Serendipitous decametre detection of ultra steep spectrum radio emission in Abell 655
Bibliographic record
Abstract
Some galaxy clusters contain non-thermal synchrotron emitting plasma that permeate the intracluster medium (ICM). The spectral properties of this radio emission are not well characterised at decametre wavelengths (ν < 30 MHz), primarily due to the severe corrupting effects of the ionosphere. Using a recently developed calibration strategy, we present LOFAR images below 30 MHz of the low-mass galaxy cluster Abell 655, which was serendipitously detected in an observation of the bright calibrator 3C 196. We combine this observation with LOFAR data at 144 MHz and new band 4 upgraded Giant Metrewave Radio Telescope observations centred at 650 MHz. In the 15–30 MHz LOFAR image, diffuse emission is seen with a physical extent of about 700 kpc. We argue that the diffuse emission detected in this galaxy cluster likely has multiple origins. At higher frequencies (650 MHz), the diffuse emission resembles a radio halo, while at lower frequencies the emission seems to consist of several components and bar-like structures. This detection of diffuse emission suggests that most low-frequency emission in this cluster comes from re-energised fossil plasma from old Active Galacitic Nucleus outbursts co-existing with the radio halo component. By counting the number of cluster radio detections in the decametre band, we estimate that around a quarter of the Planck clusters host re-energised fossil plasma that is detectable in the decametre band with LOFAR.
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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".