The Sleeping Monster: NuSTAR Observations of SGR 1806–20, 11 Years After the Giant Flare
Bibliographic record
Abstract
Abstract We report the analysis of five Nuclear Spectroscopic Telescope Array (NuSTAR) observations of SGR 1806−20 spread over a year from 2015 April to 2016 April, more than 11 years following its giant flare (GF) of 2004. The source spin frequency during the NuSTAR observations follows a linear trend with a frequency derivative Hz s−1, implying a surface dipole equatorial magnetic field G. Thus, SGR 1806−20 has finally returned to its historical minimum torque level measured between 1993 and 1998. The source showed strong timing noise for at least 12 years starting in 2000, with increasing one order of magnitude between 2005 and 2011, following its 2004 major bursting episode and GF. SGR 1806−20 has not shown strong transient activity since 2009, and we do not find short bursts in the NuSTAR data. The pulse profile is complex with a pulsed fraction of with no indication of energy dependence. The NuSTAR spectra are well fit with an absorbed blackbody, , plus a power law, . We find no evidence for variability among the five observations, indicating that SGR 1806−20 has reached a persistent and potentially its quiescent X-ray flux level after its 2004 major bursting episode. Extrapolating the NuSTAR model to lower energies, we find that the 0.5–10 keV flux decay follows an exponential form with a characteristic timescale days. Interestingly, the NuSTAR flux in this energy range is a factor of ∼2 weaker than the long-term average measured between 1993 and 2003, a behavior also exhibited in SGR 1900+14. We discuss our findings in the context of the magnetar model.
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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 | 0.001 | 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".