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1. The wide-field infrared transient explorer (WINTER)

   https://doi.org/10.1117/12.2561210  

   Lourie, Nathan P. ; Baker, John W. ; Burruss, Richard S. ; Egan, Mark D. ; Furész, Gábor ; Frostig, Danielle ; Garcia-Zych, Allan A. ; Ganciu, Nicolae ; Haworth, Kari ; Hinrichsen, Erik ; et al ( December 2020 , X-Ray, Optical, and Infrared Detectors for Astronomy IX)

   Evans, Christopher J. ; Bryant, Julia J. ; Motohara, Kentaro (Ed.)

   The Wide-Field Infrared Transient Explorer (WINTER) is a new infrared time-domain survey instrument which will be deployed on a dedicated 1 meter robotic telescope at the Palomar Observatory. WINTER will perform a seeing-limited time domain survey of the infrared (IR) sky, with a particular emphasis on identifying r -process material in binary neutron star (BNS) merger remnants detected by LIGO. We describe the scientific goals and survey design of the WINTER instrument. With a dedicated trigger and the ability to map the full LIGO O4 positional error contour in the IR to a distance of 190 Mpc within four hours, WINTER will be a powerful kilonova discovery engine and tool for multi-messenger astrophysics investigations. In addition to follow-up observations of merging binaries, WINTER will facilitate a wide range of time-domain astronomical observations, all the while building up a deep coadded image of the static infrared sky suitable for survey science. WINTER's custom camera features six commercial large-format Indium Gallium Arsenide (InGaAs) sensors and a tiled optical system which covers a <1-square-degree field of view with 90% fill factor. The instrument observes in Y, J and a short-H (Hs) band tuned to the long-wave cutoff of the InGaAs sensors, covering a wavelength range from 0.9 - 1.7 microns. We present the design of the WINTER instrument and current progress towards final integration at the Palomar Observatory and commissioning planned for mid-2021. 

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2. Readout and cooling of the WINTER InGaAs camera

   https://doi.org/10.1117/12.2630602  

   Frostig, Danielle ; Burdge, Kevin ; De, Kishalay ; Fűrész, Gábor ; Haworth, Kari ; Hinrichsen, Erik ; Karambelkar, Viraj R. ; Kasliwal, Mansi M. ; Lourie, Nathan P. ; Malonis, Andrew C. ; et al ( August 2022 , SPIE Astronomical Telescopes and Instrumentation (2022))

   Holland, Andrew D. ; Beletic, James (Ed.)

   The Wide-Field Infrared Transient Explorer (WINTER) is a new time-domain instrument which will perform a seeing-limited survey of the near-infrared sky. Deployed on a dedicated 1-meter robotic telescope at Palomar Observatory, WINTER is designed to study transients of particular interest in the near-infrared including kilo-novae from gravitational-wave sources, supernovae, tidal disruption events, and transiting exoplanets around low mass stars with surveys to a depth of J=21 magnitudes. WINTER's custom camera combines six commercial large-format Indium Gallium Arsenide (InGaAs) sensors, observing in Y, J, and a short-H (Hs) band filters (0.9-1.7 microns), and employs a novel tiled optical design to cover a >1 degree squared field of view with 90% fill factor. Each wide-format (1920 x 1080 pixels) InGaAs sensor operates at T = -50°C with a thermoelectric cooler, achieving background-limited photometry without cryogenic cooling. The tiled InGaAs sensors result in a wide field-of-view instrument with significant cost savings when compared to HgCdTe sensors. We present WINTER's novel readout scheme, which includes custom electronics, firmware, and software for low-noise, real-time readout of the InGaAs sensors, including up to a 30x speed up of data reduction using GPUs. This work also outlines the cooling design for warm (T = -50°C) operation of the sensors with a two-stage thermometric cooler, copper heat pipes, and liquid cooling. We conclude with updates on the alignment, integration, and test of the WINTER instrument with a projected first light in Fall 2022. 

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3. Panoramic SETI: program update and high-energy astrophysics applications

   https://doi.org/10.1117/12.2630772  

   Maire, Jérôme ; Wright, Shelley A. ; Holder, Jamie ; Anderson, David P. ; Benbow, Wynstan ; Brown, Aaron ; Cosens, Maren ; Foote, Gregory ; Hanlon, William . ; Hervet, Olivier ; et al ( August 2022 , Proceedings of the SPIE)

   Evans, Christopher J. ; Bryant, Julia J. ; Motohara, Kentaro (Ed.)

   Optical SETI (Search for Extraterrestrial Intelligence) instruments that can explore the very fast time domain, especially with large sky coverage, offer an opportunity for new discoveries that can complement multimessenger and time domain astrophysics. The Panoramic SETI experiment (PANOSETI) aims to observe optical transients with nanosecond to second duration over a wide field-of-view (∼2,500 sq.deg.) by using two assemblies of tens of telescopes to reject spurious signals by coincidence detection. Three PANOSETI telescopes, connected to a White Rabbit timing network used to synchronize clocks at the nanosecond level, have been deployed at Lick Observatory on two sites separated by a distance of 677 meters to distinguish nearby light sources (such as Cherenkov light from particle showers in the Earth’s atmosphere) from astrophysical sources at large distances. In parallel to this deployment, we present results obtained during four nights of simultaneous observations with the four 12-meter VERITAS gamma-ray telescopes and two PANOSETI telescopes at the Fred Lawrence Whipple Observatory. We report PANOSETI’s first detection of astrophysical gamma rays, comprising three events with energies in the range between ∼15 TeV and ∼50 TeV. These were emitted by the Crab Nebula, and identified as gamma rays using joint VERITAS observations. 

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4. Performance testing and end-to-end mapping of the fiber cable on the SALT NIR integral field spectrograph

   https://doi.org/10.1117/12.2630176  

   Oppor, Joshua E. ; Bershady, Matthew A. ; Wolf, Marsha J. ; Smith, Michael P. ; Chattopadhyay, Sabyasachi ; Jaehnig, Kurt P. ; Percival, Jeffrey W. ; Mulligan, Mark P. ; Jurgella, Kathleen M. ; Wirag, Briana ( August 2022 , Performance testing and end-to-end mapping of the fiber cable on the SALT NIR integral field spectrograph)

   Geyl, Roland ; Navarro, Ramón (Ed.)

   The optical fiber integral field unit (IFU) built to feed the near infrared (NIR) spectrograph for the 11-meter Southern African Large Telescope (SALT) has undergone prototyping and rigorous performance testing at Wash- burn Astronomical Laboratories of the University of Wisconsin-Madison Astronomy Department. The 43 m length of 256 fibers which make up the object and sky arrays and spares are routed from the SALT payload down into the spectrograph room in four separate cables. The IFU covers 344 arcsec2 on the sky, with the object array spanning a 552 arcsec2 near-rectangular area at roughly 56% fill-factor. Companion papers describe the mechanical design of the fiber cable that mitigates potential sources of mechanical strain on the optical fiber (Smith et al.) and details of the spectrograph (Wolf et al.). Here we present the results of the performance testing of various test cables as well as performance testing and end-to-end mapping of the fully-assembled science cable. The fiber optics experience an extreme temperature gradient at the ingress to the instrument enclosure held at -40 ◦C during operation. We find an increase in focal ratio degradation (FRD) when holding progressively longer lengths of test fiber at reduced temperature. However, we confirm that this temperature dependent FRD is negligible for our designed length of cold fiber. We also find negligible contributions to FRD from the rubber seal that breaches the room temperature strain relief box and the cold instrument enclosure. Our measure- ments characterize performance including the effects of internal fiber inhomogeneities, stress induced from fiber handling and termination, as well as any imperfections from end-polishing. We present the room-temperature laboratory performance measurements of the fully-assembled science cable; the effective total throughput the fiber cable delivers to the spectrograph collimator is 81±2.5% across all fibers accounting for all losses. 

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5. An Infrared Search for Kilonovae with the WINTER Telescope. I. Binary Neutron Star Mergers

   https://doi.org/10.3847/1538-4357/ac4508  

   Frostig, Danielle ; Biscoveanu, Sylvia ; Mo, Geoffrey ; Karambelkar, Viraj ; Dal Canton, Tito ; Chen, Hsin-Yu ; Kasliwal, Mansi ; Katsavounidis, Erik ; Lourie, Nathan P. ; Simcoe, Robert A. ; et al ( February 2022 , The Astrophysical Journal)

   The Wide-Field Infrared Transient Explorer (WINTER) is a new 1 deg²seeing-limited time-domain survey instrument designed for dedicated near-infrared follow-up of kilonovae from binary neutron star (BNS) and neutron star–black hole mergers. WINTER will observe in the near-infraredY,J, and short-Hbands (0.9–1.7μm, toJ_AB= 21 mag) on a dedicated 1 m telescope at Palomar Observatory. To date, most prompt kilonova follow-up has been in optical wavelengths; however, near-infrared emission fades more slowly and depends less on geometry and viewing angle than optical emission. We present an end-to-end simulation of a follow-up campaign during the fourth observing run (O4) of the LIGO, Virgo, and KAGRA interferometers, including simulating 625 BNS mergers, their detection in gravitational waves, low-latency and full parameter estimation skymaps, and a suite of kilonova lightcurves from two different model grids. We predict up to five new kilonovae independently discovered by WINTER during O4, given a realistic BNS merger rate. Using a larger grid of kilonova parameters, we find that kilonova emission is ≈2 times longer lived and red kilonovae are detected ≈1.5 times further in the infrared than in the optical. For 90% localization areas smaller than 150 (450) deg², WINTER will be sensitive to more than 10% of the kilonova model grid out to 350 (200) Mpc. We develop a generalized toolkit to create an optimal BNS follow-up strategy with any electromagnetic telescope and present WINTER’s observing strategy with this framework. This toolkit, all simulated gravitational-wave events, and skymaps are made available for use by the community.

    

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