The Primordial Inflation Polarization Explorer (PIPER) is a stratospheric balloon payload to measure the polarization of the cosmic microwave background. Twin telescopes mounted within an open-aperture bucket dewar couple the sky to bolometric detector arrays. We reduce detector loading and photon noise by cooling the entire optical chain to 1.7 K or colder. A set of fountain-effect pumps sprays superfluid liquid helium onto each optical surface, producing helium flows of 50-100 cm3 s-1 at heights up to 200 cm above the liquid level. We describe the fountain-effect pumps and the cryogenic performance of the PIPER payload during two flights in 2017 and 2019.

Departures of the energy spectrum of the cosmic microwave background (CMB) from a perfect blackbody probe a fundamental property of the universe -- its thermal history. Current upper limits, dating back some 25 years, limit such spectral distortions to 50 parts per million and provide a foundation for the Hot Big Bang model of the early universe. Modern upgrades to the 1980's-era technology behind these limits enable three orders of magnitude or greater improvement in sensitivity. The standard cosmological model provides compelling targets at this sensitivity, spanning cosmic history from the decay of primordial density perturbations to the role of baryonic feedback in structure formation. Fully utilizing this sensitivity requires concurrent improvements in our understanding of competing astrophysical foregrounds. We outline a program using proven technologies capable of detecting the minimal predicted distortions even for worst-case foreground scenarios.

Following the pioneering observations with COBE in the early 1990s, studies of the cosmic microwave background (CMB) have focused on temperature and polarization anisotropies. CMB spectral distortions - tiny departures of the CMB energy spectrum from that of a perfect blackbody - provide a second, independent probe of fundamental physics, with a reach deep into the primordial Universe. The theoretical foundation of spectral distortions has seen major advances in recent years, which highlight the immense potential of this emerging field. Spectral distortions probe a fundamental property of the Universe - its thermal history - thereby providing additional insight into processes within the cosmological standard model (CSM) as well as new physics beyond. Spectral distortions are an important tool for understanding inflation and the nature of dark matter. They shed new light on the physics of recombination and reionization, both prominent stages in the evolution of our Universe, and furnish critical information on baryonic feedback processes, in addition to probing primordial correlation functions at scales inaccessible to other tracers. In principle the range of signals is vast: many orders of magnitude of discovery space could be explored by detailed observations of the CMB energy spectrum. Several CSM signals are predicted and provide clear experimental targets, some of which are already observable with present-day technology. Confirmation of these signals would extend the reach of the CSM by orders of magnitude in physical scale as the Universe evolves from the initial stages to its present form. The absence of these signals would pose a huge theoretical challenge, immediately pointing to new physics.

While the upcoming telescopes will reveal correspondingly fainter, more distant galaxies, a question will persist: what more is there that these telescopes cannot see? One answer is the source-subtracted Cosmic Infrared Background (CIB). The CIB is comprised of the collective light from all sources remaining after known, resolved sources are accounted for. Ever-more-sensitive surveys will identify the brightest of these, allowing them to be removed, and - like peeling layers off an onion - reveal deeper layers of the CIB. In this way it is possible to measure the contributions from populations not accessible to direct telescopic observation. Measurement of fluctuations in the source-subtracted CIB, i.e., the spatial power spectrum of the CIB after subtracting resolved sources, provides a robust means of characterizing its faint, and potentially new, populations. Studies over the past 15 years have revealed source-subtracted CIB fluctuations on scales out to ~100' which cannot be explained by extrapolating from known galaxy populations. Moreover, they appear highly coherent with the unresolved Cosmic X-ray Background, hinting at a significant population of accreting black holes among the CIB sources. Characterizing the source-subtracted CIB with high accuracy, and thereby constraining the nature of the new populations, is feasible with upcoming instruments and would produce critically important cosmological information in the next decade. New coextensive deep and wide-area near-infrared, X-ray, and microwave surveys will bring decisive opportunities to examine, with high fidelity, the spatial spectrum and origin of the CIB fluctuations and their cross-correlations with cosmic microwave and X-ray backgrounds, and determine the formation epochs and the nature of the new sources (stellar nucleosynthetic or accreting black holes).

1 NASA/GSFC, Mail Code: 665, Greenbelt, MD 20771, USA 2 University of Oxford, Denys Wilkinson Building, Keble Road, Oxford, OX1 3RH, UK 3 Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, U.K. 4 Laboratoire Astroparticule et Cosmologie (APC), CNRS/IN2P3, 10, rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France 5 Département d’Astrophysique, CEA Saclay DSM/Irfu, 91191 Gif-sur-Yvette, France 6 Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA 7 Institute for Advanced Study, Princeton, NJ 08540, USA 8 Center for Computational Astrophysics, Flatiron Institute, 162 5th Avenue, New York, NY 10010, USA 9 Niels Bohr International Academy and Discovery Center, Blegdamsvej 17, 2100 Copenhagen, Denmark

We summarize the radio synchrotron background workshop that took place 2017 July 19–21 at the University of Richmond. This first scientific meeting dedicated to the topic was convened because current measurements of the diffuse radio monopole reveal a surface brightness that is several times higher than can be straightforwardly explained by known Galactic and extragalactic sources and processes, rendering it by far the least well understood photon background at present. It was the conclusion of a majority of the participants that the radio monopole level is at or near that reported by the ARCADE 2 experiment and inferred from several absolutely calibrated zero-level lower frequency radio measurements, and unanimously agreed that the production of this level of surface brightness, if confirmed, represents a major outstanding question in astrophysics. The workshop reached a consensus on the next priorities for investigations of the radio synchrotron background.

Modern cosmology has sharpened questions posed for millennia about the origin of our cosmic habitat. The age-old questions have been transformed into two pressing issues primed for attack in the coming decade: How did the Universe begin? and What physical laws govern the Universe at the highest energies? The clearest window onto these questions is the pattern of polarization in the Cosmic Microwave Background (CMB), which is uniquely sensitive to primordial gravity waves. A detection of the special pattern produced by gravity waves would be not only an unprecedented discovery, but also a direct probe of physics at the earliest observable instants of our Universe. Experiments which map CMB polarization over the coming decade will lead us on our first steps towards answering these age-old questions.

In this report we discuss the impact of polarized foregrounds on a future CMBPol satellite mission. We review our current knowledge of Galactic polarized emission at microwave frequencies, including synchrotron and thermal dust emission. We use existing data and our understanding of the physical behavior of the sources of foreground emission to generate sky templates, and start to assess how well primordial gravitational wave signals can be separated from foreground contaminants for a CMBPol mission. At the estimated foreground minimum of similar to 100 GHz, the polarized foregrounds are expected to be lower than a primordial polarization signal with tensor-to-scalar ratio r = 0.01, in a small patch (similar to 1%) of the sky known to have low Galactic emission. Over 75% of the sky we expect the foreground amplitude to exceed the primordial signal by about a factor of eight at the foreground minimum and on scales of two degrees. Only on the largest scales does the polarized foreground amplitude exceed the primordial signal by a larger factor of about 20. The prospects for detecting an r = 0.01 signal including degree-scale measurements appear promising, with 5 sigma(r) similar to 0.003 forecast from multiple methods. A mission that observes a range of scales offers better prospects from the foregrounds perspective than one targeting only the lowest few multipoles. We begin to explore how optimizing the composition of frequency channels in the focal plane can maximize our ability to perform component separation, with a range of typically 40 less than or similar to nu less than or similar to 300 GHz preferred for ten channels. Foreground cleaning methods are already in place to tackle a CMBPol mission data set, and further investigation of the optimization and detectability of the primordial signal will be useful for mission design.

In this report we discuss the impact of polarized foregrounds on a future CMBPol satellite mission. We review our current knowledge of Galactic polarized emission at microwave frequencies, including synchrotron and thermal dust emission. We use existing data and our understanding of the physical behavior of the sources of foreground emission to generate sky templates, and start to assess how well primordial gravitational wave signals can be separated from foreground contaminants for a CMBPol mission. At the estimated foreground minimum of ~100 GHz, the polarized foregrounds are expected to be lower than a primordial polarization signal with tensor-to-scalar ratio r=0.01, in a small patch (~1%) of the sky known to have low Galactic emission. Over 75% of the sky we expect the foreground amplitude to exceed the primordial signal by about a factor of eight at the foreground minimum and on scales of two degrees. Only on the largest scales does the polarized foreground amplitude exceed the primordial signal by a larger factor of about 20. The prospects for detecting an r=0.01 signal including degree-scale measurements appear promising, with 5 sigma_r ~0.003 forecast from multiple methods. A mission that observes a range of scales offers better prospects from the foregrounds perspective than one targeting only the lowest few multipoles. We begin to explore how optimizing the composition of frequency channels in the focal plane can maximize our ability to perform component separation, with a range of typically 40 < nu < 300 GHz preferred for ten channels. Foreground cleaning methods are already in place to tackle a CMBPol mission data set, and further investigation of the optimization and detectability of the primordial signal will be useful for mission design.

The Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE) is a balloon-borne instrument designed to measure the temperature of the cosmic microwave background at centimeter wavelengths. ARCADE searches for deviations from a blackbody spectrum resulting from energy releases in the early universe. Long-wavelength distortions in the CMB spectrum are expected in all viable cosmological models. Detecting these distortions or showing that they do not exist is an important step for understanding the early universe. We describe the ARCADE instrument design, current status, and future plans.

The primordial anisotropy polarization pathfinder array (PAPPA) is a balloon-based instrument to measure the polarization of the cosmic microwave background and search for the signal from gravity waves excited during an inflationary epoch in the early universe. PAPPA will survey a 20° × 20° patch at the North Celestial Pole using 32 pixels in 3 passbands centered at 89, 212, and 302 GHz. Each pixel uses MEMS switches in a superconducting microstrip transmission line to combine the phase modulation techniques used in radio astronomy with the sensitivity of transition-edge superconducting bolometers. Each switched circuit modulates the incident polarization on a single detector, allowing nearly instantaneous characterization of the Stokes I, Q, and U parameters. We describe the instrument design and status.

We present a data simulation package designed to create a series of simulated data samples for a detector with non-destructive sampling capability. The original intent of this software was to provide a method for generating simulated images for the Next Generation Space Telescope, but it is general enough to apply to almost any non-destructive detector or instrument. MultiDataSim can be used to generate “practice” sampling strategies for an instrument or field-of-view, and thus can be used to identify optimal observation strategies.

The Laboratory for Astronomy and Solar Physics ͑LASP͒ continues to conduct a broad program of research and instrument technology development in ultraviolet and infrared astronomy and in optical/UV, X-ray, gamma-ray, and visible-light studies of the Sun. The program encompasses theoretical, observational, and experimental work, using platforms in space such as the Hubble Space Telescope ͑HST͒ Space Telescope Imaging Spectrograph ͑STIS͒ and ground-based supporting facilities. The staff provides important enabling services to the scientific community in support of major NASA observatory missions in space astronomy and solar physics. The current missions include Hubble Space Besides the above spacecraft and others mentioned in the report below, the Laboratory conducts experiments through the Spacelab program of Shuttle-attached payloads and via balloon and airborne observatories, such as the Stratospheric Observatory for Infrared Astronomy/Submillimeter and Far Infrared Experiment ͑SOFIA/SAFIRE͒. We also conduct rocket experiments for solar and ultraviolet astronomy. We manage or support several ground-based facilities for research in instrument development, solar physics, and come-tary science ͑as it pertains to physics of the solar wind͒. Updates on facility and instrumental progress and research highlights, including a bibliography of recent contributions , appear below. 1.A. INTRODUCTION The Branch engages in theoretical and observational in-frared, submillimeter, and radio astrophysics, notably in studies of diffuse infrared and microwave background radiations , both galactic and cosmic. The Branch develops detectors for infrared, submillimeter, and X-ray astronomy, and develops instruments for suborbital projects and space missions. The Branch develops instrumentation for the Hubble 1.C. FLIGHT PROGRAMS NGST. The Next Generation Space Telescope ͑NGST͒ is a large aperture follow-on mission to the Hubble telescope under the Origins program. It is an 8 m class cooled infrared telescope optimized to observe the first stars and galaxies, and was given top priority by the National Academy of Sciences Decadal Survey. It is planned for launch in 2008. Mather serves as the NGST Study Scientist, while Greenhouse is the Deputy Study Scientist for instruments, and is the prime NGST contact for the six NASA-funded instrument studies as well as Canadian and ESA studies. Greenhouse led a GSFC engineering team to design the Yardstick instrument package for NGST, which would implement the recommendations of the NGST report ''Visiting a Time when Galaxies were Young.'' This package includes a four-bay near IR camera, a multi-object spectrometer with a micro-mirror array as an object selector, and a mid-IR camera and spectrometer. Greenhouse also leads the development of …

A direct measurement of the extragalactic background light (EBL) can provide important constraints on the integrated cosmological history of star formation, metal and dust production, and the conversion of starlight into infrared emission by dust. In this paper we examine the cosmological implications of the recent detection of the EBL in the 125 to 5000 μm wavelength region by the Diffuse Infrared Background Experiment (DIRBE) and Far Infrared Absolute Spectrophotometer (FIRAS) on board the Cosmic Background Explorer (COBE). We first show that the 140 and 240 μm isotropic residual emission found in the DIRBE data cannot be produced by foreground emission sources in the solar system or the Galaxy. The DIRBE 140 and 240 μm isotropic residuals, and by inference the FIRAS residuals as well, are therefore extragalactic. Assuming that most of the 140 and 240 μm emission is from dust yields a 2 σ lower limit of νI(ν) ≈ 5 nW m-2 sr-1 for the EBL at 100 μm. The integrated EBL detected by the COBE between 140 and 5000 μm is ~16 nW m-2 sr-1, roughly 20%-50% of the integrated EBL intensity expected from energy release by nucleosynthesis throughout cosmic history. This also implies that at least ~5%-15% of the baryonic mass density implied by big bang nucleosynthesis has been processed through stars. The COBE observations provide important constraints on the cosmic star formation rate, and we calculate the EBL spectrum for various star formation histories. The results show that the UV and optically determined cosmic star formation rates fall short in producing the observed 140 to 5000 μm background. The COBE observations require the star formation rate at redshifts of z ≈ 1.5 to be larger than that inferred from UV-optical observations by at least a factor of 2. This excess stellar energy must be mainly generated by massive stars, since it otherwise would result in a local K-band luminosity density that is larger than observed. The energy sources could either be yet undetected dust-enshrouded galaxies, or extremely dusty star-forming regions in observed galaxies, and they may be responsible for the observed iron enrichment in the intracluster medium. The exact star formation history or scenarios required to produce the EBL at far-IR wavelengths cannot be unambiguously resolved by the COBE observations and must await future observations.

The NASA Yardstick design for the Integrated Science Instrument Module (ISIM) utilizes 64 1k x 1k InSb imagers. Since multiple readouts per image are required to remove cosmic ray events and to reduce the readout noise, the implied downlink rates can approach 0.7 Tbytes per day. These would exceed the downlink capabilities of RF links from L2 or more distant orbits. Some form of on-board data analysis and compression is mandatory: a factor of 100 compression for an L2 orbit, factors of 1000-10000 for a 1 AU drift-away or 1 x 3 AU elliptical orbit. Supported by funding from JPL to study the uses of low-cost, on- board parallel processors, we are studying algorithms and architectures to perform cosmic-ray rejection and lossless compression of the NIR images, while optimizing the resulting signal- to-noise.

Annals of the New York Academy of SciencesVolume 688, Issue 1 p. 801-803 Preliminary Results of the Medium Scale Anisotropy Measurement1 J. Puchalla, J. Puchalla Massachusetts Institute of Technology, Room 20B–145, Cambridge, MA 02139Search for more papers by this authorE. Cheng, E. Cheng NASA/Goddard Space Flight Center, Code 685.0, Greenbelt, MD 20771Search for more papers by this authorD. Cottingham, D. Cottingham Universities Space Research Association, NASA/GSFC Code 685.3, Greenbelt, MD 20771Search for more papers by this authorD. Fixsen, D. Fixsen Applied Research Corporation, NASA/GSFC Code 685.3, Greenbelt, MD 20771Search for more papers by this authorE.P. Gentieu, E.P. Gentieu NASA/Goddard Space Flight Center, Code 685.0, Greenbelt, MD 20771Search for more papers by this authorC. Inman, C. Inman Massachusetts Institute of Technology, Room 20B–145, Cambridge, MA 02139Search for more papers by this authorM. Kowitt, M. Kowitt NASA/Goddard Space Flight Center, Code 685.0, Greenbelt, MD 20771Search for more papers by this authorS. Meyer, S. Meyer Massachusetts Institute of Technology, Room 20B–145, Cambridge, MA 02139Search for more papers by this authorL. Page, L. Page Princeton University Physics Dept., Princeton, NJ 08544Search for more papers by this authorR. Silverberg, R. Silverberg NASA/Goddard Space Flight Center, Code 685.0, Greenbelt, MD 20771Search for more papers by this author J. Puchalla, J. Puchalla Massachusetts Institute of Technology, Room 20B–145, Cambridge, MA 02139Search for more papers by this authorE. Cheng, E. Cheng NASA/Goddard Space Flight Center, Code 685.0, Greenbelt, MD 20771Search for more papers by this authorD. Cottingham, D. Cottingham Universities Space Research Association, NASA/GSFC Code 685.3, Greenbelt, MD 20771Search for more papers by this authorD. Fixsen, D. Fixsen Applied Research Corporation, NASA/GSFC Code 685.3, Greenbelt, MD 20771Search for more papers by this authorE.P. Gentieu, E.P. Gentieu NASA/Goddard Space Flight Center, Code 685.0, Greenbelt, MD 20771Search for more papers by this authorC. Inman, C. Inman Massachusetts Institute of Technology, Room 20B–145, Cambridge, MA 02139Search for more papers by this authorM. Kowitt, M. Kowitt NASA/Goddard Space Flight Center, Code 685.0, Greenbelt, MD 20771Search for more papers by this authorS. Meyer, S. Meyer Massachusetts Institute of Technology, Room 20B–145, Cambridge, MA 02139Search for more papers by this authorL. Page, L. Page Princeton University Physics Dept., Princeton, NJ 08544Search for more papers by this authorR. Silverberg, R. Silverberg NASA/Goddard Space Flight Center, Code 685.0, Greenbelt, MD 20771Search for more papers by this author First published: June 1993 https://doi.org/10.1111/j.1749-6632.1993.tb43975.x 1 The National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC) supports this research through grants NAGW 1841, NGT 50908, NGT 50720 and the Sigma Xi Society through grant 9203. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume688, Issue1Texas/Pascos '92: Relativistic Astrophysics and Particle CosmologyJune 1993Pages 801-803 RelatedInformation