The Neutron Star Population in M28: A Joint Chandra/GBT Look at Pulsar Paradise
Bibliographic record
Abstract
Abstract We present the results of a deep study of the neutron star (NS) population in the globular cluster M28 (NGC 6626), using the full 330 ks 2002–2015 ACIS data set from the Chandra X-ray Observatory and coordinated radio observations taken with the Green Bank Telescope (GBT) in 2015. We investigate the X-ray luminosity (L X ), spectrum, and orbital modulation of the seven known compact binary millisecond pulsars in the cluster. We report two simultaneous detections of the redback PSR J1824−2452I (M28I) and its X-ray counterpart at L X = [8.3 ± 0.9] × 1031 erg s−1. We discover a double-peaked X-ray orbital flux modulation in M28I during its pulsar state, centered around pulsar inferior conjunction. We analyze the spectrum of the quiescent NS low-mass X-ray binary to constrain its mass and radius. Using both hydrogen and helium NS atmosphere models, we find an NS radius of R = 9.2–11.5 km and R = 13.0–17.5 km, respectively, for an NS mass of 1.4 M ⊙ (68% confidence ranges). We also search for long-term variability in the 46 brightest X-ray sources and report the discovery of six new variable low-luminosity X-ray sources in M28.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".