arXiv subjects

E. V. Linder

Publications and source records attributed to E. V. Linder.

17 recordsLinked to original sources

arXiv2019

Testing Gravity Using Type Ia Supernovae Discovered by Next-Generation Wide-Field Imaging Surveys

In the upcoming decade cadenced wide-field imaging surveys will increase the number of identified $z<0.3$ Type~Ia supernovae (SNe~Ia) from the hundreds to the hundreds of thousands. The increase in the number density and solid-angle coverage of SNe~Ia, in parallel with improvements in the standardization of their absolute magnitudes, now make them competitive probes of the growth of structure and hence of gravity. The peculiar velocity power spectrum is sensitive to the growth index $γ$, which captures the effect of gravity on the linear growth of structure through the relation $f=Ω_M^γ$. We present the first projections for the precision in $γ$ for a range of realistic SN peculiar-velocity survey scenarios. In the next decade the peculiar velocities of SNe~Ia in the local $z<0.3$ Universe will provide a measure of $γ$ to $\pm 0.01$ precision that can definitively distinguish between General Relativity and leading models of alternative gravity.

astro-ph.CO↗

arXiv2016

POLARBEAR-2: an instrument for CMB polarization measurements

POLARBEAR-2 (PB-2) is a cosmic microwave background (CMB) polarization experiment that will be located in the Atacama highland in Chile at an altitude of 5200 m. Its science goals are to measure the CMB polarization signals originating from both primordial gravitational waves and weak lensing. PB-2 is designed to measure the tensor to scalar ratio, r, with precision σ(r) < 0.01, and the sum of neutrino masses, Σmν, with σ(Σmν) < 90 meV. To achieve these goals, PB-2 will employ 7588 transition-edge sensor bolometers at 95 GHz and 150 GHz, which will be operated at the base temperature of 250 mK. Science observations will begin in 2017.

astro-ph.IM↗

arXiv2013

Dark energy with gravitational lens time delays

Strong lensing gravitational time delays are a powerful and cost effective probe of dark energy. Recent studies have shown that a single lens can provide a distance measurement with 6-7 % accuracy (including random and systematic uncertainties), provided sufficient data are available to determine the time delay and reconstruct the gravitational potential of the deflector. Gravitational-time delays are a low redshift (z~0-2) probe and thus allow one to break degeneracies in the interpretation of data from higher-redshift probes like the cosmic microwave background in terms of the dark energy equation of state. Current studies are limited by the size of the sample of known lensed quasars, but this situation is about to change. Even in this decade, wide field imaging surveys are likely to discover thousands of lensed quasars, enabling the targeted study of ~100 of these systems and resulting in substantial gains in the dark energy figure of merit. In the next decade, a further order of magnitude improvement will be possible with the 10000 systems expected to be detected and measured with LSST and Euclid. To fully exploit these gains, we identify three priorities. First, support for the development of software required for the analysis of the data. Second, in this decade, small robotic telescopes (1-4m in diameter) dedicated to monitoring of lensed quasars will transform the field by delivering accurate time delays for ~100 systems. Third, in the 2020's, LSST will deliver 1000's of time delays; the bottleneck will instead be the aquisition and analysis of high resolution imaging follow-up. Thus, the top priority for the next decade is to support fast high resolution imaging capabilities, such as those enabled by the James Webb Space Telescope and next generation adaptive optics systems on large ground based telescopes.

astro-ph.CO↗

arXiv2012

Feasibility of a Small, Rapid Optical-to-IR Response, Next Generation Gamma Ray Burst Mission

We present motivations for and study feasibility of a small, rapid optical to IR response gamma ray burst (GRB) space observatory. By analyzing existing GRB data, we give realistic detection rates for X-ray and optical/IR instruments of modest size under actual flight conditions. Given new capabilities of fast optical/IR response (about 1 s to target) and simultaneous multi-band imaging, such an observatory can have a reasonable event rate, likely leading to new science. Requiring a Swift-like orbit, duty cycle, and observing constraints, a Swift-BAT scaled down to 190 square cm of detector area would still detect and locate about 27 GRB per yr. for a trigger threshold of 6.5 sigma. About 23 percent of X-ray located GRB would be detected optically for a 10 cm diameter instrument (about 6 per yr. for the 6.5 sigma X-ray trigger).

astro-ph.HE↗

arXiv2012

A next generation Ultra-Fast Flash Observatory (UFFO-100) for IR/optical observations of the rise phase of gamma-ray bursts

The Swift Gamma-ray Burst (GRB) observatory responds to GRB triggers with optical observations in ~ 100 s, but cannot respond faster than ~ 60 s. While some ground-based telescopes respond quickly, the number of sub-60 s detections remains small. In mid- to late-2013, the Ultra-Fast Flash Observatory-Pathfinder is to be launched on the Lomonosov spacecraft to investigate early optical GRB emission. This pathfinder mission is necessarily limited in sensitivity and event rate; here we discuss a next generation rapid-response space observatory. We list science topics motivating our instruments, those that require rapid optical-IR GRB response, including: A survey of GRB rise shapes/times, measurements of optical bulk Lorentz factors, investigation of magnetic dominated (vs. non-magnetic) jet models, internal vs. external shock origin of prompt optical emission, the use of GRBs for cosmology, and dust evaporation in the GRB environment. We also address the impacts of the characteristics of GRB observing on our instrument and observatory design. We describe our instrument designs and choices for a next generation observatory as a second instrument on a low-earth orbit spacecraft, with a 120 kg instrument mass budget. Restricted to relatively modest mass and power, we find that a coded mask X-ray camera with 1024 cm2 of detector area could rapidly locate about 64 GRB triggers/year. Responding to the locations from the X-ray camera, a 30 cm aperture telescope with a beam-steering system for rapid (~ 1 s) response and a near-IR camera should detect ~ 29 GRB, given Swift GRB properties. Am additional optical camera would give a broadband optical-IR slope, allowing dynamic measurement of dust extinction at the source, for the first time.

astro-ph.IM↗

arXiv2011

Data Acquisition System for the UFFO Pathfinder

The Ultra-Fast Flash Observatory (UFFO) Pathfinder is a payload on the Russian Lomonosov satellite, scheduled to be launched in November 2011. The Observatory is designed to detect early UV/Optical photons from Gamma-Ray Bursts (GRBs). There are two telescopes and one main data acquisition system: the UFFO Burst Alert & Trigger Telescope (UBAT), the Slewing Mirror Telescope (SMT), and the UFFO Data Acquisition (UDAQ) system. The UDAQ controls and manages the operation and communication of each telescope, and is also in charge of the interface with the satellite. It will write the data taken by each telescope to the NOR flash memory and sends them to the satellite via the Bus-Interface system (BI). It also receives data from the satellite including the coordinates and time of an external trigger from another payload, and distributes them to two telescopes. These functions are implemented in field programmable gates arrays (FPGA) for low power consumption and fast processing without a microprocessor. The UDAQ architecture, control of the system, and data flow will be presented.

astro-ph.IM↗

arXiv2011

Design and Fabrication of Detector Module for UFFO Burst Alert & Trigger Telescope

The Ultra-Fast Flash Observatory (UFFO) pathfinder is a space mission devoted to the measurement of Gamma-Ray Bursts (GRBs), especially their early light curves which will give crucial information on the progenitor stars and central engines of the GRBs. It consists of two instruments: the UFFO Burst Alert & Trigger telescope (UBAT) for the detection of GRB locations and the Slewing Mirror Telescope (SMT) for the UV/optical afterglow observations, upon triggering by UBAT. The UBAT employs a coded-mask γ/X-ray camera with a wide field of view (FOV), and is comprised of three parts: a coded mask, a hopper, and a detector module (DM). The UBAT DM consists of a LYSO scintillator crystal array, multi-anode photo multipliers, and analog and digital readout electronics. We present here the design and fabrication of the UBAT DM, as well as its preliminary test results.

astro-ph.CO↗

arXiv2011

Optical Performances of Slewing Mirror Telescope for UFFO-Pathfinder

The Ultra-Fast Flash Observatory-Pathfinder (UFFO-P) is to be launched onboard Lomonosov spacecraft in November 2011. It is to measure early UV/Optical photons from Gamma Ray Bursts (GRBs). Slewing Mirror Telescope (SMT) is one of two instruments designed for detection of UV/Optical images of the GRBs. SMT is a Ritchey-Chrétien telescope of 100 mm in diameter with a motorized slewing mirror at the entrance providing 17\times17 arcmin2 in Field of View (FOV) and 4 arcsec in pixel resolution. Its sky coverage can be further expanded up to 35 degrees in FOV by tilting a motorized slewing mirror. All mirrors were fabricated to about RMS 0.02 waves in wave front error (WFE) and 84.7% (in average reflectivity) over 200nm~650nm range. SMT was aligned to RMS 0.05 waves in WFE (test wavelength 632.8nm). From the static gravity test result, SMT optics system is expected to survive during launch. The technical details of SMT assembly and laboratory performance test results are reported.

astro-ph.CO↗

arXiv2011

The UFFO (Ultra Fast Flash Observatory) Pathfinder: Science and Mission

Hundreds of gamma-ray burst (GRB) optical light curves have been measured since the discovery of optical afterglows. However, even after nearly 7 years of operation of the Swift Observatory, only a handful of measurements have been made soon (within a minute) after the gamma ray signal. This lack of early observations fails to address burst physics at short time scales associated with prompt emissions and progenitors. Because of this lack of sub-minute data, the characteristics of the rise phase of optical light curve of short-hard type GRB and rapid-rising GRB, which may account for ~30% of all GRB, remain practically unknown. We have developed methods for reaching sub-minute and sub-second timescales in a small spacecraft observatory. Rather than slewing the entire spacecraft to aim the optical instrument at the GRB position, we use rapidly moving mirror to redirect our optical beam. As a first step, we employ motorized slewing mirror telescope (SMT), which can point to the event within 1s, in the UFFO Pathfinder GRB Telescope onboard the Lomonosov satellite to be launched in Nov. 2011. UFFO's sub-minute measurements of the optical emission of dozens of GRB each year will result in a more rigorous test of current internal shock models, probe the extremes of bulk Lorentz factors, provide the first early and detailed measurements of fast-rise GRB optical light curves, and help verify the prospect of GRB as a new standard candle. We will describe the science and the mission of the current UFFO Pathfinder project, and our plan of a full-scale UFFO-100 as the next step.

astro-ph.HE↗

arXiv2011

Implementation of the readout system in the UFFO Slewing Mirror Telescope

The Ultra-Fast Flash Observatory (UFFO) is a new space-based experiment to observe Gamma-Ray Bursts (GRBs). GRBs are the most luminous electromagnetic events in the universe and occur randomly in any direction. Therefore the UFFO consists of two telescopes; UFFO Burst Alert & Trigger Telescope (UBAT) to detect GRBs using a wide field-of-view (FOV), and a Slewing Mirror Telescope (SMT) to observe UV/optical events rapidly within the narrow, targeted FOV. The SMT is a Ritchey-Chretien telescope that uses a motorized mirror system and an Intensified Charge-Coupled Device (ICCD). When the GRB is triggered by the UBAT, the SMT receives the position information and rapidly tilts the mirror to the target. The ICCD start to take the data within a second after GRB is triggered. Here we give the details about the SMT readout electronics that deliver the data.

astro-ph.IM↗

arXiv2011

The Hubble Space Telescope Cluster Supernova Survey: V. Improving the Dark Energy Constraints Above z>1 and Building an Early-Type-Hosted Supernova Sample

We present ACS, NICMOS, and Keck AO-assisted photometry of 20 Type Ia supernovae SNe Ia from the HST Cluster Supernova Survey. The SNe Ia were discovered over the redshift interval 0.623 < z < 1.415. Fourteen of these SNe Ia pass our strict selection cuts and are used in combination with the world's sample of SNe Ia to derive the best current constraints on dark energy. Ten of our new SNe Ia are beyond redshift $z=1$, thereby nearly doubling the statistical weight of HST-discovered SNe Ia beyond this redshift. Our detailed analysis corrects for the recently identified correlation between SN Ia luminosity and host galaxy mass and corrects the NICMOS zeropoint at the count rates appropriate for very distant SNe Ia. Adding these supernovae improves the best combined constraint on the dark energy density ρ_{DE}(z) at redshifts 1.0 < z < 1.6 by 18% (including systematic errors). For a LambdaCDM universe, we find Ω_Λ= 0.724 +0.015/-0.016 (68% CL including systematic errors). For a flat wCDM model, we measure a constant dark energy equation-of-state parameter w = -0.985 +0.071/-0.077 (68% CL). Curvature is constrained to ~0.7% in the owCDM model and to ~2% in a model in which dark energy is allowed to vary with parameters w_0 and w_a. Tightening further the constraints on the time evolution of dark energy will require several improvements, including high-quality multi-passband photometry of a sample of several dozen z>1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on HST.

astro-ph.CO↗

arXiv2011

Cosmological and Astrophysical Neutrino Mass Measurements

Cosmological and astrophysical measurements provide powerful constraints on neutrino masses complementary to those from accelerators and reactors. Here we provide a guide to these different probes, for each explaining its physical basis, underlying assumptions, current and future reach.

astro-ph.CO↗

arXiv2010

Reducing Zero-point Systematics in Dark Energy Supernova Experiments

We study the effect of filter zero-point uncertainties on future supernova dark energy missions. Fitting for calibration parameters using simultaneous analysis of all Type Ia supernova standard candles achieves a significant improvement over more traditional fit methods. This conclusion is robust under diverse experimental configurations (number of observed supernovae, maximum survey redshift, inclusion of additional systematics). This approach to supernova fitting considerably eases otherwise stringent mission calibration requirements. As an example we simulate a space-based mission based on the proposed JDEM satellite; however the method and conclusions are general and valid for any future supernova dark energy mission, ground or space-based.

astro-ph.CO↗

arXiv2009

The UFFO (Ultra-Fast Flash Observatory) Pathfinder

Hundreds of gamma-ray burst (GRB) UV-optical light curves have been measured since the discovery of optical afterglows, however, even after nearly 5 years of operation of the SWIFT observatory, only a handful of measurements have been made soon (within a minute) after the gamma ray signal. This lack of early observations fails to address burst physics at the short time scales associated with burst events and progenitors. Because of this lack of sub-minute data, the characteristics of the UV-optical light curve of short-hard type GRB and rapid-rising GRB, which may account for ~30% of all GRB, remain practically unknown. We have developed methods for reaching the sub-minute and the sub-second timescales in a small spacecraft observatory appropriate for launch on a microsatellite. Rather than slewing the entire spacecraft to aim the UV-optical instrument at the GRB position, we use rapidly moving mirrors to redirect our optical beam. Our collaboration has produced a unique MEMS (microelectromechanical systems) micromirror array which can point and settle on target in only 1 ms. This technology is proven, flying successfully as the MTEL (MEMS Telescope for Extreme Lightning) on the Tatiana-2 Spacecraft in September 2009 and as the KAMTEL on the International Space Station in April 2008. The sub-minute measurements of the UV-optical emission of dozens of GRB each year will result in a more rigorous test of current internal shock models, probe the extremes of bulk Lorentz factors, and provide the first early and detailed measurements of fast-rise and short type GRB UV-optical light curves.

astro-ph.CO↗

arXiv2009

An Intensive HST Survey for z>1 Supernovae by Targeting Galaxy Clusters

We present a new survey strategy to discover and study high redshift Type Ia supernovae (SNe Ia) using the Hubble Space Telescope (HST). By targeting massive galaxy clusters at 0.9 0.95, nine of which were in galaxy clusters. This strategy provides a SN sample that can be used to decouple the effects of host galaxy extinction and intrinsic color in high redshift SNe, thereby reducing one of the largest systematic uncertainties in SN cosmology.

astro-ph.CO↗

arXiv2008

Looking Beyond Lambda with the Union Supernova Compilation

The recent robust and homogeneous analysis of the world's supernova distance-redshift data, together with cosmic microwave background and baryon acoustic oscillation data, provides a powerful tool for constraining cosmological models. Here we examine particular classes of scalar field, modified gravity, and phenomenological models to assess whether they are consistent with observations even when their behavior deviates from the cosmological constant Lambda. Some models have tension with the data, while others survive only by approaching the cosmological constant, and a couple are statistically favored over LCDM. Dark energy described by two equation of state parameters has considerable phase space to avoid Lambda and next generation data will be required to constrain such physics.

astro-ph↗

arXiv2008

Improved Cosmological Constraints from New, Old and Combined Supernova Datasets

We present a new compilation of Type Ia supernovae (SNe Ia), a new dataset of low-redshift nearby-Hubble-flow SNe and new analysis procedures to work with these heterogeneous compilations. This ``Union'' compilation of 414 SN Ia, which reduces to 307 SNe after selection cuts, includes the recent large samples of SNe Ia from the Supernova Legacy Survey and ESSENCE Survey, the older datasets, as well as the recently extended dataset of distant supernovae observed with HST. A single, consistent and blind analysis procedure is used for all the various SN Ia subsamples, and a new procedure is implemented that consistently weights the heterogeneous data sets and rejects outliers. We present the latest results from this Union compilation and discuss the cosmological constraints from this new compilation and its combination with other cosmological measurements (CMB and BAO). The constraint we obtain from supernovae on the dark energy density is $Ω_Λ= 0.713^{+0.027}_{-0.029} (stat)}^{+0.036}_{-0.039} (sys)}$, for a flat, LCDM Universe. Assuming a constant equation of state parameter, $w$, the combined constraints from SNe, BAO and CMB give $w=-0.969^{+0.059}_{-0.063}(stat)^{+0.063}_{-0.066} (sys)$. While our results are consistent with a cosmological constant, we obtain only relatively weak constraints on a $w$ that varies with redshift. In particular, the current SN data do not yet significantly constrain $w$ at $z>1$. With the addition of our new nearby Hubble-flow SNe Ia, these resulting cosmological constraints are currently the tightest available.

astro-ph↗