An Upper Limit on the Expansion Velocity of Gamma-Ray Burst Candidate SN 2001em
Bibliographic record
Abstract
We report on VLBI observations of the Type I b/c supernova SN 2001em, 3 years after the explosion. It has been suggested that SN 2001em might be a jet-driven gamma-ray burst (GRB), with the jet oriented far from the line of sight so that the GRB would not be visible from Earth. To test this conjecture, we determined the size of SN 2001em. It is only marginally resolved at our resolution of ~0.9 mas. The 3 σ upper limit on the major axis angular size of the radio source was 0.59 mas (FWHM of an elliptical Gaussian), corresponding to a one-sided apparent expansion velocity of 70,000 km s -1 for a distance of 80 Mpc. No low-brightness jet was seen in our image to a level of 4% of the peak brightness. If we assume instead a spherical shell geometry typical of a supernova, we find the angular radius of SN 2001em was 0.17 mas, implying an isotropic expansion velocity of 20,000 km s -1 , which is comparable to the expansion velocities of supernova shells. Our observations are therefore not consistent with a relativistically expanding radio source in SN 2001em but are instead consistent with a supernova shell origin of SN 2001's radio emission.
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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 | 0.001 | 0.001 |
| 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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".