The Gamow Explorer will use Gamma Ray Bursts (GRBs) to: 1) probe the high redshift universe (z < 6) when the first stars were born, galaxies formed and Hydrogen was reionized; and 2) enable multi-messenger astrophysics by rapidly identifying Electro-Magnetic (IR/Optical/X-ray) counterparts to Gravitational Wave (GW) events. GRBs have been detected out to z ~ 9 and their afterglows are a bright beacon lasting a few days that can be used to observe the spectral fingerprints of the host galaxy and intergalactic medium to map the period of reionization and early metal enrichment. Gamow Explorer is optimized to quickly identify high-z events to trigger follow-up observations with JWST and large ground-based telescopes. A wide field of view Lobster Eye X-ray Telescope (LEXT) will search for GRBs and locate them with arc-minute precision. When a GRB is detected, the rapidly slewing spacecraft will point the 5 photometric channel Photo-z Infra-Red Telescope (PIRT) to identify high redshift (z < 6) long GRBs within 100s and send an alert within 1000s of the GRB trigger. An L2 orbit provides < 95% observing efficiency with pointing optimized for follow up by the James Webb Space Telescope (JWST) and ground observatories. The predicted Gamow Explorer high-z rate is <10 times that of the Neil Gehrels Swift Observatory. The instrument and mission capabilities also enable rapid identification of short GRBs and their afterglows associated with GW events. The Gamow Explorer will be proposed to the 2021 NASA MIDEX call and if approved, launched in 2028.
KEYWORDS: Sensors, James Webb Space Telescope, Space telescopes, Calibration, Target acquisition, Signal to noise ratio, Coronagraphy, Spatial resolution
The Mid-Infrared Instrument (MIRI), a result of the collaborative work of a consortium of European and US institutes, is the only Mid-IR science instrument on the James Webb Space Telescope (JWST). The combination of MIRI0 s sensitivity and angular resolution over the 5-28.5 µm wavelength range will enable investigations into many different science topics, ranging from the local to the high-redshift Universe. The MIRI team has defined and published a set of ”Recommended Strategies” to help observers optimally plan and execute their science programs. Some of these recommendations are generic and applicable to any science case; others are tailored to specific observing modes. Here we summarize key generic recommendations for MIRI observers, with emphasis on detector usage. All this information is available to observers as part of the James Webb Telescope User’s Documentation System and will be updated as needed.1
We describe here the performance and operational concept for the Low Resolution Spectrometer (LRS) of the mid-infrared instrument (MIRI) for the James Webb Space Telescope. The LRS will provide R∼100 slit and
slitless spectroscopy from 5 to 12 micron, and its design is optimised for observations of compact sources, such as exoplanet host stars. We provide here an overview of the design of the LRS, and its performance as measured during extensive test campaigns, examining in particular the delivered image quality, dispersion, and resolving power, as well as spectrophotometric performance. The instrument also includes a slitless spectroscopy mode, which is optimally suited for transit spectroscopy of exoplanet atmospheres. We provide an overview of the operational procedures and the differences ahead of the JWST launch in 2018.
We report on tests of the Mid-Infrared Instrument (MIRI) focal plane electronics (FPE) and detectors conducted at the Jet Propulsion Laboratory (JPL). The goals of these tests are to: characterize the performance of readout modes; establish subarray operations; characterize changes to performance when switching between subarrays and/or readout modes; fine tune detector settings to mitigate residual artifacts; optimize anneal effectiveness; and characterize persistence. The tests are part of a continuing effort to support the MIRI pipeline development through better understanding of the detector behavior. An extensive analysis to determine the performance of the readout modes was performed. We report specifically on the comparison of the fast and slow readout modes and subarray tests.
The Observational Cosmology Laboratory at NASA’s Goddard Space Flight Center (GSFC), in collaboration with the
University of Maryland, is building the Rapid Infrared Imager/Spectrometer (RIMAS) for the new 4.3 meter Discovery
Channel Telescope (DCT). The instrument is designed to observe gamma-ray burst (GRB) afterglows following their
initial detection by the Swift satellite. RIMAS will operate in the near infrared (0.9 – 2.4 microns) with all of its optics
cooled to ~60 K. The primary optical design includes a collimator lens assembly, a dichroic dividing the wavelength
coverage into the “YJ band” and “HK band” optical arms, and camera lens assemblies for each arm. Additionally, filters
and dispersive elements are attached to wheels positioned prior to each arm’s camera, allowing the instrument to quickly
change from its imaging modes to spectroscopic modes. Optics have also been designed to image the sky surrounding
spectroscopic slits to help observers pass light from target sources through these slits. Because the optical systems are
entirely cryogenic, it was necessary to account for changing refractive indices and model the effects of thermal
contraction. One result of this work is a lens mount design that keeps lenses centered on the optical axis as the system is
cooled. Efforts to design, tolerance and assemble these cryogenic optical systems are presented.
The Reionization And Transients Infra-Red camera has been built for rapid Gamma-Ray Burst followup and
will provide simultaneous optical and infrared photometric capabilities. The infrared portion of this camera
incorporates two Teledyne HgCdTe HAWAII-2RG detectors, controlled by Teledyne’s SIDECAR ASICs. While
other ground-based systems have used the SIDECAR before, this system also utilizes Teledyne’s JADE2 interface
card and IDE development environment. Together, this setup comprises Teledyne’s Development Kit, which is
a bundled solution that can be efficiently integrated into future ground-based systems. In this presentation, we
characterize the system’s read noise, dark current, and conversion gain.
The Reionization And Transients InfraRed (RATIR) camera has been built for rapid Gamma-Ray Burst (GRB)
followup and will provide quasi-simultaneous imaging in ugriZY JH. The optical component uses two 2048 × 2048
pixel Finger Lakes Imaging ProLine detectors, one optimized for the SDSS u, g, and r bands and one optimized
for the SDSS i band. The infrared portion incorporates two 2048 × 2048 pixel Teledyne HgCdTe HAWAII-2RG
detectors, one with a 1.7-micron cutoff and one with a 2.5-micron cutoff. The infrared detectors are controlled by
Teledyne's SIDECAR (System for Image Digitization Enhancement Control And Retrieval) ASICs (Application
Specific Integrated Circuits). While other ground-based systems have used the SIDECAR before, this system
also utilizes Teledyne's JADE2 (JWST ASIC Drive Electronics) interface card and IDE (Integrated Development
Environment). Here we present a summary of the software developed to interface the RATIR detectors with
Remote Telescope System, 2nd Version (RTS2) software. RTS2 is an integrated open source package for remote
observatory control under the Linux operating system and will autonomously coordinate observatory dome,
telescope pointing, detector, filter wheel, focus stage, and dewar vacuum compressor operations. Where necessary
we have developed custom interfaces between RTS2 and RATIR hardware, most notably for cryogenic focus stage
motor drivers and temperature controllers. All detector and hardware interface software developed for RATIR
is freely available and open source as part of the RTS2 distribution.
The Reionization and Transients InfraRed camera (RATIR) is a simultaneous optical/NIR multi-band imaging
camera which is 100% time-dedicated to the followup of Gamma-ray Bursts. The camera is mounted on the
1.5-meter Johnson telescope of the Mexican Observatorio Astronomico Nacional on Sierra San Pedro Martir in
Baja California. With rapid slew capability and autonomous interrupt capabilities, the system will image GRBs
in 6 bands (i, r, Z, Y, J, and H) within minutes of receiving a satellite position, detecting optically faint afterglows
in the NIR and quickly alerting the community to potential GRBs at high redshift (z>6-10). We report here
on this Spring's first light observing campaign with RATIR. We summarize the instrumental characteristics,
capabilities, and observing modes.
In this article we present the mechanical design and the manufacturing of the support structure for the Reionization And
Transients InfraRed (RATIR) camera. The instrument is mounted at the f/13 Cassegrain focus of the 1.5-meter Harold
Johnson telescope of the Observatorio Astronómico Nacional at San Pedro Mártir (OAN/SPM) in Mexico. We describe
the high-level requirements and explain their translation to the mechanical specifications and requirements. We describe
the structural finite-element analysis and the boundary conditions, loads, and general assumptions included in the
simulations. We summarize the expected displacements, rotations and stresses. We present the optomechanical
components and the elements used to attach the instrument to the telescope. Finally, we show the instrument installed on
the telescope.
Alan Watson, Michael Richer, Joshua Bloom, Nathaniel Butler, Urania Ceseña, David Clark, Enrique Colorado, Antolín Córdova, Alejandro Farah, Lester Fox-Machado, Ori Fox, Benjamín García, Leonid Georgiev, J. Jesús González, Gerardo Guisa, Leonel Gutiérrez, Joel Herrera, Christopher Klein, Alexander Kutyrev, Francisco Lazo, William Lee, Eduardo López, Esteban Luna, Benjamín Martínez, Francisco Murillo, José Manuel Murillo, Juan Manuel Núñez, J. Xavier Prochaska, José Luís Ochoa, Fernando Quirós, David Rapchun, Carlos Román-Zúñiga, Gennady Valyavin
The Reionization And Transients Infra-Red (RATIR) camera is intended for robotic operation on the 1.5-meter Harold
Johnson telescope of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
This paper describes the work we have carried out to successfully automate the telescope and prepare it for RATIR. One
novelty is our use of real-time absolute astrometry from the finder telescopes to point and guide the main telescope.
The James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec) incorporates two 5 μm cutoff
(λco =5 μm) 2048×2048 pixel Teledyne HgCdTe HAWAII-2RG sensor chip assemblies. These detector arrays,
and the two Teledyne SIDECAR application specific integrated circuits that control them, are operated in space
at Τ ~ 37 K. This article focuses on the measured performance of the first flight-candidate, and near-flight
candidate, detector arrays. These are the first flight-packaged detector arrays that meet NIRSpec's challenging
6 e- rms total noise requirement. The current version of this paper has had a correction made to it at the request of the author. Please see the linked Errata for further details.
The accurate determination of a detector's fundamental parameters, including read noise, dark current, and QE, relies on a proper measurement of a detector's conversion gain (e- ADU-1). Charge coupling effects, such as interpixel capacitance, attenuate photon shot noise and result in an overestimation of conversion gain when implementing the photon transfer technique. An approach involving 55Fe X-rays provides a potentially straightforward measurement of conversion gain by comparing the observed instrumental counts (ADU) to the known charge (e-) liberated by the X-ray. This technique is already preferred within the CCD community, as the pair production energy for silicon is well established. In contrast, to date the pair production energy is unknown for HgCdTe, a material commonly used for near-infrared detectors. In this paper, we derive a preliminary calibration of the 55Fe X-ray energy response of HgCdTe using 8 HST WFC3 1.7 μm flight grade detectors. Our conversion of the X-ray intensities from counts into electrons implements a technique that restores the "true" gain via classical propagation of errors. For these detectors, our analysis yields preliminary results of good statistical precision: each Kα event generates 1849 ± 46 electrons, which corresponds to a pair production energy of 3.21 ± 0.08 eV. We are continuing to assess potential systematic effects to further refine the accuracy of this result.
We present interim results from the characterization test development for the Detector Subsystem of the Near-Infrared
Spectrograph (NIRSpec). NIRSpec will be the primary near-infrared spectrograph on the James Webb Space Telescope
(JWST). The Detector Subsystem consists of a Focal Plane Assembly containing two Teledyne HAWAII-2RG arrays,
two Teledyne SIDECAR cryogenic application specific integrated circuits, and a warm Focal Plane Electronics box. The
Detector Characterization Laboratory at NASA's Goddard Space Flight Center will perform the Detector Subsystem
characterization tests. In this paper, we update the initial test results obtained with engineering grade components.
We present early results from the performance test development for the Detector Subsystem of the Near-Infrared
Spectrograph (NIRSpec). NIRSpec will be the primary near-infrared spectrograph on the James Webb Space Telescope
(JWST). The Detector Subsystem consists of a Focal Plane Assembly containing two Teledyne HAWAII-2RG arrays,
two Teledyne SIDECAR cryogenic application specific integrated circuits, and a warm Focal Plane Electronics box. The
Detector Characterization Laboratory at NASA's Goddard Space Flight Center will perform the Detector Subsystem
characterization tests. In this paper, we summarize the initial test results obtained with engineering grade components.
We report the results of a program to mitigate defect induced (tunneling) dark current which arises from lattice
mismatch between In0.82Ga0.18As 'extended wavelength' detector material and the InP substrate upon which
it is grown. Our goal is to produce material suitable for ground-based broadband astronomical observation by
achieving a dark current level in individual 25x25μm array pixels which is less than the atmospheric airglow
and telescope thermal emission in the astronomical H (1.50-1.80 μm) and Ks (2.00-2.32 μm) bands. We have
cryogenically tested multiple growths of candidate materials, packaged as both individual diodes and focal plane
arrays, supplied by Sensors Unlimited, Inc. (SU). Results indicate dark current levels, in the current generation
of array materials, surpassing the requirements for broadband imaging, and with the potential to be used for
narrow band imaging and low-resolution spectroscopy.
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