A new Bowen fluorescence flare and extreme coronal line emitter discovered by SRG/eROSITA
Bibliographic record
Abstract
The nuclear X-ray transient eRASSt J012026.5−292727 (J012026 hereafter) was discovered in the second SRG/eROSITA all-sky survey (eRASS2). The source appeared more than one order of magnitude brighter than the eRASS1 upper limits (peak eRASS2 0.2–2.3 keV flux of 1.14 × 10−12 erg cm−2 s−1) and with a soft X-ray spectrum (photon index of Γ = 4.3). Over the following months, the X-ray flux started decaying and demonstrated significant flaring activity on both short (hour) and long (year) timescales. By inspecting the multiwavelength light curves of time-domain wide-field facilities, we detected a strong mid-infrared flare, which evolved over two years, and a weaker optical counterpart, with possible hints of a rise > 3 years prior to the X-ray discovery. Follow-up optical spectroscopy revealed transient features, including redshifted Balmer lines (FWHM of ∼1500 km s−1), strong Fe II emission, He II, Bowen fluorescence lines, and high-ionization coronal lines such as [Fe X] and [Fe XIV]. One spectrum displayed a triple-peaked Hβ line, consistent with emission from a face-on elliptical accretion disk. The spectroscopic features and the slow evolution of the event place J012026 within the nuclear-transient classifications of Bowen fluorescence flares (BFFs) and extreme coronal line emitters (ECLEs). BFFs have been associated with rejuvenated accreting supermassive black holes, although the mechanism triggering the onset of the new accretion flow is yet to be understood, while ECLEs have been linked to the disruption and accretion of stars in gas-rich environments. The association of J012026 with both classes, combined with the X-ray, multiwavelength, and spectroscopic information, supports the idea that the BFF emission could be, at least in some cases, triggered by tidal disruption events (TDEs) perturbing gaseous environments. The observed short- and long-term X-ray variability, uncommon in standard TDEs, adds complexity to these families of nuclear transients. These results highlight the diverse phenomenology of nuclear accretion events and demonstrate the value of systematic X-ray surveys, such as eROSITA and Einstein Probe, for uncovering such transients and characterizing their physical origin.
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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 | 0.001 | 0.000 |
| 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".