From Neutrino- to Photon-cooled in Three Years: Can Fallback Accretion Explain the X-Ray Excess in GW170817?
Bibliographic record
Abstract
Abstract Excess X-ray emission from the neutron star merger GW170817 above the predicted afterglow was recently detected t ≈ 3.4 yr post-merger. One possible origin is accretion onto the newly unshrouded black hole (BH) remnant. While fallback of bound dynamical ejecta is insufficient to generate the excess luminosity, L X ∼ 5 × 10 38 erg s −1 , fallback from the disk wind ejecta—due to their larger mass and lower velocity—remains a possibility. We present hydrodynamic α -viscosity simulations of the post-merger disk evolution that extend to timescales t ≈ 35 s post-merger, necessary to capture the asymptotic evolution into the radiatively inefficient regime. Due to inefficient neutrino cooling, the BH accretion rate decays rapidly at late times ( M ̇ bh ∝ t − β bh , where β bh ≈ 2.4–2.8), which is incompatible with the late-time excess. However, matter falls back to the inner disk from the equatorial region more gradually, M ̇ fb ∝ t − β fb with β fb ≈ 1.43 in our α ≈ 0.03 simulations. By the present epoch t ≈ 3.4 yr, the fallback rate has become sub-Eddington and the disk can again accrete efficiently, i.e., M ̇ bh ≈ M ̇ fb , this time due to photon instead of neutrino cooling. The predicted present-day X-ray accretion luminosity, L X ≈ 0.1 M ̇ bh c 2 ≈ ( 2 – 70 ) × 10 38 erg s
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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 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".