Search

Fast radio bursts (FRBs) are short-time-scale transients of extragalactic origin. The number of detected FRBs has grown dramatically since their serendipitous discovery from archival data. Some FRBs have also been seen to repeat. The polarimetric properties of repeating FRBs show diverse behaviour and, at times, extreme polarimetric morphology, suggesting a complex magneto-ionic circumburst environment for this class of FRB. The polarimetric properties such as circular polarization behaviour of FRBs are crucial for understanding their surrounding magnetic-ionic environment. The circular polarization previously observed in some of the repeating FRB sources has been attributed to propagation effects such as generalized Faraday rotation (GFR), where conversion from linear to circular polarization occurs due to the non-circular modes of transmission in relativistic plasma. The discovery burst from the repeating FRB 20180301A showed significant frequency-dependent circular polarization behaviour, which was initially speculated to be instrumental due to a sidelobe detection. Here, we revisit the properties given the subsequent interferometric localization of the burst, which indicates that the burst was detected in the primary beam of the Parkes/Murriyang 20-cm multibeam receiver. We develop a Bayesian Stokes-Q, U, and V fit method to model the GFR effect, which is independent of the total polarized flux parameter. Using the GFR model we show that the rotation measure (RM) estimated is two orders of magnitude smaller and opposite sign (⁠|$\sim$| 28 rad m |$^{-2}$|⁠) than the previously reported value. We interpret the implication of the circular polarization on its local magnetic environment and reinterpret its long-term temporal evolution in RM. [ABSTRACT FROM AUTHOR]

The Molonglo Cross was first commissioned in 1965, as a transit radio (408 MHz) interferometer with the largest collecting area in the Southern hemisphere. In 1981, the telescope was redeveloped as an Earth-rotation synthesis interferometer using only the East–West arm (843 MHz), known as the Molonglo Observatory Synthesis Telescope. While the East–West arm was revitalized in the 2010s, the (slightly larger) North–South (NS) arm, which consists of two co-linear paraboloid cylindrical reflectors spanning 2 × 778 m × 12.7 m, had not been used for over 40 yr. Re-fitting this 19 800-m2 collecting area with modern electronics is a cost-effective way of producing a significant survey instrument. The upgrades made to the entire signal chain of the NS arm from the antenna through the transport, digitization, and digital signal processing are described, along with the subsequent performance of the system. The instrument was designed to undertake pulsar timing and searching for dispersed single pulses [e.g. from fast radio bursts (FRBs)]. The upgraded system operated across the 806.25–856.25-MHz frequency range, and had a primary beam that spans 12.7 × 2.5 deg. It had dual linear polarization capability and a lower system temperature and wider bandwidth compared with the East–West system. The digital signal processing was performed on servers with graphics processing units, which enabled low-latency, high-speed data processing, and made use of pipelines built from existing and custom codes. It timed around 70 pulsars per day while running concurrent FRB searches at nearly 100 per cent duty cycle during its operation. [ABSTRACT FROM AUTHOR]

The search for extraterrestrial intelligence at radio frequencies has largely been focused on continuous-wave narrowband signals. We demonstrate that broadband pulsed beacons are energetically efficient compared to narrowband beacons over longer operational timescales. Here, we report the first extensive survey searching for such broadband pulsed beacons toward 1883 stars as a part of the Breakthrough Listen’s search for advanced intelligent life. We conducted 233 hr of deep observations across 4â€"8 GHz using the Robert C. Byrd Green Bank Telescope and searched for three different classes of signals with artificial (or negative) dispersion. We report a detailed searchâ€"leveraging a convolutional neural network classifier on high-performance GPUsâ€"deployed for the very first time in a large-scale search for signals from extraterrestrial intelligence. Due to the absence of any signal-of-interest from our survey, we place a constraint on the existence of broadband pulsed beacons in our solar neighborhood: ≲1 in 1000 stars have transmitter power densities ≳105 W Hzâˆ'1 repeating ≤500 s at these frequencies. [ABSTRACT FROM AUTHOR]

Radio magnetars are exotic sources noted for their diverse spectrotemporal phenomenology and pulse profile variations over weeks to months. Unusual for radio magnetars, the Galactic Center (GC) magnetar PSR J1745âˆ'2900 has been continually active since its discovery in 2013. We monitored the GC magnetar at 4â€"8 GHz for 6 hr in 2019 Augustâ€"September using the Robert C. Byrd Green Bank Telescope. During our observations, the GC magnetar emitted a flat fluence spectrum over 5â€"8 GHz to within 2 σ uncertainty. From our data, we estimate a 6.4 GHz period-averaged flux density, S ÂŻ 6.4 ≈ (240 ± 5) ÎĽ Jy. Tracking the temporal evolution of S ÂŻ 6.4 , we infer a gradual weakening of GC magnetar activity during 2016â€"2019 relative to that between 2013 and 2015.5. Typical single pulses detected in our study reveal marginally resolved subpulses with opposing spectral indices, a feature characteristic of radio magnetars but unseen in rotation-powered pulsars. However, unlike in fast radio bursts, these subpulses exhibit no perceptible radio frequency drifts. Throughout our observing span, ≃5 ms scattered pulses significantly jitter within two stable emission components of widths 220 ms and 140 ms, respectively, in the average pulse profile. [ABSTRACT FROM AUTHOR]

We present the first results of a solar radio event observed with the Owens Valley Radio Observatory Long Wavelength Array at metric wavelengths. We examine a complex event consisting of multiple radio sources/bursts associated with a fast coronal mass ejection (CME) and an M2.1 GOES soft X-ray flare from 2015 September 20. Images of 9 s cadence are used to analyze the event over a 120 minute period, and solar emission is observed out to a distance of ≈3.5 R⊙, with an instantaneous bandwidth covering 22 MHz within the frequency range of 40–70 MHz. We present our results from the investigation of the radio event, focusing particularly on one burst source that exhibits outward motion, which we classify as a moving type IV burst. We image the event at multiple frequencies and use the source centroids to obtain the velocity for the outward motion. Spatial and temporal comparison with observations of the CME in white light from the C2 coronagraph of the Large Angle and Spectrometric COronagraph, indicates an association of the outward motion with the core of the CME. By performing graduated-cylindrical-shell reconstruction of the CME, we constrain the density in the volume. The electron plasma frequency obtained from the density estimates do not allow us to completely dismiss plasma emission as the underlying mechanism. However, based on source height and smoothness of the emission in frequency and time, we argue that gyrosynchrotron is the more plausible mechanism. We use gyrosynchrotron spectral-fitting techniques to estimate the evolving physical conditions during the outward motion of this burst source. [ABSTRACT FROM AUTHOR]

Studies of solar radio bursts play an important role in understanding the dynamics and acceleration processes behind solar space weather events, and the influence of solar magnetic activity on solar system planets. Similar low-frequency bursts detected from active M-dwarfs are expected to probe their space weather environments and therefore the habitability of their planetary companions. Active M-dwarfs produce frequent, powerful flares which, along with radio emission, reveal conditions within their atmospheres. However, to date, only one candidate solar-like coherent radio burst has been identified from these stars, preventing robust observational constraints on their space weather environment. During simultaneous optical and radio monitoring of the nearby dM5.5e star Proxima Centauri, we detected a bright, long-duration optical flare, accompanied by a series of intense, coherent radio bursts. These detections include the first example of an interferometrically detected coherent stellar radio burst temporally coincident with a flare, strongly indicating a causal relationship between these transient events. The polarization and temporal structure of the trailing long-duration burst enable us to identify it as a type IV burst. This represents the most compelling detection of a solar-like radio burst from another star to date. Solar type IV bursts are strongly associated with space weather events such as coronal mass ejections and solar energetic particle events, suggesting that stellar type IV bursts may be used as a tracer of stellar coronal mass ejections. We discuss the implications of this event for the occurrence of coronal mass ejections from Proxima Cen and other active M-dwarfs. [ABSTRACT FROM AUTHOR]

Fast Radio Bursts (FRBs) are a class of short-duration transients at radio wavelengths with inferred astrophysical origin. The prototypical FRB is a broadband signal that occurs over the extent of the receiver frequency range, is narrow in time, and is highly dispersed, following a ν−2relation. However, some FRBs appear band-limited, and show apparent scintillation, complex frequency-dependent structure, or multi-component pulse shapes. While there is sufficient evidence that FRBs are indeed astrophysical, their one-off nature necessitates extra scrutiny when reporting a detection as bona fide and not a false positive. Currently, there is no formal validation framework for FRBs, rather a set of community practices. In this article, we discuss potential sources of false positives, and suggest a framework in which FRB-like events can be evaluated as real or otherwise. We present examples of false-positive events in data from the Arecibo, LOFAR, and Nanshan telescopes, which while FRB-like, are found to be due to instrumental variations, noise, and radio-frequency interference. Differentiating these false-positive detections from astrophysical events requires knowledge and tests beyond thresholded single-pulse detection. We discuss post-detection analyses, verification tests, and data sets which should be provided when reporting an FRB detection. [ABSTRACT FROM AUTHOR]