arXiv subjects

Stephen Holland

Publications and source records attributed to Stephen Holland.

At least 19 recordsLinked to original sources

arXiv2024

Sixteen Multiple-Amplifier Sensing Charge-Coupled Devices and Characterization Techniques Targeting the Next Generation of Astronomical Instruments

We present a candidate sensor for future spectroscopic applications, such as a Stage-5 Spectroscopic Survey Experiment or the Habitable Worlds Observatory. This type of charge-coupled device (CCD) sensor features multiple in-line amplifiers at its output stage allowing multiple measurements of the same charge packet, either in each amplifier or in the different amplifiers. Recently, the operation of an eight-amplifier sensor has been experimentally demonstrated, and we present the operation of a 16-amplifier sensor. This new sensor enables a noise level of ~1e-rms with a single sample per amplifier. In addition, it is shown that sub-electron noise can be achieved using multiple samples per amplifier. In addition to demonstrating the performance of the 16-amplifier sensor, we aim to create a framework for future analysis and performance optimization of this type of detectors. New models and techniques are presented to characterize specific parameters, which are absent in conventional CCDs and Skipper CCDs: charge transfer between amplifiers and independent and common noise in the amplifiers and their processing.

astro-ph.IM↗

arXiv2024

Skipper-CCD Sensors for the Oscura Experiment: Requirements and Preliminary Tests

Oscura is a proposed multi-kg skipper-CCD experiment designed for a dark matter (DM) direct detection search that will reach unprecedented sensitivity to sub-GeV DM-electron interactions with its 10 kg detector array. Oscura is planning to operate at SNOLAB with 2070 m overburden, and aims to reach a background goal of less than one event in each electron bin in the 2-10 electron ionization-signal region for the full 30 kg-year exposure, with a radiation background rate of 0.01 dru. In order to achieve this goal, Oscura must address each potential source of background events, including instrumental backgrounds. In this work, we discuss the main instrumental background sources and the strategy to control them, establishing a set of constraints on the sensors' performance parameters. We present results from the tests of the first fabricated Oscura prototype sensors, evaluate their performance in the context of the established constraints and estimate the Oscura instrumental background based on these results.

physics.ins-det↗

arXiv2023

Searching for millicharged particles with 1 kg of Skipper-CCDs using the NuMI beam at Fermilab

Oscura is a planned light-dark matter search experiment using Skipper-CCDs with a total active mass of 10 kg. As part of the detector development, the collaboration plans to build the Oscura Integration Test (OIT), an engineering test with 10% of the total mass. Here we discuss the early science opportunities with the OIT to search for millicharged particles (mCPs) using the NuMI beam at Fermilab. mCPs would be produced at low energies through photon-mediated processes from decays of scalar, pseudoscalar, and vector mesons, or direct Drell-Yan productions. Estimates show that the OIT would be a world-leading probe for mCPs in the MeV mass range.

hep-ex↗

arXiv2023

Characterization and Optimization of Skipper CCDs for the SOAR Integral Field Spectrograph

We present results from the characterization and optimization of six Skipper CCDs for use in a prototype focal plane for the SOAR Integral Field Spectrograph (SIFS). We tested eight Skipper CCDs and selected six for SIFS based on performance results. The Skipper CCDs are 6k $\times$ 1k, 15 $μ$m pixels, thick, fully-depleted, $p$-channel devices that have been thinned to $\sim 250 μ$m, backside processed, and treated with an antireflective coating. We optimize readout time to achieve $<4.3$ e$^-$ rms/pixel in a single non-destructive readout and $0.5$ e$^-$ rms/pixel in $5 \%$ of the detector. We demonstrate single-photon counting with $N_{\rm samp}$ = 400 ($σ_{\rm 0e^-} \sim$ 0.18 e$^-$ rms/pixel) for all 24 amplifiers (four amplifiers per detector). We also perform conventional CCD characterization measurements such as cosmetic defects ($ <0.45 \%$ ``bad" pixels), dark current ($\sim 2 \times 10^{-4}$ e$^-$/pixel/sec.), charge transfer inefficiency ($3.44 \times 10^{-7}$ on average), and charge diffusion (PSF $< 7.5 μ$m). We report on characterization and optimization measurements that are only enabled by photon-counting. Such results include voltage optimization to achieve full-well capacities $\sim 40,000-63,000$ e$^-$ while maintaining photon-counting capabilities, clock induced charge optimization, non-linearity measurements at low signals (few tens of electrons). Furthermore, we perform measurements of the brighter-fatter effect and absolute quantum efficiency ($\gtrsim\, 80 \%$ between 450 nm and 980 nm; $\gtrsim\,90 \%$ between 600 nm and 900 nm) using Skipper CCDs.

astro-ph.IM↗

arXiv2022

Design of a Skipper CCD Focal Plane for the SOAR Integral Field Spectrograph

We present the development of a Skipper Charge-Coupled Device (CCD) focal plane prototype for the SOAR Telescope Integral Field Spectrograph (SIFS). This mosaic focal plane consists of four 6k $\times$ 1k, 15 $μ$m pixel Skipper CCDs mounted inside a vacuum dewar. We describe the process of packaging the CCDs so that they can be easily tested, transported, and installed in a mosaic focal plane. We characterize the performance of $\sim 650 μ$m thick, fully-depleted engineering-grade Skipper CCDs in preparation for performing similar characterization tests on science-grade Skipper CCDs which will be thinned to 250$μ$m and backside processed with an antireflective coating. We achieve a single-sample readout noise of $4.5 e^{-} rms/pix$ for the best performing amplifiers and sub-electron resolution (photon counting capabilities) with readout noise $σ\sim 0.16 e^{-} rms/pix$ from 800 measurements of the charge in each pixel. We describe the design and construction of the Skipper CCD focal plane and provide details about the synchronized readout electronics system that will be implemented to simultaneously read 16 amplifiers from the four Skipper CCDs (4-amplifiers per detector). Finally, we outline future plans for laboratory testing, installation, commissioning, and science verification of our Skipper CCD focal plane.

astro-ph.IM↗

arXiv2022

Photon counting from the vacuum ultraviolet to the short wavelength infrared using semiconductor and superconducting technologies

In the last decade, several photon counting technologies have been developed opening a new window for experiments in the low photon number regime. Several ongoing and future projects in HEP benefit from these developments, which will also have a large impact outside HEP. During the next decade there is a clear technological opportunity to fully develop these sensors and produce a large impact in HEP. In this white paper we discuss the need for photon counting technologies in future projects, and present some technological opportunities to address those needs.

physics.ins-det↗

arXiv2021

Characterization of Skipper CCDs for Cosmological Applications

We characterize the response of a novel 250 $μ$m thick, fully-depleted Skipper Charged-Coupled Device (CCD) to visible/near-infrared light with a focus on potential applications for astronomical observations. We achieve stable, single-electron resolution with readout noise $σ\sim 0.18$ e$^{-}$ rms/pix from 400 non-destructive measurements of the charge in each pixel. We verify that the gain derived from photon transfer curve measurements agrees with the gain calculated from the quantized charge of individual electrons to within < 1%. We also perform relative quantum efficiency measurements and demonstrate high relative quantum efficiency at optical/near-infrared wavelengths, as is expected for a thick, fully depleted detector. Finally, we demonstrate the ability to perform multiple non-destructive measurements and achieve sub-electron readout noise over configurable subregions of the detector. This work is the first step toward demonstrating the utility of Skipper CCDs for future astronomical and cosmological applications.

astro-ph.IM↗

arXiv2019

Maintaining Capabilities in CCD Production for the Astronomy Community

CCD detectors play a vital role in all aspects of optical astronomy. Critical to advancing research is the ability to partner with commercial foundries to produce custom devices that meet the needs of specific instruments. For more than 20 years, Teledyne DALSA Semiconductor was the primary industrial partner in the manufacturing of 150 mm wafers for CCDs. DALSA is migrating the manufacturing from 150mm to 200mm wafer diameter and will not be updating their CCD processing tools for the new format wafer. As a result, DALSA will no longer serve as a partner to the astronomy community in the manufacturing of CCDs. We recommend that the Department of Energy, National Science Foundation, and NASA jointly pursue a new commercial partner in CCD fabrication to maintain capabilities in custom CCD design for astronomy applications.

astro-ph.IM↗

arXiv2018

Commercialization of micro-fabrication of antenna-coupled Transition Edge Sensor bolometer detectors for studies of the Cosmic Microwave Background

We report on the development of commercially fabricated multi-chroic antenna coupled Transition Edge Sensor (TES) bolometer arrays for Cosmic Microwave Background (CMB) polarimetry experiments. CMB polarimetry experiments have deployed instruments in stages. Stage-II experiments deployed with O(1,000) detectors and reported successful detection of B-mode (divergent free) polarization pattern in the CMB. Stage-III experiments have recently started observing with O(10,000) detectors with wider frequency coverage. A concept for a Stage-IV experiment, CMB-S4, is emerging to make a definitive measurement of CMB polarization from the ground with O(400,000) detectors. The orders of magnitude increase in detector count for CMB-S4 requires a new approach in detector fabrication to increase fabrication throughput.and reduce cost. We report on collaborative efforts with two commercial micro-fabrication foundries to fabricate antenna coupled TES bolometer detectors. The detector design is based on the sinuous antenna coupled dichroic detector from the POLARBEAR-2 experiment. The TES bolometers showed the expected I-V response and the RF performance agrees with simulation. We will discuss the motivation, design consideration, fabrication processes, test results, and how industrial detector fabrication could be a path to fabricate hundreds of detector wafers for future CMB polarimetry experiments.

astro-ph.IM↗

arXiv2014

SOUSA: the Swift Optical/Ultraviolet Supernova Archive

The Ultra-Violet Optical Telescope on the Swift spacecraft has observed hundreds of supernovae, covering all major types and most subtypes. Here we introduce the Swift Optical/Ultraviolet Supernova Archive (SOUSA), which will contain all of the supernova images and photometry. We describe the observation and reduction procedures and how they impact the final data. We show photometry from well-observed examples of most supernova classes, whose absolute magnitudes and colors may be used to infer supernova types in the absence of a spectrum. A full understanding of the variety within classes and a robust photometric separation of the groups requires a larger sample, which will be provided by the final archive. The data from the existing Swift supernovae are also useful for planning future observations with Swift as well as future UV observatories.

astro-ph.HE↗

arXiv2014

Ultraviolet Observations of Super-Chandrasekhar Mass Type Ia Supernova Candidates with Swift UVOT

Among Type Ia supernovae (SNe~Ia) exist a class of overluminous objects whose ejecta mass is inferred to be larger than the canonical Chandrasekhar mass. We present and discuss the UV/optical photometric light curves, colors, absolute magnitudes, and spectra of three candidate Super-Chandrasekhar mass SNe--2009dc, 2011aa, and 2012dn--observed with the Swift Ultraviolet/Optical Telescope. The light curves are at the broad end for SNe Ia, with the light curves of SN~2011aa being amongst the broadest ever observed. We find all three to have very blue colors which may provide a means of excluding these overluminous SNe from cosmological analysis, though there is some overlap with the bluest of "normal" SNe Ia. All three are overluminous in their UV absolute magnitudes compared to normal and broad SNe Ia, but SNe 2011aa and 2012dn are not optically overluminous compared to normal SNe Ia. The integrated luminosity curves of SNe 2011aa and 2012dn in the UVOT range (1600-6000 Angstroms) are only half as bright as SN~2009dc, implying a smaller 56Ni yield. While not enough to strongly affect the bolometric flux, the early time mid-UV flux makes a significant contribution at early times. The strong spectral features in the mid-UV spectra of SNe 2009dc and 2012dn suggest a higher temperature and lower opacity to be the cause of the UV excess rather than a hot, smooth blackbody from shock interaction. Further work is needed to determine the ejecta and 56Ni masses of SNe 2011aa and 2012dn and fully explain their high UV luminosities.

astro-ph.HE↗

arXiv2012

A Swift Look at SN 2011fe: The Earliest Ultraviolet Observations of a Type Ia Supernova

We present the earliest ultraviolet (UV) observations of the bright Type Ia supernova SN 2011fe/PTF11kly in the nearby galaxy M101 at a distance of only 6.4 Mpc. It was discovered shortly after explosion by the Palomar Transient Factory and first observed by Swift/UVOT about a day after explosion. The early UV light is well-defined, with ~20 data points per filter in the five days after explosion. These early and well-sampled UV observations form new template light curves for comparison with observations of other SNe Ia at low and high redshift. We report fits from semi-empirical models of the explosion and find the time evolution of the early UV flux to be well fit by the superposition of two parabolic curves. Finally, we use the early UV flux measurements to examine a possible shock interaction with a non-degenerate companion. From models predicting the measurable shock emission, we find that even a solar mass companion at a distance of a few solar radii is unlikely at more than 95% confidence.

astro-ph.CO↗

arXiv2006

Infrared and Optical Observations of GRB 030115 and its Extremely Red Host Galaxy: Implications for Dark Bursts

We present near-infrared (nIR) and optical observations of the afterglow of GRB 030115. Discovered in an infrared search at Kitt Peak 5 hours after the burst trigger, this afterglow is amongst the faintest observed in the R-band at an early epoch, and exhibits very red colors, with $R-K\approx 6$. The magnitude of the optical afterglow of GRB 030115 is fainter than many upper limits for other bursts, suggesting that without early nIR observations it would have been classified as a ``dark'' burst. Both the color and optical magnitude of the afterglow are likely due to dust extinction and indicate that at least some optical afterglows are very faint due to dust along the line of sight. Multicolor {\it Hubble Space Telescope} observations were also taken of the host galaxy and the surrounding field. Photometric redshifts imply that the host, and a substantial number of faint galaxies in the field are at $z \sim 2.5$. The overdensity of galaxies is sufficiently great that GRB 030115 may have occurred in a rich high-redshift cluster. The host galaxy shows extremely red colors (R-K=5) and is the first GRB host to be classified as an Extremely Red Object (ERO). Some of the galaxies surrounding the host also show very red colors, while the majority of the cluster are much bluer, indicating ongoing unobscured star formation. As it is thought that much of high redshift star formation occurs in highly obscured environments it may be that GRB 030115 represent a transition object, between the relatively unobscured afterglows seen to date and a population which are very heavily extinguished, even in the nIR.

astro-ph↗

arXiv2003

23 High Redshift Supernovae from the IfA Deep Survey: Doubling the SN Sample at z>0.7

We present photometric and spectroscopic observations of 23 high redshift supernovae spanning a range of z=0.34-1.03, 9 of which are unambiguously classified as Type Ia. These supernovae were discovered during the IfA Deep Survey, which began in September 2001 and observed a total of 2.5 square degrees to a depth of approximately m=25-26 in RIZ over 9-17 visits, typically every 1-3 weeks for nearly 5 months, with additional observations continuing until April 2002. We give a brief description of the survey motivations, observational strategy, and reduction process. This sample of 23 high-redshift supernovae includes 15 at z>0.7, doubling the published number of objects at these redshifts, and indicates that the evidence for acceleration of the universe is not due to a systematic effect proportional to redshift. In combination with the recent compilation of Tonry et al. (2003), we calculate cosmological parameter density contours which are consistent with the flat universe indicated by the CMB (Spergel et al. 2003). Adopting the constraint that Omega_total = 1.0, we obtain best-fit values of (Omega_m, Omega_Lambda)=(0.33, 0.67) using 22 SNe from this survey augmented by the literature compilation. We show that using the empty-beam model for gravitational lensing does not eliminate the need for Omega_Lambda > 0. Experience from this survey indicates great potential for similar large-scale surveys while also revealing the limitations of performing surveys for z>1 SNe from the ground.

astro-ph↗

arXiv2001

Optical observations of the dark Gamma-Ray Burst GRB 000210

We report on optical observations on GRB 000210 obtained with the 2.56-m Nordic Optical Telescope and the 1.54-m Danish Telescope starting 12.4 hours after the gamma-ray event. The content of the X-ray error box determined by the Chandra satellite is discussed.

astro-ph↗

arXiv2000

The late afterglow and host galaxy of GRB 990712

We present deep HST imaging, as well as ground-based imaging and spectroscopy, of the optical afterglow associated with the long-duration gamma-ray burst GRB 990712 and its host galaxy. The data were obtained 48--123 days after the burst occurred. The magnitudes of the host (R = 21.9, V = 22.5) and optical afterglow (R = 25.4, V = 25.8, 47.7 days after the burst) favor a scenario where the optical light follows a pure power-law decay with an index of alpha ~ -1.0. We find no evidence for a contribution from a supernova like SN1998bw. This suggests that either there are multiple classes of long-duration gamma-ray bursts, or that the peak luminosity of the supernova was > 1.5 mag fainter than SN1998bw. The HST images and EFOSC2 spectra indicate that the gamma-ray burst was located in a bright, extended feature (possibly a star-forming region) 1.4 kpc from the nucleus of a 0.2 L^*_B galaxy at z = 0.434, possibly a Seyfert 2 galaxy. The late-time afterglow and host galaxy of GRB 990712 bear some resemblance to those of GRB 970508.

astro-ph↗

arXiv1999

Globular Clusters in NGC 5128

We used the Wide Field Planetary Camera 2 aboard the Hubble Space Telescope to search for globular clusters in the inner regions of the nearby giant elliptical galaxy NGC 5128. This galaxy is believed to be the product of a merger between a large elliptical galaxy and a small late-type spiral between 160 and 500 Myr ago. We identified 21 globular cluster candidates and measured their core radii, tidal radii, half-mass radii, ellipticities, position angles, and V-I colors. We find evidence that the NGC 5128 globular cluster candidates are systematically more elliptical than are those of the Milky Way. Approximately half of the candidates have (V-I)_0 colors that are consistent with their being either old, unreddened globular clusters, similar to those found in the Milky Way, or young, reddened globular clusters that may have formed during the recent merger event. Most of the rest have colors that are consistent with their being old globular clusters similar to those found in the Milky Way. We find one blue object with (V-I)_0 < 0.26 +/- 0.09. The color, reddening, and integrated magnitude of this object are consistent with its being a small globular cluster with an age of approximately 100 Myr and a mass (based on its integrated luminosity) of <= 4000 Solar masses. We find no evidence for bimodality in the colors of the globular cluster candidates in our sample beyond what can be explained by uncertainties in the differential reddening.

astro-ph↗

arXiv1999

Star-Forming Regions near GRB 990123

We reduced the Hubble Space Telescope Space Telescope Imaging Spectrograph images of the gamma-ray burst GRB 990123 that were obtained on 8-9 February 1999 and find V_0 = 25.36 +/- 0.10, which corresponds to a flux of 0.258 +/- 0.023 micro-Jy for the optical transient 16.644 days after the burst's peak. The probable host galaxy has V_0 = 24.25 +/- 0.07 (= 0.716 +/- 0.046 micro-Jy) and the optical transient is located 0.65 arcseconds (= 5.5 kpc) south of the galaxy's nucleus. We fit and subtracted a scaled point-spread function to the optical transient and found evidence for three bright knots situated within 0.5 arcseconds (= 4.3 kpc) of the optical transient. Each knot has V_0 ~ 28.1 +/- 0.3, a rest-frame V-band luminosity of between approximately 5e8 L_Sun and 8e8 L_Sun, and a star-formation rate of at least 0.1-0.2 Solar masses per year. The knots are centrally concentrated with full-width at half-maximum of approximately 0.17 arcseconds (= 1.5 kpc). Their sizes and luminosities are consistent with their being star-forming regions. The optical transient is located 0.15 arcseconds (= 1.3 kpc) southeast of the centre of one of these knots.

astro-ph↗