The 2025 outburst of IGR J17511-3057: timing and spectral insights from NICER and NuSTAR
Bibliographic record
Abstract
Context. IGR J17511−3057 is an accreting millisecond X-ray pulsar and a known type-I burster. The source was observed in outburst for the first time in 2009 and again in 2015, followed by a decade-long quiescence phase. Aims. The source was observed in a new outburst phase starting in February 2025 and lasting at least nine days. We investigated the spectral and temporal properties of IGR J17511−3057, aiming to characterize its current status and highlight possible long-term evolution of its properties. Methods. We analyzed the available NICER and NuSTAR observations performed during the latest outburst of the source. We updated the ephemerides of the neutron star and compared them to previous outbursts to investigate its long-term evolution. We also performed a spectral analysis of the broadband energy spectrum in different outburst phases and investigated the time-resolved spectrum of the type-I X-ray burst event observed with NuSTAR. Results. We detected X-ray pulsations at the frequency of ∼245 Hz. The long-term evolution of the neutron star ephemerides suggests a spin-down derivative of ∼−2.3 × 10−15 Hz/s, compatible with a rotation-powered phase while in quiescence. Moreover, the evolution of the orbital period and the time of the ascending node suggests a fast orbital shrinkage, which challenges the standard evolution scenario for this class of pulsars involving angular momentum loss via gravitational wave emission. The spectral analysis revealed a dominant power law-like Comptonization component, along with a thermal blackbody component, consistent with a hard state. Weak broad emission residuals around 6.6 keV suggest the presence of a Kα transition of neutral or He-like Fe originating from the inner region of the accretion disk. A set of self-consistent reflection models confirmed the moderate ionization of the disk truncated at around (82–370) km from the neutron star. Finally, the study of the type-I X-ray burst revealed no signature of photospheric radius expansion. We found marginally significant burst oscillations during the rise and decay of the event, consistent with the neutron star spin frequency.
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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) | 0.000 | 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".