4XMM J181330.1−175110: A new supergiant fast X-ray transient
Bibliographic record
Abstract
Context. Supergiant fast X-ray transients (SFXTs) are a subclass of high-mass X-ray binaries (HMXBs) in which a compact object accretes part of the clumpy wind of the blue supergiant companion, triggering series of brief X-ray flares lasting a few kiloseconds. Currently, only about 15 SFXTs are known. Aims. The EXTraS (Exploring the X-ray Transient and variable Sky) catalog provides the timing signatures of every source observed by the EPIC instrument onboard XMM-Newton. Among the most peculiar sources in terms of variability, we identified a new member of the SFXT family: 4XMM J181330.1−175110 (J1813). Methods. We analyzed all publicly available XMM-Newton, Chandra, Swift, and NuSTAR data pointed at the J1813 position to determine the source’s duty cycle and to provide a comprehensive description of its timing and spectral behavior during its active phase. Additionally, we searched for the optical and infrared counterpart of the X-ray source in public databases and fitted its spectral energy distribution (SED). Results. The optical-to-mid infrared SED of J1813 is consistent with a highly absorbed (AV ∼ 38) B0 star at ∼10 kpc. During its X-ray active phase, the source is characterized by continuous thousands seconds-long flares with peak luminosities (2–12 keV) ranging from 1034 to 4 × 1035 erg s−1. Its X-ray spectrum is consistent with a high-absorbed power-law model with NH ∼ 1.8 × 1023 cm−2 and Γ ∼ 1.66. No spectral variability was observed as a function of time or flux. J1813 is in a quiescent state ∼60% of the time, with an upper-limit luminosity of 8 × 1032 erg s−1 (at 10 kpc), implying an observed long-term X-ray flux variability > 500. Conclusions. The optical counterpart alone indicates J1813 is an HMXB. Its transient nature, duty cycle, the amplitude of observed X-ray variability, the shape and luminosity of the X-ray flares – and the lack of known X-ray outbursts (> 1036 erg s−1) – strongly support the identification of J1813 as an SFXT.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 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) | 0.003 | 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".