Discovery of a Meter-Wavelength Radio Transient in the Swire Deep Field: 1046+59

Abstract

We report the results of a low frequency radio variability and slow transient search using archival observations from the Very Long Array. We selected six 325 MHz radio observations from the spring of 2006, each centered on the Spitzer-Space-Telescope Wide-area Infrared Extragalactic Survey (SWIRE) Deep Field: 1046+59. Observations were spaced between one day to three months, with a typical single-epoch peak flux sensitivity below 0.2 mJy beam −1 near the field pointing center. We describe the observation parameters, data post-processing, and search methodology used to identify variable and transient emission. Our search revealed multiple variable sources and the presence of one, day-scale transient event with no apparent astronomical counterpart. This detection implies a transient rate of 1 ± 1 event per 6.5 deg 2 per 72 observing hours in the direction of 1046+59 and an isotropic transient surface density Σ = 0.12 deg −2 at 95% confidence for sources with average peak flux density higher than 2.1 mJy over 12 hr.

A Matched Filter Technique for Slow Radio Transient Detection and First Demonstration with the Murchison Widefield Array

“…The transient reported by Jaeger et al (2012) was much fainter than the sensitivity we could achieve with our data even though it occurred on a timescale that we probed (∼day); if we assume a typical spectral index of −0.7, the source they detected at 2.1 mJy at 325 MHz would be 3.2 mJy at 182 MHz, which is an order of magnitude fainter than our best flux density sensitivity at ∼20 mJy. While our limit for the day-to-month search appears to overlap with the transient detection reported by Hyman et al (2009), our results are still consistent with a nondetection.…”

“…In this region, we assumed that there were no transient events; existing limits on the rate of radio transients at low frequencies suggest that these events are relatively rare (e.g., Jaeger et al 2012;Rowlinson et al 2016), so our assumption should be valid. Significant transients would appear as a tail in the r distribution that we would examine further.…”

“…However, recent blind surveys with new widefield radio interferometers, such as the Murchison Widefield Array 21 (MWA; Lonsdale et al 2009;Tingay et al 2013) and the Low-Frequency Array 22 (LOFAR; van Haarlem et al 2013), are setting increasingly stringent limits on the surface density of radio transients at different sensitivities and over a wide range of timescales. In particular, Bell et al (2014) reported a limit of <´-7.5 10 5 deg −2 above 5.5 Jy at 154 MHz for minute-to-hour transients, Carbone et al (2016) reported a limit of <´-1.0 10 3 deg −2 above 500 mJy at 152 MHz for minute-to-hour transients, Cendes et al (2014) reported a limit of <´-2.2 10 2 deg −2 above 500 mJy at 149 MHz for 11-minute transients, Rowlinson et al (2016) reported a limit of <´-6.4 10 7 deg −2 above 210 mJy at 182 MHz for 30 s transients up to <´-6.6 10 3 deg −2 for 1 yr transients, Polisensky et al (2016) reported a range of limits (~-10 4 deg −2 above 100 mJy) for 10-minute and 6 hr transients at 340 MHz, and Murphy et al (2017) reported a limit of <´-1.8 10 4 deg −2 above 100 mJy between 150 and 200 MHz for transients that lasted 1-3 yr. Jaeger et al (2012) reported a transient detection that corresponded to a surface density of 0.12 deg −2 above 2.1 mJy over 12 hr at 325 MHz, while Stewart et al (2016) reported a transient detection that implied a surface density of´-1.5 10 5 deg −2 above 7.9 Jy for ∼10-minute transients at 60 MHz.…”

Explosive and Radio-Selected Transients: Transient Astronomy with Square Kilometre Array and its Precursors

“…In the last decade, use of wide frequency imaging techniques have resulted in several reported detections. These include: (i) detection of a transient GCRT J1745−3009 with flux density ≤ 1 Jy at 325 MHz about a degree away from the Galactic centre emitting coherent emission (Hyman et al, 2005;Roy et al, 2010), (ii) ten transients from multi-epoch (22 years) observations of a single field from archival VLA data at 4.8 and 8.4 GHz at ∼a few hundred µJy or higher level of flux density (Bower et al, 2007), (iii) detection of a single transient at 1.4 GHz with ∼ 1 Jy flux density using Nasu observatory in Japan (Niinuma et al, 2007), (iv) detection of a single transient GCRT J1742−3001 at 240 MHz with flux density ∼ 0.1 Jy near the Galactic centre (Hyman et al, 2009), (v) detection of 15 transients at 843 MHz from a 22-yr survey with Molonglo observatory synthesis telescope (Bannister et al, 2011) at ∼ 10 mJy or higher, (vi) detection of a single transient from about 12 hours of observation at 325 MHz at a few mJy level (Jaeger et al, 2012), (vii) detection of a single transient from 4 months of observations at 60 MHz with LOFAR at ∼ 10 Jy level (Stewart et al, 2016).…”

“…However, at metre wavelengths or larger, some of the flares recorded are ∼100 Jy (Abdul-Aziz et al, 1995). Therefore, occasional radio emission from magnetically dominated flare stars which are quite common in the Solar neighbourhood could explain some of these transient emission (Bower et al, 2007;Roy et al, 2010;Jaeger et al, 2012;Stewart et al, 2016) and could dominate the transient emissions at metre or decameter wavelengths.…”