Serendipitous VLBI detection of rapid, large-amplitude, intraday variability in QSO 1156+295

Abstract

We report a serendipitous detection of rapid, large amplitude flux density variations in the highly core-dominated, flat-spectrum radio quasar 1156+295 during an observing session at the Very Long Baseline Array (VLBA). The source was observed as a part of the MOJAVE survey programme with the VLBA at 15 GHz on February 5, 2007. Large amplitude variability in the correlated flux density, unexplainable in terms of the source structure, was first discovered while processing the data, and later confirmed by calibrating the antenna gains using 24 other sources observed in the experiment. The source shows variations in the correlated flux density as high as 40% on a timescale of only 2.7 hours. This places 1156+295 between the classical IDV sources and the so-called intra-hour variables. The observed variability timescale and the modulation index of 13% are consistent with interstellar scintillation by a nearby, highly turbulent scattering screen. The large modulation index at 15 GHz implies a scattering measure that is atypically high for a high galactic latitude source such as 1156+295.

Accepted for publication in Astronomy & Astrophysics

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• The connection between the parsec-scale radio jet and gamma-ray flares in the blazar 1156+295
• Tracing Milky Way scattering by compact extragalactic radio sources
• The MASIV Survey IV: relationship between intra-day scintillation and intrinsic variability of radio AGNs
• Emission Line Variability during a Nonthermal Outburst in the Gamma-Ray Bright Quasar 1156+295
• First detection of VHE gamma-ray signal from the FSRQ TON 0599
• Heavy interstellar scattering toward the near end of the Galactic bar