The Thermal Design, Characterization, and Performance of the SPIDER Long-Duration Balloon Cryostat

We describe the SPIDER flight cryostat, which is designed to cool six millimeter-wavelength telescopes during an Antarctic long-duration balloon flight. The cryostat, one of the largest to have flown on a stratospheric payload, uses liquid helium-4 to deliver cooling power to stages at 4.2 and 1.6 K. Stainless steel capillaries facilitate a high flow impedance connection between the main liquid helium tank and a smaller superfluid tank, allowing the latter to operate at 1.6 K as long as there is liquid in the 4.2 K main tank. Each telescope houses a closed cycle helium-3 adsorption refrigerator that further cools the focal planes down to 300 mK. Liquid helium vapor from the main tank is routed through heat exchangers that cool radiation shields, providing negative thermal feedback. The system performed successfully during a 17 day flight in the 2014-2015 Antarctic summer. The cryostat had a total hold time of 16.8 days, with 15.9 days occurring during flight.Comment: 15 pgs, 17 fig

A cryogenic rotation stage with a large clear aperture for the half-wave plates in the Spider instrument

We describe the cryogenic half-wave plate rotation mechanisms built for and used in Spider, a polarization-sensitive balloon-borne telescope array that observed the Cosmic Microwave Background at 95 GHz and 150 GHz during a stratospheric balloon flight from Antarctica in January 2015. The mechanisms operate at liquid helium temperature in flight. A three-point contact design keeps the mechanical bearings relatively small but allows for a large (305 mm) diameter clear aperture. A worm gear driven by a cryogenic stepper motor allows for precise positioning and prevents undesired rotation when the motors are depowered. A custom-built optical encoder system monitors the bearing angle to an absolute accuracy of +/- 0.1 degrees. The system performed well in Spider during its successful 16 day flight

A New Limit on CMB Circular Polarization from SPIDER

We present a new upper limit on cosmic microwave background (CMB) circular polarization from the 2015 flight of Spider, a balloon-borne telescope designed to search for B-mode linear polarization from cosmic inflation. Although the level of circular polarization in the CMB is predicted to be very small, experimental limits provide a valuable test of the underlying models. By exploiting the nonzero circular-to-linear polarization coupling of the half-wave plate polarization modulators, data from Spider's 2015 Antarctic flight provide a constraint on Stokes V at 95 and 150 GHz in the range $33\lt {\ell }\lt 307$. No other limits exist over this full range of angular scales, and Spider improves on the previous limit by several orders of magnitude, providing 95% C.L. constraints on ${\ell }({\ell }+1){C}_{{\ell }}^{{VV}}/(2\pi )$ ranging from 141 to 255 μK2 at 150 GHz for a thermal CMB spectrum. As linear CMB polarization experiments become increasingly sensitive, the techniques described in this paper can be applied to obtain even stronger constraints on circular polarization

Particle response of antenna-coupled TES arrays: results from SPIDER and the laboratory

Future mm-wave and sub-mm space missions will employ large arrays of multiplexed transition-edge-sensor (TES) bolometers. Such instruments must contend with the high flux of cosmic rays beyond our atmosphere that induce ‘glitches’ in bolometer data, which posed a challenge to data analysis from the Planck bolometers. Future instruments will face the additional challenges of shared substrate wafers and multiplexed readout wiring. In this work, we explore the susceptibility of modern TES arrays to the cosmic ray environment of space using two data sets: the 2015 long-duration balloon flight of the SPIDER cosmic microwave background polarimeter, and a laboratory exposure of SPIDER flight hardware to radioactive sources. We find manageable glitch rates and short glitch durations, leading to minimal effect on SPIDER analysis. We constrain energy propagation within the substrate through a study of multi-detector coincidences and give a preliminary look at pulse shapes in laboratory data

Planck 2013 results. I. Overview of products and scientific results

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First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole

When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42 ± 3 μas, which is circular and encompasses a central depression in brightness with a flux ratio 10:1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M = (6.5 ± 0.7) × 109 Me. Our radiowave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible

First M87 Event Horizon Telescope Results. II. Array and Instrumentation

The Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array that comprises millimeter- and submillimeter-wavelength telescopes separated by distances comparable to the diameter of the Earth. At a nominal operating wavelength of ~1.3 mm, EHT angular resolution (λ/D) is ~25 μas, which is sufficient to resolve nearby supermassive black hole candidates on spatial and temporal scales that correspond to their event horizons. With this capability, the EHT scientific goals are to probe general relativistic effects in the strong-field regime and to study accretion and relativistic jet formation near the black hole boundary. In this Letter we describe the system design of the EHT, detail the technology and instrumentation that enable observations, and provide measures of its performance. Meeting the EHT science objectives has required several key developments that have facilitated the robust extension of the VLBI technique to EHT observing wavelengths and the production of instrumentation that can be deployed on a heterogeneous array of existing telescopes and facilities. To meet sensitivity requirements, high-bandwidth digital systems were developed that process data at rates of 64 gigabit s−1, exceeding those of currently operating cm-wavelength VLBI arrays by more than an order of magnitude. Associated improvements include the development of phasing systems at array facilities, new receiver installation at several sites, and the deployment of hydrogen maser frequency standards to ensure coherent data capture across the array. These efforts led to the coordination and execution of the first Global EHT observations in 2017 April, and to event-horizon-scale imaging of the supermassive black hole candidate in M87

Pre-flight integration and characterization of the SPIDER balloon-borne telescope

We present the results of integration and characterization of the Spider instrument after the 2013 pre-flight campaign. SPIDER is a balloon-borne polarimeter designed to probe the primordial gravitational wave signal in the degree-scale B-mode polarization of the cosmic microwave background. With six independent telescopes housing over 2000 detectors in the 94 GHz and 150 GHz frequency bands, SPIDER will map 7.5% of the sky with a depth of 11 to 14 mu K.arcmin at each frequency, which is a factor of similar to 5 improvement over Planck. We discuss the integration of the pointing, cryogenic, electronics, and power sub-systems, as well as pre-flight characterization of the detectors and optical systems. SPIDER is well prepared for a December 2014 flight from Antarctica, and is expected to be limited by astrophysical foreground emission, and not instrumental sensitivity, over the survey region

280 GHz Focal Plane Unit Design and Characterization for the SPIDER-2 Suborbital Polarimeter

We describe the construction and characterization of the 280 GHz bolometric focal plane units (FPUs) to be deployed on the second flight of the balloon-borne SPIDER instrument. These FPUs are vital to SPIDER's primary science goal of detecting or placing an upper limit on the amplitude of the primordial gravitational wave signature in the cosmic microwave background (CMB) by constraining the B-mode contamination in the CMB from Galactic dust emission. Each 280 GHz focal plane contains a 16 x 16 grid of corrugated silicon feedhorns coupled to an array of aluminum-manganese transition-edge sensor (TES) bolometers fabricated on 150 mm diameter substrates. In total, the three 280 GHz FPUs contain 1,530 polarization sensitive bolometers (765 spatial pixels) optimized for the low loading environment in flight and read out by time-division SQUID multiplexing. In this paper we describe the mechanical, thermal, and magnetic shielding architecture of the focal planes and present cryogenic measurements which characterize yield and the uniformity of several bolometer parameters. The assembled FPUs have high yields, with one array as high as 95% including defects from wiring and readout. We demonstrate high uniformity in device parameters, finding the median saturation power for each TES array to be ~3 pW at 300 mK with a less than 6% variation across each array at one standard deviation. These focal planes will be deployed alongside the 95 and 150 GHz telescopes in the SPIDER-2 instrument, slated to fly from McMurdo Station in Antarctica in December 2018

Design of 280 GHz feedhorn-coupled TES arrays for the balloon-borne polarimeter SPIDER

We describe 280 GHz bolometric detector arrays that instrument the balloon-borne polarimeter SPIDER. A primary science goal of SPIDER is to measure the large-scale B-mode polarization of the cosmic microwave background (CMB) in search of the cosmic-inflation, gravitational-wave signature. 280 GHz channels aid this science goal by constraining the level of B-mode contamination from galactic dust emission. We present the focal plane unit design, which consists of a 16x16 array of conical, corrugated feedhorns coupled to a monolithic detector array fabricated on a 150 mm diameter silicon wafer. Detector arrays are capable of polarimetric sensing via waveguide probe-coupling to a multiplexed array of transition-edge-sensor (TES) bolometers. The SPIDER receiver has three focal plane units at 280 GHz, which in total contains 765 spatial pixels and 1,530 polarization sensitive bolometers. By fabrication and measurement of single feedhorns, we demonstrate 14.7 degrees FHWM Gaussian-shaped beams with <1% ellipticity in a 30% fractional bandwidth centered at 280 GHz. We present electromagnetic simulations of the detection circuit, which show 94% band-averaged, single-polarization coupling efficiency, 3% reflection and 3% radiative loss. Lastly, we demonstrate a low thermal conductance bolometer, which is well-described by a simple TES model and exhibits an electrical noise equivalent power (NEP) = 2.6 x 10(-17) W/root Hz, consistent with the phonon noise prediction