Engineering topics

Price, P. A.

Publications and source records attributed to Price, P. A..

5 records

DOE OSTI2020

The LSST DESC data challenge 1: generation and analysis of synthetic images for next-generation surveys

Data Challenge 1 (DC1) is the first synthetic data set produced by the Rubin Observatory Legacy Survey of Space and Time (LSST) Dark Energy Science Collaboration (DESC). DC1 is designed to develop and validate data reduction and analysis and to study the impact of systematic effects that will affect the LSST data set. DC1 is comprised of r -band observations of 40 deg 2 to 10 yr LSST depth. In this paper, we present each stage of the simulation and analysis process: (a) generation, by synthesizing sources from cosmological N -body simulations in individual sensor-visit images with different observing conditions; (b) reduction using a development version of the LSST Science Pipelines; and (c) matching to the input cosmological catalogue for validation and testing. We verify that testable LSST requirements pass within the fidelity of DC1. We establish a selection procedure that produces a sufficiently clean extragalactic sample for clustering analyses and we discuss residual sample contamination, including contributions from inefficiency in star–galaxy separation and imperfect deblending. We compute the galaxy power spectrum on the simulated field and conclude that: (i) survey properties have an impact of 50 per cent of the statistical uncertainty for the scales and models used in DC1; (ii) a selection to eliminate artefacts in the catalogues is necessary to avoid biases in the measured clustering; and (iii) the presence of bright objects has a significant impact (2σ–6σ) in the estimated power spectra at small scales (ℓ > 1200), highlighting the impact of blending in studies at small angular scales in LSST.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS2013

The Galex Time Domain Survey. I. Selection And Classification of Over a Thousand Ultraviolet Variable Sources

We present the selection and classification of over a thousand ultraviolet (UV) variable sources discovered in approximately 40 deg(exp 2) of GALEX Time Domain Survey (TDS) NUV images observed with a cadence of 2 days and a baseline of observations of approximately 3 years. The GALEX TDS fields were designed to be in spatial and temporal coordination with the Pan-STARRS1 Medium Deep Survey, which provides deep optical imaging and simultaneous optical transient detections via image differencing. We characterize the GALEX photometric errors empirically as a function of mean magnitude, and select sources that vary at the 5 sigma level in at least one epoch. We measure the statistical properties of the UV variability, including the structure function on timescales of days and years. We report classifications for the GALEX TDS sample using a combination of optical host colors and morphology, UV light curve characteristics, and matches to archival X-ray, and spectroscopy catalogs. We classify 62% of the sources as active galaxies (358 quasars and 305 active galactic nuclei), and 10% as variable stars (including 37 RR Lyrae, 53 M dwarf flare stars, and 2 cataclysmic variables). We detect a large-amplitude tail in the UV variability distribution for M-dwarf flare stars and RR Lyrae, reaching up to absolute value(Δm) = 4.6 mag and 2.9 mag, respectively. The mean amplitude of the structure function for quasars on year timescales is five times larger than observed at optical wavelengths. The remaining unclassified sources include UV-bright extragalactic transients, two of which have been spectroscopically confirmed to be a young core-collapse supernova and a flare from the tidal disruption of a star by dormant supermassive black hole. We calculate a surface density for variable sources in the UV with NUV less than 23 mag and absolute value(Δm) greater than 0.2 mag of approximately 8.0, 7.7, and 1.8 deg(exp −2) for quasars, active galactic nuclei, and RR Lyrae stars, respectively. We also calculate a surface density rate in the UV for transient sources, using the effective survey time at the cadence appropriate to each class, of approximately 15 and 52 deg(exp −2 yr−1 for M dwarfs and extragalactic transients, respectively.

Gezari, S.↗

NASA NTRS2007

GRB070610: A Curious Galactic Transient

GRB 070610 is a typical high-energy event with a duration of 5s.Yet within the burst localization we detect a highly unusual X-ray and optical transient, SwiftJ195509.6+261406. We see high amplitude X-ray and optical variability on very short time scares even at late times. Using near-infrared imaging assisted by a laser guide star and adaptive optics, we identified the counterpart of SwiftJl95509.6+261406. Late-time optical and near-infrared imaging constrain the spectral type of the counterpart to be fainter than a K-dwarf assuming it is of Galactic origin. It is possible that GRB 070610 and Swift J195509.6+261406 are unrelated sources. However, the absence of a typical X-ray afterglow from GRB 070610 in conjunction with the spatial and temporal coincidence of the two motivate us to suggest that the sources are related. The closest (imperfect) analog to Swift J195509.6+261406 is V4641 Sgr, an unusual black hole binary. We suggest that Swift J195509.6+261406 along with V4641 Sgr define a sub-class of stellar black hole binaries -- the fast X-ray novae. We further suggest that fast X-ray novae are associated with bursts of gamma-rays. If so, GRB 070610 defines a new class of celestial gamma-ray bursts and these bursts dominate the long-duration GRB demographics

Kasliwal, M. M.↗

NASA NTRS2007

GRB 060505: A Possible Short-Duration Gamma-Ray Burst in a Star Forming Region at Redshift of 0.09

On May 5, 2006 a four-second duration, low-energy, approximately 10(exp 59) erg, Gamma-Ray Burst (GRB) was observed, spatially associated with a z=0.0894 galaxy. Here, we report the discovery of the GRB optical afterglow and observations of its environment using gemini-south, Hubble Space Telescope (HST), Chandra, Swift and the Very Large Array. The optical afterglow of this GRB is spatially associated with a prominent star forming region in the Sc-type galaxy 2dFGRS S173Z112. Its proximity to a star forming region suggests that the progenitor delay time, from birth to explosion, is smaller than about 10 Myr. Our HST deep imaging rules out the presence of a supernova brighter than an absolute magnitude of about -11 (or -126 in case of 'maximal' extinction) at about two weeks after the burst, and limits the ejected mass of radioactive Nickel 56 to be less than about 2x10(exp -4) solar mass (assuming no extinction). Although it was suggested that GRB 060505 may belong to a new class of long-duration GRBs with no supernova, we argue that the simplest interpretation is that the physical mechanism for this burst is the same as for short-duration GRBs.

Ofek, E. O.↗

NASA NTRS2007

A Spectacular Radio Flare from XRF 050416a at 40 Days and Implications for the Nature of X-Ray Flashes

We present detailed optical, near-infrared, and radio observations of the X-ray flash 050416a obtained with Palomar and Siding Springs Observatories as well as HST and the VLA, placing this event among the best-studied X-ray flashes to date. In addition, we present an optical spectrum from Keck LRIS from which we measure the redshift of the burst, Z=0.6528. At this redshift the isotropic-equivalent prompt energy release was about 10(exp 51) erg, and using a standard afterglow synchrotron model we find that the blastwave kinetic energy is a factor of 10 larger, E-K,iso approximately equals 10 (exp 52) erg. The lack of an observed jet break to t - 20 days indicates that the opening angle is larger than 7 deg and the total beaming-corrected relativistic energy is larger than 10 exp (50) erg. We further show that the burst produced a strong radio flare at t is similar to 40 days accompanied by an observed flattening in the X-ray band which we attribute to an abrupt circumburst density jump or an episode of energy injection (either from a refreshed shock or off-axis ejecta). Late-time observations with HST show evidence for an associated supernova with peak optical luminosity roughly comparable to that of SN 1998bw. Next, we show that the host galaxy of XRF 050416a is actively forming stars at a rate of at least 2 M-solar per year with a luminosity of L-B is similar to 0.5L* and metallicity of Z is similar to 0.2-0.8 Z-solar. Finally, we discuss the nature of XRF 050416a in the context of short-hard gamma-ray bursts and under the framework of off-axis and dirty fireball models for X-ray flashes.

Soderberg, A. M.↗