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SPT-3G finds no extragalactic flares in four observing seasons

A new preprint reports no significant brief extragalactic flares in four seasons of South Pole Telescope observations. SPT-3G searched the southern sky in two millimetre-wave bands. Strong events were traced mainly to nearby stars, while the absence of extragalactic candidates was compared with models of gamma-ray burst reverse shocks.

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A white radio telescope on snowy South Pole terrain.

Four seasons yield no significant extragalactic candidate

A search with SPT-3G, a camera on the South Pole Telescope, found no significant short-duration extragalactic flares in observations from 2019–2022. The study was released as an arXiv preprint. Its southern-sky footprint measured 1,500 square degrees. Observations spanned approximately 1,000 days, separated on average by 12 hours.[1]

Data from two bands, one centred at 95 gigahertz and the other at 150 gigahertz, were analysed together. The search evaluated when a flare occurred, how long it lasted and its peak brightness in each band. To estimate the noise background, the team used events with negative amplitudes.[1]

Nearby stars match most strong events

Many strong positive events were associated with nearby stars, and some were associated with weather balloons. Two events lacked clear counterparts. Neither exceeded the threshold for a detection, and both were compatible with fluctuating noise. Simulations of different flare shapes and durations accounted for the instrument’s cadence and noise when estimating detection probabilities.[1]

The null search constrains reverse-shock models

The team used simulated gamma-ray burst populations to interpret the null result, focusing on reverse-shock emission. For several simulated populations, the expected detection count exceeded the survey’s limit. A smaller fraction of bursts producing that emission, or dimmer emission, could reconcile the predictions with the observations. The constraints depend on the burst models and on what the survey could detect within its field and sensitivity.[1]

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References

  1. News sourcearXivSPT-3G search constrains short extragalactic flares↩1↩2↩3↩4
Space and explorationEnergy transition and climate

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