Detection of Galactic and Extragalactic Millimeter-Wavelength Transient Sources with SPT-3G

TL;DR

This paper reports the first survey of millimeter-wavelength transient sources using the SPT-3G camera, detecting 15 events including variable stars and extragalactic sources, expanding understanding of transient populations at these wavelengths.

Contribution

First large-area survey of millimeter transient sources with SPT-3G, identifying new variable stars and extragalactic transients, and demonstrating the potential for real-time detection.

Findings

Detected 15 transient events, including variable stars and extragalactic sources.

Stellar flares are unpolarized, bright, and last from minutes to hours.

Some stellar flares show concurrent optical activity.

Abstract

High-angular-resolution cosmic microwave background experiments provide a unique opportunity to conduct a survey of time-variable sources at millimeter wavelengths, a population which has primarily been understood through follow-up measurements of detections in other bands. Here we report the first results of an astronomical transient survey with the South Pole Telescope (SPT) using the SPT-3G camera to observe 1500 square degrees of the southern sky. The observations took place from March to November 2020 in three bands centered at 95, 150, and 220 GHz. This survey yielded the detection of fifteen transient events from sources not previously detected by the SPT. The majority are associated with variable stars of different types, expanding the number of such detected flares by more than a factor of two. The stellar flares are unpolarized and bright, in some cases exceeding 1 Jy, and have durations from a few minutes to several hours. Another population of detected events last for 2--3 weeks and appear to be extragalactic in origin. Though data availability at other wavelengths is limited, we find evidence for concurrent optical activity for two of the stellar flares. Future data from SPT-3G and forthcoming instruments will provide real-time detection of millimeter-wave transients on timescales of minutes to months.