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The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission concept to measure cosmological signals from both linear polarization of the cosmic microwave background and spectral distortions from a perfect blackbody. The targeted measurement sensitivity is 2--4 orders of magnitude below competing astrophysical foregrounds, placing stringent requirements on instrument calibration. An on-board blackbody calibrator presents a polarizing Fourier transform spectrometer with a known signal to enable conversion of the sampled interference fringe patterns from telemetry units to physical units. We describe the instrumentation and operations needed to calibrate PIXIE, derive the expected uncertainty for the intensity, polarization, and frequency scales, and show the effect of calibration uncertainty in the derived cosmological signals. In-flight calibration is expected to be accurate to a few parts in $10^6$ at frequencies dominated by the CMB, and a few parts in $10^4$ at higher frequencies dominated by the diffuse dust foreground., Comment: 18 pages including 8 figures. Added material on frequency calibration, matches final published version

The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne telescope mission to search for inflationary gravitational waves from the early universe. PIPER employs two 32x40 arrays of superconducting transition-edge sensors, which operate at 100 mK. An open bucket dewar of liquid helium maintains the receiver and telescope optics at 1.7 K. We describe the thermal design of the receiver and sub-kelvin cooling with a continuous adiabatic demagnetization refrigerator (CADR). The CADR operates between 70-130 mK and provides ~10 uW cooling power at 100 mK, nearly five times the loading of the two detector assemblies. We describe electronics and software to robustly control the CADR, overall CADR performance in flight-like integrated receiver testing, and practical considerations for implementation in the balloon float environment., Comment: 14 pages, 12 figures

The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission concept to measure the gravitational-wave signature of primordial inflation through its distinctive imprint on the linear polarization of the cosmic microwave background (CMB). Its optical system couples a polarizing Fourier transform spectrometer to the sky to measure the differential signal between orthogonal linear polarization states from two co-pointed beams on the sky. The double differential nature of the four-port measurement mitigates beam-related systematic errors common to the two-port systems used in most CMB measurements. Systematic errors coupling unpolarized temperature gradients to a false polarized signal cancel to first order for any individual detector. This common-mode cancellation is performed optically, prior to detection, and does not depend on the instrument calibration. Systematic errors coupling temperature to polarization cancel to second order when comparing signals from independent detectors. We describe the polarized beam patterns for PIXIE and assess the systematic error for measurements of CMB polarization., Comment: 18 pages including 10 figurers Published in the Journal of Astronomical Telescopes, Instruments, and Systems

New determinations are presented of the cosmic infrared background monopole brightness in the Planck HFI bands from 100 GHz to 857 GHz. Planck was not designed to measure the monopole component of sky brightness, so cross-correlation of the 2015 HFI maps with COBE/FIRAS data is used to recalibrate the zero level of the HFI maps. For the HFI 545 and 857 GHz maps, the brightness scale is also recalibrated. Correlation of the recalibrated HFI maps with a linear combination of Galactic H I and H alpha data is used to separate the Galactic foreground emission and determine the cosmic infrared background brightness in each of the HFI bands. We obtain CIB values of 0.007 +- 0.014, 0.010 +- 0.019, 0.060 +- 0.023, 0.149 +- 0.017, 0.371 +- 0.018, and 0.576 +- 0.034 MJy/sr at 100, 143, 217, 353, 545, and 857 GHz, respectively. The estimated uncertainties for the 353 to 857 GHz bands are about 3 to 6 times smaller than those of previous direct CIB determinations at these frequencies. Our results are compared with integrated source brightness results from selected recent submillimeter and millimeter wavelength imaging surveys., Comment: 29 pages, 18 figures, accepted for publication in ApJ; minor changes in v2 to match published version

We describe the results of principal component analysis (PCA) of up-the-ramp sampled IR array data from the HST WFC3 IR, JWST NIRSpec, and prototype WFIRST WFI detectors. These systems use respectively Teledyne H1R, H2RG, and H4RG-10 near-IR detector arrays with a variety of IR array controllers. The PCA shows that the Legendre polynomials approximate the principal components of these systems (i.e. they roughly diagonalize the covariance matrix). In contrast to the monomial basis that is widely used for polynomial fitting and linearization today, the Legendre polynomials are an orthonormal basis. They provide a quantifiable, compact, and (nearly) linearly uncorrelated representation of the information content of the data. By fitting a few Legendre polynomials, nearly all of the meaningful information in representative WFC3 astronomical datacubes can be condensed from 15 up-the-ramp samples down to 6 compressible Legendre coefficients per pixel. The higher order coefficients contain time domain information that is lost when one projects up-the-ramp sampled datacubes onto 2-dimensional images by fitting a straight line, even if the data are linearized before fitting the line. Going forward, we believe that this time domain information is potentially important for disentangling the various non-linearities that can affect IR array observations, i.e. inherent pixel non-linearity, persistence, burn in, brighter-fatter effect, (potentially) non-linear inter-pixel capacitance (IPC), and perhaps others., Comment: 26 pages, 10 figures, accepted by Journal of Astronomical Telescopes, Instruments, and Systems (JATIS)

We measure linearly polarized beam patterns for a multi-moded concentrator and compare the results to a simple model based on geometric optics. We convolve the measured co-polar and cross-polar beams with simulated maps of CMB polarization to estimate the amplitude of the systematic error resulting from the cross-polar beam response. The un-corrected error signal has typical amplitude of 3 nK, corresponding to inflationary B-mode amplitude r ~ 10^{-3}. Convolving the measured cross-polar beam pattern with maps of the CMB E-mode polarization provides a template for correcting the cross-polar response, reducing it to negligible levels., Comment: 16 pages including 8 figurers. Accepted for publication in the Journal of Astronomical Telescopes, Instruments, and Systems

Near-infrared array detectors, like the \JWST NIRSpec's Teledyne's H2RGs, often provide reference pixels and a reference output. These are used to remove correlated noise. Improved Reference Sampling and Subtraction (\IRSSquare, pronounced "IRS-square") is a statistical technique for using this reference information optimally in a least squares sense. Compared to "traditional" H2RG readout, \IRSSquare uses a different clocking pattern to interleave many more reference pixels into the data than is otherwise possible. Compared to standard reference correction techniques, \IRSSquare subtracts the reference pixels and reference output using a statistically optimized set of frequency dependent weights. The benefits include somewhat lower noise variance and much less obvious correlated noise. NIRSpec's \IRSSquare images are cosmetically clean, with less $1/f$ banding than in traditional data from the same system. This article describes the \IRSSquare clocking pattern and presents the equations that are needed to use \IRSSquare in systems other than NIRSpec. For NIRSpec, applying these equations is already an option in the calibration pipeline. As an aid to instrument builders, we provide our prototype \IRSSquare calibration software and sample \JWST NIRSpec data. The same techniques are applicable to other detector systems, including those based on Teledyne's H4RG arrays. The H4RG's "interleaved reference pixel readout" mode is effectively one \IRSSquare pattern.

We use simple toy models of far-IR dust emission to estimate the accuracy to which the polarization of the cosmic microwave background can be recovered using multi-frequency fits, if the parametric form chosen for the fitted dust model differs from the actual dust emission. Commonly used approximations to the far-IR dust spectrum yield CMB residuals comparable to or larger than the sensitivities expected for the next generation of CMB missions, despite fitting the combined CMB + foreground emission to precision 0.1% or better. The Rayleigh-Jeans approximation to the dust spectrum biases the fitted dust spectral index by Delta beta_d = 0.2 and the inflationary B-mode amplitude by Delta r = 0.03. Fitting the dust to a modified blackbody at a single temperature biases the best-fit CMB by Delta r > 0.003 if the true dust spectrum contains multiple temperature components. A 13-parameter model fitting two temperature components reduces this bias by an order of magnitude if the true dust spectrum is in fact a simple superposition of emission at different temperatures, but fails at the level Delta r = 0.006 for dust whose spectral index varies with frequency. Restricting the observing frequencies to a narrow region near the foreground minimum reduces these biases for some dust spectra but can increase the bias for others. Data at THz frequencies surrounding the peak of the dust emission can mitigate these biases while providing a direct determination of the dust temperature profile., Comment: 9 pages including 8 figures. Accepted for publication in The Astrophysical Journal

Variable-delay Polarization Modulators (VPMs) are currently being implemented in experiments designed to measure the polarization of the cosmic microwave background on large angular scales because of their capability for providing rapid, front-end polarization modulation and control over systematic errors. Despite the advantages provided by the VPM, it is important to identify and mitigate any time-varying effects that leak into the synchronously modulated component of the signal. In this paper, the effect of emission from a $300$ K VPM on the system performance is considered and addressed. Though instrument design can greatly reduce the influence of modulated VPM emission, some residual modulated signal is expected. VPM emission is treated in the presence of rotational misalignments and temperature variation. Simulations of time-ordered data are used to evaluate the effect of these residual errors on the power spectrum. The analysis and modeling in this paper guides experimentalists on the critical aspects of observations using VPMs as front-end modulators. By implementing the characterizations and controls as described, front-end VPM modulation can be very powerful for mitigating $1/f$ noise in large angular scale polarimetric surveys. None of the systematic errors studied fundamentally limit the detection and characterization of B-modes on large scales for a tensor-to-scalar ratio of $r=0.01$. Indeed, $r<0.01$ is achievable with commensurately improved characterizations and controls., Comment: 13 pages, 13 figures, 1 table, matches published version

We present the design and performance of a non-imaging concentrator for use in broad-band polarimetry at millimeter through submillimeter wavelengths. A rectangular geometry preserves the input polarization state as the concentrator couples f/2 incident optics to a 2 pi sr detector. Measurements of the co-polar and cross-polar beams in both the few-mode and highly over-moded limits agree with a simple model based on mode truncation. The measured co-polar beam pattern is nearly independent of frequency in both linear polarizations. The cross-polar beam pattern is dominated by a uniform term corresponding to polarization efficiency 94%. After correcting for efficiency, the remaining cross-polar response is -18 dB., Comment: 9 pages including 8 figures. Accepted for publication in the Journal of the Optical Society of America A

We describe a mission architecture designed to substantially increase the science capability of the NASA Science Mission Directorate (SMD) Astrophysics Explorer Program for all AO proposers working within the near-UV to far-infrared spectrum. We have demonstrated that augmentation of Falcon 9 Explorer launch services with a 13 kW Solar Electric Propulsion (SEP) stage can deliver a 700 kg science observatory payload to extra-Zodiacal orbit. This new capability enables up to ~13X increased photometric sensitivity and ~160X increased observing speed relative to a Sun-Earth L2, Earth-trailing, or Earth orbit with no increase in telescope aperture. All enabling SEP stage technologies for this launch service augmentation have reached sufficient readiness (TRL-6) for Explorer Program application in conjunction with the Falcon 9. We demonstrate that enabling Astrophysics Explorers to reach extra-zodiacal orbit will allow this small payload program to rival the science performance of much larger long development time systems; thus, providing a means to realize major science objectives while increasing the SMD Astrophysics portfolio diversity and resiliency to external budget pressure. The SEP technology employed in this study has strong applicability to SMD Planetary Science community-proposed missions. SEP is a stated flight demonstration priority for NASA's Office of the Chief Technologist (OCT). This new mission architecture for astrophysics Explorers enables an attractive realization of joint goals for OCT and SMD with wide applicability across SMD science disciplines., Comment: Submitted to proceedings of the SPIE Astronomical Telescopes and Instrumentation conference, Amsterdam, The Netherlands, July 2012

We show that a one-component variable-emissivity-spectral-index model (the free-{\alpha} model) provides more physically motivated estimates of dust temperature at the Galactic polar caps than one- or two-component fixed-emissivity-spectral-index models (fixed-{\alpha} models) for interstellar dust thermal emission at far-infrared and millimeter wavelengths. For the comparison we have fit all-sky one-component dust models with fixed or variable emissivity spectral index to a new and improved version of the 210-channel dust spectra from the COBE-FIRAS, the 100 - 240 {\mu}m maps from the COBE-DIRBE and the 94 GHz dust map from the WMAP. The best model, the free-{\alpha} model, is well constrained by data at 60-3000 GHz over 86 per cent of the total sky area. It predicts dust temperature (Tdust) to be 13.7-22.7 (+/-1.3) K, the emissivity spectral index ({\alpha}) to be 1.2 - 3.1 (+/-0.3) and the optical depth ({\tau}) to range 0.6 - 46 x 10^(-5) at \nu 0 = 900 GHz (\lambda 0 = 333 {\mu}m) with a 23 per cent uncertainty. Using these estimates, we present all-sky evidence for an inverse correlation between the emissivity spectral index and dust temperature, which fits the relation {\alpha} = 1/({\delta}+{\omega} Tdust) with {\delta} = -0.510 +/- 0.011 and {\omega} = 0.059 +/- 0.001. This best model will be useful to cosmic microwave background experiments for removing foreground dust contamination and it can serve as an all-sky extended-frequency reference for future higher resolution dust models., Comment: 20 pages, 21 figures, submitted to MNRAS; corrected typos, added more details, additional graphics

The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission to measure the gravity-wave signature of primordial inflation through its distinctive imprint on the linear polarization of the cosmic microwave background. The instrument consists of a polarizing Michelson interferometer configured as a nulling polarimeter to measure the difference spectrum between orthogonal linear polarizations from two co-aligned beams. Either input can view the sky or a temperature-controlled absolute reference blackbody calibrator. PIXIE will map the absolute intensity and linear polarization (Stokes I, Q, and U parameters) over the full sky in 400 spectral channels spanning 2.5 decades in frequency from 30 GHz to 6 THz (1 cm to 50 um wavelength). Multi-moded optics provide background-limited sensitivity using only 4 detectors, while the highly symmetric design and multiple signal modulations provide robust rejection of potential systematic errors. The principal science goal is the detection and characterization of linear polarization from an inflationary epoch in the early universe, with tensor-to-scalar ratio r < 10^{-3} at 5 standard deviations. The rich PIXIE data set will also constrain physical processes ranging from Big Bang cosmology to the nature of the first stars to physical conditions within the interstellar medium of the Galaxy., Comment: 37 pages including 17 figures. Submitted to the Journal of Cosmology and Astroparticle Physics

Conventional interpretation of the observed cosmic microwave background (CMB) dipole is that all of it is produced by local peculiar motions. Alternative explanations requiring part of the dipole to be primordial have received support from measurements of large-scale bulk flows. A test of the two hypothesis is whether other cosmic dipoles produced by collapsed structures later than last scattering coincide with the CMB dipole. One background is the cosmic infrared background (CIB) whose absolute spectrum was measured to ~30% by the COBE satellite. Over the 100 to 500 {\mu}m wavelength range its spectral energy distribution can provide a probe of its alignment with CMB. This is tested with the COBE FIRAS dataset which is available for such a measurement because of its low noise and frequency resolution important for Galaxy subtraction. Although the FIRAS instrument noise is in principle low enough to determine the CIB dipole, the Galactic foreground is sufficiently close spectrally to keep the CIB dipole hidden. A similar analysis is performed with DIRBE, which - because of the limited frequency coverage - provides a poorer a dataset. We discuss strategies for measuring the CIB dipole with future instruments to probe the tilt and apply it to the Planck, Herschel and the proposed Pixie missions. We demonstrate that a future FIRAS-like instrument with instrument noise a factor of ~10 lower than FIRAS would make a statistically significant measurement of the CIB dipole. We find that the Planck and Herschel data sets will not allow a robust CIB dipole measurement. The Pixie instrument promises a determination of the CIB dipole and its alignment with either the CMB dipole or the dipole galaxy acceleration vector., Comment: 9 pages 9 figures

We present results of 2 mm observations of the Crab Nebula, obtained using the Goddard-IRAM Superconducting 2 Millimeter Observer (GISMO) bolometer camera on the IRAM 30 m telescope. Additional 3.3 mm observations with the MUSTANG bolometer array on the Green Bank Telescope are also presented. The integrated 2 mm flux density of the Crab Nebula provides no evidence for the emergence of a second synchrotron component that has been proposed. It is consistent with the radio power law spectrum, extrapolated up to a break frequency of log(nu_{b} [GHz]) = 2.84 +/- 0.29 or nu_{b} = 695^{+651}_{-336} GHz. The Crab Nebula is well-resolved by the ~16.7" beam (FWHM) of GISMO. Comparison to radio data at comparable spatial resolution enables us to confirm significant spatial variation of the spectral index between 21 cm and 2 mm. The main effect is a spectral flattening in the inner region of the Crab Nebula, correlated with the toroidal structure at the center of the nebula that is prominent in the near-IR through X-ray regime., Comment: Accepted for publication in the ApJ

The FIRAS data are independently recalibrated using the WMAP data to obtain a CMB temperature of 2.7260 +/- 0.0013. Measurements of the temperature of the cosmic microwave background are reviewed. The determination from the measurements from the literature is cosmic microwave background temperature of 2.72548 +/- 0.00057 K., Comment: 6 Pages 3 figures

We use absolutely calibrated data from the ARCADE 2 flight in July 2006 to model Galactic emission at frequencies 3, 8, and 10 GHz. The spatial structure in the data is consistent with a superposition of free-free and synchrotron emission. Emission with spatial morphology traced by the Haslam 408 MHz survey has spectral index beta_synch = -2.5 +/- 0.1, with free-free emission contributing 0.10 +/- 0.01 of the total Galactic plane emission in the lowest ARCADE 2 band at 3.15 GHz. We estimate the total Galactic emission toward the polar caps using either a simple plane-parallel model with csc|b| dependence or a model of high-latitude radio emission traced by the COBE/FIRAS map of CII emission. Both methods are consistent with a single power-law over the frequency range 22 MHz to 10 GHz, with total Galactic emission towards the north polar cap T_Gal = 0.498 +/- 0.028 K and spectral index beta = -2.55 +/- 0.03 at reference frequency 1 GHz. The well calibrated ARCADE 2 maps provide a new test for spinning dust emission, based on the integrated intensity of emission from the Galactic plane instead of cross-correlations with the thermal dust spatial morphology. The Galactic plane intensity measured by ARCADE 2 is fainter than predicted by models without spinning dust, and is consistent with spinning dust contributing 0.4 +/- 0.1 of the Galactic plane emission at 22 GHz., Comment: 10 poges, 9 figures. Submitted to The Astrophysical Journal

The second generation Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE 2) instrument is a balloon-borne experiment to measure the radiometric temperature of the cosmic microwave background and Galactic and extra-Galactic emission at six frequencies from 3 to 90 GHz. ARCADE 2 utilizes a double-nulled design where emission from the sky is compared to that from an external cryogenic full-aperture blackbody calibrator by cryogenic switching radiometers containing internal blackbody reference loads. In order to further minimize sources of systematic error, ARCADE 2 features a cold fully open aperture with all radiometrically active components maintained at near 2.7 K without windows or other warm objects, achieved through a novel thermal design. We discuss the design and performance of the ARCADE 2 instrument in its 2005 and 2006 flights., Comment: 12 pages, 14 figues, 3 tables, 2 figures added, Accepted to ApJ

We use absolutely calibrated data between 3 and 90 GHz from the 2006 balloon flight of the ARCADE 2 instrument, along with previous measurements at other frequencies, to constrain models of extragalactic emission. Such emission is a combination of the Cosmic Microwave Background (CMB) monopole, Galactic foreground emission, the integrated contribution of radio emission from external galaxies, any spectral distortions present in the CMB, and any other extragalactic source. After removal of estimates of foreground emission from our own Galaxy, and the estimated contribution of external galaxies, we present fits to a combination of the flat-spectrum CMB and potential spectral distortions in the CMB. We find 2 sigma upper limits to CMB spectral distortions of mu < 5.8 x 10^{-5} and Y_ff < 6.2 x 10^{-5}. We also find a significant detection of a residual signal beyond that which can be explained by the CMB plus the integrated radio emission from galaxies estimated from existing surveys. After subtraction of an estimate of the contribution of discrete radio sources, this unexplained signal is consistent with extragalactic emission in the form of a power law with amplitude 1.06 \pm 0.11 K at 1 GHz and a spectral index of -2.56 \pm 0.04., Comment: 8 pages, 4 figures

The ARCADE 2 instrument has measured the absolute temperature of the sky at frequencies 3, 8, 10, 30, and 90 GHz, using an open-aperture cryogenic instrument observing at balloon altitudes with no emissive windows between the beam-forming optics and the sky. An external blackbody calibrator provides an {\it in situ} reference. Systematic errors were greatly reduced by using differential radiometers and cooling all critical components to physical temperatures approximating the CMB temperature. A linear model is used to compare the output of each radiometer to a set of thermometers on the instrument. Small corrections are made for the residual emission from the flight train, balloon, atmosphere, and foreground Galactic emission. The ARCADE 2 data alone show an extragalactic rise of $50\pm7$ mK at 3.3 GHz in addition to a CMB temperature of $2.730\pm .004$ K. Combining the ARCADE 2 data with data from the literature shows a background power law spectrum of $T=1.26\pm 0.09$ [K] $(\nu/\nu_0)^{-2.60\pm 0.04}$ from 22 MHz to 10 GHz ($\nu_0=1$ GHz) in addition to a CMB temperature of $2.725\pm .001$ K., Comment: 11 pages 5 figures Submitted to ApJ

Frequency Selective Bolometers (FSBs) are a new type of detector for millimeter and sub-millimeter wavelengths that are transparent to all but a narrow range of frequencies as set by characteristics of the absorber itself. Therefore, stacks of FSBs tuned to different frequencies provide a low-loss compact method for utilizing a large fraction of the light collected by a telescope. Tests of prototype FSBs, described here, indicate that the absorption spectra are well predicted by models, that peak absolute absorption efficiencies of order 50% are attainable, and that their out-of-band transmission is high., Comment: 32 pages, 9 figures

The Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE) is a balloon-borne instrument to measure the temperature of the cosmic microwave background at centimeter wavelengths. ARCADE uses narrow-band cryogenic radiometers to compare the sky to an external full-aperture calibrator. To minimize potential sources of systematic error, ARCADE uses a novel open-aperture design which maintains the antennas and calibrator at temperatures near 3 K at the mouth of an open bucket Dewar, without windows or other warm objects between the antennas and the sky. We discuss the design and performance of the ARCADE instrument from its 2001 and 2003 flights., Comment: 6 pages including 5 figures. Submitted to The Astrophysical Journal

We describe the design and calibration of an external cryogenic blackbody calibrator used for the first two flights of the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE) instrument. The calibrator consists of a microwave absorber weakly coupled to a superfluid liquid helium bath. Half-wave corrugations viewed 30 deg off axis reduce the return loss below -35 dB. Ruthenium oxide resistive thermometers embedded within the absorber monitor the temperature across the face of the calibrator. The thermal calibration transfers the calibration of a reference thermometer to the flight thermometers using the flight thermometer readout system. Data taken near the superfluid transition in 8 independent calibrations 4 years apart agree within 0.3 mK, providing an independent verification of the thermometer calibration at temperatures near that of the cosmic microwave background., Comment: 5 pages including 5 figures. Submitted to Review of Scientific Instruments

We report the results of an effort to measure the low frequency portion of the spectrum of the Cosmic Microwave Background Radiation (CMB), using a balloon-borne instrument called ARCADE (Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission). These measurements are to search for deviations from a thermal spectrum that are expected to exist in the CMB due to various processes in the early universe. The radiometric temperature was measured at 10 and 30 GHz using a cryogenic open-aperture instrument with no emissive windows. An external blackbody calibrator provides an in situ reference. A linear model is used to compare the radiometer output to a set of thermometers on the instrument. The unmodeled residuals are less than 50 mK peak-to-peak with a weighted RMS of 6 mK. Small corrections are made for the residual emission from the flight train, atmosphere, and foreground Galactic emission. The measured radiometric temperature of the CMB is 2.721 +/- 0.010 K at 10 GHz and 2.694 +/- 0.032 K at 30 GHz., Comment: 8 pages including 5 figures. Submitted to The Astrophysical Journal

We present measurements of the integrated flux relative to the local background of the Large and Small Magellanic Clouds and the region 30-Doradus (the Tarantula Nebula) in the LMC in four frequency bands centered at 245, 400, 460, and 630 GHz, based on observations made with the TopHat telescope. We combine these observations with the corresponding measurements for the DIRBE bands 8, 9, and 10 to cover the frequency range 245 - 3000 GHz (100 - 1220 micrometers) for these objects. We present spectra for all three objects and fit these spectra to a single-component greybody emission model and report best-fit dust temperatures, optical depths, and emissivity power-law indices, and we compare these results with other measurements in these regions and elsewhere. Using published dust grain opacities, we estimate the mass of the measured dust component in the three regions., Comment: 41 pages, 4 figures. Accepted for publication in Astrophysical Journal

The frequency at which a large space telescope's (e.g. NGST's) detector chips are read, or the sample rate, is tightly coupled to many hardware and operational aspects of the telescope's instrument and data handling elements. In this paper we discuss many of the drivers and important implications fo the sample rate: the data rate to the ground; onboard computer storage, bandwidth, and speed; the number of A->D chips, and therefore the overall size and power requirements of the analog electronics; cryocabling requirements; and detector noise and power. We discuss and parametrize these and other elements related to sample rate. Finally, we discuss the implications of sample rate in the context of achieving the most important science goals under the constraint of fixed cost., Comment: 15 pages

The thermometer and thermal control system, for the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE) experiment, is described, including the design, testing, and results from the first flight of ARCADE. The noise is equivalent to about 1 Omega or 0.15 mK in a second for the RuO_2 resistive thermometers at 2.7 K. The average power dissipation in each thermometer is 1 nW. The control system can take full advantage of the thermometers to maintain stable temperatures. Systematic effects are still under investigation, but the measured precision and accuracy are sufficient to allow measurement of the cosmic background spectrum. Journal-ref: Review of Scientific Instruments Vol 73 #10 (Oct 2002), Comment: 5 pages text 7 figures

The problem of formulating a fully consistent quantum gravity theory (QGT) has not yet been solved. Even before we are able to work out the details of a complete theory, however, we do know some important qualitative features to be expected in any quantum theory. Fluctuations of the metric, for example, are expected and are associated with fluctuations of the lightcone. Lightcone fluctuations affect the arrival time of signals from distant sources in potentially measurable ways, broadening the spectra. In this paper, we start with a thermal spectrum and derive the form of spectral changes expected in a wide class of QGTs. We apply these results, valid for any thermal spectrum, to the cosmic microwave background (CMB). The CMB offers two advantages: (1) deviations from a thermal spectrum are well constrained, and (2) the radiation emanates from the most distant source of light, the surface of last scattering. We use existing CMB data to derive an upper bound on the value of $\Delta t,$ the mean spread in arrival times due to metric fluctuations: ${\Delta t} < 2.1 \times 10^{-14}$ s at the 95% confidence limit. This limit applies to a wide range of QGTs, and falsifies those predicting a larger spread in arrival times. We find this limit rules out at least one QGT, the 5-dimensional theory in which the "extra" dimension is flat. Tests of other models may also be possible, depending on the results of calculations to predict values of \Delta t,$ and also a second time scale, $\tau_c,$ the correlation time, which is the characteristic time scale of the metric fluctuations. We show that stronger limits on the value of $\Delta t,$ hence on lightcone fluctuations, can likely be derived through observations of of higher-T sources, e.g., in the X-ray and gamma-ray regimes., Comment: Submitted to ApJ, 30 pages, 8 figures

We examine cosmic ray rejection methodology on data collected from InSb and Si:As detectors. The application of an Up-the-Ramp sampling technique with cosmic ray identification and mitigation is the focus of this study. This technique is valuable for space-based observatories which are exposed to high-radiation environments. We validate the Up-the-Ramp approach on radiation-test data sets with InSb and Si:As detectors which were generated for SIRTF. The Up-the-Ramp sampling method studied in this paper is over 99.9% effective at removing cosmic rays and preserves the structure and photometric quality of the image to well within the measurement error., Comment: 30 pages, 13 figures. Accepted for publication in the PASP, 25 October 2000

We present an algorithm to optimally process uniformly sampled array image data obtained with a nondestructive readout. The algorithm discards full wells, removes cosmic ray (particle) hits and other glitches, and makes a nearly optimum estimate of the signal on each pixel. The algorithm also compresses the data. The computer requirements are modest, and the results are robust. The results are shown and compared to results of Fowler sampled and processed data. Non-ideal detector performance may require some additional code, but this is not expected to cost much processing time. Known types of detector faults are addressed., Comment: This paper has been accepted for publication in the PASP

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., Comment: Short paper plus source code for the MultiDataSim software

With high sensitivity imaging arrays, accurate calibration is essential to achieve the limits of detection of space observatories. One can simultaneously extract information about the scene being observed and the calibration properties of the detector and imaging system from redundant dithered images of a scene. There are large differences in the effectiveness of dithering strategies for allowing the separation of detector properties from sky brightness measurements. In this paper, we quantify these differences by developing a figure of merit (FOM) for dithering procedures based on their usefulness for allowing calibration on all spatial scales. The figure of merit measures how well the gain characteristics of the detector are encoded in the measurements, and is independent of the techniques used to analyze the data. Patterns similar to the antenna arrangements of radio interferometers with good u-v plane coverage, are found to have good figures of merit. We present patterns for both deep surveys of limited sky areas and for shallow surveys. By choosing a strategy that encodes the calibration in the observations in an easily extractable way, we enhance our ability to calibrate our detector systems and to reach the ultimate limits of sensitivity which are required to achieve the promise of many missions., Comment: Scheduled for ApJ, June 10, 2000 (22 pages, 9 figures)

The development of sensitive large format imaging arrays for the infrared promises to provide revolutionary capabilities for space astronomy. For example, the Infrared Array Camera (IRAC) on SIRTF will use four 256 x 256 arrays to provide background limited high spatial resolution images of the sky in the 3 to 8 micron spectral region. In order to reach the performance limits possible with this generation of sensitive detectors, calibration procedures must be developed so that uncertainties in detector calibration will always be dominated by photon statistics from the dark sky as a major system noise source. In the near infrared, where the faint extragalactic sky is observed through the scattered and reemitted zodiacal light from our solar system, calibration is particularly important. Faint sources must be detected on this brighter local foreground. We present a procedure for calibrating imaging systems and analyzing such data. In our approach, by proper choice of observing strategy, information about detector parameters is encoded in the sky measurements. Proper analysis allows us to simultaneously solve for sky brightness and detector parameters, and provides accurate formal error estimates. This approach allows us to extract the calibration from the observations themselves; little or no additional information is necessary to allow full interpretation of the data. Further, this approach allows refinement and verification of detector parameters during the mission, and thus does not depend on a priori knowledge of the system or ground calibration for interpretation of images., Comment: Scheduled for ApJS, June 2000 (16 pages, 3 JPEG figures)

We present new cosmic microwave background (CMB) anisotropy results from the combined analysis of the three flights of the first Medium Scale Anisotropy Measurement (MSAM1). This balloon-borne bolometric instrument measured about 10 square degrees of sky at half-degree resolution in 4 frequency bands from 5.2 icm to 20 icm with a high signal-to-noise ratio. Here we present an overview of our analysis methods, compare the results from the three flights, derive new constraints on the CMB power spectrum from the combined data and reduce the data to total-power Wiener-filtered maps of the CMB. A key feature of this new analysis is a determination of the amplitude of CMB fluctuations at $\ell \sim 400$. The analysis technique is described in a companion paper by Knox., Comment: 9 pages, 6 included figures

The COBE Far InfraRed Absolute Spectrophotometer (FIRAS) observations constitute an unbiased survey over the wavelength range from 100 um to 1 cm over 99% of the sky. Improved calibration of the FIRAS instrument and the inclusion of all of the FIRAS data allow an improved signal to noise determination of the spectral lines by a factor of ~2 over our previous results. The resolution is low (0.45 cm^{-1}) so only the strongest lines are observable. The CO chain from J=1-0 to J=8-7 is observed towards the Galactic center. The line ratios are roughly consistent with a 40 K excitation temperature. The 157.7 um C II and 205.3 um N II lines are observable over most of the sky. The 370.4 um and 609.1 um lines of C I, and the 121.9 um line of N II are observed in the Galactic plane. The line ratios at the Galactic center are consistent with a density of n_0 ~30 cm^{-3} and a UV flux of G_0 ~15 uW m^{-2} sr^{-1} (10 Habing units). The 269 um H2O line is observed toward the Galactic center in absorption., Comment: 12 pages, 5 Postscript Figures, uses aaspp4.sty, minor revisions to conform to the version accepted by ApJ

The photometric errors of the external calibrator for the FIRAS instrument on the COBE are smaller than the measurement errors on the cosmic microwave background (CMBR) spectrum (typically 0.02 MJy/sr, 1 sigma), and smaller than 0.01% of the peak brightness of the CMBR. The calibrator is a re-entrant cone, shaped like a trumpet mute, made of Eccosorb iron-loaded epoxy. It fills the entire beam of the instrument and is the source of its accuracy. Its known errors are caused by reflections, temperature gradients, and leakage through the material and around the edge. Estimates and limits are given for all known error sources. Improvements in understanding the temperature measurements of the calibrator allow an improved CMBR temperature determination of 2.725 +/- 0.002 K., Comment: 30 pages, 9 Postscript figures, uses aasms4.sty, ApJ, 1999, 512, xxx

The COBE FIRAS data contain foreground emission from interplanetary, Galactic interstellar dust and extragalactic background emission. We use three different methods to separate the various emission components, and derive the spectrum of the extragalactic Far InfraRed Background (FIRB). Each method relies on a different set of assumptions, which affect the FIRB spectrum in different ways. Despite this, the FIRB spectra derived by these different methods are remarkably similar. The average spectrum that we derive in the \nu = 5 - 80 cm^{-1} (2000-125 \um) frequency interval is: I(\nu) = (1.3 \pm 0.4)\times10^{-5} (\nu /\nu_0)^{0.64 \pm 0.12} P_{\nu}(18.5 \pm 1.2 K), where \nu_0=100 cm^{-1} (\lambda_0=100 \um) and P is the Planck function. The derived FIRB spectrum is consistent with the DIRBE 140 and 240 \um detections. The total intensity received in the 5 - 80 cm^{-1} frequency interval is 14 nW m^{-2} sr^{-1}, and comprises about 20% of the total intensity expected from the energy release from nucleosynthesis throughout the history of the universe., Comment: 12 pages Latex (AAS macro), 4 Postscript figures, accepted by The Astrophysical Journal

We compare the independent FIRAS and DIRBE observations from the COBE in the wavelength range 100-300 microns. This cross calibration provides checks of both data sets. The results show that the data sets are consistent within the estimated gain and offset uncertainties of the two instruments. They show the possibility of improving the gain and offset determination of DIRBE at 140 and 240 microns., Comment: Accepted for publication in the Astrophysical Journal 11 pages, plus 3 figures in separate postscript files. Figure 3 has three parts

The third flight of the Medium Scale Anisotropy Measurement (MSAM1), in June 1995, observed a new strip of sky, doubling the sky coverage of the original MSAM1 dataset. MSAM1 observes with a 0.5 deg beam size in four bands from 5-20 icm. From these four bands we derive measurements of cosmic microwave background radiation (CMBR) anisotropy and interstellar dust emission. Our measurement of dust emission correlates well with the 100 um IRAS Sky Survey Atlas; from this comparison we determine an effective emissivity spectral index between 100 um and 444 um of 1.46 +/- 0.28. Analysis of our measurement of CMBR anisotropy shows that for Gaussian-shaped correlation functions with theta_c = 0.3 deg, we place a limit on total rms anisotropy of 2.2 x 10^{-5} < Delta T/T < 3.9 x 10^{-5} (90% confidence interval, including calibration error). The band-power limits are = ^{1/2} = 50^{+16}_{-11} uK at l = 160, and = 65^{+18}_{-13} uK at l = 270 (1 sigma limits, including calibration error). The corresponding limits with statistical errors only are = 50^{+13}_{-9} uK and = 65^{+14}_{-10} uK respectively. These measurements are consistent with a standard adiabatic cold dark matter model; we discuss constraints on h, n, and the redshift of reionization., Comment: 13 pages, 3 figures, Latex, aastex4.0. To appear in ApJ

We analyze the Cosmic Microwave Background (CMB) anisotropy data from the independent COBE FIRAS and DMR observations. We extract the frequency spectrum of the FIRAS signal that has the spatial distribution seen by DMR and show that it is consistent with CMB temperature fluctuations in the radiation well into the Wien region of the spectrum. Conversely, we form a map of the Planckian component of the sky temperature from FIRAS and show that it correlates with the DMR anisotropy map. The rms fluctuations at angular scales of 7 degrees are 48 \pm 14 uK for the FIRAS data compared with 35 \pm 2 uK for the DMR data and 31 \pm 6 uK for the correlated combination (1 sigma uncertainties). The consistency of these data, from very different instruments with very different observing strategies, provide compelling support for the interpretation that the signal seen by DMR is, in fact, temperature anisotropy of cosmological origin. The data also limit rms fluctuations in the Compton y parameter, observable via the Sunyaev- Zel'dovich effect, to Delta_y < 3 x 10^{-6} (95% CL) on 7 degree angular scales., Comment: 15 pages, Latex (AASv4 macro) including 3 Postscript figures, to appear in ApJ, vol. 486, Sept 10, 1997

Whole disk brightness ratios for Jupiter, Saturn, and Mars are reported at 5.7, 9.5, 16.4, and 22.5 cm$^{-1}$. Using models for the brightness temperature of Mars, the whole disk brightness temperatures for Jupiter and Saturn are also given for the four frequencies., Comment: 13 pages, LaTeX+aasms4 package, 2 included PostScript figures. Submitted to Ap.J Letters

Observations from the first flight of the Medium Scale Anisotropy Measurement (MSAM1-92) are analyzed to search for the Sunyaev-Zel'dovich (SZ) effect towards the Coma cluster. This balloon-borne instrument uses a $28\arcmin$ FWHM beam and a three position chopping pattern with a throw of $\pm40\arcmin$. With spectral channels at 5.7, 9.3, 16.5, and 22.6~\icm, the observations simultaneously sample the frequency range where the SZ spectral distortion in the intensity transitions from a decrement to an increment and where the fractional intensity change is substantially larger than in the Rayleigh-Jeans region. We set limits on the Comptonization parameter integrated over our antenna pattern, $\Delta y \leq 8.0 \times 10^{-5}$($2 \sigma$). For a spherically symmetric isothermal model, this implies a central Comptonization parameter, $y_o \leq 2.0 \times 10^{-4}$, or a central electron density, $n_o \leq 5.8 \times10^{-3}$cm$^{-3}h_{50}$, a result consistent with central densities implied by X-ray brightness measurements and central Comptonization estimates from lower frequency observations of the SZ effect., Comment: 11 pages, LaTeX+aasms4 package, 1 PostScript figure. Submitted to Ap.J Letters

We have refined the analysis of the data from the FIRAS (Far InfraRed Absolute Spectrophotometer) on board the COBE (COsmic Background Explorer). The FIRAS measures the difference between the cosmic microwave background and a precise blackbody spectrum. We find new tighter upper limits on general deviations from a blackbody spectrum. The RMS deviations are less than 50 parts per million of the peak of the CMBR. For the Comptonization and chemical potential we find $|y| < 15\times10^{-6}$ and $|\mu| < 9\times10^{-5}$ (95\% CL). There are also refinements in the absolute temperature, 2.728 $\pm$ 0.004 K (95\% CL), and dipole direction, $(\ell,b)=(264.14^\circ\pm0.30, 48.26^\circ\pm0.30)$ (95\% CL), and amplitude, $3.372 \pm 0.007$ mK (95\% CL). All of these results agree with our previous publications., Comment: 32 pages, LaTeX+aasms package, 6 figures as separate PostScript file. Submitted to Ap.J

We report the characterization of bright, compact features in the cosmic microwave background radiation (CMBR) detected during the June 1992 and June 1994 balloon flights of the Medium Scale Anisotropy Measurement (MSAM1-92 and MSAM1-94, respectively). Spectral flux densities are determined for each feature at 5.7, 9.3, and 16.5 cm$^{-1}$. No viable counterparts for these features were found in source catalogs at 5 GHz or at 100 $\mu$m. The measured spectrum of each feature is consistent with a temperature fluctuation in the CMBR. The existence of these features is consistent with adiabatic fluctuation models of anisotropy in the CMBR., Comment: 17 pages, LaTeX+aasms4 package, 2 included PostScript figures. Submitted to Ap.J Letters

The goal of the second flight of the Medium Scale Anisotropy Measurement (MSAM1-94) was to confirm the measurement of cosmic microwave background radiation (CMBR) anisotropy made in the first flight (MSAM1-92). The CMBR anisotropy and interstellar dust emission signals from the two flights are compared by forming the sum and difference of those portions of the data with the same pointings on the sky. The difference data are consistent with a null detection, while the summed data show significant signal. We conclude that MSAM1-92 and MSAM1-94 measured the same celestial signal., Comment: 9 pages, LaTeX+aasms4 package, 1 included encapsulated PostScript figure. Submitted to Ap.J Letters

We report on the characteristics and design details of the Medium Scale Anisotropy Measurement (MSAM), a millimeter-wave, balloon-borne telescope that has been used to observe anisotropy in the Cosmic Microwave Background Radiation (CMBR) on 0\fdg5 angular scales. The gondola is capable of determining and maintaining absolute orientation to a few arcminutes during a one-night flight. Emphasis is placed on the optical and pointing performance as well as the weight and power budgets. We also discuss the total balloon/gondola mechanical system. The pendulation from this system is a ubiquitous perturbation on the pointing system. A detailed understanding in these areas is needed for developing the next generation of balloon-borne instruments., Comment: 37 pages, 15 figures, uses BoxedEPS.tex

The second flight of the Medium Scale Anisotropy Measurement (MSAM1-94) observed the same field as the first flight (MSAM1-92) to confirm our earlier measurement of cosmic microwave background radiation (CMBR) anisotropy. This instrument chops a 30\arcmin\ beam in a 3 position pattern with a throw of $\pm40\arcmin$, and simultaneously measures single and double differenced sky signals. We observe in four spectral channels centered at 5.6, 9.0, 16.5, and 22.5~\icm, providing sensitivity to the peak of the CMBR and to thermal emission from interstellar dust. The dust component correlates well with the \IRAS\ 100~\micron\ map. The CMBR observations in our double difference channel correlate well with the earlier observations, but the single difference channel shows some discrepancies. We obtain a detection of fluctuations in the MSAM1-94 dataset that match CMBR in our spectral bands of $\Delta T/T = 1.9^{+1.3}_{-0.7}\times 10^{-5}$ (90\% confidence interval, including calibration uncertainty) for total rms Gaussian fluctuations with correlation angle 0\fdg3, using the double difference demodulation., Comment: 11 pages, 4 postscript figures, uses aastex 4.0. Transmitted in uuencoded gzipped tar file

We derive Galactic continuum spectra from 5-96/cm from COBE/FIRAS observations. The spectra are dominated by warm dust emission, which may be fit with a single temperature in the range 16-21 K (for nu^2 emissivity) along each line of sight. Dust heated by the attenuated radiation field in molecular clouds gives rise to intermediate temperature (10-14 K) emission in the inner Galaxy only. A widespread, very cold component (4-7 K) with optical depth that is spatially correlated with the warm component is also detected. The cold component is unlikely to be due to very cold dust shielded from starlight, because it is present at high latitude. We consider hypotheses that the cold component is due to enhanced submillimeter emissivity of the dust that gives rise to the warm component, or that it may be due to very small, large, or fractal particles. Lack of substantial power above the emission from warm dust places strong constraints on the amount of cold gas in the Galaxy. The microwave sky brightness due to interstellar dust is dominated by the cold component, and its angular variation could limit our ability to discern primordial fluctuations in the cosmic microwave background radiation., Comment: UUencoded tar file, including LaTeX manuscript file and 11 postscript figure files; accepted for publication in the Astrophysical Journal, scheduled for 20 Sep 1995 issue

The FIRAS instrument on the COBE satellite has conducted an unbiased survey of the far-infrared emission from our Galaxy. The first results of this survey were reported by Wright et al. (1991). We report the results of new analyses of this spectral survey, which includes emission lines from 158 um C+, 122 um and 205 um N+, 370 um and 609 um C, and CO J=2-1 through 5-4. We report the morphological distribution along the galactic plane (b=0) of the spectral line emission, and the high galactic latitude intensities of the C+ and 205 um N+ emission. The high galactic latitude intensity cosecant of the 158 um fine structure transition from C+ is presented, and C+ is seen to decrease more rapidly than the far infrared intensity with increasing galactic latitude. C+ and H I emission are closely correlated with a C+ cooling rate of (2.65 +/- 0.15)x10^{-26} erg/s/H-atom. We conclude that this emission arises almost entirely from the Cold Neutral Medium. The high galactic latitude intensity of the 205 um fine structure transition from N+ arises entirely from the Warm Ionized Medium, and its cosecant is presented. We estimate the total ionizing photon rate in the Galaxy to be 3.5x10^{53} ionizing photons per second, based on the 205 um N+ transition., Comment: 32 pages, 5 figures, uuencoded Postscript, COBE #93-11

Observations from the first flight of the Medium Scale Anisotropy Measurement (MSAM) are analyzed to place limits on Gaussian fluctuations in the Cosmic Microwave Background Radiation (CMBR). This instrument chops a 30\arcmin\ beam in a 3 position pattern with a throw of $\pm40\arcmin$; the resulting data is analyzed in statistically independent single and double difference datasets. We observe in four spectral channels at 5.6, 9.0, 16.5, and 22.5~\icm, allowing the separation of interstellar dust emission from CMBR fluctuations. The dust component is correlated with the \IRAS\ 100~\micron\ map. The CMBR component has two regions where the signature of an unresolved source is seen. Rejecting these two source regions, we obtain a detection of fluctuations which match CMBR in our spectral bands of $0.6 \times 10^{-5} < \Delta T/T < 2.2 \times 10^{-5}$ (90\% CL interval) for total rms Gaussian fluctuations with correlation angle 0\fdg5, using the single difference demodulation. For the double difference demodulation, the result is $1.1 \times 10^{-5} < \Delta T/T < 3.1 \times 10^{-5}$ (90\% CL interval) at a correlation angle of 0\fdg3., Comment: 13 pages + 3 figures (included), LaTeX + AASTeX v3.0