scholarly journals A Census of Southern Pulsars at 185 MHz

2017 ◽  
Vol 34 ◽  
Author(s):  
Mengyao Xue ◽  
N. D. R. Bhat ◽  
S. E. Tremblay ◽  
S. M. Ord ◽  
C. Sobey ◽  
...  
Keyword(s):  
Phase 1 ◽  
Low Frequency ◽  
Frequency Component ◽  
Frequency Resolution ◽  
Large Field ◽  
Initial Time ◽  
Wide Field ◽  
Processing Load ◽  
Square Kilometre Array ◽  
Murchison Widefield Array

AbstractThe Murchison Widefield Array, and its recently developed Voltage Capture System, facilitates extending the low-frequency range of pulsar observations at high-time and -frequency resolution in the Southern Hemisphere, providing further information about pulsars and the ISM. We present the results of an initial time-resolved census of known pulsars using the Murchison Widefield Array. To significantly reduce the processing load, we incoherently sum the detected powers from the 128 Murchison Widefield Array tiles, which yields ~10% of the attainable sensitivity of the coherent sum. This preserves the large field-of-view (~450 deg2 at 185 MHz), allowing multiple pulsars to be observed simultaneously. We developed a WIde-field Pulsar Pipeline that processes the data from each observation and automatically folds every known pulsar located within the beam. We have detected 50 pulsars to date, 6 of which are millisecond pulsars. This is consistent with our expectation, given the telescope sensitivity and the sky coverage of the processed data (~17 000 deg2). For 10 pulsars, we present the lowest frequency detections published. For a subset of the pulsars, we present multi-frequency pulse profiles by combining our data with published profiles from other telescopes. Since the Murchison Widefield Array is a low-frequency precursor to the Square Kilometre Array, we use our census results to forecast that a survey using the low-frequency component of the Square Kilometre Array Phase 1 can potentially detect around 9 400 pulsars.

scholarly journals The Low-Frequency Environment of the Murchison Widefield Array: Radio-Frequency Interference Analysis and Mitigation

2015 ◽  
Vol 32 ◽  
Author(s):  
A. R. Offringa ◽  
R. B. Wayth ◽  
N. Hurley-Walker ◽  
D. L. Kaplan ◽  
N. Barry ◽  
...  
Keyword(s):  
Radio Frequency ◽  
Low Frequency ◽  
Digital Tv ◽  
Frequency Resolution ◽  
Interference Detection ◽  
Radio Frequency Interference ◽  
Receiver Design ◽  
Square Kilometre Array ◽  
Atmospheric Propagation ◽  
Murchison Widefield Array

AbstractThe Murchison Widefield Array is a new low-frequency interferometric radio telescope built in Western Australia at one of the locations of the future Square Kilometre Array. We describe the automated radio-frequency interference detection strategy implemented for the Murchison Widefield Array, which is based on the aoflagger platform, and present 72–231 MHz radio-frequency interference statistics from 10 observing nights. Radio-frequency interference detection removes 1.1% of the data. Radio-frequency interference from digital TV is observed 3% of the time due to occasional ionospheric or atmospheric propagation. After radio-frequency interference detection and excision, almost all data can be calibrated and imaged without further radio-frequency interference mitigation efforts, including observations within the FM and digital TV bands. The results are compared to a previously published Low-Frequency Array radio-frequency interference survey. The remote location of the Murchison Widefield Array results in a substantially cleaner radio-frequency interference environment compared to Low-Frequency Array’s radio environment, but adequate detection of radio-frequency interference is still required before data can be analysed. We include specific recommendations designed to make the Square Kilometre Array more robust to radio-frequency interference, including: the availability of sufficient computing power for radio-frequency interference detection; accounting for radio-frequency interference in the receiver design; a smooth band-pass response; and the capability of radio-frequency interference detection at high time and frequency resolution (second and kHz-scale respectively).

scholarly journals Source counts and confusion at 72–231 MHz in the MWA GLEAM survey

2019 ◽  
Vol 36 ◽  
Author(s):  
T. M. O. Franzen ◽  
T. Vernstrom ◽  
C. A. Jackson ◽  
N. Hurley-Walker ◽  
R. D. Ekers ◽  
...  
Keyword(s):  
Thermal Noise ◽  
Low Frequency ◽  
Radio Continuum ◽  
Large Area ◽  
Design Study ◽  
Array Design ◽  
Square Kilometre Array ◽  
Noise Limit ◽  
Murchison Widefield Array ◽  
Extended Emission

Abstract The GaLactic and Extragalactic All-sky Murchison Widefield Array survey is a radio continuum survey at 72–231 MHz of the whole sky south of declination +30º, carried out with the Murchison Widefield Array. In this paper, we derive source counts from the GaLactic and Extragalactic All-sky Murchison data at 200, 154, 118, and 88 MHz, to a flux density limit of 50, 80, 120, and 290 mJy respectively, correcting for ionospheric smearing, incompleteness and source blending. These counts are more accurate than other counts in the literature at similar frequencies as a result of the large area of sky covered and this survey’s sensitivity to extended emission missed by other surveys. At S154 MHz > 0.5 Jy, there is no evidence of flattening in the average spectral index (α ≈ −0.8 where S ∝ vα) towards the lower frequencies. We demonstrate that the Square Kilometre Array Design Study model by Wilman et al. significantly underpredicts the observed 154-MHz GaLactic and Extragalactic All-sky Murchison counts, particularly at the bright end. Using deeper Low-Frequency Array counts and the Square Kilometre Array Design Study model, we find that sidelobe confusion dominates the thermal noise and classical confusion at v ≳ 100 MHz due to both the limited CLEANing depth and the undeconvolved sources outside the field-of-view. We show that we can approach the theoretical noise limit using a more efficient and automated CLEAN algorithm.

scholarly journals Science with the Murchison Widefield Array

2013 ◽  
Vol 30 ◽  
Author(s):  
Judd D. Bowman ◽  
Iver Cairns ◽  
David L. Kaplan ◽  
Tara Murphy ◽  
Divya Oberoi ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Early Universe ◽  
Western Australia ◽  
Space Weather ◽  
Time Domain ◽  
Angular Resolution ◽  
Low Frequency ◽  
Performance Properties ◽  
Square Kilometre Array ◽  
Murchison Widefield Array

AbstractSignificant new opportunities for astrophysics and cosmology have been identified at low radio frequencies. The Murchison Widefield Array is the first telescope in the southern hemisphere designed specifically to explore the low-frequency astronomical sky between 80 and 300 MHz with arcminute angular resolution and high survey efficiency. The telescope will enable new advances along four key science themes, including searching for redshifted 21-cm emission from the EoR in the early Universe; Galactic and extragalactic all-sky southern hemisphere surveys; time-domain astrophysics; and solar, heliospheric, and ionospheric science and space weather. The Murchison Widefield Array is located in Western Australia at the site of the planned Square Kilometre Array (SKA) low-band telescope and is the only low-frequency SKA precursor facility. In this paper, we review the performance properties of the Murchison Widefield Array and describe its primary scientific objectives.

scholarly journals Modified Method to Detect the Turbulent Layers in the Atmospheric Boundary Layer for the Large Solar Vacuum Telescope

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 159
Author(s):  
Artem Yurievich Shikhovtsev ◽  
Pavel Gavrilovich Kovadlo ◽  
Alexander Victorovich Kiselev ◽  
Dmitriy Yurievich Kolobov ◽  
Vladimir Petrovich Lukin ◽  
...  
Keyword(s):  
Atmospheric Turbulence ◽  
Adaptive Optics ◽  
Low Frequency ◽  
Frequency Component ◽  
Wide Field ◽  
Height Distribution ◽  
Modified Method ◽  
Cross Correlation Analysis ◽  
Time Changes ◽  
Angular Shift

A method to detect the atmospheric turbulent layers using a single Shack–Hartmann wavefront sensor is discussed. In order to determine the height distribution of the atmospheric turbulence above a telescope, we register the wavefront distortions at different regions of the aperture from a single light solar object moving in time. Changes of the spatial position of the solar object on the sky give us the possibility to estimate the angular shift of an object. Cross-correlation analysis of the low-frequency component of wavefront slopes spaced on the telescope aperture at different times allows us to estimate characteristics for different atmospheric layers. Knowledge of the height profiles of atmospheric turbulence as well as the Fried parameter is critical for wide-field adaptive optics (AO).

scholarly journals The Challenges of Low-Frequency Radio Polarimetry: Lessons from the Murchison Widefield Array

2017 ◽  
Vol 34 ◽  
Author(s):  
E. Lenc ◽  
C. S. Anderson ◽  
N. Barry ◽  
J. D. Bowman ◽  
I. H. Cairns ◽  
...  
Keyword(s):  
Imaging Techniques ◽  
Low Frequency ◽  
Field Of View ◽  
Wide Field ◽  
Low Mass Stars ◽  
Future Directions ◽  
Low Frequencies ◽  
Wide Field Of View ◽  
Low Mass ◽  
Murchison Widefield Array

AbstractWe present techniques developed to calibrate and correct Murchison Widefield Array low-frequency (72–300 MHz) radio observations for polarimetry. The extremely wide field-of-view, excellent instantaneous (u, v)-coverage and sensitivity to degree-scale structure that the Murchison Widefield Array provides enable instrumental calibration, removal of instrumental artefacts, and correction for ionospheric Faraday rotation through imaging techniques. With the demonstrated polarimetric capabilities of the Murchison Widefield Array, we discuss future directions for polarimetric science at low frequencies to answer outstanding questions relating to polarised source counts, source depolarisation, pulsar science, low-mass stars, exoplanets, the nature of the interstellar and intergalactic media, and the solar environment.

Correction of Low Frequency Component in Spectrum Analysis Based on Hilbert Transform

2013 ◽  
Vol 584 ◽  
pp. 154-158
Author(s):  
Jun Jie Wang ◽  
Zhi Jiang Xie ◽  
Ping Chen
Keyword(s):  
Hilbert Transform ◽  
Low Frequency ◽  
Frequency Component ◽  
Side Lobe ◽  
Spectral Lines ◽  
Frequency Resolution ◽  
Ratio Method ◽  
Frequency Correction ◽  
The Impact ◽  
Frequency Phase

Because of the serious interference coming from the negative frequency in low frequency correction, the traditional correction methods no longer work. This paper proposes an improved ratio method to correct the frequency, phase and amplitude of spectrum peak when the spectral line locates near the left end in spectrum. The Hilbert Transform is used to diminish the impact of interference of the mirror frequency. The barycenter of two spectral lines is used to obtain the correcting value. A new formula is developed when the frequency is less than the frequency resolution. One of the spectral lines is located in the main lobe and the other is in the first side lobe. Furthermore, the direct current has nearly no impact on this new method theoretically which is a key problem in low frequency correction. The simulation shows that the frequency, phase and amplitude of a theoretical low frequency can be corrected satisfactorily. The result of the correction improves a lot compared with the traditional method. However, this method could not correct the spectrum with multiple components of low frequency.

scholarly journals A SETI survey of the Vela region using the Murchison Widefield Array: Orders of magnitude expansion in search space

2020 ◽  
Vol 37 ◽  
Author(s):  
C. D. Tremblay ◽  
S. J. Tingay
Keyword(s):  
Large Scale ◽  
Detection Threshold ◽  
Search Space ◽  
Frequency Resolution ◽  
Large Field ◽  
Galactic Centre ◽  
Dimensional Parameter ◽  
Low Frequencies ◽  
Upper Limits ◽  
Murchison Widefield Array

Abstract Following the results of our previous low-frequency searches for extraterrestrial intelligence (SETI) using the Murchison Widefield Array (MWA), directed towards the Galactic Centre and the Orion Molecular Cloud (Galactic Anticentre), we report a new large-scale survey towards the Vela region with the lowest upper limits thus far obtained with the MWA. Using the MWA in the frequency range 98–128 MHz over a 17-h period, a $400\,\textrm{deg}^{2}$ field centred on the Vela Supernova Remnant was observed with a frequency resolution of 10 kHz. Within this field, there are six known exoplanets. At the positions of these exoplanets, we searched for narrow-band signals consistent with radio transmissions from intelligent civilisations. No unknown signals were found with a 5 $\sigma$ detection threshold. In total, across this work plus our two previous surveys, we have now examined 75 known exoplanets at low frequencies. In addition to the known exoplanets, we have included in our analysis the calculation of the Effective Isotropic Radiated Power (EIRP) upper limits towards over 10 million stellar sources in the Vela field with known distances from Gaia (assuming a 10-kHz transmission bandwidth). Using the methods of Wright, Kanodia, & Lubar (2018) to describe an eight-dimensional parameter space for SETI searches, our survey achieves the largest search fraction yet, two orders of magnitude higher than the previous highest (our MWA Galactic Anticentre survey), reaching a search fraction of $\ \sim2\,{\times}\,10^{-16}$ . We also compare our results to previous SETI programs in the context of the $\mbox{EIRP}_{\textrm{min}}$ —Transmitter Rate plane. Our results clearly continue to demonstrate that SETI has a long way to go. But, encouragingly, the MWA SETI surveys also demonstrate that large-scale SETI surveys, in particular for telescopes with a large field-of-view, can be performed commensally with observations designed primarily for astrophysical purposes.

scholarly journals The POlarised GLEAM Survey (POGS) I: First results from a low-frequency radio linear polarisation survey of the southern sky

2018 ◽  
Vol 35 ◽  
Author(s):  
C. J. Riseley ◽  
E. Lenc ◽  
C. L. Van Eck ◽  
G. Heald ◽  
B. M. Gaensler ◽  
...  
Keyword(s):  
Faraday Rotation ◽  
Low Frequency ◽  
Frequency Component ◽  
Radio Sources ◽  
First Results ◽  
Order Of Magnitude ◽  
Murchison Widefield Array ◽  
Using Data ◽  
New Generation ◽  
Right Ascension

AbstractThe low-frequency polarisation properties of radio sources are poorly studied, particularly in statistical samples. However, the new generation of low-frequency telescopes, such as the Murchison Widefield Array (the precursor for the low-frequency component of the Square Kilometre Array) offers an opportunity to probe the physics of radio sources at very low radio frequencies. In this paper, we present a catalogue of linearly polarised sources detected at 216 MHz, using data from the Galactic and Extragalactic All-sky Murchison Widefield Array survey. Our catalogue covers the Declination range –17° to –37° and 24 h in Right Ascension, at a resolution of around 3 arcminutes. We detect 81 sources (including both a known pulsar and a new pulsar candidate) with linearly polarised flux densities in excess of 18 mJy across a survey area of approximately 6 400 deg2, corresponding to a surface density of 1 source per 79 deg2. The level of Faraday rotation measured for our sources is broadly consistent with those recovered at higher frequencies, with typically more than an order of magnitude improvement in the uncertainty compared to higher-frequency measurements. However, our catalogue is likely incomplete at low Faraday rotation measures, due to our practice of excluding sources in the region where instrumental leakage appears. The majority of sources exhibit significant depolarisation compared to higher frequencies; however, a small sub-sample repolarise at 216 MHz. We also discuss the polarisation properties of four nearby, large-angular-scale radio galaxies, with a particular focus on the giant radio galaxy ESO 422–G028, in order to explain the striking differences in polarised morphology between 216 MHz and 1.4 GHz.

scholarly journals MWA tied-array processing I: Calibration and beamformation

2019 ◽  
Vol 36 ◽  
Author(s):  
S. M. Ord ◽  
S. E. Tremblay ◽  
S. J. McSweeney ◽  
N. D. R. Bhat ◽  
C. Sobey ◽  
...  
Keyword(s):  
Western Australia ◽  
Radio Astronomy ◽  
Low Frequency ◽  
Frequency Resolution ◽  
Science Program ◽  
Astronomy Observatory ◽  
Beam Formation ◽  
Imaging Telescope ◽  
Signal Path ◽  
Murchison Widefield Array

AbstractThe Murchison Widefield Array is a low-frequency Square Kilometre Array precursor located at the Murchison Radio-astronomy Observatory in Western Australia. Primarily designed as an imaging telescope, but with a flexible signal path, the capabilities of this telescope have recently been extended to include off-line incoherent and tied-array beam formation using recorded antenna voltages. This has provided the capability for high-time and frequency resolution observations, including a pulsar science program. This paper describes the algorithms and pipeline that we have developed to form the tied-array beam products from the summation of calibrated signals of the antenna elements, and presents example polarimetric profiles for PSRs J0437-4715 and J1900-2600 at 185 MHz.

scholarly journals The Engineering Development Array: A Low Frequency Radio Telescope Utilising SKA Precursor Technology

2017 ◽  
Vol 34 ◽  
Author(s):  
Randall Wayth ◽  
Marcin Sokolowski ◽  
Tom Booler ◽  
Brian Crosse ◽  
David Emrich ◽  
...  
Keyword(s):  
Radio Telescope ◽  
Low Frequency ◽  
Dipole Antennas ◽  
Modular Architecture ◽  
Low Frequencies ◽  
Square Kilometre Array ◽  
Engineering Development ◽  
Staged Approach ◽  
Murchison Widefield Array ◽  
And Performance

AbstractWe describe the design and performance of the Engineering Development Array, which is a low-frequency radio telescope comprising 256 dual-polarisation dipole antennas working as a phased array. The Engineering Development Array was conceived of, developed, and deployed in just 18 months via re-use of Square Kilometre Array precursor technology and expertise, specifically from the Murchison Widefield Array radio telescope. Using drift scans and a model for the sky brightness temperature at low frequencies, we have derived the Engineering Development Array’s receiver temperature as a function of frequency. The Engineering Development Array is shown to be sky-noise limited over most of the frequency range measured between 60 and 240 MHz. By using the Engineering Development Array in interferometric mode with the Murchison Widefield Array, we used calibrated visibilities to measure the absolute sensitivity of the array. The measured array sensitivity matches very well with a model based on the array layout and measured receiver temperature. The results demonstrate the practicality and feasibility of using Murchison Widefield Array-style precursor technology for Square Kilometre Array-scale stations. The modular architecture of the Engineering Development Array allows upgrades to the array to be rolled out in a staged approach. Future improvements to the Engineering Development Array include replacing the second stage beamformer with a fully digital system, and to transition to using RF-over-fibre for the signal output from first stage beamformers.

Sign in / Sign up

Export Citation Format

Share Document