We describe a large-angle survey for fast, optical transients: gamma ray bursts (GRBs), supernovae (SNe), lensed and transiting planets, AGNs and serendipitously found objects. The principal science goals are to obtain light curves for all transients and to obtain redshifts of GRBs and orphan afterglows. The array is called Xian. In conjunction with the gamma-ray satellites, ECLAIRs/SVOM and GLAST, the data will be used to study sources from z=0.1 to >6. The telescope array has 400 Schmidt telescopes, each with ~20 sq. degree focal planes and apertures of ~0.5 meters. The passively cooled, multiple CCD arrays have a total of 16000x16000 pixels, up to 13 readout channels per 1K x 4K CCD and work in TDI mode. The system provides continuous coverage of the circumpolar sky, from the Antarctic plateau, every few seconds. Images averaged over longer time intervals allow searches for the host galaxies of the detected transients, as well as for fainter, longer timescale transients. Complete, data at high time resolution are only stored for selected objects. The telescopes are fixed and use a single filter: there are few (or no) moving parts. Expected detection rates are 0.3 GRBs afterglows per day, >100 orphan afterglows per day and >0.1 blue flashes per day from Type II or Type Ib/c supernovae. On-site computers compare successive images and trigger follow-up observations of selected objects with a co-sited, well-instrumented telescope (optical, IR; spectroscopy, photometry, polarimetry), for rapid follow-up of transients. Precursor arrays with 20-100 square degrees are planned for the purpose of developing trigger software, testing observing strategies and deriving good cost estimates for a full set of telescope units.
We describe the development, construction, and testing of two 384 element arrays of ion-implanted semiconducting cryogenic bolometers designed for use in far-infrared and submillimeter cameras. These two dimensional arrays are assembled from a number of 32 element linear arrays of monolithic Pop-Up bolometer Detectors (PUD) developed at NASA/Goddard Space Flight Center. PUD technology allows the construction of large, high filling factor, arrays that make efficient use of available focal plane area in far-infrared and submillimeter astronomical instruments. Such arrays can be used to provide a significant increase in mapping speed over smaller arrays. A prototype array has been delivered and integrated into a ground-based camera, the Submillimeter High Angular Resolution Camera (SHARC II), a facility instrument at the Caltech Submillimeter Observatory (CSO). A second array has recently been delivered for integration into the High-resolution Airborne Widebandwidth Camera (HAWC), a far-infrared imaging camera for the Stratospheric Observatory for Infrared Astronomy (SOFIA). HAWC is scheduled for commissioning in 2005.
The Stratospheric Observatory For Infrared Astronomy's (SOFIA's) High resolution Airborne Wideband Camera (HAWC) will use an ion-implanted silicon bolometer array developed at NASA's Goddard Space Flight Center (GSFC). The GSFC Pop-Up Detectors (PUDs) use a unique "folding" technique to enable a 12 x 32 element close-packed array of bolometers with a filling factor greater than 95%. The HAWC detector uses a resistive metal film on silicon to provide frequency independent, ~50% absorption over the 40 - 300 micron band. The silicon bolometers are manufactured in 32-element rows within silicon frames using Micro Electro Mechanical Systems (MEMS) silicon etching techniques. The frames are then cut, "folded", and glued onto a metallized, ceramic, thermal bus "bar". Optical alignment using micrometer jigs ensures their uniformity and correct placement. The rows are then stacked side-by-side to create the final 12 x 32 element array. A kinematic Kevlar suspension system isolates the 200 mK bolometer cold stage from the rest of the 4K detector housing. GSFC - developed silicon bridge chips make electrical connection to the bolometers, while maintaining thermal isolation. The Junction Field Effect Transistor (JFET) preamplifiers for all the signal channels operate at 120 K, yet they are electrically connected and located in close proximity to the bolometers. The JFET module design provides sufficient thermal isolation and heat sinking for these, so that their heat is not detected by the bolometers. Preliminary engineering results from the flight detector dark test run are expected to be available in July 2004. This paper describes the array assembly and mechanical and thermal design of the HAWC detector and the JFET module.
HAWC (High-resolution Airborne Wideband Camera) is a facility science instrument for SOFIA (Stratospheric Observatory for Infrared Astronomy). It is a far-infrared camera designed for diffraction-limited imaging in four spectral passbands centered at wavelengths of 53, 89, 155, and 216 μm. Its detector is a 12x32 array of bolometers cooled to 0.2 K by an adiabatic demagnetization refrigerator. In this paper, we report on the development and testing of the instrument and its subsystems.
We describe an "Origins Survey" that will provide a comprehensive picture of the era of galaxy formation and assembly. The survey data will allow us to develop and test models of when and how the first condensed objects in the universe are formed. We propose to do this by accumulating enough redshifts to have 10,000 galaxies of each of 20 types (defined empirically by the real state of galaxies) in each of 10 time zones of duration 1.5 Gyr each. Discounting the first two such zones which will be covered by the SDSS, the 2DF, and other surveys, our plan is to obtain redshifts for a total of 2 million galaxies. The hardware design is driven by the requirement to see the earliest galaxies (z ~ 10) and the capability to carry out this high z survey in an elapsed time of five years on a dedicated telescope. These considerations lead to a tentative design that uses a 20 - 40 meter diameter telescope with an Integral Field Unit (IFU) high-resolution spectrograph (R=6000 operating in the 1 - 2.5 micron spectral range. We require a 1 - 3 arc minute field of view with a modest adaptive-optics-corrected 0.2 arc-sec half power diameter point spread function (in the near-IR). Simultaneous, complementary observations will be made in the far-infrared/submm (350 - 850) microns to view the "hidden" starbursts known to exist from SCUBA data and the (non-CMB) infrared background. These observations require a low water vapor site. With appropriate instrumentation the same telescope can be used to study proto-planetary disks and star formation regions in the low z Universe. In this paper we present the scientific case for the survey, the basis for our requirements, and the results of our preliminary studies of how best to meet these goals.
When SOFIA enters operation, it will be the largest far- infrared telescope available, so it will have the best intrinsic angular resolution. HAWC (High-resolution Airborne Wideband Camera) is a far-infrared camera designed to cover the 40 - 300 micron spectral range at the highest possible angular resolution. Its purpose is to provide a sensitive, versatile, and reliable facility-imaging capability for SOFIA's user community during its first operational use.
Many IR sources are dusty; embedded stars are obscured, often completely, and their light is absorbed. The starlight heats the dust, typically to temperatures of tens or hundreds of Kelvin, and the heated dust radiates in the far IR, at wavelengths for which the Stratospheric Observatory for IR Astronomy (SOFIA) is optimized. These dusty targets radiate most or all of their energy in the far IR: broadband imaging with the highest possible spatial resolution is the natural starting point form which to develop an understanding of their morphology and energetics. Because SOFIA is the largest far IR telescope, it delivers the best spatial resolution. The wealth of detail revealed when resolution improves often result in startling insights, as new pictures of old favorites from the Hubble Space Telescope so regularly remind us. We therefore believe that most SOFIA studies will begin with high spatial resolution broadband imaging, and that a facility science instrument is required to serve this heavy and continuing workload.
ABU is a NOAO IR imaging camera designed for evaluating the performance of the 1024x1024 Aladdth InSb array. For this experiment, it was outfitted with five filters (see Figure 9) m the 3-5 micron range to exploit the low water vapor and lower air temperatures at the South Pole. At the South Pole it was integrated with the CARA SPIREX (South Pole Infrared Explorer) telescope. Figure 1 is a picture of the telescope showing the environmental box (the white box by the author). which protected ABU and its electronics from ambient environmental conditions.
The lower stratosphere in the polar regions offers conditions for observation in the near-infrared comparable to those obtained from space. We describe a concept for a 6-meter, diluted aperture, near-infrared telescope carried by a tethered aerostat flying at 12 km altitude, to serve as a testbed for future space astronomical observatories while producing frontier science.
This paper describes the near-infrared grism spectrometer and imager (GRIM) designed for use on the Astrophysical Research Consortium telescope. The GRIM system incorporates a wide range of imaging, spectroscopic, and polarimetric capabilities. Attention is given to the mechanical and optical layout of GRIM, the details of the optical design, and the basic components of the remote observing system.
This paper describes the design and the performance of the Astrophysical Research Consortium prototype near-infrared camera (pNIC) designed to test focal plane arrays both on and off the telescope. Special attention is given to the detector in pNIC, the mechanical and optical designs, the electronics, and the instrument interface. Experiments performed to illustrate the most salient aspects of pNIC are described.