Search

We analyse the properties of the CIV broad emission line in connection with the X-ray emission of 30 bright SDSS quasars at z~3.0-3.3 with pointed XMM-Newton observations, which were selected to test the suitability of AGN as cosmological tools. In our previous work, we found that a large fraction (~25%) of the quasars in this sample are X-ray underluminous by factors of >3-10. As absorbing columns of >10$^{23}$ cm$^{-2}$ can be safely ruled out, their weakness is most likely intrinsic. Here we explore possible correlations between the UV and X-ray features of these sources to investigate the origin of X-ray weakness. We fit their UV SDSS spectra and analyse their CIV properties (e.g., equivalent width, EW; line peak velocity, $\upsilon_{\rm peak}$) as a function of the X-ray photon index and 2-10 keV flux. We confirm the trends of CIV $\upsilon_{\rm peak}$ and EW with UV luminosity at 2500 angstrom for both X-ray weak and X-ray normal quasars, as well as the correlation between X-ray weakness and CIV EW. In contrast to some recent work, we do not observe any clear relation between the 2-10 keV luminosity and $\upsilon_{\rm peak}$. We find a correlation between the hard X-ray flux and the integrated CIV flux for X-ray normal quasars, whilst X-ray weak quasars deviate from the main trend by more than 0.5 dex. We argue that X-ray weakness might be interpreted in a starved X-ray corona picture associated with an ongoing disc-wind phase. If the wind is ejected in the vicinity of the black hole, the extreme-UV radiation that reaches the corona will be depleted, depriving the corona of seeds photons and generating an X-ray weak quasar. Yet, at the largest UV luminosities (>10$^{47}$ erg s$^{-1}$), there will still be an ample reservoir of ionising photons that can explain the excess CIV emission observed in the X-ray weak quasars with respect to normal sources of similar X-ray luminosities., Comment: 22 pages, 15 figures (with 3 more figures in the Appendix), abstract abridged. Accepted for publication in A&A

This work provides evidence that a large fraction of \ion{C}{IV} narrow absorption lines (NALs) seen along the line of sight to distant quasars are due to accretion disk winds, while also seeking to understand the relationship between NALs and certain quasar-intrinsic properties. We extend the results from past work in the literature using $\sim105,000$ NALs from a sample of $\sim58,000$ SDSS quasars. The primary results of this work are summarized as follows: (1) the velocity distribution (${\rm d}N/{\rm d}\beta$) of NALs is not a function of radio loudness (or even detection) once marginalized by optical/UV luminosity; (2) there are significant differences in the number and distribution of NALs as a function of both radio spectral index and optical/UV luminosity, and these two findings are not entirely interdependent; (3) improvements in quasar systemic redshift measurements and differences in the NAL distribution as a combined function of optical luminosity and radio spectral index together provide evidence that a significant portion of NALs are due to outflows; (4) the results are consistent with standard models of accretion disk winds governed by the $L_{\rm UV}$-$\alpha_{ox}$ relationship and line-of-sight orientation indicated by radio spectral index, and (5) possibly support a magnetically arrested disk model as an explanation for the semi-stochastic nature of strong radio emission in a fraction of quasars., Comment: 21 pages, 14 figures, 2 tables

We discuss a probe of the contribution of wind-related shocks to the radio emission in otherwise radio-quiet quasars. Given 1) the non-linear correlation between UV and X-ray luminosity in quasars, 2) that such correlation leads to higher likelihood of radiation-line-driven winds in more luminous quasars, and 3) that luminous quasars are more abundant at high redshift, deep radio observations of high-redshift quasars are needed to probe potential contributions from accretion disk winds. We target a sample of 50 $z\simeq 1.65$ color-selected quasars that span the range of expected accretion disk wind properties as traced by broad CIV emission. 3-GHz observations with the Very Large Array to an rms of $\approx10\mu$Jy beam$^{-1}$ probe to star formation rates of $\approx400\,M_{\rm Sun}\,{\rm yr}^{-1}$, leading to 22 detections. Supplementing these pointed observations are survey data of 388 sources from the LOFAR Two-metre Sky Survey Data Release 1 that reach comparable depth (for a typical radio spectral index), where 123 sources are detected. These combined observations reveal a radio detection fraction that is a non-linear function of \civ\ emission-line properties and suggest that the data may require multiple origins of radio emission in radio-quiet quasars. We find evidence for radio emission from weak jets or coronae in radio-quiet quasars with low Eddingtion ratios, with either (or both) star formation and accretion disk winds playing an important role in optically luminous quasars and correlated with increasing Eddington ratio. Additional pointed radio observations are needed to fully establish the nature of radio emission in radio-quiet quasars., Comment: 21 pages, 7 figures, submitted to AAS journals

The orientation of the disk of material accreting onto supermassive black holes that power quasars is one of most important quantities that are needed to understand quasars -- both individually and in the ensemble average. We present a hypothesis for determining comparatively edge-on orientation in a subset of quasars (both radio loud and radio quiet). If confirmed, this orientation indicator could be applicable to individual quasars without reference to radio or X-ray data and could identify some 10-20% of quasars as being more edge-on than average, based only on moderate resolution and signal-to-noise spectroscopy covering the CIV 1549A emission feature. We present a test of said hypothesis using X-ray observations and identify additional data that are needed to confirm this hypothesis and calibrate the metric., 7 pages, 2 figures, accepted for publication in ApJL

We present spectroscopic measurements for 226 sources from the Gemini Near Infrared Spectrograph - Distant Quasar Survey (GNIRS-DQS). Being the largest uniform, homogeneous survey of its kind, it represents a flux-limited sample (mi . 19.0 mag, H . 16.5 mag) of Sloan Digital Sky Survey (SDSS) quasars at 1.5 . z . 3.5 with a monochromatic luminosity (λLλ) at 5100 ˚A in the range of 1044 − 1046 erg s−1 . A combination of the GNIRS and SDSS spectra covers principal quasar diagnostic features, chiefly the C iv λ1549, Mg ii λλ2798, 2803, Hβ λ4861, and [O iii] λλ4959, 5007 emission lines, in each source. The spectral inventory will be utilized primarily to develop prescriptions for obtaining more accurate and precise redshifts, black hole masses, and accretion rates for all quasars. Additionally, the measurements will facilitate an understanding of the dependence of rest-frame ultraviolet-optical spectral properties of quasars on redshift, luminosity, and Eddington ratio, and test whether the physical properties of the quasar central engine evolve over cosmic time., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

The Galactic Center (GC) region hosts a variety of powerful astronomical sources and rare astrophysical processes that emit a large flux of non-thermal radiation. The inner 375 pc x 600 pc region, called the Central Molecular Zone, is home to the supermassive black hole Sagittarius A*, massive cloud complexes, and particle accelerators such as supernova remnants. We present the results of our improved analysis of the very-high-energy (VHE) gamma-ray emission above 2 TeV from the GC using 125 hours of data taken with the VERITAS imaging-atmospheric Cherenkov telescope between 2010 and 2018. The central source VER J1745-290, consistent with the position of Sagittarius A*, is detected at a significance of 38 standard deviations above the background level $(38\sigma)$, and we report its spectrum and light curve. Its differential spectrum is consistent with a power law with exponential cutoff, with a spectral index of $2.12^{+0.22}_{-0.17}$, a flux normalization at 5.3 TeV of $1.27^{+0.22}_{-0.23}\times 10^{-13}$ TeV-1 cm-2 s-1, and cutoff energy of $10.0^{+4.0}_{-2.0}$ TeV. We also present results on the diffuse emission near the GC, obtained by combining data from multiple regions along the GC ridge which yield a cumulative significance of $9.5\sigma$. The diffuse GC ridge spectrum is best fit by a power law with a hard index of 2.19 $\pm$ 0.20, showing no evidence of a cutoff up to 40 TeV. This strengthens the evidence for a potential accelerator of PeV cosmic rays being present in the GC. We also provide spectra of the other sources in our field of view with significant detections, composite supernova remnant G0.9+0.1 and HESS J1746-285., Comment: 19 pages, 8 figures, Accepted for publication in Astrophysical Journal

Full list of authors: EHT MWL Science Working Group; Algaba, J. C.; Anczarski, J.; Asada, K.; Baloković, M.; Chandra, S.; Cui, Y. -Z.; Falcone, A. D.; Giroletti, M.; Goddi, C.; Hada, K.; Haggard, D.; Jorstad, S.; Kaur, A.; Kawashima, T.; Keating, G.; Kim, J. -Y.; Kino, M.; Komossa, S.; Kravchenko, E. V.; Krichbaum, T. P.; Lee, S. -S.; Lu, R. -S.; Lucchini, M.; Markoff, S.; Neilsen, J.; Nowak, M. A.; Park, J.; Principe, G.; Ramakrishnan, V.; Reynolds, M. T.; Sasada, M.; Savchenko, S. S.; Williamson, K. E.; Event Horizon Telescope Collaboration; Akiyama, Kazunori; Alberdi, Antxon; Alef, Walter; Anantua, Richard; Azulay, Rebecca; Baczko, Anne-Kathrin; Ball, David; Barrett, John; Bintley, Dan; Benson, Bradford A.; Blackburn, Lindy; Blundell, Raymond; Boland, Wilfred; Bouman, Katherine L.; Bower, Geoffrey C.; Boyce, Hope; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broderick, Avery E.; Broguiere, Dominique; Bronzwaer, Thomas; Byun, Do-Young; Carlstrom, John E.; Chael, Andrew; Chan, Chi-Kwan; Chatterjee, Shami; Chatterjee, Koushik; Chen, Ming-Tang; Chen, Yongjun; Chesler, Paul M.; Cho, Ilje; Christian, Pierre; Conway, John E.; Cordes, James M.; Crawford, Thomas M.; Crew, Geoffrey B.; Cruz-Osorio, Alejandro; Davelaar, Jordy; de Laurentis, Mariafelicia; Deane, Roger; Dempsey, Jessica; Desvignes, Gregory; Dexter, Jason; Doeleman, Sheperd S.; Eatough, Ralph P.; Falcke, Heino; Farah, Joseph; Fish, Vincent L.; Fomalont, Ed; Ford, H. Alyson; Fraga-Encinas, Raquel; Friberg, Per; Fromm, Christian M.; Fuentes, Antonio; Galison, Peter; Gammie, Charles F.; García, Roberto; Gentaz, Olivier; Georgiev, Boris; Gold, Roman; Gómez, José L.; Gómez-Ruiz, Arturo I.; Gu, Minfeng; Gurwell, Mark; Hecht, Michael H.; Hesper, Ronald; Ho, Luis C.; Ho, Paul; Honma, Mareki; Huang, Chih-Wei L.; Huang, Lei; Hughes, David H.; Ikeda, Shiro; Inoue, Makoto; Issaoun, Sara; James, David J.; Jannuzi, Buell T.; Janssen, Michael; Jeter, Britton; Jiang, Wu; Jiménez-Rosales, Alejandra; Johnson, Michael D.; Jung, Taehyun; Karami, Mansour; Karuppusamy, Ramesh; Kettenis, Mark; Kim, Dong-Jin; Kim, Jongsoo; Kim, Junhan; Koay, Jun Yi; Kofuji, Yutaro; Koch, Patrick M.; Koyama, Shoko; Kramer, Michael; Kramer, Carsten; Kuo, Cheng-Yu; Lauer, Tod R.; Levis, Aviad; Li, Yan-Rong; Li, Zhiyuan; Lindqvist, Michael; Lico, Rocco; Lindahl, Greg; Liu, Jun; Liu, Kuo; Liuzzo, Elisabetta; Lo, Wen-Ping; Lobanov, Andrei P.; Loinard, Laurent; Lonsdale, Colin; MacDonald, Nicholas R.; Mao, Jirong; Marchili, Nicola; Marrone, Daniel P.; Marscher, Alan P.; Martí-Vidal, Iván; Matsushita, Satoki; Matthews, Lynn D.; Medeiros, Lia; Menten, Karl M.; Mizuno, Izumi; Mizuno, Yosuke; Moran, James M.; Moriyama, Kotaro; Moscibrodzka, Monika; Müller, Cornelia; Musoke, Gibwa; Mejías, Alejandro Mus; Nagai, Hiroshi; Nagar, Neil M.; Nakamura, Masanori; Narayan, Ramesh; Narayanan, Gopal; Natarajan, Iniyan; Nathanail, Antonios; Neri, Roberto; Ni, Chunchong; Noutsos, Aristeidis; Okino, Hiroki; Olivares, Héctor; Ortiz-León, Gisela N.; Oyama, Tomoaki; Özel, Feryal; Palumbo, Daniel C. M.; Patel, Nimesh; Pen, Ue-Li; Pesce, Dominic W.; Piétu, Vincent; Plambeck, Richard; Popstefanija, Aleksandar; Porth, Oliver; Pötzl, Felix M.; Prather, Ben; Preciado-López, Jorge A.; Psaltis, Dimitrios; Pu, Hung-Yi; Rao, Ramprasad; Rawlings, Mark G.; Raymond, Alexander W.; Rezzolla, Luciano; Ricarte, Angelo; Ripperda, Bart; Roelofs, Freek; Rogers, Alan; Ros, Eduardo; Rose, Mel; Roshanineshat, Arash; Rottmann, Helge; Roy, Alan L.; Ruszczyk, Chet; Rygl, Kazi L. J.; Sánchez, Salvador; Sánchez-Arguelles, David; Savolainen, Tuomas; Schloerb, F. Peter; Schuster, Karl-Friedrich; Shao, Lijing; Shen, Zhiqiang; Small, Des; Sohn, Bong Won; Soohoo, Jason; Sun, He; Tazaki, Fumie; Tetarenko, Alexandra J.; Tiede, Paul; Tilanus, Remo P. J.; Titus, Michael; Toma, Kenji; Torne, Pablo; Trent, Tyler; Traianou, Efthalia; Trippe, Sascha; van Bemmel, Ilse; van Langevelde, Huib Jan; van Rossum, Daniel R.; Wagner, Jan; Ward-Thompson, Derek; Wardle, John; Weintroub, Jonathan; Wex, Norbert; Wharton, Robert; Wielgus, Maciek; Wong, George N.; Wu, Qingwen; Yoon, Doosoo; Young, André; Young, Ken; Younsi, Ziri; Yuan, Feng; Yuan, Ye-Fei; Zensus, J. Anton; Zhao, Guang-Yao; Zhao, Shan-Shan; Fermi Large Area Telescope Collaboration; Principe, G.; Giroletti, M.; D'Ammando, F.; Orienti, M.; H. E. S. S. Collaboration; Abdalla, H.; Adam, R.; Aharonian, F.; Benkhali, F. Ait; Angüner, E. O.; Arcaro, C.; Armand, C.; Armstrong, T.; Ashkar, H.; Backes, M.; Baghmanyan, V.; Barbosa Martins, V.; Barnacka, A.; Barnard, M.; Becherini, Y.; Berge, D.; Bernlöhr, K.; Bi, B.; Böttcher, M.; Boisson, C.; Bolmont, J.; de Lavergne, M. De Bony; Breuhaus, M.; Brun, F.; Brun, P.; Bryan, M.; Büchele, M.; Bulik, T.; Bylund, T.; Caroff, S.; Carosi, A.; Casanova, S.; Chand, T.; Chen, A.; Cotter, G.; Curyło, M.; Damascene Mbarubucyeye, J.; Davids, I. D.; Davies, J.; Deil, C.; Devin, J.; Dewilt, P.; Dirson, L.; Djannati-Ataï, A.; Dmytriiev, A.; Donath, A.; Doroshenko, V.; Duffy, C.; Dyks, J.; Egberts, K.; Eichhorn, F.; Einecke, S.; Emery, G.; Ernenwein, J. -P.; Feijen, K.; Fegan, S.; Fiasson, A.; de Clairfontaine, G. Fichet; Fontaine, G.; Funk, S.; Füßling, M.; Gabici, S.; Gallant, Y. A.; Giavitto, G.; Giunti, L.; Glawion, D.; Glicenstein, J. F.; Gottschall, D.; Grondin, M. -H.; Hahn, J.; Haupt, M.; Hermann, G.; Hinton, J. A.; Hofmann, W.; Hoischen, C.; Holch, T. L.; Holler, M.; Hörbe, M.; Horns, D.; Huber, D.; Jamrozy, M.; Jankowsky, D.; Jankowsky, F.; Jardin-Blicq, A.; Joshi, V.; Jung-Richardt, I.; Kasai, E.; Kastendieck, M. A.; Katarzyński, K.; Katz, U.; Khangulyan, D.; Khélifi, B.; Klepser, S.; Kluźniak, W.; Komin, Nu.; Konno, R.; Kosack, K.; Kostunin, D.; Kreter, M.; Lamanna, G.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J. -P.; Levy, C.; Lohse, T.; Lypova, I.; Mackey, J.; Majumdar, J.; Malyshev, D.; Malyshev, D.; Marandon, V.; Marchegiani, P.; Marcowith, A.; Mares, A.; Martí-Devesa, G.; Marx, R.; Maurin, G.; Meintjes, P. J.; Meyer, M.; Moderski, R.; Mohamed, M.; Mohrmann, L.; Montanari, A.; Moore, C.; Morris, P.; Moulin, E.; Muller, J.; Murach, T.; Nakashima, K.; Nayerhoda, A.; de Naurois, M.; Ndiyavala, H.; Niederwanger, F.; Niemiec, J.; Oakes, L.; O'Brien, P.; Odaka, H.; Ohm, S.; Olivera-Nieto, L.; de Ona Wilhelmi, E.; Ostrowski, M.; Panter, M.; Panny, S.; Parsons, R. D.; Peron, G.; Peyaud, B.; Piel, Q.; Pita, S.; Poireau, V.; Noel, A. Priyana; Prokhorov, D. A.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Rauth, R.; Reichherzer, P.; Reimer, A.; Reimer, O.; Remy, Q.; Renaud, M.; Rieger, F.; Rinchiuso, L.; Romoli, C.; Rowell, G.; Rudak, B.; Ruiz-Velasco, E.; Sahakian, V.; Sailer, S.; Sanchez, D. A.; Santangelo, A.; Sasaki, M.; Scalici, M.; Schutte, H. M.; Schwanke, U.; Schwemmer, S.; Seglar-Arroyo, M.; Senniappan, M.; Seyffert, A. S.; Shafi, N.; Shiningayamwe, K.; Simoni, R.; Sinha, A.; Sol, H.; Specovius, A.; Spencer, S.; Spir-Jacob, M.; Stawarz, Ł.; Sun, L.; Steenkamp, R.; Stegmann, C.; Steinmassl, S.; Steppa, C.; Takahashi, T.; Tavernier, T.; Taylor, A. M.; Terrier, R.; Tiziani, D.; Tluczykont, M.; Tomankova, L.; Trichard, C.; Tsirou, M.; Tuffs, R.; Uchiyama, Y.; van der Walt, D. J.; van Eldik, C.; van Rensburg, C.; van Soelen, B.; Vasileiadis, G.; Veh, J.; Venter, C.; Vincent, P.; Vink, J.; Völk, H. J.; Vuillaume, T.; Wadiasingh, Z.; Wagner, S. J.; Watson, J.; Werner, F.; White, R.; Wierzcholska, A.; Wong, Yu Wun; Yusafzai, A.; Zacharias, M.; Zanin, R.; Zargaryan, D.; Zdziarski, A. A.; Zech, A.; Zhu, S. J.; Zorn, J.; Zouari, S.; Żywucka, N.; MAGIC Collaboration; Acciari, V. A.; Ansoldi, S.; Antonelli, L. A.; Engels, A. Arbet; Artero, M.; Asano, K.; Baack, D.; Babić, A.; Baquero, A.; de Almeida, U. Barres; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bellizzi, L.; Bernardini, E.; Bernardos, M.; Berti, A.; Besenrieder, J.; Bhattacharyya, W.; Bigongiari, C.; Biland, A.; Blanch, O.; Bonnoli, G.; Bošnjak, Ž.; Busetto, G.; Carosi, R.; Ceribella, G.; Cerruti, M.; Chai, Y.; Chilingarian, A.; Cikota, S.; Colak, S. M.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; D'Amico, G.; D'Elia, V.; da Vela, P.; Dazzi, F.; de Angelis, A.; de Lotto, B.; Delfino, M.; Delgado, J.; Delgado Mendez, C.; Depaoli, D.; di Pierro, F.; di Venere, L.; Do Souto Espiñeira, E.; Dominis Prester, D.; Donini, A.; Dorner, D.; Doro, M.; Elsaesser, D.; Ramazani, V. Fallah; Fattorini, A.; Ferrara, G.; Fonseca, M. V.; Font, L.; Fruck, C.; Fukami, S.; García López, R. J.; Garczarczyk, M.; Gasparyan, S.; Gaug, M.; Giglietto, N.; Giordano, F.; Gliwny, P.; Godinović, N.; Green, J. G.; Green, D.; Hadasch, D.; Hahn, A.; Heckmann, L.; Herrera, J.; Hoang, J.; Hrupec, D.; Hütten, M.; Inada, T.; Inoue, S.; Ishio, K.; Iwamura, Y.; Jiménez, I.; Jormanainen, J.; Jouvin, L.; Kajiwara, Y.; Karjalainen, M.; Kerszberg, D.; Kobayashi, Y.; Kubo, H.; Kushida, J.; Lamastra, A.; Lelas, D.; Leone, F.; Lindfors, E.; Lombardi, S.; Longo, F.; López-Coto, R.; López-Moya, M.; López-Oramas, A.; Loporchio, S.; Machado de Oliveira Fraga, B.; Maggio, C.; Majumdar, P.; Makariev, M.; Mallamaci, M.; Maneva, G.; Manganaro, M.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martínez, M.; Mazin, D.; Menchiari, S.; Mender, S.; Mićanović, S.; Miceli, D.; Miener, T.; Minev, M.; Miranda, J. M.; Mirzoyan, R.; Molina, E.; Moralejo, A.; Morcuende, D.; Moreno, V.; Moretti, E.; Neustroev, V.; Nigro, C.; Nilsson, K.; Nishijima, K.; Noda, K.; Nozaki, S.; Ohtani, Y.; Oka, T.; Otero-Santos, J.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Pavletić, L.; Peñil, P.; Perennes, C.; Persic, M.; Moroni, P. G. Prada; Prandini, E.; Priyadarshi, C.; Puljak, I.; Rhode, W.; Ribó, M.; Rico, J.; Righi, C.; Rugliancich, A.; Saha, L.; Sahakyan, N.; Saito, T.; Sakurai, S.; Satalecka, K.; Saturni, F. G.; Schleicher, B.; Schmidt, K.; Schweizer, T.; Sitarek, J.; Šnidarić, I.; Sobczynska, D.; Spolon, A.; Stamerra, A.; Strom, D.; Strzys, M.; Suda, Y.; Surić, T.; Takahashi, M.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Teshima, M.; Tosti, L.; Truzzi, S.; Tutone, A.; Ubach, S.; van Scherpenberg, J.; Vanzo, G.; Vazquez Acosta, M.; Ventura, S.; Verguilov, V.; Vigorito, C. F.; Vitale, V.; Vovk, I.; Will, M.; Wunderlich, C.; Zarić, D.; VERITAS Collaboration; Adams, C. B.; Benbow, W.; Brill, A.; Capasso, M.; Christiansen, J. L.; Chromey, A. J.; Daniel, M. K.; Errando, M.; Farrell, K. A.; Feng, Q.; Finley, J. P.; Fortson, L.; Furniss, A.; Gent, A.; Giuri, C.; Hassan, T.; Hervet, O.; Holder, J.; Hughes, G.; Humensky, T. B.; Jin, W.; Kaaret, P.; Kertzman, M.; Kieda, D.; Kumar, S.; Lang, M. J.; Lundy, M.; Maier, G.; Moriarty, P.; Mukherjee, R.; Nieto, D.; Nievas-Rosillo, M.; O'Brien, S.; Ong, R. A.; Otte, A. N.; Patel, S.; Pfrang, K.; Pohl, M.; Prado, R. R.; Pueschel, E.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Ribeiro, D.; Richards, G. T.; Roache, E.; Rulten, C.; Ryan, J. L.; Santander, M.; Sembroski, G. H.; Shang, R.; Weinstein, A.; Williams, D. A.; Williamson, T. J.; Eavn Collaboration; Hirota, Tomoya; Cui, Lang; Niinuma, Kotaro; Ro, Hyunwook; Sakai, Nobuyuki; Sawada-Satoh, Satoko; Wajima, Kiyoaki; Wang, Na; Liu, Xiang; Yonekura, Yoshinori, In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M o˙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87's spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded., The financial support of the German BMBF, MPG and HGF; the Italian INFN and INAF; the Swiss National Fund SNF; the ERDF under the Spanish Ministerio de Ciencia e Innovacion (MICINN) (FPA2017-87859-P, FPA2017-85668-P, FPA2017- 82729-C6-5-R, FPA2017-90566-REDC, PID2019-104114RBC31, PID2019-104114RB-C32, PID2019-105510GB-C31,PID 2019-107847RB-C41, PID2019-107847RB-C42, PID2019- 107988GB-C22); the Indian Department of Atomic Energy; the Japanese ICRR, the University of Tokyo, JSPS, and MEXT; the Bulgarian Ministry of Education and Science, National RI Roadmap Project DO1-268/16.12.2019 and the Academy of Finland grant No. 320045 is gratefully acknowledged. This work was also supported by the Spanish Centro de Excelencia “Severo Ochoa” SEV-2016-0588 and CEX2019- 000920-S, and “Maria de Maeztu” CEX2019-000918-M, the Unidad de Excelencia “Maria de Maeztu” MDM-2015-0509- 18-2 and the “la Caixa” Foundation (fellowship LCF/BQ/ PI18/11630012) and by the CERCA program of the Generalitat de Catalunya; by the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782 and the University of Rijeka Project 13.12.1.3.02; by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3; the Polish National Research Centre grant UMO-2016/22/M/ST9/00382; and by the Brazilian MCTIC, CNPq, and FAPERJ. This research is supported by grants from the U.S. Department of Energy Office of Science, the U.S. National Science Foundation and the Smithsonian Institution, by NSERC in Canada, and by the Helmholtz Association in Germany. This research used resources provided by the Open Science Grid, which is supported by the National Science Foundation and the U.S. Department of Energy’s Office of Science, and resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under Contract No. DE-AC02-05CH11231. We acknowledge the excellent work of the technical support staff at the Fred Lawrence Whipple Observatory and at the collaborating institutions in the construction and operation of the instrument.

The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will observe several Deep Drilling Fields (DDFs) to a greater depth and with a more rapid cadence than the main survey. In this paper, we describe the ``DeepDrill'' survey, which used the Spitzer Space Telescope Infrared Array Camera (IRAC) to observe three of the four currently defined DDFs in two bands, centered on 3.6 $\mu$m and 4.5 $\mu$m. These observations expand the area which was covered by an earlier set of observations in these three fields by the Spitzer Extragalactic Representative Volume Survey (SERVS). The combined DeepDrill and SERVS data cover the footprints of the LSST DDFs in the Extended Chandra Deep Field-South field (ECDFS), the ELAIS-S1 field (ES1), and the XMM Large-Scale Structure Survey field (XMM-LSS). The observations reach an approximate $5\sigma$ point-source depth of 2 $\mu$Jy (corresponding to an AB magnitude of 23.1; sufficient to detect a 10$^{11} M_{\odot}$ galaxy out to $z\approx 5$) in each of the two bands over a total area of $\approx 29\,$deg$^2$. The dual-band catalogues contain a total of 2.35 million sources. In this paper we describe the observations and data products from the survey, and an overview of the properties of galaxies in the survey. We compare the source counts to predictions from the SHARK semi-analytic model of galaxy formation. We also identify a population of sources with extremely red ([3.6]$-$[4.5] $>1.2$) colours which we show mostly consists of highly-obscured active galactic nuclei., Comment: 20 pages, 9 figures; MNRAS in press

Broad absorption line (BAL) features in quasar spectra reveal an unambiguous signature of energetic outflows from central supermassive black holes, and thus BAL quasars are prime targets for investigating the potential process of luminous quasar feedback on galaxies. We analyzed the rest-UV spectrum of an "overlapping trough" iron low-ionization broad absorption line quasar (FeLoBAL) SDSS J135246.37+423923.5 using the novel spectral synthesis code SimBAL (Leighly et al. 2018) and discovered an extraordinarily fast and energetic BAL outflow. Our analysis revealed outflow velocities reaching $\sim -38000\rm \, km\, s^{-1}$ with a velocity width of $\sim 10000\rm \, km\, s^{-1}$ which is the largest FeLoBAL outflow velocity measured to date. The column density of the outflow gas is log$N_H\sim23.2\,[\rm cm^{-1}]$ with the log kinetic luminosity $\log L_{KE}\sim48.1$ [erg $\rm s^{-1}$] which exceeds the bolometric luminosity of the quasar and is energetic enough to effectively drive quasar feedback. The energy estimate for the outflow is far greater than the estimates from any BAL object previously reported. The object also shows "anomalous reddening" and a significant scattered component that we were able to model with SimBAL. We found the first definitive case for radiation filtering in an additional zero-velocity absorption component that required an absorbed continuum to produce the particular absorption lines observed (MgII, AlIII and AlII) without also producing the high ionization lines such as CIV.

HESS J0632+057 is a gamma-ray binary composed of a compact object orbiting a Be star with a period of about $315$ days. Extensive X-ray and TeV gamma-ray observations have revealed a peculiar light curve containing two peaks, separated by a dip. We present the results of simultaneous observations in hard X-rays with NuSTAR and in TeV gamma-rays with VERITAS, performed in November and December 2017. These observations correspond to the orbital phases $\phi\approx0.22$ and $0.3$, where the fluxes are rising towards the first light-curve peak. A significant variation of the spectral index from 1.77$\pm$0.05 to 1.56$\pm$0.05 is observed in the X-ray data. The multi-wavelength spectral energy distributions (SED) derived from the observations are interpreted in terms of a leptonic model, in which the compact object is assumed to be a pulsar and non-thermal radiation is emitted by high-energy electrons accelerated at the shock formed by the collision between the stellar and pulsar wind. The results of the SED fitting show that our data can be consistently described within this scenario, and allow us to estimate the magnetization of the pulsar wind at the location of the shock formation. The constraints on the pulsar-wind magnetization provided by our results are shown to be consistent with those obtained from other systems., Comment: Accepted for publication in The Astrophysical Journal

Using data from SDSS, UKIDSS and WISE, we investigate the properties of the high-frequency cutoff to the infrared emission in $\simeq$5000 carefully selected luminous ($L_{bol} \simeq 10^{47}$) type 1 quasars. The strength of $\simeq$2 $\mu$m emission, corresponding to emission from the hottest (T>1200K) dust in the sublimation zone surrounding the central continuum source, is observed to correlate with the blueshift of the C IV $\lambda$1550 emission line. We therefore find that objects with stronger signatures of nuclear outflows tend to have a larger covering fraction of sublimation-temperature dust. When controlling for the observed outflow strength, the hot dust covering fraction does not vary significantly across our sample as a function of luminosity, black hole mass or Eddington fraction. The correlation between the hot dust and the C IV line blueshifts, together with the lack of correlation between the hot dust and other parameters, therefore provides evidence of a link between the properties of the broad emission line region and the infrared-emitting dusty regions in quasars., Comment: 11 pages, 6 figures, plus appendices. Accepted to MNRAS 10 Dec 2020

Using a sample of $\simeq$144,000 quasars from the Sloan Digital Sky Survey data release 14 we investigate the outflow properties, evident both in absorption and emission, of high-ionization Broad Absorption Line (BAL) and non-BAL quasars with redshifts 1.6 $\lesssim z \leq$ 3.5 and luminosities 45.3 $< \log_{10}(L_{bol}) < $ 48.2 erg s$^{-1}$. Key to the investigation is a continuum and emission-line reconstruction scheme, based on mean-field independent component analysis, that allows the kinematic properties of the CIV$\lambda$1550 emission line to be compared directly for both non-BAL and BAL quasars. CIV-emission blueshift and equivalent-width (EW) measurements are thus available for both populations. Comparisons of the emission-line and BAL-trough properties reveal strong systematic correlations between the emission and absorption properties. The dependence of quantitative outflow indicators on physical properties such as quasar luminosity and luminosity relative to Eddington-luminosity are also shown to be essentially identical for the BAL and non-BAL populations. There is an absence of BALs in quasars with the hardest spectral energy distributions (SEDs), revealed by the presence of strong HeII$\lambda$1640 emission, large CIV$\lambda$1550-emission EW and no measurable blueshift. In the remainder of the CIV-emission blueshift versus EW space, BAL and non-BAL quasars are present at all locations; for every BAL-quasar it is possible to identify non-BAL quasars with the same emission-line outflow properties and SED-hardness. The co-location of BAL and non-BAL quasars as a function of emission-line outflow and physical properties is the key result of our investigation, demonstrating that (high-ionization) BALs and non-BALs represent different views of the same underlying quasar population., Comment: 22 pages, 18 figures, plus Appendices. Minor changes to reflect published version in MNRAS

The astrophysical journal 896(1), 41 - (2020). doi:10.3847/1538-4357/ab910e, The radio source 3C 264, hosted by the giant elliptical galaxy NGC 3862, was observed with VERITAS between February 2017 and May 2019. These deep observations resulted in the discovery of very-high-energy (VHE; E $>100$ GeV) $\gamma$-ray emission from this active galaxy. An analysis of $\sim$57 hours of quality-selected live time yields a detection at the position of the source, corresponding to a statistical significance of 7.8 standard deviations above background. The observed VHE flux is variable on monthly time scales, with an elevated flux seen in 2018 observations. The VHE emission during this elevated state is well-characterized by a power-law spectrum with a photon index $\Gamma = 2.20 \pm 0.27$ and flux F($>315$ GeV) = ($7.6\pm 1.2_{\mathrm stat} \pm 2.3_{\mathrm syst})\times 10^{-13}$ cm$^{-2}$ s$^{-1}$, or approximately 0.7% of the Crab Nebula flux above the same threshold. 3C 264 ($z = 0.0217$) is the most distant radio galaxy detected at VHE, and the elevated state is thought to be similar to that of the famously outbursting jet in M 87. Consequently, extensive contemporaneous multi-wavelength data were acquired in 2018 at the time of the VHE high state. An analysis of these data, including VLBA, VLA, HST, Chandra and Swift observations in addition to the VERITAS data, is presented, along with a discussion of the resulting spectral energy distribution., Published by Univ.8743, Chicago, Ill. [u.a.]

In this paper, we provide updated constraints on the bolometric quasar luminosity function (QLF) from $z=0$ to $z=7$. The constraints are based on an observational compilation that includes observations in the rest-frame IR, B band, UV, soft and hard X-ray in past decades. Our method follows Hopkins et al. 2007 with an updated quasar SED model and bolometric and extinction corrections. The new best-fit bolometric quasar luminosity function behaves qualitatively different from the Hopkins et al. 2007 model at high redshift. Compared with the old model, the number density normalization decreases towards higher redshift and the bright-end slope is steeper at $z\gtrsim 2$. Due to the paucity of measurements at the faint end, the faint end slope at $z\gtrsim 5$ is quite uncertain. We present two models, one featuring a progressively steeper faint-end slope at higher redshift and the other featuring a shallow faint-end slope at $z\gtrsim 5$. Further multi-band observations of the faint-end QLF are needed to distinguish between these models. The evolutionary pattern of the bolometric QLF can be interpreted as an early phase likely dominated by the hierarchical assembly of structures and a late phase likely dominated by the quenching of galaxies. We explore the implications of this model on the ionizing photon production by quasars, the CXB spectrum, the SMBH mass density and mass functions. The predicted hydrogen photoionization rate contributed by quasars is subdominant during the epoch of reionization and only becomes important at $z\lesssim 3$. The predicted CXB spectrum, cosmic SMBH mass density and SMBH mass function are generally consistent with existing observations., Comment: Accepted by MNRAS. The code and data are available at https://bitbucket.org/ShenXuejian/quasarlf/src/master/

The $\textit{Kepler}$ satellite potentially provides the highest precision photometry of active galactic nuclei (AGN) available to investigate short-timescale optical variability. We targeted quasars from the Sloan Digital Sky Survey that lie in the fields of view of the $\textit{Kepler/K2}$ campaigns. Based on those observations, we report the discovery and properties of a previously unidentified instrumental signature in K2. Systematic errors in K2, beyond those due to the motion of the detector, plague our AGN and other faint-target, guest-observer science proposals. Weakly illuminated pixels are dominated by low frequency trends that are both non-astrophysical and correlated from object to object. A critical clue to understanding this instrumental noise is that different targets observed in the same channels of Campaign 8 (rear facing) and Campaign 16 (forward facing) had nearly identical light curves after time reversal of one of the campaigns. This observation strongly suggests that the underlying problem relates to the relative Sun-spacecraft-field orientation, which was approximately the same on day 1 of Campaign 8 as the last day of Campaign 16. Furthermore, we measure that the instrumental signature lags in time as a function of radius from the center of the detector, crossing channel boundaries. Systematics documented in this investigation are unlikely to be due to Moir\'{e} noise, rolling band, or pointing jitter. Instead this work strongly suggests temperature-dependent focus changes that are further subject to channel variations. Further characterization of this signature is crucial for rehabilitating K2 data for use in investigations of AGN light curves., Comment: 21 pages, 16 figures

The extragalactic background light (EBL), a diffuse photon field in the optical and infrared range, is a record of radiative processes over the Universe's history. Spectral measurements of blazars at very high energies ($>$100 GeV) enable the reconstruction of the spectral energy distribution (SED) of the EBL, as the blazar spectra are modified by redshift- and energy-dependent interactions of the gamma-ray photons with the EBL. The spectra of 14 VERITAS-detected blazars are included in a new measurement of the EBL SED that is independent of EBL SED models. The resulting SED covers an EBL wavelength range of 0.56--56 $��$m, and is in good agreement with lower limits obtained by assuming that the EBL is entirely due to radiation from cataloged galaxies., Accepted for publication in The Astrophysical Journal

It has been known for 20 years that the absorbing gas in broad absorption line quasars does not completely cover the continuum emission region, and that partial covering must be accounted for to accurately measure the column density of the outflowing gas. However, the nature of partial covering itself is not understood. Extrapolation of the SimBAL spectral synthesis model of the HST COS UV spectrum from SDSS J0850+4451 reported by Leighly et al. 2018 to non-simultaneous rest-frame optical and near-infrared spectra reveals evidence that the covering fraction has wavelength dependence, and is a factor of 2.5 times higher in the UV than in the optical and near-infrared bands. The difference in covering fraction can be explained if the outflow consists of clumps that are small and either structured or clustered relative to the projected size of the UV continuum emission region, and have a more diffuse distribution on size scales comparable to the near-infrared continuum emission region size. The lower covering fraction over the larger physical area results in a reduction of the measured total column density by a factor of 1.6 compared with the UV-only solution. This experiment demonstrates that we can compare rest-frame UV and near-infrared absorption lines, specifically HeI*10830, to place constraints on the uniformity of absorption gas in broad absorbing line quasars., Revised version after responding to referee report

The astrophysical journal / 1 876(2), 95 (2019). doi:10.3847/1538-4357/ab14f4, We conduct a search for periodic emission in the very high-energy (VHE) gamma-ray band (E > 100 GeV) from a total of 13 pulsars in an archival VERITAS data set with a total exposure of over 450 hr. The set of pulsars includes many of the brightest young gamma-ray pulsars visible in the Northern Hemisphere. The data analysis resulted in nondetections of pulsed VHE gamma-rays from each pulsar. Upper limits on a potential VHE gamma-ray flux are derived at the 95% confidence level above three energy thresholds using two methods. These are the first such searches for pulsed VHE emission from each of the pulsars, and the obtained limits constrain a possible flux component manifesting at VHEs as is seen for the Crab pulsar., Published by Institute of Physics Publ., London

We characterise ionised gas outflows using a large sample of ~330 high-luminosity (45.5 < log(L_bol/erg s^-1) < 49.0), high-redshift (1.5 < z < 4.0) quasars via their [OIII]4960,5008 emission. The median velocity width of the [OIII] emission line is 1540 kms^-1, increasing with increasing quasar luminosity. Broad, blue-shifted wings are seen in the [OIII] profiles of 42 per cent of the sample. Rest-frame ultraviolet spectra with well-characterised CIV 1550 emission line properties are available for more than 210 quasars, allowing an investigation of the relationship between the Broad Line Region (BLR) and Narrow Line Region (NLR) emission properties. The [OIII] blueshift is correlated with CIV blueshift, even when the dependence of both quantities on quasar luminosity has been taken into account. A strong anti-correlation between the [OIII] equivalent width (EW) and CIV blueshift also exists. Furthermore, [OIII] is very weak, with EW, MNRAS in press

Nature astronomy 3(6), 511 - 516 (2019). doi:10.1038/s41550-019-0741-z, The angular size of a star is a critical factor in determining its basic properties$^1$. Direct measurement of stellar angular diameters is difficult: at interstellar distances stars are generally too small to resolve by any individual imaging telescope. This fundamental limitation can be overcome by studying the diffraction pattern in the shadow cast when an asteroid occults a star$^2$, but only when the photometric uncertainty is smaller than the noise added by atmospheric scintillation$^3$. Atmospheric Cherenkov telescopes used for particle astrophysics observations have not generally been exploited for optical astronomy due to the modest optical quality of the mirror surface. However, their large mirror area makes them well suited for such high-time-resolution precision photometry measurements$^4$. Here we report two occultations of stars observed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS)$^5$ Cherenkov telescopes with millisecond sampling, from which we are able to provide a direct measurement of the occulted stars’ angular diameter at the ≤0.1 mas scale. This is a resolution never achieved before with optical measurements and represents an order of magnitude improvement over the equivalent lunar occultation method$^6$. We compare the resulting stellar radius with empirically derived estimates from temperature and brightness measurements, confirming the latter can be biased for stars with ambiguous stellar classifications., Published by Nature Publishing Group, London

Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multi-wavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z=0.130), with a focus on its gamma-ray emission from 100 MeV to 30 TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by VLBA at 43.1, 22.2, and 15.3 GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed., Comment: Accepted for publication in the Astrophysical Journal

Clustering measurements of obscured and unobscured quasars show that obscured quasars reside in more massive dark matter halos than their unobscured counterparts. These results are inconsistent with simple unified (torus) scenarios, but might be explained by models in which the distribution of obscuring material depends on Eddington ratio or galaxy stellar mass. We test these possibilities by constructing simple physical models to compare to observed AGN populations. We find that previously observed relationships between obscuration and Eddington ratio or stellar mass are not sufficient reproduce the observed quasar clustering results ($\langle \log M_{\text{halo}}/M_{\odot} \rangle = 12.94 ^{+ 0.10}_{- 0.11}$ and $\langle \log M_{\text{halo}}/M_{\odot} \rangle = 12.49 ^{+ 0.08}_{- 0.08}$ for obscured and unobscured populations, respectively) while maintaining the observed fraction of obscured quasars (30-65$\%$). This work suggests that evolutionary models, in which obscuration evolves on the typical timescale for black hole growth, are necessary to understand the observed clustering of mid-IR selected quasars., 14 pages, 10 figures, accepted for publication in ApJ

We present XMM-Newton imaging spectroscopy of ten weak emission-line quasars (WLQs) at $0.928\leq z \leq 3.767$, six of which are radio quiet and four which are radio intermediate. The new X-ray data enabled us to measure the power-law photon index, at rest-frame energies $>2$ keV, in each source with relatively high accuracy. These measurements allowed us to confirm previous reports that WLQs have steeper X-ray spectra, suggesting higher accretion rates with respect to 'typical' quasars. A comparison between the photon indices of our radio-quiet WLQs and those of a control sample of 85 sources shows that the first are significantly higher, at the >~$3\sigma$ level. Collectively, the four radio-intermediate WLQs have lower photon indices with respect to the six radio-quiet WLQs, as may be expected if the spectra of the first group are contaminated by X-ray emission from a jet. Therefore, in the absence of significant jet emission along our line of sight, these results are in agreement with the idea that WLQs constitute the extreme high end of the accretion rate distribution in quasars. We detect soft excess emission in our lowest-redshift radio-quiet WLQ, in agreement with previous findings suggesting that the prominence of this feature is associated with a high accretion rate. We have not detected signatures of Compton reflection, Fe K$\alpha$ lines, or strong variability between two X-ray epochs in any of our WLQs, which can be attributed to their relatively high luminosity., Comment: 14 pages (emulateapj), 7 figures. Accepted for publication in ApJ

We present results from deep observations towards the Cygnus region using 300 hours of very-high-energy (VHE) $\gamma$-ray data taken with the VERITAS Cherenkov telescope array and over seven years of high-energy $\gamma$-ray data taken with the Fermi satellite at an energy above 1 GeV. As the brightest region of diffuse $\gamma$-ray emission in the northern sky, the Cygnus region provides a promising area to probe the origins of cosmic rays. We report the identification of a potential Fermi-LAT counterpart to VER J2031+415 (TeV J2032+4130), and resolve the extended VHE source VER J2019+368 into two source candidates (VER J2018+367* and VER J2020+368*) and characterize their energy spectra. The Fermi-LAT morphology of 3FGL 2021.0+4031e (the Gamma-Cygni supernova remnant) was examined and a region of enhanced emission coincident with VER J2019+407 was identified and jointly fit with the VERITAS data. By modeling 3FGL J2015.6+3709 as two sources, one located at the location of the pulsar wind nebula CTB 87 and one at the quasar QSO J2015+371, a continuous spectrum from 1 GeV to 10 TeV was extracted for VER J2016+371 (CTB 87). An additional 71 locations coincident with Fermi-LAT sources and other potential objects of interest were tested for VHE $\gamma$-ray emission, with no emission detected and upper limits on the differential flux placed at an average of 2.3% of the Crab Nebula ux. We interpret these observations in a multiwavelength context and present the most detailed $\gamma$-ray view of the region to date., Comment: 49 Pages, 22 Figures, 13 Tables, Accepted to ApJ

Most active galactic nuclei (AGNs) are radio-quiet, and the origin of their radio emission is not well-understood. One hypothesis is that this radio emission is a by-product of quasar-driven winds. In this paper, we present the radio properties of 108 extremely red quasars (ERQs) at $z=2-4$. ERQs are among the most luminous quasars ($L_{bol} \sim 10^{47-48}$ erg/s) in the Universe, with signatures of extreme ($\gg 1000$ km/s) outflows in their [OIII]$\lambda$5007 \AA\ emission, making them the best subjects to seek the connection between radio and outflow activity. All ERQs but one are unresolved in the radio on $\sim 10$ kpc scales, and the median radio luminosity of ERQs is $\nu L_\nu [{\rm 6\,GHz}] = 10^{41.0}$ erg/s, in the radio-quiet regime, but one to two orders of magnitude higher than that of other quasar samples. The radio spectra are steep, with a mean spectral index $\langle \alpha \rangle = -1.0$. In addition, ERQs neatly follow the extrapolation of the low-redshift correlation between radio luminosity and the velocity dispersion of [OIII]-emitting ionized gas. Uncollimated winds, with a power of one per cent of the bolometric luminosity, can account for all these observations. Such winds would interact with and shock the gas around the quasar and in the host galaxy, resulting in acceleration of relativistic particles and the consequent synchrotron emission observed in the radio. Our observations support the picture in which ERQs are signposts of extremely powerful episodes of quasar feedback, and quasar-driven winds as a contributor of the radio emission in the intermediate regime of radio luminosity $\nu L_\nu = 10^{39}-10^{42}$ erg/s., Comment: accepted by MNRAS

HESS J1943+213 is a very-high-energy (VHE; $>$100 GeV) $\gamma$-ray source in the direction of the Galactic Plane. Studies exploring the classification of the source are converging towards its identification as an extreme synchrotron BL Lac object. Here we present 38 hours of VERITAS observations of HESS J1943+213 taken over two years. The source is detected with $\sim$20 standard deviations significance, showing a remarkably stable flux and spectrum in VHE $\gamma$-rays. Multi-frequency very-long-baseline array (VLBA) observations of the source confirm the extended, jet-like structure previously found in the 1.6 GHz band with European VLBI Network and detect this component in the 4.6 GHz and the 7.3 GHz bands. The radio spectral indices of the core and the jet and the level of polarization derived from the VLBA observations are in a range typical for blazars. Data from VERITAS, $Fermi$-LAT, $Swift$-XRT, FLWO 48$''$ telescope, and archival infrared and hard X-ray observations are used to construct and model the spectral energy distribution (SED) of the source with a synchrotron-self-Compton model. The well-measured $\gamma$-ray peak of the SED with VERITAS and $Fermi$-LAT provides constraining upper limits on the source redshift. Possible contribution of secondary $\gamma$-rays from ultra-high-energy cosmic ray-initiated electromagnetic cascades to the $\gamma$-ray emission is explored, finding that only a segment of the VHE spectrum can be accommodated with this process. A variability search is performed across X-ray and $\gamma$-ray bands. No statistically significant flux or spectral variability is detected., Comment: Accepted for publication in The Astrophysical Journal

Combined with measurements made by very-long-baseline interferometry, the observations of fast TeV gamma-ray flares probe the structure and emission mechanism of blazar jets. However, only a handful of such flares have been detected to date, and only within the last few years have these flares been observed from lower-frequency-peaked BL Lac objects and flat-spectrum radio quasars. We report on a fast TeV gamma-ray flare from the blazar BL Lacertae observed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS). with a rise time of ∼2.3 hr and a decay time of ∼36 min. The peak flux above 200 GeV is (4.2 ± 0.6) ×10 photon m s measured with a 4-minute-binned light curve, corresponding to ∼180% of the flux that is observed from the Crab Nebula above the same energy threshold. Variability contemporaneous with the TeV gamma-ray flare was observed in GeV gamma-ray, X-ray, and optical flux, as well as in optical and radio polarization. Additionally, a possible moving emission feature with superluminal apparent velocity was identified in Very Long Baseline Array observations at 43 GHz, potentially passing the radio core of the jet around the time of the gamma-ray flare. We discuss the constraints on the size, Lorentz factor, and location of the emitting region of the flare, and the interpretations with several theoretical models that invoke relativistic plasma passing stationary shocks.© 2018. The American Astronomical Society. All rights reserved., VERITAS is supported by grants from the U.S. Department of Energy Office of Science, the U.S. National Science Foundation and the Smithsonian Institution, and by NSERC in Canada. We acknowledge the excellent work of the technical support staff at the Fred Lawrence Whipple Observatory and at the collaborating institutions in the construction and operation of the instrument. The research at Boston University was supported in part by NASA Fermi Guest Investigator Program grant 80NSSC17K 0694. The VLBA is an instrument of the Long Baseline Observatory (LBO). The LBO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This research has made use of data from the MOJAVE database that is maintained by the MOJAVE team (Lister et al. 2009) and supported by NASA Fermi grant NNX15AU76G. This work made use of the Swinburne University of Technology software correlator (Deller et al. 2011), developed as part of the Australian Major National Research Facilities Programme and operated under licence. Y.Y.K. and A.B.P. are partly supported by the Russian Foundation for Basic Research (project 17-02-00197), the government of the Russian Federation (agreement 05.Y09.21.0018), and the Alexander von Humboldt Foundation. T.S. was funded by the Academy of Finland projects 274477 and 284495. This research has made use of data from the OVRO 40 m monitoring program (Richards et al. 2011) which is supported in part by NASA grants NNX08AW31G, NNX11A043G, and NNX14AQ89G and NSF grants AST-0808050 and AST-1109911. The monitoring of BL. Lacertae and other blazars at the Steward Observatory is supported through NASA Fermi Guest Investigator grant NNX15AU81G. I.A. acknowledges support by a Ramon y Cajal grant of the Ministerio de Economia y Competitividad (MINECO) of Spain. Acquisition and reduction of the MAPCAT data was supported in part by MINECO through grants AYA2010-14844, AYA2013-40825-P, and AYA2016-80889-P, and by the Regional Government of Andalucia through grant P09-FQM-4784. The MAPCAT observations were carried out at the German-Spanish Calar Alto Observatory, which is jointly operated by the Max-Planck-Institut fur Astronomie and the Instituto de Astrofisica de Andalucia-CSIC. The St. Petersburg University team acknowledges support from Russian Science Foundation grant 17-12-01029.

Commission 42 began life as Photometric Double Stars in 1948 at the 7th General Assembly in Zurich, under the presidency of Zdenek Kopal. As early as 1961, then General Secretary Lukas Plaut recommended a merger between C42 and C26, Double Stars, one of the original 32 commissions going back to 1919-22 (first president Aitken, assistant director at Lick). C42 became Close Binary Stars in 1970, at the 14th GA in Brighton (the first one I attended). Table 1 shows the presidents of C42, and vice presidents, from when the office started, through the history of the Commission.

Active Galactic Nuclei (AGN) are energetic astrophysical sources powered by accretion onto supermassive black holes in galaxies, and present unique observational signatures that cover the full electromagnetic spectrum over more than twenty orders of magnitude in frequency. The rich phenomenology of AGN has resulted in a large number of different "flavours" in the literature that now comprise a complex and confusing AGN "zoo". It is increasingly clear that these classifications are only partially related to intrinsic differences between AGN, and primarily reflect variations in a relatively small number of astrophysical parameters as well the method by which each class of AGN is selected. Taken together, observations in different electromagnetic bands as well as variations over time provide complementary windows on the physics of different sub-structures in the AGN. In this review, we present an overview of AGN multi-wavelength properties with the aim of painting their "big picture" through observations in each electromagnetic band from radio to gamma-rays as well as AGN variability. We address what we can learn from each observational method, the impact of selection effects, the physics behind the emission at each wavelength, and the potential for future studies. To conclude we use these observations to piece together the basic architecture of AGN, discuss our current understanding of unification models, and highlight some open questions that present opportunities for future observational and theoretical progress., Comment: Accepted for publication in Astronomy & Astrophysics Review, 56 pages, 25 figures

We present very-high-energy $\gamma$-ray observations of the BL Lac object 1ES 2344+514 taken by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) between 2007 and 2015. 1ES 2344+514 is detected with a statistical significance above background of $20.8\sigma$ in $47.2$ hours (livetime) of observations, making this the most comprehensive very-high-energy study of 1ES 2344+514 to date. Using these observations the temporal properties of 1ES 2344+514 are studied on short and long times scales. We fit a constant flux model to nightly- and seasonally-binned light curves and apply a fractional variability test, to determine the stability of the source on different timescales. We reject the constant-flux model for the 2007-2008 and 2014-2015 nightly-binned light curves and for the long-term seasonally-binned light curve at the $> 3\sigma$ level. The spectra of the time-averaged emission before and after correction for attenuation by the extragalactic background light are obtained. The observed time-averaged spectrum above 200 GeV is satisfactorily fitted (${\chi^2/NDF = 7.89/6}$) by a power-law function with index $\Gamma = 2.46 \pm 0.06_{stat} \pm 0.20_{sys} $ and extends to at least 8 TeV. The extragalactic-background-light-deabsorbed spectrum is adequately fit (${\chi^2/NDF = 6.73/6}$) by a power-law function with index $\Gamma = 2.15 \pm 0.06_{stat} \pm 0.20_{sys} $ while an F-test indicates that the power-law with exponential cutoff function provides a marginally-better fit ($\chi^2/NDF $ = $2.56 / 5 $) at the 2.1$\sigma$ level. The source location is found to be consistent with the published radio location and its spatial extent is consistent with a point source., Comment: 7 pages, 2 figures. Published in Monthly Notices of the Royal Astronomical Society

We present constraints on the annihilation cross section of WIMP dark matter based on the joint statistical analysis of four dwarf galaxies with VERITAS. These results are derived from an optimized photon weighting statistical technique that improves on standard imaging atmospheric Cherenkov telescope (IACT) analyses by utilizing the spectral and spatial properties of individual photon events. We report on the results of $\sim$230 hours of observations of five dwarf galaxies and the joint statistical analysis of four of the dwarf galaxies. We find no evidence of gamma-ray emission from any individual dwarf nor in the joint analysis. The derived upper limit on the dark matter annihilation cross section from the joint analysis is $1.35\times 10^{-23} {\mathrm{ cm^3s^{-1}}}$ at 1 TeV for the bottom quark ($b\bar{b}$) final state, $2.85\times 10^{-24}{\mathrm{ cm^3s^{-1}}}$ at 1 TeV for the tau lepton ($\tau^{+}\tau^{-}$) final state and $1.32\times 10^{-25}{\mathrm{ cm^3s^{-1}}}$ at 1 TeV for the gauge boson ($\gamma\gamma$) final state., Comment: 14 pages, 9 figures, published in PRD, Ascii tables containing annihilation cross sections limits are available for download as ancillary files with readme.txt file description of limits

We present the most precise estimate to date of the clustering of quasars on very small scales, based on a sample of 47 binary quasars with magnitudes of $g, 16 pages, 8 figures, 6 tables, Accepted for publication in MNRAS

The astrophysical journal 836(1), 23 (2017). doi:10.3847/1538-4357/836/1/23, High-energy gamma-ray emission from supernova remnants (SNRs) has provided a unique perspective for studies of Galactic cosmic-ray acceleration. Tycho's SNR is a particularly good target because it is a young, type Ia SNR that has been well-studied over a wide range of energies and located in a relatively clean environment. Since the detection of gamma-ray emission from Tycho's SNR by VERITAS and Fermi-LAT, there have been several theoretical models proposed to explain its broadband emission and high-energy morphology. We report on an update to the gamma-ray measurements of Tycho's SNR with 147 hr of VERITAS and 84 months of Fermi-LAT observations, which represent about a factor of two increase in exposure over previously published data. About half of the VERITAS data benefited from a camera upgrade, which has made it possible to extend the TeV measurements toward lower energies. The TeV spectral index measured by VERITAS is consistent with previous results, but the expanded energy range softens a straight power-law fit. At energies higher than 400 GeV, the power-law index is 2.92 ± 0.42$_{stat}$ ± 0.20$_{sys}$. It is also softer than the spectral index in the GeV energy range, 2.14 ± 0.09$_{stat}$ ± 0.02$_{sys}$, measured in this study using Fermi-LAT data. The centroid position of the gamma-ray emission is coincident with the center of the remnant, as well as with the centroid measurement of Fermi-LAT above 1 GeV. The results are consistent with an SNR shell origin of the emission, as many models assume. The updated spectrum points to a lower maximum particle energy than has been suggested previously., Published by IOP Publ., Chicago, Ill. [u.a.]

Multi-wavelength surveys covering large sky volumes are necessary to obtain an accurate census of rare objects such as high luminosity and/or high redshift active galactic nuclei (AGN). Stripe 82X is a 31.3 deg$^2$ X-ray survey with $Chandra$ and $XMM$-Newton observations overlapping the legacy Sloan Digital Sky Survey (SDSS) Stripe 82 field, which has a rich investment of multi-wavelength coverage from the ultraviolet to the radio. The wide-area nature of this survey presents new challenges for photometric redshifts for AGN compared to previous work on narrow-deep fields because it probes different populations of objects that need to be identified and represented in the library of templates. Here we present an updated X-ray plus multi-wavelength matched catalog, including $Spitzer$ counterparts, and estimated photometric redshifts for 5961 (96% of a total of 6181) X-ray sources, which have a normalized median absolute deviation, $\sigma_{\rm nmad}$ = 0.06 and an outlier fraction, $\eta$ = 13.7%. The populations found in this survey, and the template libraries used for photometric redshifts, provide important guiding principles for upcoming large-area surveys such as $eROSITA$ and 3$XMM$ (in X-ray) and the Large Synoptic Survey Telescope (LSST; optical)., Comment: Accepted for publication by The Astrophysical Journal (33 pages, 20 figures, 13 tables). Final catalog of counterparts and photo-z supplementing the paper available here: http://stripe82x.com/docs/stripe82x-photometric-redshifts-and-multiwavelength-data-catalog/

Astroparticle physics 91, 34 - 43 (2017). doi:10.1016/j.astropartphys.2017.03.001, Imaging atmospheric Cherenkov telescopes (IACTs) are equipped with sensitive photomultiplier tube (PMT) cameras. Exposure to high levels of background illumination degrades the efficiency of and potentially destroys these photo-detectors over time, so IACTs cannot be operated in the same configuration in the presence of bright moonlight as under dark skies. Since September 2012, observations have been carried out with the VERITAS IACTs under bright moonlight (defined as about three times the night-sky-background (NSB) of a dark extragalactic field, typically occurring when Moon illumination > 35%) in two observing modes, firstly by reducing the voltage applied to the PMTs and, secondly, with the addition of ultra-violet (UV) bandpass filters to the cameras. This has allowed observations at up to about 30 times previous NSB levels (around 80% Moon illumination), resulting in 30% more observing time between the two modes over the course of a year. These additional observations have already allowed for the detection of a flare from the 1ES 1727 + 502 and for an observing program targeting a measurement of the cosmic-ray positron fraction. We provide details of these new observing modes and their performance relative to the standard VERITAS observations., Published by Elsevier, Amsterdam [u.a.]

We have analyzed the {\it XMM-Newton} and {\it Chandra} data overlapping $\sim$16.5 deg$^2$ of Sloan Digital Sky Survey Stripe 82, including $\sim$4.6 deg$^2$ of proprietary {\it XMM-Newton} data that we present here. In total, 3362 unique X-ray sources are detected at high significance. We derive the {\it XMM-Newton} number counts and compare them with our previously reported {\it Chandra} Log$N$-Log$S$ relations and other X-ray surveys. The Stripe 82 X-ray source lists have been matched to multi-wavelength catalogs using a maximum likelihood estimator algorithm. We discovered the highest redshift ($z=5.86$) quasar yet identified in an X-ray survey. We find 2.5 times more high luminosity (L$_x \geq 10^{45}$ erg s$^{-1}$) AGN than the smaller area {\it Chandra} and {\it XMM-Newton} survey of COSMOS and 1.3 times as many identified by XBo\"otes. Comparing the high luminosity AGN we have identified with those predicted by population synthesis models, our results suggest that this AGN population is a more important component of cosmic black hole growth than previously appreciated. Approximately a third of the X-ray sources not detected in the optical are identified in the infrared, making them candidates for the elusive population of obscured high luminosity AGN in the early universe., Comment: 25 pages, 18 figures, 5 tables. accepted for publication in MNRAS. Catalogs can be downloaded at http://www.astro.yale.edu/lamassa/s82x.html

Transient X-ray binaries produce major outbursts in which the X-ray flux can increase over the quiescent level by factors as large as $10^7$. The low-mass X-ray binary V 404 Cyg and the high-mass system 4U 0115+634 underwent such major outbursts in June and October 2015, respectively. We present here observations at energies above hundreds of GeV with the VERITAS observatory taken during some of the brightest X-ray activity ever observed from these systems. No gamma-ray emission has been detected by VERITAS in 2.5 hours of observations of the microquasar V 404 Cyg from 2015, June 20-21. The upper flux limits derived from these observations on the gamma-ray flux above 200 GeV of F $< 4.4\times 10^{-12}$ cm$^{-2}$ s$^{-1}$ correspond to a tiny fraction (about $10^{-6}$) of the Eddington luminosity of the system, in stark contrast to that seen in the X-ray band. No gamma rays have been detected during observations of 4U 0115+634 in the period of major X-ray activity in October 2015. The flux upper limit derived from our observations is F $< 2.1\times 10^{-12}$ cm$^{-2}$ s$^{-1}$ for gamma rays above 300 GeV, setting an upper limit on the ratio of gamma-ray to X-ray luminosity of less than 4%., Accepted for publication in the Astrophysical Journal

Quasar emission lines are often shifted from the systemic velocity due to various dynamical and radiative processes in the line-emitting region. The level of these velocity shifts depends both on the line species and on quasar properties. We study velocity shifts for the line peaks of various narrow and broad quasar emission lines relative to systemic using a sample of 849 quasars from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project. The coadded (from 32 epochs) spectra of individual quasars have sufficient signal-to-noise ratio (SNR) to measure stellar absorption lines to provide reliable systemic velocity estimates, as well as weak narrow emission lines. The sample also covers a large dynamic range in quasar luminosity (~2 dex), allowing us to explore potential luminosity dependence of the velocity shifts. We derive average line peak velocity shifts as a function of quasar luminosity for different lines, and quantify their intrinsic scatter. We further quantify how well the peak velocity can be measured for various lines as a function of continuum SNR, and demonstrate there is no systematic bias in the line peak measurements when the spectral quality is degraded to as low as SNR~3 per SDSS pixel. Based on the observed line shifts, we provide empirical guidelines on redshift estimation from [OII]3728, [OIII]5008, [NeV]3426, MgII, CIII], HeII1640, broad Hbeta, CIV, and SiIV, which are calibrated to provide unbiased systemic redshifts in the mean, but with increasing intrinsic uncertainties of 46, 56, 119, 205, 233, 242, 400, 415, and 477 km/s, in addition to the measurement uncertainties. These more realistic redshift uncertainties are generally much larger than the formal uncertainties reported by the redshift pipelines for spectroscopic quasar surveys, and demonstrate the infeasibility of measuring quasar redshifts to better than ~200 km/s with only broad lines., matched to the published version; minor changes and conclusions unchanged

The CIV broad emission line is visible in optical spectra to redshifts exceeding z~5. CIV has long been known to exhibit significant displacements to the blue and these `blueshifts' almost certainly signal the presence of strong outflows. As a consequence, single-epoch virial black hole (BH) mass estimates derived from CIV velocity-widths are known to be systematically biased compared to masses from the hydrogen Balmer lines. Using a large sample of 230 high-luminosity (log $L_{\rm Bol}$ = 45.5-48 erg/s), redshift 1.55000 km/s. Using the monotonically increasing relationship between the CIV blueshift and the mass ratio BH(CIV)/BH(H$\alpha$) we derive an empirical correction to all CIV BH-masses. The scatter between the corrected CIV masses and the Balmer masses is 0.24 dex at low CIV blueshifts (~0 km/s) and just 0.10 dex at high blueshifts (~3000 km/s), compared to 0.40 dex before the correction. The correction depends only on the CIV line properties - i.e. full-width at half maximum and blueshift - and can therefore be applied to all quasars where CIV emission line properties have been measured, enabling the derivation of un-biased virial BH mass estimates for the majority of high-luminosity, high-redshift, spectroscopically confirmed quasars in the literature., Comment: Accepted for publication in MNRAS; fixed typo in CIV wavelength

We describe the first data release from the Spitzer-IRAC Equatorial Survey (SpIES); a large-area survey of 115 deg^2 in the Equatorial SDSS Stripe 82 field using Spitzer during its 'warm' mission phase. SpIES was designed to probe sufficient volume to perform measurements of quasar clustering and the luminosity function at z > 3 to test various models for "feedback" from active galactic nuclei (AGN). Additionally, the wide range of available multi-wavelength, multi-epoch ancillary data enables SpIES to identify both high-redshift (z > 5) quasars as well as obscured quasars missed by optical surveys. SpIES achieves 5{\sigma} depths of 6.13 {\mu}Jy (21.93 AB magnitude) and 5.75 {\mu}Jy (22.0 AB magnitude) at 3.6 and 4.5 microns, respectively - depths significantly fainter than WISE. We show that the SpIES survey recovers a much larger fraction of spectroscopically-confirmed quasars (98%) in Stripe 82 than are recovered by WISE (55%). This depth is especially powerful at high-redshift (z > 3.5), where SpIES recovers 94% of confirmed quasars, whereas WISE only recovers 25%. Here we define the SpIES survey parameters and describe the image processing, source extraction, and catalog production methods used to analyze the SpIES data. In addition to this survey paper, we release 234 images created by the SpIES team and three detection catalogs: a 3.6 {\mu}m-only detection catalog containing 6.1 million sources, a 4.5 {\mu}m-only detection catalog containing 6.5 million sources, and a dual-band detection catalog containing 5.4 million sources., Comment: 25 pages, 17 Figures, Accepted by ApJs 3/21/2016

The BL Lacertae object 1ES 1440+122 was observed in the energy range from 85 GeV to 30 TeV by the VERITAS array of imaging atmospheric Cherenkov telescopes. The observations, taken between 2008 May and 2010 June and totalling 53 hours, resulted in the discovery of $\gamma$-ray emission from the blazar, which has a redshift $z$=0.163. 1ES 1440+122 is detected at a statistical significance of 5.5 standard deviations above the background with an integral flux of (2.8$\pm0.7_{\mathrm{stat}}\pm0.8_{\mathrm{sys}}$) $\times$ 10$^{-12}$ cm$^{-2}$ s$^{-1}$ (1.2\% of the Crab Nebula's flux) above 200 GeV. The measured spectrum is described well by a power law from 0.2 TeV to 1.3 TeV with a photon index of 3.1 $\pm$ 0.4$_{\mathrm{stat}}$ $\pm$ 0.2$_{\mathrm{sys}}$. Quasi-simultaneous multi-wavelength data from the Fermi Large Area Telescope (0.3--300 GeV) and the Swift X-ray Telescope (0.2--10 keV) are additionally used to model the properties of the emission region. A synchrotron self-Compton model produces a good representation of the multi-wavelength data. Adding an external-Compton or a hadronic component also adequately describes the data., Comment: 8 pages, 4 figures. Accepted for publication in MNRAS

Black-hole masses are crucial to understanding the physics of the connection between quasars and their host galaxies and measuring cosmic black hole-growth. At high redshift, z > 2.1, black hole masses are normally derived using the velocity-width of the CIV broad emission line, based on the assumption that the observed velocity-widths arise from virial-induced motions. In many quasars, the CIV-emission line exhibits significant blue asymmetries (`blueshifts') with the line centroid displaced by up to thousands of km/s to the blue. These blueshifts almost certainly signal the presence of strong outflows, most likely originating in a disc wind. We have obtained near-infrared spectra, including the H$��$ emission line, for 19 luminous ($L_{Bol}$ = 46.5-47.5 erg/s) Sloan Digital Sky Survey quasars, at redshifts 2 < z < 2.7, with CIV emission lines spanning the full-range of blueshifts present in the population. A strong correlation between CIV-velocity width and blueshift is found and, at large blueshifts, > 2000 km/s, the velocity-widths appear to be dominated by non-virial motions. Black-hole masses, based on the full width at half maximum of the CIV-emission line, can be overestimated by a factor of five at large blueshifts. A larger sample of quasar spectra with both CIV and H$��$, or H$��$, emission lines will allow quantitative corrections to CIV-based black-hole masses as a function of blueshift to be derived. We find that quasars with large CIV blueshifts possess high Eddington luminosity ratios and that the fraction of high-blueshift quasars in a flux-limited sample is enhanced by a factor of approximately four relative to a sample limited by black hole mass., Accepted for publication in MNRAS (21 pages, 11 figures, 4 tables)

Machine learning can provide powerful tools to detect patterns in multi-dimensional parameter space. We use K-means -a simple yet powerful unsupervised clustering algorithm which picks out structure in unlabeled data- to study a sample of quasar UV spectra from the Quasar Catalog of the 10th Data Release of the Sloan Digital Sky Survey of Paris et al. (2014). Detecting patterns in large datasets helps us gain insights into the physical conditions and processes giving rise to the observed properties of quasars. We use K-means to find clusters in the parameter space of the equivalent width (EW), the blue- and red-half-width at half-maximum (HWHM) of the Mg II 2800 A line, the C IV 1549 A line, and the C III] 1908 A blend in samples of Broad Absorption-Line (BAL) and non-BAL quasars at redshift 1.6-2.1. Using this method, we successfully recover correlations well-known in the UV regime such as the anti-correlation between the EW and blueshift of the C IV emission line and the shape of the ionizing Spectra Energy distribution (SED) probed by the strength of He II and the Si III]/C III] ratio. We find this to be particularly evident when the properties of C III] are used to find the clusters, while those of Mg II proved to be less strongly correlated with the properties of the other lines in the spectra such as the width of C IV or the Si III]/C III] ratio. We conclude that unsupervised clustering methods (such as K-means) are powerful methods for finding "natural" binning boundaries in multidimensional datasets and discuss caveats and future work., 17 pages, color figures, accepted for publication in MNRAS