New Limits on the Low-frequency Radio Transient Sky Using 31 hr of All-sky Data with the OVRO–LWA

Anderson, Marin; Hallinan, Gregg; Eastwood, Michael; Monroe, Ryan; Callister, T. A.; Dowell, Jayce; Hicks, B. C.; Huang, Yuping; Kassim, N. E.; Kocz, J.; Lazio, T. Joseph W.; Price, Danny C.; Schinzel, F. K.; Taylor, G. B.

doi:10.3847/1538-4357/ab4f87

Cited by 25 publications

(24 citation statements)

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“…In this paper we report the first analysis of solar data from the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA), located near Big Pine, CA. At the time of observation, the array consisted of 288 dual-polarization dipole antennas which are optimized to minimize side-lobes; 256 residing in a 200 m diameter core, and the remaining 32 extending to maximum baselines of ≈1.6 km (Anderson et al 2019;Eastwood et al 2019), allowing it to spatially resolve the Sun in the frequency range 27-85 MHz with high spectral resolution. The spatial resolution is about 8 5 at 80 MHz.…”

Section: Introductionmentioning

confidence: 99%

Imaging Spectroscopy of CME-associated Solar Radio Bursts using OVRO-LWA

Chhabra

Gary

Hallinan

et al. 2021

ApJ

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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 e , 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.

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Section: Introductionmentioning

confidence: 99%

Imaging Spectroscopy of CME-associated Solar Radio Bursts using OVRO-LWA

Chhabra

Gary

Hallinan

et al. 2021

ApJ

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“…While a detailed analysis is beyond the scope of this paper, the upper limit calculated in Section 8.2 is at least several times higher (up to a factor ≈20) than the transient surface densities reported by Obenberger et al (2015), Varghese et al (2019), and Kuiack et al (2020b); for example, see Figure 3 in the latter study, or Figure 6 in Anderson et al (2019). Our sensitivity level (42 ± 15 Jy) is deeper than the flux densities of the transients detected by Varghese et al (2019) and Kuiack (2020aKuiack ( , 2020b, as well as the sensitivity levels in the Obenberger et al (2015) study, with the caveat that our study was conducted at higher observing frequencies.…”

Section: Comparison With Other Low-frequency Surveysmentioning

confidence: 70%

“…Furthermore, the all-sky imaging searches have resulted in very stringent limits on transient surface densities (e.g. Anderson et al 2019;Kuiack et al 2020b). Extremely interesting detections already obtained by all-sky monitoring systems prove that these systems are powerful transient-instruments complementing wide-field and all-sky telescopes using other electromagnetic wavelengths or messengers (e.g.…”

Section: Introductionmentioning

confidence: 99%

A Southern-Hemisphere all-sky radio transient monitor for SKA-Low prototype stations

Sokołowski

Wayth

Price

et al. 2021

Publ. Astron. Soc. Aust.

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We present the first Southern-Hemisphere all-sky imager and radio-transient monitoring system implemented on two prototype stations of the low-frequency component of the Square Kilometre Array (SKA-Low). Since its deployment, the system has been used for real-time monitoring of the recorded commissioning data. Additionally, a transient searching algorithm has been executed on the resulting all-sky images. It uses a difference imaging technique to enable identification of a wide variety of transient classes, ranging from human-made radio-frequency interference to genuine astrophysical events. Observations at the frequency 159.375 MHz and higher in a single coarse channel ( $\approx$ 0.926 MHz) were made with 2 s time resolution, and multiple nights were analysed generating thousands of images. Despite having modest sensitivity ( $\sim$ few Jy beam–1), using a single coarse channel and 2-s imaging, the system was able to detect multiple bright transients from PSR B0950+08, proving that it can be used to detect bright transients of an astrophysical origin. The unusual, extreme activity of the pulsar PSR B0950+08 (maximum flux density $\sim$ 155 Jy beam–1) was initially detected in a ‘blind’ search in the 2020 April 10/11 data and later assigned to this specific pulsar. The limitations of our data, however, prevent us from making firm conclusions of the effect being due to a combination of refractive and diffractive scintillation or intrinsic emission mechanisms. The system can routinely collect data over many days without interruptions; the large amount of recorded data at 159.375 and 229.6875 MHz allowed us to determine a preliminary transient surface density upper limit of $1.32 \times 10^{-9} \text{deg}^{-2}$ for a timescale and limiting flux density of 2 s and 42 Jy, respectively. In the future, we plan to extend the observing bandwidth to tens of MHz and improve time resolution to tens of milliseconds in order to increase the sensitivity and enable detections of fast radio bursts below 300 MHz.

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“…"The Burper"), i.e., high circular polarization, a steep spectrum, and the absence of quiescent counterpart at other wavelengths (Roy et al 2010;Spreeuw et al 2009;Hyman et al 2005). The similarities diverge from there, however, as GCRT J1745−3009 appears to be a unique transient (Polisensky et al 2016;Anderson et al 2019), discovered initially as five Jansky-like flares of 10-min duration with a 77-min recurrence timescale (Hyman et al 2005), followed by some additional bursts before fading away altogether (Hyman et al 2006(Hyman et al , 2007. Another unique GC source is magnetar PSR J1745−2900, and although it is polarized like the sources here, it pulsates at a known period of 3.76 s, and is time-variable in both X-rays, and radio and has a flat radio spectrum (Shannon & Johnston 2013;Lynch et al 2015;Pearlman et al 2018).…”

Section: Discussionmentioning

confidence: 99%

Two Extreme Steep-Spectrum, Polarized Radio Sources Towards the Galactic Bulge

Hyman,

Frail,

Deneva

et al. 2021

Preprint

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From an on-going survey of the Galactic bulge, we have discovered a number of compact, steep spectrum radio sources. In this present study we have carried out more detailed observations for two of these sources, located 43 ′ and 12.7 • from the Galactic Center. Both sources have a very steep spectrum (α ≃ −3) and are compact, with upper limits on the angular size of 1-2 ′′ . Their flux densities appear to be relatively steady on timescales of years, months, and hours, with no indications of rapid variability or transient behavior. We detect significant circularly polarized emission from both sources, but only weak or upper limits on linear polarization. Neither source has a counterpart at other wavelengths and deep, high-frequency searches fail to find pulsations. We compare their source properties with other known compact, non-thermal source populations in the bulge (e.g. X-ray binaries, magnetars, the Burper, cataclysmic variables). Our existing data support the hypothesis that they are scatter broadened millisecond or recycled pulsars, either at the bulge or along the line of sight. We also consider the possibility that they may be a new population of Galactic radio sources which share similar properties as pulsars but lack pulsations; a hypothesis that can be tested by future large-scale synoptic surveys.

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New Limits on the Low-frequency Radio Transient Sky Using 31 hr of All-sky Data with the OVRO–LWA

Cited by 25 publications

References 61 publications

Imaging Spectroscopy of CME-associated Solar Radio Bursts using OVRO-LWA

Imaging Spectroscopy of CME-associated Solar Radio Bursts using OVRO-LWA

A Southern-Hemisphere all-sky radio transient monitor for SKA-Low prototype stations

Two Extreme Steep-Spectrum, Polarized Radio Sources Towards the Galactic Bulge

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