A search for variable and transient radio sources in the extended Chandra Deep Field South at 5.5 GHz

Bell, M. E.; Huynh, Minh; Hancock, P. J.; Murphy, Tara; Gaensler, B. M.; Burlon, D.; Trott, Cathryn M.; Bannister, K. W.

doi:10.1093/mnras/stv882

Cited by 32 publications

(49 citation statements)

References 51 publications

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“…The three epochs are summarised in Table 1. An analysis of the variable sources is presented in Bell et al (2015). Here we present a reduction of the full dataset, i.e.…”

Section: Observing Strategymentioning

confidence: 99%

The ATLAS 5.5 GHz survey of the extendedChandraDeep Field South: the second data release

Huynh¹,

Bell²,

Hopkins³

et al. 2015

Mon. Not. R. Astron. Soc.

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We present a new image of the 5.5 GHz radio emission from the extended Chandra Deep Field South. Deep radio observations at 5.5 GHz were obtained in 2010 and presented in the first data release. A further 76 hours of integration has since been obtained, nearly doubling the integration time. This paper presents a new analysis of all the data. The new image reaches 8.6 µJy rms, an improvement of about 40% in sensitivity. We present a new catalogue of 5.5 GHz sources, identifying 212 source components, roughly 50% more than were detected in the first data release. Source counts derived from this sample are consistent with those reported in the literature for S 5.5GHz > 0.1 mJy but significantly lower than published values in the lowest flux density bins (S 5.5GHz < 0.1 mJy), where we have more detected sources and improved statistical reliability. The 5.5 GHz radio sources were matched to 1.4 GHz sources in the literature and we find a mean spectral index of −0.35 ± 0.10 for S 5.5GHz > 0.5 mJy, consistent with the flattening of the spectral index observed in 5 GHz sub-mJy samples. The median spectral index of the whole sample is α med = −0.58, indicating that these observations may be starting to probe the star forming population. However, even at the faintest levels (0.05 < S 5.5GHz < 0.1 mJy), 39% of the 5.5 GHz sources have flat or inverted radio spectra. Four flux density measurements from our data, across the full 4.5 to 6.5 GHz bandwidth, are combined with those from literature and we find 10% of sources (S 5.5GHz 0.1 mJy) show significant curvature in their radio spectral energy distribution spanning 1.4 to 9 GHz.

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“…The three epochs are summarised in Table 1. An analysis of the variable sources is presented in Bell et al (2015). Here we present a reduction of the full dataset, i.e.…”

Section: Observing Strategymentioning

confidence: 99%

The ATLAS 5.5 GHz survey of the extendedChandraDeep Field South: the second data release

Huynh¹,

Bell²,

Hopkins³

et al. 2015

Mon. Not. R. Astron. Soc.

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“…The recent revival of interest in time-domain astronomy across all wavelengths has generated a number of variability studies using new and archival data on existing radio telescopes such as the Karl G. Jansky Very Large Array (VLA, Ofek & Frail 2011;Hodge et al 2013), the Allen Telescope Array (ATA, Bower et al 2011), the Australia Telescope Compact Array (ATCA, Bell et al 2015;Hancock et al 2016) and the Murchison Widefield Array (MWA, Bell et al 2014). While single-field studies are improving our understanding of the sky density of variable sources and its dependence on the flux-limits of these surveys (e.g., Mooley et al 2016), there is only a cursory understanding of the origin of the observed AGN variability in these studies.…”

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confidence: 99%

The MASIV Survey – IV. Relationship between intra-day scintillation and intrinsic variability of radio AGNs

Koay

Macquart

Jauncey

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We investigate the relationship between 5 GHz interstellar scintillation (ISS) and 15 GHz intrinsic variability of compact, radio-selected AGNs drawn from the Microarcsecond Scintillation-Induced Variability (MASIV) Survey and the Owens Valley Radio Observatory (OVRO) blazar monitoring program. We discover that the strongest scintillators at 5 GHz (modulation index, m 5 ≥ 0.02) all exhibit strong 15 GHz intrinsic variability (m 15 ≥ 0.1). This relationship can be attributed mainly to the mutual dependence of intrinsic variability and ISS amplitudes on radio core compactness at ∼ 100 µas scales, and to a lesser extent, on their mutual dependences on source flux density, arcsec-scale core dominance and redshift. However, not all sources displaying strong intrinsic variations show high amplitude scintillation, since ISS is also strongly dependent on Galactic line-of-sight scattering properties. This observed relationship between intrinsic variability and ISS highlights the importance of optimizing the observing frequency, cadence, timespan and sky coverage of future radio variability surveys, such that these two effects can be better distinguished to study the underlying physics. For the full MASIV sample, we find that Fermi-detected gamma-ray loud sources exhibit significantly higher 5 GHz ISS amplitudes than gamma-ray quiet sources. This relationship is weaker than the known correlation between gamma-ray loudness and the 15 GHz variability amplitudes, most likely due to jet opacity effects.

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“…Observationally, a source with these varability metrics is rare and, by these measures, both Bell et al (2015) and Mooley et al (2016) would clearly classify this source as a variable. Ofek et al (2011) have only 12 out of 464 sources (∼0.5 percent) with χ 2 greater than 100, of these only 2 have a modulation index in excess of 0.2.…”

Section: Variabilitymentioning

confidence: 99%

“…Follow-up observations using the Australia Telescope Compact Array (ATCA) and the Subaru optical telescope led to Keane et al (2016) claiming that a fading radio transient was associated with the galaxy WISE J071634.59−190039.2 at redshift z = 0.49. The low probability of finding such a radio source within the field of view of the Parkes telescope (Bell et al 2015;Mooley et al 2016) meant that Keane et al (2016) were able to argue that the transient was associated with the FRB and hence located in the optical galaxy.…”

Section: Introductionmentioning

confidence: 99%

Radio light curve of the galaxy possibly associated with FRB 150418

Johnston

Keane

Bhandari

et al. 2016

Mon. Not. R. Astron. Soc.

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We present observations made with the Australia Telescope Compact Array (ATCA), the Jansky Very Large Array (JVLA) and the Giant Metre-Wave Telescope of the radio source within the galaxy WISE J071634.59−190039.2, claimed to be host of FRB 150418 by Keane et al. (2016). We have established a common flux density scale between the ATCA and JVLA observations, the main result of which is to increase the flux densities obtained by Keane et al. At a frequency of 5.5 GHz, the source has a mean flux density of 140 µJy and is variable on short timescales with a modulation index of 0.36. Statistical analysis of the flux densities shows that the variations seen are consistent with refractive interstellar scintillation of the weak active galactic nucleus at the centre of the galaxy. It may therefore be the case that the FRB and the galaxy are not associated. However, taking into account the rarity of highly variable sources in the radio sky, and our lack of knowledge of the progenitors of FRBs as a class, the association between WISE J071634.59−190039.2 and FRB 150418 remains a possibility.

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A search for variable and transient radio sources in the extended Chandra Deep Field South at 5.5 GHz

Cited by 32 publications

References 51 publications

The ATLAS 5.5 GHz survey of the extendedChandraDeep Field South: the second data release

The ATLAS 5.5 GHz survey of the extendedChandraDeep Field South: the second data release

The MASIV Survey – IV. Relationship between intra-day scintillation and intrinsic variability of radio AGNs

Radio light curve of the galaxy possibly associated with FRB 150418

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