A census of compact sources at 162 MHz: First data release from the MWA Phase II IPS Survey

Abstract

We present a catalogue of over 7000 sources from the GLEAM survey which have significant structure on sub-arcsecond scales at 162 MHz. The compact nature of these sources was detected and quantified via their Interplanetary Scintillation (IPS) signature, measured in interferometric images from the Murchison Widefield Array. The advantage of this approach is that all sufficiently compact sources across the survey area are included down to a well-defined flux density limit. The survey is based on ${\sim}250\times 10\hbox{-}\mathrm{min}$ observations, and the area covered is somewhat irregular, but the area within $1\,\mathrm{h}<\mathrm{RA}<11\,\mathrm{h}$ ; $-10^\circ<\mathrm{Decl.}<+20^\circ$ is covered entirely, and over 85% of this area has a detection limit for compact structure below 0.2 Jy. 7839 sources clearly showing IPS were detected ( ${>}5\sigma$ confidence), with a further 5550 tentative ( ${>}2\sigma$ confidence) detections. Normalised Scintillation Indices (NSI; a measure of the fraction of flux density coming from a compact component) are reported for these sources. Robust and informative upper limits on the NSI are reported for a further 31081 sources. This represents the largest survey of compact sources at radio frequencies ever undertaken.

Resolving Moving Heliospheric Structures Using Interplanetary Scintillation Observations With the Murchison Widefield Array

“…The survey sampled from 6 principal target fields at a ϵ of 30° (∼107 solar radii from the Sun) at ϕ of 60°, 90°, 120°, 240°, 270°, 300°, with an occasional additional 5 target fields at 30°, 150°, 180°, 210°, 330° (Morgan et al., 2022); see left‐most panel of Figure 1. However, only 263 of the total observations were selected for the first data release (Morgan et al., 2022), a large number of observations remain unprocessed. For the first blind search for space weather events we chose to focus on a set of 93 observation spanning over 49 contiguous days (spanning from 2019‐JUN‐25 to 2019‐AUG‐14, with two days with no observations taken, 2019‐JUL‐16 and 2019‐AUG‐01), with two pointing directions (E and SE, specified with a solid line outline in Figure 1) observed on all but five days (2019‐JUN‐25, 2019‐JUN‐29, 2019‐JUL‐02, 2019‐JUL‐27, and 2019‐AUG‐06) which only had the SE pointing direction processed.…”

“…The constant of proportionality for m pt , the ellipticity term e, and the power-law index b, will all vary during the solar cycle, as well as between solar cycles. Where applicable we have used their long term average values for solar minimum which have been established as a constant of proportionality of 0.06 and a power law index, b ≈ 1.6 (Morgan et al, 2022;Morgan et al, 2019, and references therein). We use as our starting point the scintillation indices, error estimations, and normalized scintillation indices (NSI, Chhetri et al, 2018) for each source in each observation from the processed observations used in Morgan et al (2022).…”

“…Where applicable we have used their long term average values for solar minimum which have been established as a constant of proportionality of 0.06 and a power law index, b ≈ 1.6 (Morgan et al, 2022;Morgan et al, 2019, and references therein). We use as our starting point the scintillation indices, error estimations, and normalized scintillation indices (NSI, Chhetri et al, 2018) for each source in each observation from the processed observations used in Morgan et al (2022). Sources in general vary in scintillation level due to the inherent source structure, therefore we use the NSI per source as it gives the scintillation of a source relative to a compact source.…”

“…At the time of writing, the observations used in this paper are public, and can be identified by their GPS start times (example g-map: 1247722256, detected structure: 1248929800 and 1248935560) which serve as unique identifiers of these observations within the MWA archive. All the IPS observations described in Morgan et al (2022) are also archived, under project code D0011. Coronal Mass Ejection public catalogues that were queried for this work are as follows; SOHO LASCO CME Catalog (Gopalswamy et al, 2009), STEREO COR1 CME Catalog (Xie, 2019), CACTus LASCO C2/C3 catalogue and COR2 catalogue (Robbrecht & Berghmans, 2004;Robbrecht et al, 2009), SEEDS LASCO C2 catalogue (Zhang & Dhakal, 2020a), SEEDS SECCHI COR2 catalogue (Zhang & Dhakal, 2020b), and WIND ICME Catalogue (Nieves-Chinchilla et al, 2018).…”

“…More recently, Morgan et al (2023) demonstrated that a Coronal Mass Ejection (CME), detected at launch in white-light coronagraph images, could be detected in interplanetary space using MWA IPS observations, with the unprecedented number of lines of sight allowing the CME to be mapped in exquisite detail, using just two 5-min observations. More recent data, taken by the upgraded Phase II MWA (Wayth et al, 2018) has been synthesized by Morgan et al (2022) into the first data release of the Phase II IPS survey, which catalogs the IPS properties of over 40,000 sources from the GLEAM survey (Hurley-Walker et al, 2017;Wayth et al, 2015), with IPS strongly detected in over 7000 of them. As well as providing baseline scintillation levels for all of these sources, facilitating space weather studies, a further byproduct of this survey is a set of 250 10-min MWA IPS observations, with the scintillation index of several hundred IPS sources measured in each of them.…”