BL LAC PKSB1144-379 an extreme scintillator

TL;DR

This paper investigates rapid radio flux variability in the BL Lac object PKSB1144-379, attributing it to extreme interstellar scintillation, and demonstrates how such surveys can identify highly compact, high-brightness temperature AGN.

Contribution

It provides the first detailed analysis linking rapid variability to extreme scintillation in PKSB1144-379 and shows how scintillation surveys can identify ultra-compact AGN.

Findings

Variability explained by interstellar scintillation.

Source size estimated at 20-40 microarcseconds.

Brightness temperature around 6.2 x 10^12 K.

Abstract

Rapid variability in the radio flux density of the BL Lac object PKSB1144-379 has been observed at four frequencies, ranging from 1.5 to 15 GHz, with the VLA and the University of Tasmania's Ceduna antenna. Intrinsic and line of sight effects were examined as possible causes of this variability, with interstellar scintillation best explaining the frequency dependence of the variability timescales and modulation indices. This scintillation is consistent with a compact source 20-40 microarcseconds, or 0.15-0.3 pc in size. The inferred brightness temperature for PKSB1144-379 (assuming that the observed variations are due to scintillation) is 6.2e12 K at 4.9 GHz, with approximately 10 percent of the total flux in the scintillating component. We show that scintillation surveys aimed at identifying variability timescales of days to weeks are an effective way to identify the AGN with the highest brightness temperatures.