Supernova 1996cr: SN 1987A’s Wild Cousin?
Bibliographic record
Abstract
We report on new VLT optical spectroscopic and multiwavelength archival observations of SN 1996cr, a previously identified ultraluminous X-ray source known as Circinus galaxy X-2. Our optical spectrum confirms SN 1996cr as a bona fide Type IIn supernova, while archival imaging from the Anglo-Australian Telescope archive isolates the explosion date to between 1995 February 28 and 1996 March 16. SN 1996cr is one of the closest SNe (≈3.8 Mpc) in the last several decades, and in terms of flux ranks among the brightest radio and X-ray SNe ever detected. The wealth of optical, X-ray, and radio observations that exist for this source provide relatively detailed constraints on its postexplosion expansion and progenitor history, including a preliminary angular size constraint from VLBI. Archival X-ray and radio data imply that the progenitor of SN 1996cr evacuated a large cavity just prior to exploding: the blast wave likely spent ~1-2 yr in relatively uninhibited expansion before eventually striking the dense circumstellar material which surrounds SN 1996cr. The X-ray and radio emission, which trace the progenitor mass-loss rate, have respectively risen by a factor of ≳2 and remained roughly constant over the past 7 years. This behavior is reminiscent of the late rise of SN 1987A, but 1000 times more luminous and much more rapid to onset. SN 1996cr may likewise provide us with a younger example of SN 1978K and SN 1979C, both of which exhibit flat X-ray evolution at late times. Complex oxygen line emission hints at a possible concentric shell or ringlike structure. The discovery of SN 1996cr suggests that a substantial fraction of the closest SNe observed in the last several decades have occurred in wind-blown bubbles, and argues for the phenomena being widespread.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.005 | 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".