Millijansky Radio Variability in SDSS Stripe 82

Abstract

We report on a blind survey for extragalactic radio variability that was carried out by comparing two epochs of data from the FIRST survey with a third epoch from a new 1.4 GHz survey of SDSS Stripe 82. The three epochs are spaced seven years apart and have an overlapping area of 60 deg^2. We uncover 89 variable sources down to the millijansky level, 75 of which are newly-identified, and we find no evidence for transient phenomena. This new sample of variable sources allows us to infer an upper limit to the mean characteristic timescale of AGN radio variability of 14 years. We find that only 1% of extragalactic sources have fractional variability f_var >3, while 44% of Galactic sources vary by this much. The variable sample contains a larger fraction of quasars than a comparable non-variable control sample, though the majority of the variable sources appear to be extended galaxies in the optical. This implies that either quasars are not the dominant contributor to the variability of the sample, or that the deep optical data allow us to detect the host galaxies of some low-z quasars. We use the new, higher resolution data to report on the morphology of the variable sources. Finally, we show that the fraction of sources that are variable remains constant or increases at low flux densities. This may imply that next generation radio surveys with telescopes like the Australian Square Kilometer Array Pathfinder and MeerKAT will see a constant or even increasing fraction of variable sources down into the submillijansky regime.

Published in ApJ

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• Parsec-scale radio morphology and variability of a changing-look AGN: the case of Mrk 590
• CHILES VERDES: Radio variability at an unprecedented depth and cadence in the COSMOS field
• Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A
• An insight into the extragalactic transient and variable microJy radio sky across multiple decades
• Radio variability in the Phoenix Deep Survey at 1.4GHz
• The MASIV Survey IV: relationship between intra-day scintillation and intrinsic variability of radio AGNs
• Search and identification of transient and variable radio sources using MeerKAT observations: a case study on the MAXI J1820+070 field
• Radio-X-ray Synergy to discover and Study Jetted Tidal Disruption Events
• Multi-band optical variability of a newly discovered twelve blazars sample from 2013-2019
• Multi-epoch Low Radio Frequency Surveys of the Kepler K2 Mission Campaign Fields 3, 4, and 5 with the Murchison Widefield Array
• Late-Time X-ray Observations of the Transient Source Cygnus A-2