A CubeSat for Calibrating Ground-Based and Sub-Orbital Millimeter-Wave Polarimeters (CalSat)

Abstract

We describe a low-cost, open-access, CubeSat-based calibration instrument that is designed to support ground-based and sub-orbital experiments searching for various polarization signals in the cosmic microwave background (CMB). All modern CMB polarization experiments require a robust calibration program that will allow the effects of instrument-induced signals to be mitigated during data analysis. A bright, compact and linearly polarized astrophysical source with polarization properties known to adequate precision does not exist. Therefore, we designed a space-based millimeter-wave calibration instrument, called CalSat, to serve as an open-access calibrator, and this paper describes the results of our design study. The calibration source on board CalSat is composed of five “tones” with one each at 47.1, 80.0, 140, 249 and 309[Formula: see text]GHz. The five tones we chose are well matched to (i) the observation windows in the atmospheric transmittance spectra, (ii) the spectral bands commonly used in polarimeters by the CMB community and (iii) the Amateur Satellite Service bands in the Table of Frequency Allocations used by the Federal Communications Commission. CalSat would be placed in a polar orbit allowing visibility from observatories in the Northern Hemisphere, such as Mauna Kea in Hawaii and Summit Station in Greenland, and the Southern Hemisphere, such as the Atacama Desert in Chile and the South Pole. CalSat also would be observable by balloon-borne instruments launched from a range of locations around the world. This global visibility makes CalSat the only source that can be observed by all terrestrial and sub-orbital observatories, thereby providing a universal standard that permits comparison between experiments using appreciably different measurement approaches.

Foreground-induced biases in CMB polarimeter self-calibration

“…et al 2014). At millimetre wavelengths, the best celestial source appears to be Tau A, though it is not ideal because (i) it is not bright enough to give a high signal-to-noise ratio measurement with a short integration time, (ii) the source is extended with a complicated polarisation intensity morphology, (iii) the millimetre-wave spectrum of Tau A is not precisely known, which is important for polarimeters that have frequency-dependent performance, and (iv) Tau A is not observable from Antarctica where many ground-based and balloon-borne experiments are sited (see Johnson et al (2015) and references therein). Since an ideal celestial calibration source does not exist, many current experiments (Kaufman et al 2014;Barkats et al 2014;Naess et al 2014; The Polarbear Collaboration: P. A. R. Ade et al 2014;BICEP2 Collaboration et al 2015a) use a 'self-calibration' method (Keating et al 2013).…”

Recovery of Large Angular Scale CMB Polarization for Instruments Employing Variable-Delay Polarization Modulators

“…Alternatively, the grid-angle systematic can be determined by fitting for a rotation angle from the TB and EB power spectra and correcting the transfer function similar to the self-calibration procedure of Keating et al (2013). This would preclude a measurement of isotropic cosmic birefringence, so a hardware calibration system (Johnson et al 2015) would likely be implemented. We have shown that the temperature to polarization leakage due to VPM emission can be mitigated by removing a template from the TOD.…”

Development of calibration strategies for the Simons Observatory

“…The polarized sources can be mounted on a tripod, tower, drone, weather balloon, or a CubeSat. 34,35 The distance to the telescope far field and the telescope elevation range determines which mounting options are available. For the SO SATs, the far field ranges from ∼ 30 m to ∼ 300 m depending on the observation frequency, which is within the range of a tripod-, tower-, or dronemounted polarizaton calibrator.…”