Brightness temperature constraints from interferometric visibilities

TL;DR

This paper introduces a visibility-based method for estimating brightness temperature in interferometric data, especially useful when imaging is limited, and validates it against existing image-based estimates.

Contribution

A new method for directly calculating brightness temperature limits from visibility data, applicable to experiments with poor spatial frequency coverage.

Findings

Method agrees with image-based estimates at high spatial frequencies.

Effective for interferometric data with limited imaging capability.

Provides bounds on brightness temperature without full imaging.

Abstract

The brightness temperature is an effective parameter that describes the physical properties of emitting material in astrophysical objects. It is commonly determined by imaging and modeling the structure of the emitting region and estimating its flux density and angular size. Reliable approaches for visibility-based estimates of brightness temperature are needed for interferometric experiments in which poor coverage of spatial frequencies prevents successful imaging of the source structure, for example, in interferometric measurements made at millimeter wavelengths or with orbiting antennas. Such approaches can be developed by analyzing the relations between brightness temperature and visibility amplitude and its r.m.s. error. A method is introduced for directly calculating the lower and upper limits of the brightness temperature from visibility measurements. The visibility-based brightness temperature estimates are shown to agree well with the image-based estimates obtained in the 2\,cm MOJAVE survey and the 3\,mm CMVA survey, with good agreement achieved for interferometric measurements at spatial frequencies exceeding $\approx 2\times 10^8$. The method provides an essential tool for constraining brightness temperature in all interferometric experiments with poor imaging capability.