arXiv subjects

Juan Estrada

Publications and source records attributed to Juan Estrada.

86 records · Page 5Linked to original sources

arXiv2015

Discovery of two gravitationally lensed quasars in the Dark Energy Survey

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.

astro-ph.GA↗

arXiv2014

Charge Coupled Devices for detection of coherent neutrino-nucleus scattering

This article details the potential for using Charge Coupled Devices (CCD) to detect low-energy neutrinos through their coherent scattering with nuclei. The detection of neutrinos through this standard model process has not been accessible because of the small energy deposited in such interactions with the detector nuclei. Typical particle detectors have thresholds of a few keV, and most of the energy deposition expected from coherent scattering is well below this level. The devices we discuss can be operated at a threshold of approximately 30 eV, making them ideal for observing this signal. For example, the number of coherent scattering events expected on a 52 gram CCD array located next to a power nuclear reactor is estimated as approximately 626 events/year. The results of our study show that detection at a confidence level of 99% can be reached within three months for this kind of detector array.

physics.ins-det↗

arXiv2014

Development of a novel neutron detection technique by using a boron layer coating a Charge Coupled Device

This article describes the design features and the first test measurements obtained during the installation of a novel high resolution 2D neutron detection technique. The technique proposed in this work consists of a boron layer (enriched in ${^{10}}$B) placed on a scientific Charge Coupled Device (CCD). After the nuclear reaction ${^{10}}$B(n,$α$)${^{7}}$Li, the CCD detects the emitted charge particles thus obtaining information on the neutron absorption position. The above mentioned ionizing particles, with energies in the range 0.5-5.5 MeV, produce a plasma effect in the CCD which is recorded as a circular spot. This characteristic circular shape, as well as the relationship observed between the spot diameter and the charge collected, is used for the event recognition, allowing the discrimination of undesirable gamma events. We present the first results recently obtained with this technique, which has the potential to perform neutron tomography investigations with a spatial resolution better than that previously achieved. Numerical simulations indicate that the spatial resolution of this technique will be about 15 $μ$m, and the intrinsic detection efficiency for thermal neutrons will be about 3 %. We compare the proposed technique with other neutron detection techniques and analyze its advantages and disadvantages.

physics.ins-det↗

arXiv2014

DAMIC at SNOLAB

We introduce the fully-depleted charge-coupled device (CCD) as a particle detector. We demonstrate its low energy threshold operation, capable of detecting ionizing energy depositions in a single pixel down to 50 eVee. We present results of energy calibrations from 0.3 keVee to 60 keVee, showing that the CCD is a fully active detector with uniform energy response throughout the silicon target, good resolution (Fano ~0.16), and remarkable linear response to electron energy depositions. We show the capability of the CCD to localize the depth of particle interactions within the silicon target. We discuss the mode of operation and unique imaging capabilities of the CCD, and how they may be exploited to characterize and suppress backgrounds. We present the first results from the deployment of 250 um thick CCDs in SNOLAB, a prototype for the upcoming DAMIC100. DAMIC100 will have a target mass of 0.1 kg and should be able to directly test the CDMS-Si signal within a year of operation.

physics.ins-det↗

arXiv2013

The SOAR Gravitational Arc Survey - I: Survey overview and photometric catalogs

We present the first results of the SOAR (Southern Astrophysical Research) Gravitational Arc Survey (SOGRAS). The survey imaged 47 clusters in two redshift intervals centered at $z=0.27$ and $z=0.55$, targeting the richest clusters in each interval. Images were obtained in the $g'$, $r'$ and $i'$ bands using the SOAR Optical Imager (SOI), with a median seeing of 0.83, 0.76 and 0.71 arcsec, respectively, in these filters. Most of the survey clusters are located within the Sloan Digital Sky Survey (SDSS) Stripe 82 region and all of them are in the SDSS footprint. Photometric calibration was therefore performed using SDSS stars located in our SOI fields. We reached for galaxies in all fields the detection limits of $g \sim 23.5$, $r \sim 23$ and $i \sim 22.5$ for a signal-to-noise ratio (S/N) = 3. As a by-product of the image processing, we generated a source catalogue with 19760 entries, the vast majority of which are galaxies, where we list their positions, magnitudes and shape parameters. We compared our galaxy shape measurements to those of local galaxies and concluded that they were not strongly affected by seeing. From the catalogue data, we are able to identify a red sequence of galaxies in most clusters in the lower $z$ range. We found 16 gravitational arc candidates around 8 clusters in our sample. They tend to be bluer than the central galaxies in the lensing cluster. A preliminary analysis indicates that $\sim 10%$ of the clusters have arcs around them, with a possible indication of a larger efficiency associated to the high-$z$ systems when compared to the low-$z$ ones. Deeper follow-up images with Gemini strengthen the case for the strong lensing nature of the candidates found in this survey.

astro-ph.CO↗

arXiv2011

Deep sub electron noise readout in CCD systems using digital filtering techniques

Scientific CCDs designed in thick high resistivity silicon (Si) are excellent detectors for astronomy, high energy and nuclear physics, and instrumentation. Many applications can benefit from CCDs ultra low noise readout systems. The present work shows how sub electron noise CCD images can be achieved using digital signal processing techniques. These techniques allow readout bandwidths of up to 10 K pixels per second and keep the full CCD spatial resolution and signal dynamic range.

astro-ph.IM↗

arXiv2011

Achieving sub-electron readout noise in Skipper CCDs

The readout noise for Charge-Coupled Devices (CCDs) has been the main limitation when using these detectors for measuring small amplitude signals. A readout system for a new scientific, low noise CCD is presented in this paper. The Skipper CCD architecture, and its advantages for low noise applications are discussed. A technique for obtaining sub-electron readout noise levels is presented, and its noise and signal characteristics are derived. We demonstrate a very low readout noise of $0.2e^{-}$ RMS. Also, we show the results using the detector in a low-energy X-ray detection experiment.

astro-ph.IM↗

arXiv2011

Plasma effect in Silicon Charge Coupled Devices (CCDs)

Plasma effect is observed in CCDs exposed to heavy ionizing alpha-particles with energies in the range 0.5 - 5.5 MeV. The results obtained for the size of the charge clusters reconstructed on the CCD pixels agrees with previous measurements in the high energy region (>3.5 MeV). The measurements were extended to lower energies using alpha-particles produced by (n,alpha) reactions of neutrons in a Boron-10 target. The effective linear charge density for the plasma column is measured as a function of energy. The results demonstrate the potential for high position resolution in the reconstruction of alpha particles, which opens an interesting possibility for using these detectors in neutron imaging applications.

physics.ins-det↗

arXiv2010

Measuring the flatness of focal plane for very large mosaic CCD camera

Large mosaic multiCCD camera is the key instrument for modern digital sky survey. DECam is an extremely red sensitive 520 Megapixel camera designed for the incoming Dark Energy Survey (DES). It is consist of sixty two 4k$\times$2k and twelve 2k x 2k 250-micron thick fully-depleted CCDs, with a focal plane of 44 cm in diameter and a field of view of 2.2 square degree. It will be attached to the Blanco 4-meter telescope at CTIO. The DES will cover 5000 square-degrees of the southern galactic cap in 5 color bands (g, r, i, z, Y) in 5 years starting from 2011. To achieve the science goal of constraining the Dark Energy evolution, stringent requirements are laid down for the design of DECam. Among them, the flatness of the focal plane needs to be controlled within a 60-micron envelope in order to achieve the specified PSF variation limit. It is very challenging to measure the flatness of the focal plane to such precision when it is placed in a high vacuum dewar at 173 K. We developed two image based techniques to measure the flatness of the focal plane. By imaging a regular grid of dots on the focal plane, the CCD offset along the optical axis is converted to the variation the grid spacings at different positions on the focal plane. After extracting the patterns and comparing the change in spacings, we can measure the flatness to high precision. In method 1, the regular dots are kept in high sub micron precision and cover the whole focal plane. In method 2, no high precision for the grid is required. Instead, we use a precise XY stage moves the pattern across the whole focal plane and comparing the variations of the spacing when it is imaged by different CCDs. Simulation and real measurements show that the two methods work very well for our purpose, and are in good agreement with the direct optical measurements.

astro-ph.IM↗

arXiv2009

Direct Dark Matter Search using CCDs

There is currently vast evidence for Dark Matter (DM) from astronomical observations. However, in spite of tremendous efforts by large experimental groups, there is no confirmed direct detection of the dark matter in our galaxy. Recent experimental results and theoretical developments suggest the possibility of a DM particle with mass below 10 GeV, such a particle would escape most of the direct searches due to the large thresholds for the detection of nuclear recoils typically used. In this work we study the possibility of a new Dark Matter search with an unprecedented low threshold for the detection of nuclear recoils using high-resistivity CCD detectors (hr-CCD). Due to their extremely low readout noise and the relatively large active mass, these detectors present a unique opportunity in this field.

astro-ph.IM↗

arXiv2008

The Correlation Function of Optically Selected Galaxy Clusters in the Sloan Digital Sky Survey

We measure the two-point spatial correlation function for clusters selected from the photometric MaxBCG galaxy cluster catalog for the Sloan Digital Sky Survey (SDSS). We evaluate the correlation function for several cluster samples using different cuts in cluster richness. Fitting the results to power-laws, $ξ_{cc}(r) = (r/R_0)^{-γ}$, the estimated correlation length $R_0$ as a function of richness is broadly consistent with previous cluster observations and with expectations from N-body simulations. We study how the linear bias parameter scales with richness and compare our results to theoretical predictions. Since these measurements extend to very large scales, we also compare them to models that include the baryon acoustic oscillation feature and that account for the smoothing effects induced by errors in the cluster photometric redshift estimates. For the largest cluster sample, corresponding to a richness threshold of $\Ng\ge 10$, we find only weak evidence, of about $1.4-1.7σ$ significance, for the baryonic acoustic oscillation signature in the cluster correlation function.

astro-ph↗

arXiv2005

The Fall 2004 SDSS Supernova Survey

In preparation for the Supernova Survey of the Sloan Digital Sky Survey (SDSS) II, a proposed 3-year extension to the SDSS, we have conducted an early engineering and science run during the fall of 2004, which consisted of approximately 20 scheduled nights of repeated imaging of half of the southern equatorial stripe. Transient supernova-like events were detected in near real-time and photometric measurements were made in the five SDSS filter bandpasses with a cadence of ~2 days. Candidate type Ia supernovae (SNe) were pre-selected based on their colors, light curve shape, and the properties of the host galaxy. Follow-up spectroscopic observations were performed with the Astrophysical Research Consortium 3.5m telescope and the 9.2m Hobby-Eberly Telescope to confirm their types and measure the redshifts. The 2004 campaign resulted in 22 spectroscopically confirmed SNe, which includes 16 type Ia, 5 type II, and 1 type Ib/c. These SN Ia will help fill in the sparsely sampled redshift interval of z = 0.05 - 0.35, the so-called 'redshift desert', in the Hubble diagram. Detailed investigation of the spectral properties of these moderate-redshift SNe Ia will also provide a bridge between local SNe and high-redshift objects, and will help us understand the systematics for future cosmological applications that require high photometric precision. Finally, the large survey volume also provides the opportunity to select unusual supernovae for spectroscopic study that are poorly sampled in other surveys. We report on some of the early results from this program and discuss potential future applications.

astro-ph↗

arXiv2003

Optimal use of Information for Measuring $M_t$ in Lepton+jets $t\bar{t}$ Events

We present a novel approach that is being developed at DZero for extracting information from data through a direct comparison of all measured variables in an event with a matrix element that describes the entire production process. The method is exemplified in the extraction of the mass of the top quark in top-antitop events in the lepton+jets final state. Monte Carlo studies suggest that an improvement of about a factor of two in statistical uncertainty on the mass of the top quark can be achieved relative to previously published work for the same channel. Preliminary results from the re-analysis provide a reduction in the statistical uncertainty of almost a factor of 1.6, corresponding to an effective factor of 2.4 increase in the size of the data sample.

hep-ex↗

arXiv1997

Dynamical Cosmological Constant and Relations Among Pseudo Goldstone Bosons

The present apparent cosmological constant is interpreted as the potential of the lightest pseudo Goldstone boson. Some numerical relations among cosmological parameters and particle masses are shown to arise from the mixture of this very light particle, whose interaction is of the gravitational order, with other pseudo Goldstone bosons like the pion and the axion which feel the strong interaction.

hep-ph↗