Large-amplitude intraday variability in QSO 1156+295 observed during a VLBI experiment

TL;DR

This paper reports the discovery of rapid, large-amplitude intraday variability in the quasar 1156+295, observed during a VLBI experiment, likely caused by interstellar scintillation, with significant implications for understanding compact radio source behavior.

Contribution

First detection of large-amplitude, rapid intraday variability in 1156+295 during a VLBI survey, highlighting interstellar scintillation effects in such sources.

Findings

40% flux density variation at 15 GHz within 2.7 hours

Variability occurs in a single compact component

High scattering measure indicates turbulent interstellar medium

Abstract

We present here the discovery of rapid, large amplitude intraday variability in the compact flat-spectrum radio quasar 1156+295. The detection of 40% flux density variations at 15 GHz on a timescale of only 2.7 hours was serendipitously made when the source was observed with the Very Long Baseline Array as a part of the MOJAVE survey programme on February 5, 2007. Intraday variability on timescales of a few hours or less is rare, and there exist very few sources that show large-amplitude variations on a timescale as short as what is now observed for 1156+295. The shape of the visibility function of the source changes very little during the observation, although the correlated flux density changes by 40%. This suggests that the variability occurs in a single dominant compact component. The observed variability characteristics are consistent with interstellar scintillation in nearby, highly turbulent medium. The rms amplitude of modulation at 15 GHz is unusually large and it implies a rather high scattering measure along the line-of-sight towards 1156+295.