Abstract
We characterize Galactic dust filaments by correlating BICEP/Keck and Planck data with polarization templates based on neutral hydrogen (H
i
) observations. Dust polarization is important ...for both our understanding of astrophysical processes in the interstellar medium (ISM) and the search for primordial gravitational waves in the cosmic microwave background (CMB). In the diffuse ISM, H
i
is strongly correlated with the dust and partly organized into filaments that are aligned with the local magnetic field. We analyze the deep BICEP/Keck data at 95, 150, and 220 GHz, over the low-column-density region of sky where BICEP/Keck has set the best limits on primordial gravitational waves. We separate the H
i
emission into distinct velocity components and detect dust polarization correlated with the local Galactic H
i
but not with the H
i
associated with Magellanic Stream
i
. We present a robust, multifrequency detection of polarized dust emission correlated with the filamentary H
i
morphology template down to 95 GHz. For assessing its utility for foreground cleaning, we report that the H
i
morphology template correlates in
B
modes at a ∼10%–65% level over the multipole range 20 <
ℓ
< 200 with the BICEP/Keck maps, which contain contributions from dust, CMB, and noise components. We measure the spectral index of the filamentary dust component spectral energy distribution to be
β
= 1.54 ± 0.13. We find no evidence for decorrelation in this region between the filaments and the rest of the dust field or from the inclusion of dust associated with the intermediate velocity H
i
. Finally, we explore the morphological parameter space in the H
i
-based filamentary model.
Abstract
We present estimates of line-of-sight distortion fields derived from the 95 and 150 GHz data taken by BICEP2, BICEP3, and the Keck Array up to the 2018 observing season, leading to ...cosmological constraints and a study of instrumental and astrophysical systematics. Cosmological constraints are derived from three of the distortion fields concerning gravitational lensing from large-scale structure, polarization rotation from magnetic fields or an axion-like field, and the screening effect of patchy reionization. We measure an amplitude of the lensing power spectrum
A
L
ϕ
ϕ
=
0.95
±
0.20
. We constrain polarization rotation, expressed as the coupling constant of a Chern–Simons electromagnetic term
g
a
γ
≤ 2.6 × 10
−2
/
H
I
, where
H
I
is the inflationary Hubble parameter, and an amplitude of primordial magnetic fields smoothed over 1 Mpc
B
1Mpc
≤ 6.6 nG at 95 GHz. We constrain the rms of optical depth fluctuations in a simple “crinkly surface” model of patchy reionization, finding
A
τ
< 0.19 (2
σ
) for the coherence scale of
L
c
= 100. We show that all of the distortion fields of the 95 and 150 GHz polarization maps are consistent with simulations including lensed ΛCDM, dust, and noise, with no evidence for instrumental systematics. In some cases, the
EB
and
TB
quadratic estimators presented here are more sensitive than our previous map-based null tests at identifying and rejecting spurious
B
-modes that might arise from instrumental effects. Finally, we verify that the standard deprojection filtering in the BICEP/Keck data processing is effective at removing temperature to polarization leakage.
The BICEP/
Keck
series of experiments target the cosmic microwave background at degree-scale resolution from the South Pole. Over the next few years, the “Stage-3” BICEP Array (BA) telescope will ...improve the program’s frequency coverage and sensitivity to primordial B-mode polarization by an order of magnitude. The first receiver in the array, BA1, began observing at 30/40 GHz in early 2020. The next two receivers, BA2 and BA3, are currently being assembled and will map the southern sky at frequencies ranging from 95 to 150 GHz. Common to all BA receivers is a refractive, on-axis, cryogenic optical design that focuses microwave radiation onto a focal plane populated with antenna-coupled bolometers. High-performance antireflective coatings up to 760 mm in aperture are needed for each element in the optical chain, and must withstand repeated thermal cycles down to 4 K. Here, we present the design and fabrication of the 30/40 GHz anti-reflection coatings for the recently deployed BA1 receiver, with indices matched to its various polyethylene, nylon and alumina optical components. We describe an epoxy coating technique designed for alumina optics, which achieves better than 80% transmission at room temperature. For polyethylene optical elements, we present a new heat-compression approach that allows low-density polytetrafluoroethylene AR layers to reach sub-percent reflected power. We describe the planned use of these methods for the next BA cryostats, which may inform technological choices for future small-aperture telescopes of the CMB-S4 experiment.
The Background Imaging of Cosmic Extragalactic Polarization (BICEP)/Keck (BK) collaboration is currently leading the quest for the highest-sensitivity measurements of the polarized cosmic microwave ...background (CMB) anisotropies on a degree scale with a series of cryogenic telescopes, of which BICEP Array (BA) is the latest Stage-3 upgrade with a total of
∼
32,000 detectors. The instrument comprises 4 receivers spanning 30–270 GHz, with the low-frequency 30/40 GHz deployed to the South Pole Station in late 2019. The full complement of receivers is forecast to set the most stringent constraints on the tensor-to-scalar ratio
r
. Building on these advances, the overarching small-aperture telescope concept is already being used as the reference for further Stage-4 experiment design. This paper describes the development of the BICEP Array 150 GHz detector module and its fabrication requirements, with highlights on the high-density time division multiplexing (TDM) design of the cryogenic circuit boards. The low-impedance wiring required between the detectors and the first stage of superconducting quantum interference device amplifiers is crucial to maintaining a stable bias current on the detectors. A novel multi-layer FR4 Printed Circuit Board with superconducting traces, capable of reading out up to 648 detectors, is detailed along with its validation tests. An ultra-high-density TDM detector module concept we developed for a CMB-S4-like experiment that allows up to 1920 detectors to be read out is also presented. TDM has been chosen as the detector readout technology for the Cosmic Microwave Background Stage-4 (CMB-S4) experiment based on its proven low-noise performance, predictable costs, and overall maturity of the architecture. The heritage for TDM is rooted in mm- and sub-mm-wave experiments dating back 20 years and has since evolved to support a multiplexing factor of 64x in Stage-3 experiments.
Time-division multiplexing is the readout architecture of choice for many ground and space experiments, as it is a very mature technology with proven outstanding low-frequency noise stability, which ...represents a central challenge in multiplexing. Once fully populated, each of the two BICEP Array high-frequency receivers, observing at 150 GHz and 220/270 GHz, will have 7776 TES detectors tiled on the focal plane. The constraints set by these two receivers required a redesign of the warm readout electronics. The new version of the standard multichannel electronics, developed and built at the University of British Columbia, is presented here for the first time. BICEP Array operates time-division multiplexing readout technology to the limits of its capabilities in terms of multiplexing rate, noise and cross talk, and applies them in rigorously demanding scientific application requiring extreme noise performance and systematic error control. Future experiments like CMB-S4 plan to use TES bolometers with time-division/SQUID-based readout for an even larger number of detectors.
Results on timing and spectral properties of the Be/X-ray binary pulsar 3A 0726-260 (4U 0728-25) are presented. The binary was observed on 2016 May 6-7 with the Large Area X-ray Proportional Counter ...(LAXPC) and Soft X-ray Telescope (SXT) instruments onboard the AstroSat satellite. During this observation the source was in non-flaring persistent state at a flux level of \(\sim\) 8.6 \(\pm\) 0.3 \(\times\)10\(^{-11}\) ergs cm\(^{-2}\) sec\(^{-1}\) in 0.4-20 keV. Strong X-ray pulsations with a period of 103.144\(\pm\)0.001 seconds are detected in 0.3-7 keV with the SXT and in 3-40 keV with the LAXPC. The pulse profile is energy dependent, and there is an indication that the pulse shape changes from a broad single pulse to a double pulse at higher energy. At energies above 20 keV, we report the first time detection of pulsation period 103.145\(\pm\)0.001 seconds and the double peaked pulse profile from the source. The energy spectrum of the source is derived from the combined analysis of the SXT and LAXPC spectral data in 0.4-20 keV. The best spectral fit is obtained by a power law model with a photon index (1.7\(\pm\)0.03) with high energy spectral cut-off at 12.9 \(\pm\) 0.7 keV. A broad Iron line at \(\sim\) 6.3 keV is detected in the energy spectrum. We briefly discuss the implications of these results.
The BICEP/\(\textit{Keck}\) (BK) series of cosmic microwave background (CMB) polarization experiments has, over the past decade and a half, produced a series of field-leading constraints on cosmic ...inflation via measurements of the "B-mode" polarization of the CMB. Primordial B modes are directly tied to the amplitude of primordial gravitational waves (PGW), their strength parameterized by the tensor-to-scalar ratio, \(r\), and thus the energy scale of inflation. Having set the most sensitive constraints to-date on \(r\), \(\sigma(r)=0.009\) (\(r_{0.05}<0.036, 95\%\) C.L.) using data through the 2018 observing season ("BK18"), the BICEP/\(\textit{Keck}\) program has continued to improve its dataset in the years since. We give a brief overview of the BK program and the "BK18" result before discussing the program's ongoing efforts, including the deployment and performance of the \(\textit{Keck Array}\)'s successor instrument, BICEP Array, improvements to data processing and internal consistency testing, new techniques such as delensing, and how those will ultimately serve to allow BK reach \(\sigma(r) \lesssim 0.003\) using data through the 2027 observing season.
