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Full list of authors: Silber, Joseph Harry; Fagrelius, Parker; Fanning, Kevin; Schubnell, Michael; Aguilar, Jessica Nicole; Ahlen, Steven; Ameel, Jon; Ballester, Otger; Baltay, Charles; Bebek, Chris; Beard, Dominic Benton; Besuner, Robert; Cardiel-Sas, Laia; Casas, Ricard; Castander, Francisco Javier; Claybaugh, Todd; Dobson, Carl; Duan, Yutong; Dunlop, Patrick; Edelstein, Jerry; Emmet, William T.; Elliott, Ann; Evatt, Matthew; Gershkovich, Irena; Guy, Julien; Harris, Stu; Heetderks, Henry; Heetderks, Ian; Honscheid, Klaus; Maria Illa, Jose; Jelinsky, Patrick; Jelinsky, Sharon R.; Jimenez, Jorge; Karcher, Armin; Kent, Stephen; Kirkby, David; Kneib, Jean-Paul; Lambert, Andrew; Lampton, Mike; Leitner, Daniela; Levi, Michael; McCauley, Jeremy; Meisner, Aaron; Miller, Timothy N.; Miquel, Ramon; Mundet, Julia; Poppett, Claire; Rabinowitz, David; Reil, Kevin; Roman, David; Schlegel, David; Serrano, Santiago; Van Shourt, William; Sprayberry, David; Tarle, Gregory; Tie, Suk Sien; Weaverdyck, Curtis; Zhang, Kai; Azzaro, Marco; Bailey, Stephen; Becerril, Santiago; Blackwell, Tami; Bouri, Mohamed; Brooks, David; Buckley-Geer, Elizabeth; Penate Castro, Jose; Derwent, Mark; Dey, Arjun; Dhungana, Govinda; Doel, Peter; Eisenstein, Daniel J.; Fahim, Nasib; Garcia-Bellido, Juan; Gaztanaga, Enrique; Gontcho, Satya Gontcho A.; Gutierrez, Gaston; Horler, Philipp; Kehoe, Robert; Kisner, Theodore; Kremin, Anthony; Kronig, Luzius; Landriau, Martin; Le Guillou, Laurent; Martini, Paul; Moustakas, John; Palanque-Delabrouille, Nathalie; Peng, Xiyan; Percival, Will; Prada, Francisco; Allende Prieto, Carlos; Gonzalez de Rivera, Guillermo; Sanchez, Eusebio; Sanchez, Justo; Sharples, Ray; Soares-Santos, Marcelle; Schlafly, Edward; Weaver, Benjamin Alan; Zhou, Zhimin; Zhu, Yaling; Zou, Hu; DESI Collaboration.--This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., A system of 5020 robotic fiber positioners was installed in 2019 on the Mayall Telescope, at Kitt Peak National Observatory. The robots automatically retarget their optical fibers every 10–20 minutes, each to a precision of several microns, with a reconfiguration time of fewer than 2 minutes. Over the next 5 yr, they will enable the newly constructed Dark Energy Spectroscopic Instrument (DESI) to measure the spectra of 35 million galaxies and quasars. DESI will produce the largest 3D map of the universe to date and measure the expansion history of the cosmos. In addition to the 5020 robotic positioners and optical fibers, DESI's Focal Plane System includes six guide cameras, four wave front cameras, 123 fiducial point sources, and a metrology camera mounted at the primary mirror. The system also includes associated structural, thermal, and electrical systems. In all, it contains over 675,000 individual parts. We discuss the design, construction, quality control, and integration of all these components. We include a summary of the key requirements, the review and acceptance process, on-sky validations of requirements, and lessons learned for future multiobject, fiber-fed spectrographs. © 2022. The Author(s). Published by the American Astronomical Society., The authors in the Barcelona-Madrid Regional Participation Group (BCN-MAD RPG) wish to acknowledge support by MICIN under grants PID2019-111317 GB, PGC2018-094773, PGC2018-102021, SEV-2016-0588, SEV-2016-0597, MDM-2015-0509, and CEX2020-001058-M, some of which include ERDF funds from the European Union. IFAE is partially funded by the CERCA program of the Generalitat de Catalunya. M.A., S.B., N.F., F.P., G.G.R., and J.S. acknowledge support from the Spanish MICINN grants MultiDark CSD2009-00064, IFT-UAM/CSIC Severo Ochoa Award SEV-2012-0249 and AYA2014-60641-C2-1-P, CSIC-AVS contract through MICINN grant AYA2010-21231-C02-01 and CDTI grant IDC-20101033, and support from the Campus of International Excellence UAM+CSIC. This research is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences under Contract No. AST-0950945 to the NSF's National Optical-Infrared Astronomy Research Laboratory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Science and Technology of Mexico (CONACYT); the Ministry of Science and Innovation of Spain (MICINN), and by the DESI Member Institutions: https://www.desi.lbl.gov/collaborating-institutions., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).

We describe the simulated sky survey underlying the second data challenge (DC2) carried out in preparation for analysis of the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) by the LSST Dark Energy Science Collaboration (LSST DESC). Significant connections across multiple science domains will be a hallmark of LSST; the DC2 program represents a unique modeling effort that stresses this interconnectivity in a way that has not been attempted before. This effort encompasses a full end-to-end approach: starting from a large N-body simulation, through setting up LSST-like observations including realistic cadences, through image simulations, and finally processing with Rubin's LSST Science Pipelines. This last step ensures that we generate data products resembling those to be delivered by the Rubin Observatory as closely as is currently possible. The simulated DC2 sky survey covers six optical bands in a wide-fast-deep (WFD) area of approximately 300 deg^2 as well as a deep drilling field (DDF) of approximately 1 deg^2. We simulate 5 years of the planned 10-year survey. The DC2 sky survey has multiple purposes. First, the LSST DESC working groups can use the dataset to develop a range of DESC analysis pipelines to prepare for the advent of actual data. Second, it serves as a realistic testbed for the image processing software under development for LSST by the Rubin Observatory. In particular, simulated data provide a controlled way to investigate certain image-level systematic effects. Finally, the DC2 sky survey enables the exploration of new scientific ideas in both static and time-domain cosmology., 39 pages, 19 figures, version accepted for publication in ApJS

Electro-optical testing and characterization of the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) Camera focal plane, consisting of 205 charge-coupled devices (CCDs) arranged into 21 stand-alone Raft Tower Modules (RTMs) and 4 Corner Raft Tower Modules (CRTMs), is currently being performed at the SLAC National Accelerator Laboratory. Testing of the camera sensors is performed using a set of custom-built optical projectors, designed to illuminate the full focal plane or specific regions of the focal plane with a series of light illumination patterns: the crosstalk projector, the flat illuminator projector, and the spot grid projector. In addition to measurements of crosstalk, linearity and full well, the ability to project realistically-sized sources, using the spot grid projector, makes possible unique measurements of instrumental signatures such as deferred charge distortions, astrometric shifts due to sensor effects, and the brighter-fatter effect, prior to camera first light. Here we present the optical projector designs and usage, the electro-optical measurements and how these results have been used in testing and improving the LSST Camera instrumental signature removal algorithms., 21 pages, 16 figures. SPIE Astronomical Telescopes + Instrumentation Digital Forum December 2020

In late 2021, the Rubin Observatory LSST Camera will be shipped from SLAC National Laboratory in California to Cerro Pach´on in Chile. The Camera shipping container, designed based on lessons learned from previous shipments, is a standard 20 ft steel container retrofitted with a vibration-isolation system and insulation. This modified container will be shipped with a Camera mass surrogate from SLAC to the summit in early 2021 in order to verify as many aspects of the procedure and hardware as possible. Results from this preliminary shipment will guide further improvements to the shipping process prior to the shipment of the LSST Camera.

The Integration and Verification Testing and characterization of the expected performance of the Large Synoptic Survey Telescope (LSST) Camera is described. The LSST Camera will be the largest astronomical camera ever constructed, featuring a 3.2 Gpixel focal plane mosaic of 189 CCDs. In this paper, we describe the verification testing program developed in parallel with the integration of the Camera, and the results from our performance characterization of the Camera. Our testing program includes electro-optical characterization and CCD height measurements of the focal plane, at several steps during integration, as well as a complete functional and characterization program for the finished focal plane. It also includes a suite of functional tests of the major Camera mechanisms: shutter, filter exchange system and thermal control. Finally, we expect to test the fully assembled Camera prior to its scheduled completion and delivery to the LSST observatory in early calendar 2021.

The Dark Energy Survey (DES) is an optical and near-infrared imaging survey aimed at understanding the accelerating expansion of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the 6-season 5000 sq-degree wide field and the 5-season 30 sq-degree supernova surveys, the DES Collaboration built the Dark Energy Camera (DECam), a 3 square-degree, 570-Megapixel CCD camera that was installed at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). DES started its observations in “Year 1” (Y1) on Aug. 31, 2013 and completed its sixth and final observing season on January 9, 2019. This paper describes DES Y6, the survey strategy, an outline of the survey operations procedures, the efficiency of operations and the causes of lost observing time. It provides details about the quality of the final season's data, and a summary of the Y1-Y6 observing. It contains a brief description of the last night of observations.

The Multi-conjugate Adaptive Optics RelaY (MAORY) should provide 30% SR in K band (50% goal) on half of the sky at the South Galactic Pole. Assessing its performance and the sensitivity to parameter variations during the design phase is a fundamental step for the engineering of such a complex system. This step, centered on numerical simulations, is the connection between the performance requirements and the Adaptive Optics system configuration. In this work we present MAORY configuration and performance and we justify theAdaptive Optics system design choices., Comment: 9 pages, 7 figures, 1 table. SPIE conference Astronomical Telescopes and Instrumentation, 14 - 18 December 2020, digital forum

We present Magellan/IMACS spectroscopy of three recently discovered ultra-faint Milky Way satellites, Grus II, Tucana IV, and Tucana V. We measure systemic velocities of vhel=-110.0 ± 0.5 kms, vhel= 15.9 kms and vhel=-36.2 kms for the three objects, respectively. Their large relative velocities demonstrate that the satellites are unrelated despite their close physical proximity. We determine a velocity dispersion for Tuc IV of σ = 4.3 km s but we cannot resolve the velocity dispersions of the other two systems. For Gru II, we place an upper limit (90% confidence) on the dispersion of σ < 1.9 kms and for Tuc V, we do not obtain any useful limits. All three satellites have metallicities below, but none has a detectable metallicity spread. We determine proper motions for each satellite based on Gaia astrometry and compute their orbits around the Milky Way. Gru II is on a tightly bound orbit with a pericenter of 25 kpc and orbital eccentricity of 0.45 . Tuc V likely has an apocenter beyond 100 kpc and could be approaching the Milky Way for the first time. The current orbit of Tuc IV is similar to that of Gru II, with a pericenter of 25 kpc and an eccentricity of 0.36 . However, a backward integration of the position of Tuc IV demonstrates that it collided with the Large Magellanic Cloud at an impact parameter of 4 kpc ∼120 Myr ago, deflecting its trajectory and possibly altering its internal kinematics. Based on their sizes, masses, and metallicities, we classify Gru II and Tuc IV as likely dwarf galaxies, but the nature of Tuc V remains uncertain., This publication is based upon work supported by the National Science Foundation under grant AST-1714873. J.D.S. was also partially supported by program number HST-GO14734, provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. Some of this work was carried out during a stay at the Kavli Institute for Theoretical Physics, which is supported in part by the National Science Foundation under grant No. NSF PHY-1748958, for the program The Small-Scale Structure of Cold(?) Dark Matter. T.S.L. was supported by NASA through Hubble Fellowship grant HST-HF2-51439.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. We thank Dan Kelson for many helpful conversations regarding IMACS data reduction and Petchara Pattarakijwanich for early contributions to the IMACS reduction procedures, as well as the anonymous referee for comments that helped improve the paper. This research has made use of NASA’s Astrophysics Data System Bibliographic Services. Contour plots were generated using corner.py (Foreman-Mackey 2016). Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência e Tecnologia, the Deutsche Forschungsgemeinschaft, and the Collaborating Institutions in the Dark Energy Survey. The DES participants from Spanish institutions are partially supported by MINECO under grants AYA2012- 39559, ESP2013-48274, FPA2013-47986, and Centro de Excelencia Severo Ochoa SEV-2012-0234, some of which include ERDF funds from the European Union. This material is based upon work supported by the National Science Foundation under grant No. 1138766. The Collaborating Institutions are Argonne National Laboratory, the University of California at Santa Cruz, the University of Cambridge, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas-Madrid, the University of Chicago, University College London, the DES-Brazil Consortium, the Eidgenössische Technische Hochschule (ETH) Zürich, Fermi National Accelerator Laboratory, the University of Edinburgh, the University of Illinois at Urbana-Champaign, the Institut de Ciències de l’Espai (IEEC/CSIC), the Institut de Física d’Altes Energies, Lawrence Berkeley National Laboratory, the Ludwig-Maximilians Universität and the associated Excellence Cluster Universe, the University of Michigan, the National Optical Astronomy Observatory, the University of Nottingham, The Ohio State University, the University of Pennsylvania, the University of Portsmouth, SLAC National Accelerator Laboratory, Stanford University, the University of Sussex, and Texas A& M University.

The Commissioning Phase of the LSST Project is the final stage in the combined NSF and DOE funded LSST construction project. The LSST commission phase is planned to start early in 2020 and be completed near the end of 2022, ending with the LSST Observatory system ready to start survey operations. Commissioning includes the assembly of the three principal subsystems (Telescope, Camera and Data Management) into the LSST Observatory System and the integration and test (AIT Phase-1) Early System AIT Phase-2) Full System AIT and Phase-3) Science Validation where a series of mini-surveys are used to characterize the system with respect to the survey performance specifications in the SRD/LSR and functionality of the, leading to operations readiness. The Science Validation Phase concludes with an Operations Readiness Review (ORR). The LSST System Assembly, Integration and Test and Commissioning effort has been planned out over several phases The first phase of commissioning under Early AIT the scheduler will be exercised and all safety checks verified for autonomous operation; and early DM algorithm testing will be performed with on-sky data from ComCam using a commissioning computing cluster at the Base Facility. The second phase of activities under Full System AI&T is designed to complete the technical integration of the three principal subsystems and EPO, show full compliance with system level requirements as detailed in the Observatory System Specifications and system level interface control documents, and provide full scale data for further DM/EPO software and algorithmic testing and development. System level requirements that flow directly to subsystems without any further derivation will be tested for compliance, at the subsystem level and below, under the supervision of Project Systems Engineering. This document includes the general approach and goals for these tests. It is expected that roughly four (4) months into the Full System AI&T phase the telescope and camera will be fully integrated and routinely producing science grade images over the full field of view (FOV), at which point “System First Light” will be declared. Following System First Light will be an intensive data acquisition period design to test the image processing pipelines and validate the derived science products that are to be delivered by the LSST survey. The third and final phase of activities under Science Validation is designed to fully characterize the system performance specifications detailed in LSST System Requirements Document and the range of demonstrated performance per the LSST Science Requirements. These activities are based on the measured “On-Sky” performance and informed simulations of the LSST system. In this paper we describe the inputs and assumptions to the commissioning plan, a summary of the activities in each phase, management strategies and expected outcomes.

The Large Synoptic Survey Telescope, under construction in Chile, is an 8.4 m optical survey telescope with a dedicated 3.2 Giga-pixel camera. The design and construction of the camera is spearheaded at SLAC National Accelerator Laboratory and here we present a general overview of the camera integration and test activities. An overview of the methodologies used for the planning and management of this subsystem will be given, along with a high-level summary of the status of the major pieces of I&T hardware. Finally a brief update will be given on the current state of the LSST Camera integration and testing program.

The Large Synoptic Survey Telescope (LSST) Commissioning Camera (ComCam) is a smaller, simpler version of the full LSST camera (LSSTCam). It uses a single raft of 9 (instead of twenty-one rafts of 9) 4K x 4K LSST Science CCDs, has the same plate scale, and uses the same interfaces to the greatest extent possible. ComCam will be used during the Project’s 6-month Early Integration and Test period beginning in 2020. Its purpose is to facilitate testing and verification of system interfaces, initial on-sky testing of the telescope, and testing and validation of Data Management data transfer, infrastructure and algorithms prior to the delivery of the full science camera.

The Bench for Optical Testing (BOT) is a test stand that will be used for metrology and optical testing of the Large Synoptic Survey Telescope (LSST) Camera CCD sensors, immediately after the integration step where the sensors are installed into the Cryostat to form the LSST’s 3.2 gigapixel, 640mm diameter focal plane. The BOT uses existing methods to economically verify sensor performance, including measurement of focal plane flatness, CCD sensor spacing, gain stability, cross-talk, flat field images, response in each filter band, and dark level. This paper describes the requirements, design, and preliminary test results for the BOT test equipment.

We present the mechanical device used to install the Raft Tower Modules (RTMs) into the cryosat of the camera for the Large Synoptic Survey Telescope (LSST). In an RTM, the charge-coupled devices (CCDs) are packaged into a 3 x 3 Raft Sensor Assembly (RSA) and coupled to a Raft Electronics Crate (REC). An RTM weighs ~10 kg, is roughly 500 mm tall, and has a 126.5 mm-square footprint at the CCDs. The grid array which supports the RTM in the cryostat has a center-to-center distance of 127 mm. One of the key challenges for installing the RTMs in the 500 μm gap between CCDs of adjacent modules - contact between adjacent CCDs is strictly forbidden.

International audience; The Integration and Verification Testing of the Large Synoptic Survey Telescope (LSST) Camera is described. The LSST Camera will be the largest astronomical camera ever constructed, featuring a 3.2 giga-pixel focal plane mosaic of 189 CCDs with in-vacuum controllers and readout, dedicated guider and wavefront CCDs, a three element corrector with a 1.6-meter diameter initial optic, six optical filters covering wavelengths from 320 to 1000 nm with a novel filter exchange mechanism, and camera-control and data acquisition capable of digitizing each image in two seconds. In this paper, we describe the integration processes under way to assemble the Camera and the associated verification testing program. The Camera assembly proceeds along two parallel paths: one for the focal plane and cryostat and the other for the Camera structure itself. A range of verification tests will be performed interspersed with assembly to verify design requirements with a test-as-you-build methodology. Ultimately, the cryostat will be installed into the Camera structure as the two assembly paths merge, and a suite of final Camera system tests performed. The LSST Camera is scheduled for completion and delivery to the LSST observatory in 2020.

We describe the first public data release of the Dark Energy Survey, DES DR1, consisting of reduced single epoch images, coadded images, coadded source catalogs, and associated products and services assembled over the first three years of DES science operations. DES DR1 is based on optical/near-infrared imaging from 345 distinct nights (August 2013 to February 2016) by the Dark Energy Camera mounted on the 4-m Blanco telescope at Cerro Tololo Inter-American Observatory in Chile. We release data from the DES wide-area survey covering ~5,000 sq. deg. of the southern Galactic cap in five broad photometric bands, grizY. DES DR1 has a median delivered point-spread function of g = 1.12, r = 0.96, i = 0.88, z = 0.84, and Y = 0.90 arcsec FWHM, a photometric precision of < 1% in all bands, and an astrometric precision of 151 mas. The median coadded catalog depth for a 1.95" diameter aperture at S/N = 10 is g = 24.33, r = 24.08, i = 23.44, z = 22.69, and Y = 21.44 mag. DES DR1 includes nearly 400M distinct astronomical objects detected in ~10,000 coadd tiles of size 0.534 sq. deg. produced from ~39,000 individual exposures. Benchmark galaxy and stellar samples contain ~310M and ~ 80M objects, respectively, following a basic object quality selection. These data are accessible through a range of interfaces, including query web clients, image cutout servers, jupyter notebooks, and an interactive coadd image visualization tool. DES DR1 constitutes the largest photometric data set to date at the achieved depth and photometric precision., 30 pages, 20 Figures. Release page found at this url https://des.ncsa.illinois.edu/releases/dr1

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the universe using the baryon acoustic oscillations technique. The spectra of 35 million galaxies and quasars over 14,000 square degrees will be measured during a 5-year survey. A new prime focus corrector for the Mayall telescope at Kitt Peak National Observatory will deliver light to 5,000 individually targeted fiber-fed robotic positioners. The fibers in turn feed ten broadband multi-object spectrographs. We describe the ProtoDESI experiment, that was installed and commissioned on the 4-m Mayall telescope from August 14 to September 30, 2016. ProtoDESI was an on-sky technology demonstration with the goal to reduce technical risks associated with aligning optical fibers with targets using robotic fiber positioners and maintaining the stability required to operate DESI. The ProtoDESI prime focus instrument, consisting of three fiber positioners, illuminated fiducials, and a guide camera, was installed behind the existing Mosaic corrector on the Mayall telescope. A Fiber View Camera was mounted in the Cassegrain cage of the telescope and provided feedback metrology for positioning the fibers. ProtoDESI also provided a platform for early integration of hardware with the DESI Instrument Control System that controls the subsystems, provides communication with the Telescope Control System, and collects instrument telemetry data. Lacking a spectrograph, ProtoDESI monitored the output of the fibers using a Fiber Photometry Camera mounted on the prime focus instrument. ProtoDESI was successful in acquiring targets with the robotically positioned fibers and demonstrated that the DESI guiding requirements can be met., Comment: Accepted version

We study the methodology and potential theoretical systematics of measuring Baryon Acoustic Oscillations (BAO) using the angular correlation functions in tomographic bins. We calibrate and optimize the pipeline for the Dark Energy Survey Year 1 dataset using 1800 mocks. We compare the BAO fitting results obtained with three estimators: the Maximum Likelihood Estimator (MLE), Profile Likelihood, and Markov Chain Monte Carlo. The fit results from the MLE are the least biased and their derived 1-$\sigma$ error bar are closest to the Gaussian distribution value after removing the extreme mocks with non-detected BAO signal. We show that incorrect assumptions in constructing the template, such as mismatches from the cosmology of the mocks or the underlying photo-$z$ errors, can lead to BAO angular shifts. We find that MLE is the method that best traces this systematic biases, allowing to recover the true angular distance values. In a real survey analysis, it may happen that the final data sample properties are slightly different from those of the mock catalog. We show that the effect on the mock covariance due to the sample differences can be corrected with the help of the Gaussian covariance matrix or more effectively using the eigenmode expansion of the mock covariance. In the eigenmode expansion, the eigenmodes are provided by some proxy covariance matrix. The eigenmode expansion is significantly less susceptible to statistical fluctuations relative to the direct measurements of the covariance matrix because of the number of free parameters is substantially reduced, Comment: 23 pages, 23 figs, match to the published version

We perform a systematic search for long-term extreme variability quasars (EVQs) in the overlapping Sloan Digital Sky Survey (SDSS) and 3-Year Dark Energy Survey (DES) imaging, which provide light curves spanning more than 15 years. We identified ~1000 EVQs with a maximum g band magnitude change of more than 1 mag over this period, about 10% of all quasars searched. The EVQs have L_bol~10^45-10^47 erg/s and L/L_Edd~0.01-1. Accounting for selection effects, we estimate an intrinsic EVQ fraction of ~30-50% among all g, Comment: submitted to ApJ; comments welcome

We describe a multi-component matched filter cluster confirmation tool (MCMF) designed for the study of large X-ray source catalogs produced by the upcoming X-ray all-sky survey mission eROSITA. We apply the method to confirm a sample of 88 clusters with redshifts $0.05, Comment: 20 pages, 19 figures

International audience; We present results for the first three years of OzDES, a six year programme to obtain redshifts for objects in the Dark Energy Survey (DES) supernova fields using the 2dF fibre positioner and AAOmega spectrograph on the Anglo-Australian Telescope. OzDES is a multi-object spectroscopic survey targeting multiple types of targets at multiple epochs over a multiyear baseline and is one of the first multi-object spectroscopic surveys to dynamically include transients into the target list soon after their discovery. At the end of three years, OzDES has spectroscopically confirmed almost 100 supernovae, and has measured redshifts for 17 000 objects, including the redshifts of 2566 supernova hosts. We examine how our ability to measure redshifts for targets of various types depends on signal-to-noise ratio (S/N), magnitude and exposure time, finding that our redshift success rate increases significantly at a S/N of 2–3 per 1-Å bin. We also find that the change in S/N with exposure time closely matches the Poisson limit for stacked exposures as long as 10 h. We use these results to predict the redshift yield of the full OzDES survey, as well as the potential yields of future surveys on other facilities such as (i.e. the 4-m Multi-Object Spectroscopic Telescope, the Subaru Prime Focus Spectrograph and the Maunakea Spectroscopic Explorer). This work marks the first OzDES data release, comprising 14 693 redshifts. OzDES is on target to obtain over 30 000 redshifts over the 6-yr duration of the survey, including a yield of approximately 5700 supernova host-galaxy redshifts.

We present spectroscopic confirmation of two new lensed quasars via data obtained at the 6.5m Magellan/Baade Telescope. The lens candidates have been selected from the Dark Energy Survey (DES) and WISE based on their multi-band photometry and extended morphology in DES images. Images of DES J0115-5244 show two blue point sources at either side of a red galaxy. Our long-slit data confirm that both point sources are images of the same quasar at $z_{s}=1.64.$ The Einstein Radius estimated from the DES images is $0.51$". DES J2200+0110 is in the area of overlap between DES and the Sloan Digital Sky Survey (SDSS). Two blue components are visible in the DES and SDSS images. The SDSS fiber spectrum shows a quasar component at $z_{s}=2.38$ and absorption compatible with Mg II and Fe II at $z_{l}=0.799$, which we tentatively associate with the foreground lens galaxy. The long-slit Magellan spectra show that the blue components are resolved images of the same quasar. The Einstein Radius is $0.68$" corresponding to an enclosed mass of $1.6\times10^{11}\,M_{\odot}.$ Three other candidates were observed and rejected, two being low-redshift pairs of starburst galaxies, and one being a quasar behind a blue star. These first confirmation results provide an important empirical validation of the data-mining and model-based selection that is being applied to the entire DES dataset., 7 pages, 1 figure, 2 tables, MNRAS subm. This paper includes data gathered with the 6.5m Baade Telescopes located at Las Campanas Observatory, Chile. This paper has gone through internal review by the DES collaboration, FERMILAB-PUB-15-341-AE

We will report on the setup and calibration of the instrumentation for sFLASH. The sFLASH experiment is a measurement of the air fluorescence from ∼10$^{21}$ eV artificial air showers developed in an alumina target by an electron beam provided from End Station A of the Stanford Linear Accelerator Center (SLAC). sFLASH employs Photomultiplier tubes (PMTs) to detect the fluorescence photons and an Integrating Charge Transformer (ICT) to measure the beam current. The PMTs are positioned ~10m perpendicular to shower axis are used to measure the air fluorescence photons. The absolute gain of the PMTs was measured using CRAYS at the Institute of Cosmic-Ray Research, Japan. CRAYS is a PMT photo-gain calibration system consisting of a vessel containing nitrogen gas and a 14μJ nitrogen (337.1 nm) laser. The gain of each PMT was monitored during the course of the experiment using a YAP pulser (YAlO: Ce + $^{241}$Am) potted into an ultraviolet optical filter attached to the surface of the PMT window. We expect to achieve an overall experimental uncertainty of ~6%. The ICT (Bergoz) consists of 20 turns of coil to measure the beam current. In the sFLASH experiment we set it ~1 m away from beam exit to measure the beam current just prior to entering the target material. The ICT was calibrated with 2 ns pulse generator at Jet Propulsion Laboratory. The calibration uncertainty of the ICT is ~1%.

We report the results of searches for strong gravitational lens systems in the Dark Energy Survey (DES) Science Verification and Year 1 observations. The Science Verification data span approximately 250 sq. deg. with a median i-band limiting magnitude for extended objects (10 sigma) of 23.0. The Year 1 data span approximately 2000 sq. deg. and have an i-band limiting magnitude for extended objects (10 sigma) of 22.9. As these data sets are both wide and deep, they are particularly useful for identifying strong gravitational lens candidates. Potential strong gravitational lens candidate systems were initially identified based on a color and magnitude selection in the DES object catalogs or because the system is at the location of a previously identified galaxy cluster. Cutout images of potential candidates were then visually scanned using an object viewer and numerically ranked according to whether or not we judged them to be likely strong gravitational lens systems. Having scanned nearly 400,000 cutouts, we present 374 candidate strong lens systems, of which 348 are identified for the first time. We provide the R.A. and decl., the magnitudes and photometric properties of the lens and source objects, and the distance (radius) of the source(s) from the lens center for each system.

We present the discovery and preliminary characterization of a gravitationally lensed quasar with a source redshift $\textit{zs}$ = 2.74 and image separation of 2.9 arcsec lensed by a foreground $\textit{zl}$ = 0.40 elliptical galaxy. Since optical observations of gravitationally lensed quasars show the lens system as a superposition of multiple point sources and a foreground lensing galaxy, we have developed a morphology-independent multi-wavelength approach to the photometric selection of lensed quasar candidates based on Gaussian Mixture Models (GMM) supervised machine learning. Using this technique and $\textit{gi}$ multicolour photometric observations from the Dark Energy Survey (DES), near-IR $\textit{JK}$ photometry from the VISTA Hemisphere Survey (VHS) and WISE mid-IR photometry, we have identified a candidate system with two catalogue components with $\textit{iAB}$ = 18.61 and $\textit{iAB}$ = 20.44 comprising an elliptical galaxy and two blue point sources. Spectroscopic follow-up with NTT and the use of an archival AAT spectrum show that the point sources can be identified as a lensed quasar with an emission line redshift of $\textit{z}$ = 2.739 ± 0.003 and a foreground early-type galaxy with $\textit{z}$ = 0.400 ± 0.002. We model the system as a single isothermal ellipsoid and find the Einstein radius θE ∼ 1.47 arcsec, enclosed mass $\textit{M}$enc ∼ 4 × 10$^{11}$$\textit{M}$⊙ and a time delay of ∼52 d. The relatively wide separation, month scale time delay duration and high redshift make this an ideal system for constraining the expansion rate beyond a redshift of 1., FO is supported jointly by CAPES (the Science without Borders programme) and the Cambridge Commonwealth Trust. RGM, CAL, MWA, MB, SLR acknowledge the support of UK Science and Technology Research Council (STFC). AJC acknowledges the support of a Raymond and Beverly Sackler visiting fellowship at the Institute of Astronomy. For further information regarding funding please visit the publisher's website.

osmic voids are usually identified in spectroscopic galaxy surveys, where 3D information about the large-scale structure of the Universe is available. Although an increasing amount of photometric data is being produced, its potential for void studies is limited since photometric redshifts induce line-of-sight position errors of ≥50 Mpc h−1 which can render many voids undetectable. We present a new void finder designed for photometric surveys, validate it using simulations, and apply it to the high-quality photo-z redMaGiC galaxy sample of the DES Science Verification data. The algorithm works by projecting galaxies into 2D slices and finding voids in the smoothed 2D galaxy density field of the slice. Fixing the line-of-sight size of the slices to be at least twice the photo-z scatter, the number of voids found in simulated spectroscopic and photometric galaxy catalogues is within 20 per cent for all transverse void sizes, and indistinguishable for the largest voids (Rv ≥ 70 Mpc h−1). The positions, radii, and projected galaxy profiles of photometric voids also accurately match the spectroscopic void sample. Applying the algorithm to the DES-SV data in the redshift range 0.2 < z < 0.8, we identify 87 voids with comoving radii spanning the range 18–120 Mpc h−1, and carry out a stacked weak lensing measurement. With a significance of 4.4σ, the lensing measurement confirms that the voids are truly underdense in the matter field and hence not a product of Poisson noise, tracer density effects or systematics in the data. It also demonstrates, for the first time in real data, the viability of void lensing studies in photometric surveys., Monthly Notices of the Royal Astronomical Society, 465 (1), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

We characterize the ability of the Dark Energy Camera (DECam) to perform relative astrometry across its 500~Mpix, 3 deg^2 science field of view, and across 4 years of operation. This is done using internal comparisons of ~4x10^7 measurements of high-S/N stellar images obtained in repeat visits to fields of moderate stellar density, with the telescope dithered to move the sources around the array. An empirical astrometric model includes terms for: optical distortions; stray electric fields in the CCD detectors; chromatic terms in the instrumental and atmospheric optics; shifts in CCD relative positions of up to ~10 um when the DECam temperature cycles; and low-order distortions to each exposure from changes in atmospheric refraction and telescope alignment. Errors in this astrometric model are dominated by stochastic variations with typical amplitudes of 10-30 mas (in a 30 s exposure) and 5-10 arcmin coherence length, plausibly attributed to Kolmogorov-spectrum atmospheric turbulence. The size of these atmospheric distortions is not closely related to the seeing. Given an astrometric reference catalog at density ~0.7 arcmin^{-2}, e.g. from Gaia, the typical atmospheric distortions can be interpolated to 7 mas RMS accuracy (for 30 s exposures) with 1 arcmin coherence length for residual errors. Remaining detectable error contributors are 2-4 mas RMS from unmodelled stray electric fields in the devices, and another 2-4 mas RMS from focal plane shifts between camera thermal cycles. Thus the astrometric solution for a single DECam exposure is accurate to 3-6 mas (0.02 pixels, or 300 nm) on the focal plane, plus the stochastic atmospheric distortion., Comment: Submitted to PASP

Spatially-varying depth and characteristics of observing conditions, such as seeing, airmass, or sky background, are major sources of systematic uncertainties in modern galaxy survey analyses, in particular in deep multi-epoch surveys. We present a framework to extract and project these sources of systematics onto the sky, and apply it to the Dark Energy Survey (DES) to map the observing conditions of the Science Verification (SV) data. The resulting distributions and maps of sources of systematics are used in several analyses of DES SV to perform detailed null tests with the data, and also to incorporate systematics in survey simulations. We illustrate the complementarity of these two approaches by comparing the SV data with the BCC-UFig, a synthetic sky catalogue generated by forward-modelling of the DES SV images. We analyse the BCC-UFig simulation to construct galaxy samples mimicking those used in SV galaxy clustering studies. We show that the spatially-varying survey depth imprinted in the observed galaxy densities and the redshift distributions of the SV data are successfully reproduced by the simulation and well-captured by the maps of observing conditions. The combined use of the maps, the SV data and the BCC-UFig simulation allows us to quantify the impact of spatial systematics on $N(z)$, the redshift distributions inferred using photometric redshifts. We conclude that spatial systematics in the SV data are mainly due to seeing fluctuations and are under control in current clustering and weak lensing analyses. The framework presented here is relevant to all multi-epoch surveys, and will be essential for exploiting future surveys such as the Large Synoptic Survey Telescope (LSST), which will require detailed null-tests and realistic end-to-end image simulations to correctly interpret the deep, high-cadence observations of the sky., 13 pages, 12 figures

We† provide an overview of the Model Based Systems Engineering (MBSE) language, tool, and methodology being used in our development of the Operational Plan for Large Synoptic Survey Telescope (LSST) operations. LSST’s Systems Engineering (SE) team is using a model-based approach to operational plan development to: 1) capture the topdown stakeholders’ needs and functional allocations defining the scope, required tasks, and personnel needed for operations, and 2) capture the bottom-up operations and maintenance activities required to conduct the LSST survey across its distributed operations sites for the full ten year survey duration. To accomplish these complimentary goals and ensure that they result in self-consistent results, we have developed a holistic approach using the Sparx Enterprise Architect modeling tool and Systems Modeling Language (SysML). This approach utilizes SysML Use Cases, Actors, associated relationships, and Activity Diagrams to document and refine all of the major operations and maintenance activities that will be required to successfully operate the observatory and meet stakeholder expectations. We have developed several customized extensions of the SysML language including the creation of a custom stereotyped Use Case element with unique tagged values, as well as unique association connectors and Actor stereotypes. We demonstrate this customized MBSE methodology enables us to define: 1) the rolls each human Actor must take on to successfully carry out the activities associated with the Use Cases; 2) the skills each Actor must possess; 3) the functional allocation of all required stakeholder activities and Use Cases to organizational entities tasked with carrying them out; and 4) the organization structure required to successfully execute the operational survey. Our approach allows for continual refinement utilizing the systems engineering spiral method to expose finer levels of detail as necessary. For example, the bottom-up, Use Case-driven approach will be deployed in the future to develop the detailed work procedures required to successfully execute each operational activity.

We present an overview of the Integration and Verification Testing activities of the Large Synoptic Survey Telescope (LSST) Camera at the SLAC National Accelerator Lab (SLAC). The LSST Camera, the sole instrument for LSST and under construction now, is comprised of a 3.2 Giga-pixel imager and a three element corrector with a 3.5 degree diameter field of view. LSST Camera Integration and Test will be taking place over the next four years, with final delivery to the LSST observatory anticipated in early 2020. We outline the planning for Integration and Test, describe some of the key verification hardware systems being developed, and identify some of the more complicated assembly/integration activities. Specific details of integration and verification hardware systems will be discussed, highlighting some of the technical challenges anticipated.

Astrophysical Journal Letters 826.2 (2016): L29 reproduced by permission of the AAS, We report the results of a Dark Energy Camera optical follow-up of the gravitational-wave (GW) event GW151226, discovered by the Advanced Laser Interferometer Gravitational-wave Observatory detectors. Our observations cover 28.8 deg2 of the localization region in the i and z bands (containing 3% of the BAYESTAR localization probability), starting 10 hr after the event was announced and spanning four epochs at 2-24 days after the GW detection. We achieve 5σ point-source limiting magnitudes of i ≈ 21.7 and z ≈ 21.5, with a scatter of 0.4 mag, in our difference images. Given the two-day delay, we search this area for a rapidly declining optical counterpart with ≥ 3σ significance steady decline between the first and final observations. We recover four sources that pass our selection criteria, of which three are cataloged active galactic nuclei. The fourth source is offset by 5.8 arcsec from the center of a galaxy at a distance of 187 Mpc, exhibits a rapid decline by 0.5 mag over 4 days, and has a red color of i - z ≈ 0.3 mag. These properties could satisfy a set of cuts designed to identify kilonovae. However, this source was detected several times, starting 94 days prior to GW151226, in the Pan-STARRS Survey for Transients (dubbed as PS15cdi) and is therefore unrelated to the GW event. Given its long-term behavior, PS15cdi is likely a Type IIP supernova that transitioned out of its plateau phase during our observations, mimicking a kilonova-like behavior. We comment on the implications of this detection for contamination in future optical follow-up observations, P.S.C. is grateful for support provided by the NSF through the Graduate Research Fellowship Program, grant DGE1144152. R. J.F. gratefully acknowledges support from NSF grant AST– 1518052 and the Alfred P. Sloan Foundation. D.E.H. was supported by NSF CAREER grant PHY-1151836. He also acknowledges support from the Kavli Institute for Cosmological Physics at the University of Chicago through NSF grant PHY- 1125897 as well as an endowment from the Kavli Foundation. The DES Data Management System is supported by the NSF under grant number AST-1138766. The DES participants from Spanish institutions are partially supported by MINECO under grants AYA2012-39559, ESP2013-48274, FPA2013-47986, and Centro de Excelencia Severo Ochoa SEV-2012-0234. Research leading to these results has received funding from the ERC under the EU’s 7th Framework Programme including grants ERC 240672, 291329,and 306478

We present measurements of weak gravitational lensing cosmic shear two-point statistics using Dark Energy Survey Science Verification data. We demonstrate that our results are robust to the choice of shear measurement pipeline, either ngmix or im3shape, and robust to the choice of two-point statistic, including both real and Fourier-space statistics. Our results pass a suite of null tests including tests for B-mode contamination and direct tests for any dependence of the two-point functions on a set of 16 observing conditions and galaxy properties, such as seeing, airmass, galaxy color, galaxy magnitude, etc. We furthermore use a large suite of simulations to compute the covariance matrix of the cosmic shear measurements and assign statistical significance to our null tests. We find that our covariance matrix is consistent with the halo model prediction, indicating that it has the appropriate level of halo sample variance. We compare the same jackknife procedure applied to the data and the simulations in order to search for additional sources of noise not captured by the simulations. We find no statistically significant extra sources of noise in the data. The overall detection significance with tomography for our highest source density catalog is 9.7 sigma . Cosmological constraints from the measurements in this work are presented in a companion paper [DES et al., Phys. Rev. D 94, 022001 (2016).].

We report on four radio-detected cosmic-ray (CR) or CR-like events observed with the Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload. Two of the four were previously identified as stratospheric CR air showers during the ANITA-I flight. A third stratospheric CR was detected during the ANITA-II flight. Here we report on characteristics these three unusual CR events, which develop nearly horizontally, 20-30~km above the surface of the Earth. In addition, we report on a fourth steeply upward-pointing ANITA-I CR-like radio event which has characteristics consistent with a primary that emerged from the surface of the ice. This suggests a possible $\tau$-lepton decay as the origin of this event, but such an interpretation would require significant suppression of the Standard Model ${\tau}$-neutrino cross section., Comment: 5pp,4 figures, referees' comments addressed, this version accepted to Phys. Rev. Letters. Supplemental PDF material available; see source files

We present weak lensing shear catalogues for 139 square degrees of data taken during the Science Verification (SV) time for the new Dark Energy Camera (DECam) being used for the Dark Energy Survey (DES). We describe our object selection, point spread function estimation and shear measurement procedures using two independent shear pipelines, IM3SHAPE and NGMIX, which produce catalogues of 2.12 million and 3.44 million galaxies respectively. We detail a set of null tests for the shear measurements and find that they pass the requirements for systematic errors at the level necessary for weak lensing science applications using the SV data. We also discuss some of the planned algorithmic improvements that will be necessary to produce sufficiently accurate shear catalogues for the full 5-year DES, which is expected to cover 5000 square degrees., Accepted by MNRAS; 38 pages, 29 figures; v3: minor edits based on referee's comments, switched to mnras style, added figure 8, updated info about released catalogs

We present a measurement of galaxy-galaxy lensing around a magnitude-limited ($i_{AB} < 22.5$) sample of galaxies from the Dark Energy Survey Science Verification (DES-SV) data. We split these lenses into three photometric-redshift bins from 0.2 to 0.8, and determine the product of the galaxy bias $b$ and cross-correlation coefficient between the galaxy and dark matter overdensity fields $r$ in each bin, using scales above 4 Mpc/$h$ comoving, where we find the linear bias model to be valid given our current uncertainties. We compare our galaxy bias results from galaxy-galaxy lensing with those obtained from galaxy clustering (Crocce et al. 2016) and CMB lensing (Giannantonio et al. 2016) for the same sample of galaxies, and find our measurements to be in good agreement with those in Crocce et al. (2016), while, in the lowest redshift bin ($z\sim0.3$), they show some tension with the findings in Giannantonio et al. (2016). We measure $b\cdot r$ to be $0.87\pm 0.11$, $1.12 \pm 0.16$ and $1.24\pm 0.23$, respectively for the three redshift bins of width $\Delta z = 0.2$ in the range $0.2, Comment: 18 pages, 8 figures, matches the version accepted by MNRAS

We present cosmological constraints from the Dark Energy Survey (DES) using a combined analysis of angular clustering of red galaxies and their cross-correlation with weak gravitational lensing of background galaxies. We use a 139 square degree contiguous patch of DES data from the Science Verification (SV) period of observations. Using large scale measurements, we constrain the matter density of the Universe as Omega_m = 0.31 +/- 0.09 and the clustering amplitude of the matter power spectrum as sigma_8 = 0.74 +/- 0.13 after marginalizing over seven nuisance parameters and three additional cosmological parameters. This translates into S_8 = sigma_8(Omega_m/0.3)^{0.16} = 0.74 +/- 0.12 for our fiducial lens redshift bin at 0.35, Comment: 18 pages, 13 figures, submitted to MNRAS

We describe updates to the \redmapper{} algorithm, a photometric red-sequence cluster finder specifically designed for large photometric surveys. The updated algorithm is applied to $150\,\mathrm{deg}^2$ of Science Verification (SV) data from the Dark Energy Survey (DES), and to the Sloan Digital Sky Survey (SDSS) DR8 photometric data set. The DES SV catalog is locally volume limited, and contains 786 clusters with richness $\lambda>20$ (roughly equivalent to $M_{\rm{500c}}\gtrsim10^{14}\,h_{70}^{-1}\,M_{\odot}$) and $0.2, Comment: 21 pages, accepted to ApJS (The Astrophysical Journal Supplement Series, Volume 224, Issue 1, article id. 1, pp. (2016))

We have searched for correlations between the pointing directions of ultrahigh energy cosmic rays observed by the High Resolution Fly's Eye experiment and Active Galactic Nuclei (AGN) visible from its northern hemisphere location. No correlations, other than random correlations, have been found. We report our results using search parameters prescribed by the Pierre Auger collaboration. Using these parameters, the Auger collaboration concludes that a positive correlation exists for sources visible to their southern hemisphere location. We also describe results using two methods for determining the chance probability of correlations: one in which a hypothesis is formed from scanning one half of the data and tested on the second half, and another which involves a scan over the entire data set. The most significant correlation found occurred with a chance probability of 24%., 13 pages, 1 table, 5 figures

A key assumption in the reconstruction of extensive air showers using the air fluorescence technique is that fluorescence is proportional to energy deposition at all depths in the shower. This ansatz, along with the supposition that particle distribution and energy loss can be well modeled by modern shower simulation software, must be thoroughly verified. We report here the results of the first direct measurement of air fluorescence yield as a function of shower depth, as performed in the thick-target phase of the FLASH (FLuorescence in Air from SHowers) experimental program at the SLAC Final-Focus Test Beam facility. We compare observed fluorescence light yields as a function of shower depth to concurrently measured charged particle yields, to the energy deposition predictions of the EGS and GEANT software packages, and to empirical energy-deposition models. We also examine the extent to which the relative yield versus shower depth is independent of wavelength within the fluorescence spectrum. We find the proportionality hypothesis to be well supported by the data, validating the use of fluorescence profiles in the study of ultra high energy cosmic rays.

The fluorescence yield in air is reported for wavelength and pressure ranges of interest to ultra-high energy cosmic ray detectors. A 28.5 GeV electron beam was used to excite the fluorescence. Central to the approach was the system calibration, using Rayleigh scattering of a nitrogen laser beam. In atmospheric pressure dry air, at 304 K, the yield is 20.8 ± 1.6 photons per MeV.

Radiowave detection of the Cherenkov radiation produced by neutrino-ice collisions requires an understanding of the radiofrequency (RF) response of cold polar ice. We herein report on a series of radioglaciological measurements performed approximately 10 km north of Taylor Dome Station, Antarctica from December 6, 2006–December 16, 2006. Using RF signals broadcast from: (a) an englacial discone, submerged to a depth of 100 m and broadcasting to a surface dual-polarization horn receiver, and (b) a dual-polarization horn antenna on the surface transmitting signals which reflect off the underlying bed and back up to the surface receiver, we have made time-domain estimates of both the real (index-of-refraction “ n ”) and imaginary (attenuation length “ L atten ”) components of the complex ice dielectric constant. We have also measured the uniformity of ice response along two orthogonal axes in the horizontal plane. We observe an apparent wavespeed asymmetry of order 0.1% between two orthogonal linear polarizations projected into the horizontal plane, consistent with some previous measurements, but somewhat lower than others.

We report the results of a search for point-like deviations from isotropy in the arrival directions of ultra-high energy cosmic rays in the northern hemisphere. In the monocular data set collected by the High-Resolution Fly's Eye, consisting of 1,525 events with energy exceeding 10^18.5 eV, we find no evidence for point-like excesses. We place 90% c.l. upper limits less than or equal to 0.8 cosmic rays/km^2yr on the flux from such sources as a function of position in the sky., Comment: 24 pages, 16 figures

We have studied several sources of systematic uncertainty in calculating the aperture of the High Resolution Fly's Eye experiment (HiRes) in monocular mode, primarily as they affect the HiRes-II site. The energy dependent aperture is determined with detailed Monte Carlo simulations of the air showers and the detector response. We have studied the effects of changes to the input energy spectrum and composition used in the simulation. A realistic shape of the input spectrum is used in our analysis in order to avoid biases in the aperture estimate due to the limited detector resolution. We have examined the effect of exchanging our input spectrum with a simple E^{-3} power law in the "ankle" region. Uncertainties in the input composition are shown to be significant for energies below about 10^{18} eV for data from the HiRes-II detector. Another source of uncertainties is the choice of the hadronic interaction model in the air shower generator. We compare the aperture estimate for two different models: QGSJet01 and SIBYLL 2.1. We also describe the implications of employing an atmospheric database with hourly measurements of the aerosol component, instead of using an average as has been used in our previously published measurements of the monocular spectra., Comment: 27 pages, 15 figures, revision