A candidate cyclotron line at 1.89 keV in the ultraluminous X-ray source NGC 4861 X–2
Astronomy and Astrophysics, cilt.710, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 710
- Basım Tarihi: 2026
- Doi Numarası: 10.1051/0004-6361/202660614
- Dergi Adı: Astronomy and Astrophysics
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Artic & Antarctic Regions, Compendex, INSPEC, zbMATH, Directory of Open Access Journals, Academic Search Ultimate (EBSCO)
- Anahtar Kelimeler: Galaxy: general, magnetic fields, stars: magnetars, stars: neutron
- Çukurova Üniversitesi Adresli: Evet
Özet
In this Letter, we report the detection of an absorption-like feature at ∼1.89 keV in Chandra/ACIS spectra of the ultraluminous X-ray source NGC 4861 X–2, based on the deepest observation (ObsID 20992; ∼59 ks). The feature is consistently recovered across independent continuum models and significantly improves the fit statistics. Monte Carlo simulations yield a detection significance of ∼3.5–4.1σ, depending on the adopted continuum, and a blind line scan reveals a single, localized peak at the same energy. The observed properties are consistent with a proton cyclotron resonant scattering feature (CRSF), implying a magnetic field strength of B ∼ (3–4)×1014 G. The spectrum is well described by a multicolor disk blackbody (diskbb) with kTin ∼ 0.8 keV or a strongly curved continuum with a low cutoff (cutoffpl) energy (Ecut ∼ 1.3 keV). The source shows variability confined to the soft X-ray band in the two Chandra observations in which the absorption-like feature is detected. In these observations, a candidate periodic signal at P ≈ 7.4 s is also detected, with a global significance of ∼2.5σ.