scholarly journals The Array of Long Baseline Antennas for Taking Radio Observations from the Sub-Antarctic

2020 ◽  
Vol 09 (04) ◽  
pp. 2050019
Author(s):  
H. C. Chiang ◽  
T. Dyson ◽  
E. Egan ◽  
S. Eyono ◽  
N. Ghazi ◽  
...  
Keyword(s):  
Low Frequency ◽  
Neutral Hydrogen ◽  
Radio Frequency Interference ◽  
Marion Island ◽  
Radio Observations ◽  
Long Baseline ◽  
Galactic Emission ◽  
Operating Frequency Range ◽  
Order Of Magnitude ◽  
Magnitude Improvement

Measurements of redshifted 21[Formula: see text]cm emission of neutral hydrogen at [Formula: see text][Formula: see text]MHz have the potential to probe the cosmic “dark ages,” a period of the universe’s history that remains unobserved to date. Observations at these frequencies are exceptionally challenging because of bright Galactic foregrounds, ionospheric contamination, and terrestrial radio-frequency interference. Very few sky maps exist at [Formula: see text][Formula: see text]MHz, and most have modest resolution. We introduce the Array of Long Baseline Antennas for Taking Radio Observations from the Sub-Antarctic (ALBATROS), a new experiment that aims to image low-frequency Galactic emission with an order-of-magnitude improvement in resolution over existing data. The ALBATROS array will consist of antenna stations that operate autonomously, each recording baseband data that will be interferometrically combined offline. The array will be installed on Marion Island and will ultimately comprise 10 stations, with an operating frequency range of 1.2–125[Formula: see text]MHz and maximum baseline lengths of [Formula: see text][Formula: see text]km. We present the ALBATROS instrument design and discuss pathfinder observations that were taken from Marion Island during 2018–2019.

scholarly journals A New Restoration Method for Radio Frequency Interference Effects on AMSR-2 over North America

2019 ◽  
Vol 11 (24) ◽  
pp. 2917 ◽  
Author(s):  
Wangbin Shen ◽  
Zhengkun Qin ◽  
Zhaohui Lin
Keyword(s):  
Radio Frequency ◽  
Land Surface ◽  
Interpolation Method ◽  
Low Frequency ◽  
Principal Component ◽  
New Method ◽  
Radio Frequency Interference ◽  
Data Restoration ◽  
Order Of Magnitude ◽  
Restoration Method

Observations from spaceborne microwave imagers are important sources of land surface information. However, the low-frequency channels of microwave imagers are easily interfered with by active radio signals with similar frequencies. Radio frequency interference (RFI) signals are widely distributed because of the lack of frequency protection, which seriously hinders the application of microwave imager data in data assimilation and retrieval research. In this paper, a new data restoration method is proposed based on principal component analysis (PCA). Both the ideal and real reconstruction experiments show that the new method can effectively repair abnormal observations interfered by RFI compared with the commonly used Cressman interpolation method because observation information over the whole selected domain is used for restoration in the new method, whereas Cressman interpolation uses only a selection of data around the target observation. The observation errors in the data with RFI can be reduced by one order of magnitude by means of the new method and little artificial information is introduced. One-week restoration validation also proves that the new method has a stable accuracy and broad application prospects.

scholarly journals G51.04+0.07 and its environment: Identification of a new Galactic supernova remnant at low radio frequencies

2018 ◽  
Vol 616 ◽  
pp. A98 ◽  
Author(s):  
L. Supan ◽  
G. Castelletti ◽  
W. M. Peters ◽  
N. E. Kassim
Keyword(s):  
Radio Emission ◽  
Flux Density ◽  
Supernova Remnant ◽  
Low Frequency ◽  
Neutral Hydrogen ◽  
Radio Continuum ◽  
Very Large Array ◽  
Continuum Spectrum ◽  
Galactic Emission ◽  
Nonthermal Radio Emission

We have identified a new supernova remnant (SNR), G51.04+0.07, using observations at 74 MHz from the Very Large Array Low-Frequency Sky Survey Redux (VLSSr). Earlier, higher frequency radio continuum, recombination line, and infrared data had correctly inferred the presence of nonthermal radio emission within a larger, complex environment including ionised nebulae and active star formation. However, our observations have allowed us to redefine at least one SNR as a relatively small source (7.′5 × 3′in size) located at the southern periphery of the originally defined SNR candidate G51.21+0.11. The integrated flux density of G51.04+0.07 at 74 MHz is 6.1 ± 0.8 Jy, while its radio continuum spectrum has a slope α = −0.52 ± 0.05 (S v ∝ vα), typical of a shell-type remnant. We also measured spatial variations in the spectral index between 74 and 1400 MHz across the source, ranging from a steeper spectrum (α = −0.50 ± 0.04) coincident with the brightest emission to a flatter component (α = −0.30 ± 0.07) in the surrounding fainter region. To probe the interstellar medium into which the redefined SNR is likely evolving, we have analysed the surrounding atomic and molecular gas using the 21 cm neutral hydrogen (HI) and 13CO(J = 1 − 0) emissions. We found that G51.04+0.07 is confined within an elongated HI cavity and that its radio emission is consistent with the remains of a stellar explosion that occurred ~6300 yr ago at a distance of 7.7 ± 2.3 kpc. Kinematic data suggest that the newly discovered SNR lies in front of HII regions in the complex, consistent with the lack of a turnover in the low frequency continuum spectrum. The CO observations revealed molecular material that traces the central and northern parts of G51.04+0.07. The interaction between the cloud and the radio source is not conclusive and motivates further study. The relatively low flux density (~1.5 Jy at 1400 MHz) of G51.04+0.07 is consistent with this and many similar SNRs lying hidden along complex lines of sight towards inner Galactic emission complexes. It would also not be surprising if the larger complex studied here hosted additional SNRs.

scholarly journals Intensity mapping as a probe of axion dark matter

2020 ◽  
Vol 500 (3) ◽  
pp. 3162-3177
Author(s):  
Jurek B Bauer ◽  
David J E Marsh ◽  
Renée Hložek ◽  
Hamsa Padmanabhan ◽  
Alex Laguë
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Neutral Hydrogen ◽  
Matrix Formalism ◽  
Intensity Mapping ◽  
Matter Power Spectrum ◽  
Wide Range ◽  
Non Linear ◽  
Order Of Magnitude ◽  
Magnitude Improvement

ABSTRACT We consider intensity mapping (IM) of neutral hydrogen (H i) in the redshift range 0 ≲ z ≲ 3 employing a halo model approach where H i is assumed to follow the distribution of dark matter (DM) haloes. If a portion of the DM is composed of ultralight axions, then the abundance of haloes is changed compared to cold DM below the axion Jeans mass. With fixed total H i density, $\Omega _{\rm H\, \rm {\small I}}$, assumed to reside entirely in haloes, this effect introduces a scale-independent increase in the H i power spectrum on scales above the axion Jeans scale, which our model predicts consistent with N-body simulations. Lighter axions introduce a scale-dependent feature even on linear scales due to its suppression of the matter power spectrum near the Jeans scale. We use the Fisher matrix formalism to forecast the ability of future H i surveys to constrain the axion fraction of DM and marginalize over astrophysical and model uncertainties. We find that a HIRAX-like survey is a very reliable IM survey configuration, being affected minimally by uncertainties due to non-linear scales, while the SKA1MID configuration is the most constraining as it is sensitive to non-linear scales. Including non-linear scales and combining a SKA1MID-like IM survey with the Simons Observatory CMB, the benchmark ‘fuzzy DM’ model with ma = 10−22 eV can be constrained at few per cent. This is almost an order of magnitude improvement over current limits from the Ly α forest. For lighter ULAs, this limit improves below 1 per cent, and allows the possibility to test the connection between axion models and the grand unification scale across a wide range of masses.

scholarly journals The POlarised GLEAM Survey (POGS) II: Results from an all-sky rotation measure synthesis survey at long wavelengths

2020 ◽  
Vol 37 ◽  
Author(s):  
C. J. Riseley ◽  
T. J. Galvin ◽  
C. Sobey ◽  
T. Vernstrom ◽  
S. V. White ◽  
...  
Keyword(s):  
Faraday Rotation ◽  
Low Frequency ◽  
Source Population ◽  
Frequency Range ◽  
Radio Pulsars ◽  
Extragalactic Source ◽  
Rotation Measure ◽  
Order Of Magnitude ◽  
Using Data ◽  
Magnitude Improvement

Abstract The low-frequency linearly polarised radio source population is largely unexplored. However, a renaissance in low-frequency polarimetry has been enabled by pathfinder and precursor instruments for the Square Kilometre Array. In this second paper from the POlarised GaLactic and Extragalactic All-Sky MWA Survey-the POlarised GLEAM Survey, or POGS-we present the results from our all-sky MWA Phase I Faraday Rotation Measure survey. Our survey covers nearly the entire Southern sky in the Declination range $-82^\circ$ to $+30^\circ$ at a resolution between around three and seven arcminutes (depending on Declination) using data in the frequency range 169−231 MHz. We have performed two targeted searches: the first covering 25 489 square degrees of sky, searching for extragalactic polarised sources; the second covering the entire sky South of Declination $+30^\circ$ , searching for known pulsars. We detect a total of 517 sources with 200 MHz linearly polarised flux densities between 9.9 mJy and 1.7 Jy, of which 33 are known radio pulsars. All sources in our catalogues have Faraday rotation measures in the range $-328.07$ to $+279.62$ rad m−2. The Faraday rotation measures are broadly consistent with results from higher-frequency surveys, but with typically more than an order of magnitude improvement in the precision, highlighting the power of low-frequency polarisation surveys to accurately study Galactic and extragalactic magnetic fields. We discuss the properties of our extragalactic and known-pulsar source population, how the sky distribution relates to Galactic features, and identify a handful of new pulsar candidates among our nominally extragalactic source population.

scholarly journals Peering into the dark (ages) with low-frequency space interferometers

2021 ◽  
Author(s):  
Léon V. E. Koopmans ◽  
Rennan Barkana ◽  
Mark Bentum ◽  
Gianni Bernardi ◽  
Albert-Jan Boonstra ◽  
...  
Keyword(s):  
Radio Telescope ◽  
High Redshift ◽  
Low Frequency ◽  
Neutral Hydrogen ◽  
Mission Design ◽  
Radio Frequency Interference ◽  
Fundamental Physics ◽  
Frequency Space ◽  
Dark Ages ◽  
Insight Into

AbstractThe Dark Ages and Cosmic Dawn are largely unexplored windows on the infant Universe (z ~ 200–10). Observations of the redshifted 21-cm line of neutral hydrogen can provide valuable new insight into fundamental physics and astrophysics during these eras that no other probe can provide, and drives the design of many future ground-based instruments such as the Square Kilometre Array (SKA) and the Hydrogen Epoch of Reionization Array (HERA). We review progress in the field of high-redshift 21-cm Cosmology, in particular focussing on what questions can be addressed by probing the Dark Ages at z > 30. We conclude that only a space- or lunar-based radio telescope, shielded from the Earth’s radio-frequency interference (RFI) signals and its ionosphere, enable the 21-cm signal from the Dark Ages to be detected. We suggest a generic mission design concept, CoDEX, that will enable this in the coming decades.

Low frequency radio observations: critical in revealing inhomogeneous shock structures

2019 ◽  
Author(s):  
Poonam Chandra ◽  
A. J. Nayana ◽  
Claes-Ingvar Bjornsson ◽  
Peter Lundqvist ◽  
Alak K. Ray
Keyword(s):  
Low Frequency ◽  
Radio Observations

High-Density Memristor-CMOS Ternary Logic Family

2020 ◽  
Author(s):  
Xiaoyuan Wang ◽  
Pengfei Zhou ◽  
Jason Eshraghian ◽  
Chih-Yang Lin ◽  
Herbert Ho-Ching Iu ◽  
...  
Keyword(s):  
Indium Tin Oxide ◽  
Practical Implementation ◽  
Switching Speed ◽  
High Data ◽  
Fast Switching ◽  
Data Density ◽  
Order Of Magnitude ◽  
High Transconductance ◽  
Logic Functions ◽  
Magnitude Improvement

<div>This paper presents the first experimental demonstration</div><div>of a ternary memristor-CMOS logic family. We systematically</div><div>design, simulate and experimentally verify the primitive</div><div>logic functions: the ternary AND, OR and NOT gates. These are then used to build combinational ternary NAND, NOR, XOR and XNOR gates, as well as data handling ternary MAX and MIN gates. Our simulations are performed using a 50-nm process which are verified with in-house fabricated indium-tin-oxide memristors, optimized for fast switching, high transconductance, and low current leakage. We obtain close to an order of magnitude improvement in data density over conventional CMOS logic, and a reduction of switching speed by a factor of 13 over prior state-of-the-art ternary memristor results. We anticipate extensions of this work can realize practical implementation where high data density is of critical importance.</div>

scholarly journals Demonstrating the Tapered Gridded Estimator (TGE) for the Cosmological HI 21-cm Power Spectrum using 150 MHz GMRT observations

2020 ◽  
Author(s):  
Srijita Pal ◽  
Somnath Bharadwaj ◽  
Abhik Ghosh ◽  
Samir Choudhuri
Keyword(s):  
Power Spectrum ◽  
Unbiased Estimate ◽  
Power Spectra ◽  
Neutral Hydrogen ◽  
Statistical Error ◽  
Temperature Fluctuations ◽  
Radio Frequency Interference ◽  
Rectangular Region ◽  
Angular Power Spectrum ◽  
The Mean

Abstract We apply the Tapered Gridded Estimator (TGE) for estimating the cosmological 21-cm power spectrum from 150 MHz GMRT observations which corresponds to the neutral hydrogen (HI) at redshift z = 8.28. Here TGE is used to measure the Multi-frequency Angular Power Spectrum (MAPS) Cℓ(Δν) first, from which we estimate the 21-cm power spectrum P(k⊥, k∥). The data here are much too small for a detection, and the aim is to demonstrate the capabilities of the estimator. We find that the estimated power spectrum is consistent with the expected foreground and noise behaviour. This demonstrates that this estimator correctly estimates the noise bias and subtracts this out to yield an unbiased estimate of the power spectrum. More than $47\%$ of the frequency channels had to be discarded from the data owing to radio-frequency interference, however the estimated power spectrum does not show any artifacts due to missing channels. Finally, we show that it is possible to suppress the foreground contribution by tapering the sky response at large angular separations from the phase center. We combine the k modes within a rectangular region in the ‘EoR window’ to obtain the spherically binned averaged dimensionless power spectra Δ2(k) along with the statistical error σ associated with the measured Δ2(k). The lowest k-bin yields Δ2(k) = (61.47)2 K2 at k = 1.59 Mpc−1, with σ = (27.40)2 K2. We obtain a 2 σ upper limit of (72.66)2 K2 on the mean squared HI 21-cm brightness temperature fluctuations at k = 1.59 Mpc−1.

scholarly journals Low Frequency Radio Observations of GRS 1915+105 with GMRT

2005 ◽  
Vol 5 (S1) ◽  
pp. 87-92 ◽  
Author(s):  
C H Ishwara-Chandra ◽  
A Pramesh Rao ◽  
Mamta Pandey ◽  
R K Manchanda ◽  
Philippe Durouchoux
Keyword(s):  
Low Frequency ◽  
Radio Observations
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