray detection. Image differencing excels at identifying variable sources embedded in complex or blended emission regions such as Type II AGNs and other low-luminosity AGNs that may be omitted from traditional photometric or spectroscopic catalogs. To separate QSOs/AGNs from other sources using our difference image light curves, we explore several light curve statistics and parameterize optical variability by the characteristic damping timescale ($\tau$) and variability amplitude. By virtue of distinguishable variability parameters of AGNs, we are able to select them with high completeness of 93.4% and efficiency (i.e., purity) of 71.3%. Based on optical variability, we also select highly variable blazar candidates, whose infrared colors are consistent with known blazars. One third of them are also radio detected. With the X-ray selected AGN candidates, we probe the optical variability of X-ray detected optically-extended sources using their difference image light curves for the first time. A combination of optical variability and X-ray detection enables us to select various types of host-dominated AGNs. Contrary to the AGN unification model prediction, two Type II AGN candidates (out of 6) show detectable variability on long-term timescales like typical Type I AGNs. This study will provide a baseline for future optical variability studies of extended sources.
Published: 2014

48. A DESCRIPTION OF QUASAR VARIABILITY MEASURED USING REPEATED SDSS AND POSS IMAGING

Author: Brandon C. Kelly, Branimir Sesar, Zeljko Ivezic, Wim de Vries, Robert H. Lupton, Chelsea L. MacLeod, Scott F. Anderson, Andrew C. Becker, Christopher S. Kochanek, Patrick B. Hall, Gordon T. Richards, and Donald P. Schneider
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Exponential distribution, Astrophysics::High Energy Astrophysical Phenomena, media_common.quotation_subject, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, Observatory, 0103 physical sciences, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, media_common, Physics, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Quasar, Rest frame, Random walk, Wavelength, Amplitude, 13. Climate action, Space and Planetary Science, Sky, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We provide a quantitative description and statistical interpretation of the optical continuum variability of quasars. The Sloan Digital Sky Survey (SDSS) has obtained repeated imaging in five UV-to-IR photometric bands for 33,881 spectroscopically confirmed quasars. About 10,000 quasars have an average of 60 observations in each band obtained over a decade along Stripe 82 (S82), whereas the remaining ~25,000 have 2-3 observations due to scan overlaps. The observed time lags span the range from a day to almost 10 years, and constrain quasar variability at rest-frame time lags of up to 4 years, and at rest-frame wavelengths from 1000A to 6000A. We publicly release a user-friendly catalog of quasars from the SDSS Data Release 7 that have been observed at least twice in SDSS or once in both SDSS and the Palomar Observatory Sky Survey, and we use it to analyze the ensemble properties of quasar variability. Based on a damped random walk (DRW) model defined by a characteristic time scale and an asymptotic variability amplitude that scale with the luminosity, black hole mass, and rest wavelength for individual quasars calibrated in S82, we can fully explain the ensemble variability statistics of the non-S82 quasars such as the exponential distribution of large magnitude changes. All available data are consistent with the DRW model as a viable description of the optical continuum variability of quasars on time scales of ~5-2000 days in the rest frame. We use these models to predict the incidence of quasar contamination in transient surveys such as those from PTF and LSST., Comment: 33 pages, 19 figures, replaced with accepted version. Catalog is available at http://www.astro.washington.edu/users/ivezic/macleod/qso_dr7/
Published: 2012

49. QUASAR SELECTION BASED ON PHOTOMETRIC VARIABILITY

Author: Zeljko Ivezic, Christopher S. Kochanek, Chelsea L. MacLeod, K. Brooks, R. R. Gibson, W. H. de Vries, S. Kozłowski, B. Sesar, Aaron M. Meisner, and A. C. Becker
Subjects: Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), media_common.quotation_subject, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Large Synoptic Survey Telescope, Light curve, 01 natural sciences, Stars, Amplitude, Space and Planetary Science, Sky, 0103 physical sciences, 010306 general physics, 010303 astronomy & astrophysics, Stellar density, Astrophysics::Galaxy Astrophysics, Selection (genetic algorithm), Astrophysics - Cosmology and Nongalactic Astrophysics, media_common
Abstract: We develop a method for separating quasars from other variable point sources using SDSS Stripe 82 light curve data for ~10,000 variable objects. To statistically describe quasar variability, we use a damped random walk model parametrized by a damping time scale, tau, and an asymptotic amplitude (structure function), SF_inf. With the aid of an SDSS spectroscopically confirmed quasar sample, we demonstrate that variability selection in typical extragalactic fields with low stellar density can deliver complete samples with reasonable purity (or efficiency, E). Compared to a selection method based solely on the slope of the structure function, the inclusion of the tau information boosts E from 60% to 75% while maintaining a highly complete sample (98%) even in the absence of color information. For a completeness of C=90%, E is boosted from 80% to 85%. Conversely, C improves from 90% to 97% while maintaining E=80% when imposing a lower limit on tau. With the aid of color selection, the purity can be further boosted to 96%, with C= 93%. Hence, selection methods based on variability will play an important role in the selection of quasars with data provided by upcoming large sky surveys, such as Pan-STARRS and the Large Synoptic Survey Telescope (LSST). For a typical (simulated) LSST cadence over 10 years and a photometric accuracy of 0.03 mag (achieved at i~22), C is expected to be 88% for a simple sample selection criterion of tau>100 days. In summary, given an adequate survey cadence, photometric variability provides an even better method than color selection for separating quasars from stars., (v2) 50 pages, accepted to ApJ
Published: 2011

50. ERRATUM: 'DETECTION OF A COMPANION LENS GALAXY USING THE MID-INFRARED FLUX RATIOS OF THE GRAVITATIONALLY LENSED QUASAR H1413+117' (2009, ApJ, 699, 1578)

Author: Christopher S. Kochanek, Eric Agol, and Chelsea L. MacLeod
Subjects: Physics, Mid infrared, Flux, Astronomy, Astronomy and Astrophysics, Quasar, Astrophysics, Galaxy, law.invention, Lens (optics), Einstein Cross, symbols.namesake, Space and Planetary Science, law, symbols, Cardinal direction
Abstract: In the original article, an error was found in Figure 1. The image labels for images B and C should be switched, and the cardinal directions indicated are wrong. This error has no effect on the results or models presented in the article. The corrected version is presented in Figure 1.
Published: 2009

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