Spectral Flattening at Low Frequencies in Crab Giant Pulses

Meyers, Bradley W.; Tremblay, S. E.; Bhat, N. D. R.; Shannon, R. M.; Kirsten, F.; Sokołowski, M.; Tingay, S. J.; Oronsaye, S. I.; Ord, S. M.

doi:10.3847/1538-4357/aa8bba

Cited by 33 publications

(60 citation statements)

References 76 publications

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“…The MWA profile is narrower than those at higher frequencies, possibly due to the pre- and post-cursor components moving away from the main pulse and becoming less significant. The MWA has the ability to carry out multi-band observations (80–300 MHz) by taking advantage of its flexible design, and this capability has been used for detailed profile and spectral studies (Meyers et al 2017). Future MWA observations at frequencies below and above 185 MHz can therefore provide further information towards investigating the profile evolution in such pulsars.…”

Section: Discussionmentioning

confidence: 99%

A Census of Southern Pulsars at 185 MHz

Xue¹,

Tremblay²,

Ord³

et al. 2017

Publ. Astron. Soc. Aust.

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The Murchison Widefield Array (MWA), and its recently-developed Voltage Capture System (VCS), 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 MWA. To significantly reduce the processing load, we incoherently sum the detected powers from the 128 MWA tiles, which yields ∼ 10% of the attainable sensitivity of the coherent sum. This preserves the large field-of-view (∼450 deg 2 at 185 MHz), allowing multiple pulsars to be observed simultaneously. We developed a WIde-field Pulsar Pipeline (WIPP) 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 deg 2 ). For ten 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 MWA is a low-frequency precursor to the Square Kilometre Array (SKA), we use our census results to forecast that a survey using Phase 1 of SKA-Low (SKA1-Low) can potentially detect around 9400 pulsars.

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Section: Discussionmentioning

confidence: 99%

A Census of Southern Pulsars at 185 MHz

Xue¹,

Tremblay²,

Ord³

et al. 2017

Publ. Astron. Soc. Aust.

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“…The flux density calibration for our data is carried out using the approach described by Meyers et al (2017). This involves estimating the system gain (G) by simulating the tied-array beam pattern and integrating the response across the visible sky for the phased-array configuration used for observing.…”

Section: Flux Density Calibrationmentioning

confidence: 99%

“…While doing this, we also account for a "coherency factor" (cf. Meyers et al 2017), for any loss in sensitivity in the coherent beamforming process. This information is then used to estimate the flux density for all the observed frequency bands using the radiometer equation (Lorimer & Kramer 2004) and also by factoring in the duty cycle of the pulsar, which is equivalent pulse width (W) divided by the pulse period (W/P), where W is measured as integrated flux over the "on" pulse divided by the peak amplitude of the pulse.…”

Section: Flux Density Calibrationmentioning

confidence: 99%

“…a 256-tile array extending out to ∼ 6 km (Wayth et al 2018). With its voltage capture system (VCS; Tremblay et al 2015), which records data at 10-kHz/100-µs resolutions, the MWA has been producing a wide variety of pulsar science (e.g., McSweeney et al 2017;Meyers et al 2017;Xue et al 2017), including characterization of the ISM towards important southern-sky PTA targets (e.g., Bhat et al 2014Bhat et al , 2016Bhat et al , 2018.…”

Section: Introductionmentioning

confidence: 99%

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A High Time-resolution Study of the Millisecond Pulsar J2241−5236 at Frequencies Below 300 MHz

Kaur

Bhat

Tremblay

et al. 2019

ApJ

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One of the major challenges for pulsar timing array (PTA) experiments is the mitigation of the effects of the turbulent interstellar medium (ISM) from timing data. These can potentially lead to measurable delays and/or distortions in the pulse profiles and scale strongly with the inverse of the radio frequency. Low-frequency observations are therefore highly appealing for characterizing them. However, in order to achieve the necessary time resolution to resolve profile features of short-period millisecond pulsars, phase-coherent de-dispersion is essential, especially at frequencies below 300 MHz. We present the lowest-frequency (80-220 MHz), coherently de-dispersed detections of one of the most promising pulsars for current and future PTAs, PSR J2241−5236, using our new beam-former software for the MWA's voltage capture system (VCS), which reconstructs the time series at a much higher time resolution of ∼ 1 µs by re-synthesizing the recorded voltage data at 10-kHz/100-µs native resolutions. Our data reveal a dual-precursor type feature in the pulse profile that is either faint or absent in highfrequency observations from Parkes. The resultant high-fidelity detections have enabled dispersion measure (DM) determinations with very high precision, of the order of (2-6) × 10 −6 pc cm −3 , owing to the microsecond level timing achievable for this pulsar at the MWA's low frequencies. This underscores the usefulness of low-frequency observations for probing the ISM toward PTA pulsars and informing optimal observing strategies for PTA experiments.

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“…Furthermore, the sporadic and intermittent emission behaviour appears to be extremely broadband, based on simultaneous high-energy and wideband radio observations (e.g. Abdo et al, 2010;Hermsen et al, 2013;Kaplan et al, 2015b;Meyers et al, 2017;Hermsen et al, 2018). In general, low-frequency coverage is lacking for the vast majority of southern hemisphere pulsars, and in particular for pulsars with sporadic or intermittent emission.…”

Section: Sporadic and Intermittent Emissionmentioning

confidence: 99%

Science with the Murchison Widefield Array: Phase I results and Phase II opportunities

Beardsley

Johnston‐Hollitt

Trott

et al. 2019

Publ. Astron. Soc. Aust.

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The Murchison Widefield Array (MWA) is an open access telescope dedicated to studying the low frequency (80-300 MHz) southern sky. Since beginning operations in mid 2013, the MWA has opened a new observational window in the southern hemisphere enabling many science areas. The driving science objectives of the original design were to observe 21 cm radiation from the Epoch of Reionisation (EoR), explore the radio time domain, perform Galactic and extragalactic surveys, and monitor solar, heliospheric, and ionospheric phenomena. All together 60+ programs recorded 20,000 hours producing 146 papers to date. In 2016 the telescope underwent a major upgrade resulting in alternating compact and extended configurations. Other upgrades, including digital back-ends and a rapid-response triggering system, have been developed since the original array was commissioned. In this paper we review the major results from the prior operation of the MWA, and then discuss the new science paths enabled by the improved capabilities. We group these science opportunities by the four original science themes, but also include ideas for directions outside these categories.

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Spectral Flattening at Low Frequencies in Crab Giant Pulses

Cited by 33 publications

References 76 publications

A Census of Southern Pulsars at 185 MHz

A Census of Southern Pulsars at 185 MHz

A High Time-resolution Study of the Millisecond Pulsar J2241−5236 at Frequencies Below 300 MHz

Science with the Murchison Widefield Array: Phase I results and Phase II opportunities

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