The Radio Afterglow of the Ultralong GRB 220627A
Bibliographic record
Abstract
Abstract We present the discovery of the radio afterglow of the most distant ultralong gamma-ray burst (GRB) detected to date, GRB 220627A at redshift z = 3.084. Its prompt gamma-ray light curve shows a double-pulse profile, with the pulses separated by a period of quiescence lasting ∼15 minutes, leading to early speculation it could be a strongly gravitationally lensed GRB. However, our analysis of the Fermi Gamma-ray Burst Monitor spectra taken during the time intervals of both pulses show clear differences in their spectral energy distributions, disfavouring the lensing scenario. We observed the radio afterglow from 7 to 456 days postburst: an initial, steep decay ( F ν ∝ t −2 ) is followed by a shallower decline ( F ν ∝ t −1/2 ) after ∼20 days. There are three scenarios that could explain these radio properties: (i) energy injection from an additional, slower ejecta component catching up to the external shock; (ii) a stratified density profile going as n ∝ r −8/3 ; or alternatively, (iii) the presence of a slow, wide ejecta component in addition to a fast, narrow ejecta component. We also conducted an independent test of the lensing hypothesis via very long baseline interferometry (VLBI) observations at ∼12 days postburst by searching, for the first time, for multiple images of the candidate lensed GRB afterglow. Our experiment highlighted the growing need for developments in real-time correlation capabilities for time-critical VLBI experiments, particularly as we advance towards the SKA and ngVLA era of radio astronomy.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".