Report
A spectro-temporal view of normal branch oscillations in Cygnus X-2 as seen by NICER and NuSTAR
| العنوان: | A spectro-temporal view of normal branch oscillations in Cygnus X-2 as seen by NICER and NuSTAR |
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| المؤلفون: | Sudha, Malu, Ludlam, Renee M., Altamirano, Diego, Cackett, Edward M., Hare, Jeremy |
| سنة النشر: | 2024 |
| المجموعة: | Astrophysics |
| مصطلحات موضوعية: | Astrophysics - High Energy Astrophysical Phenomena |
| الوصف: | We report the spectro-temporal study of the neutron star low mass X-ray binary Cygnus X-2 using NICER and NuSTAR data while the source was in the normal branch (NB). We detect a normal branch oscillation (NBO) feature at ~ 5.41 Hz that appears in the middle portion of the NB branch. We note that the NBO appeared only in the 0.5-3 keV energy range, with maximum strength in the 1-2 keV energy band, but was absent in the 3-10 keV energy band of NuSTAR and NICER data. The energy spectrum of the source exhibits an emission feature at ~ 1 keV, previously identified as the Fe L transition in the outer region of the accretion disk. Upon considering both the Fe L and NBO features, we suggest that the originating location of the Fe L line and the NBOs may coincide and perhaps be due to the same underlying mechanism. Therefore, lags seen in the frequency/energy dependent lag spectra of Cygnus X-2 could be considered to be arising from a region of photoionized material far from the central source. We study the frequency and energy dependent lag spectra of the source, which exhibited a few milliseconds hard lag at the NBO frequency (12-15 ms) and a switch from hard to soft lags at 1 keV. The rms spectrum peaks at 1 keV and the covariance spectrum clearly resembles a thermal spectrum. We discuss the spectro-temporal behavior of the NBO and attempt to constrain its location of origin. Comment: Accepted for Publication in ApJ |
| نوع الوثيقة: | Working Paper |
| URL الوصول: | http://arxiv.org/abs/2411.12803 |
| رقم الانضمام: | edsarx.2411.12803 |
| قاعدة البيانات: | arXiv |
| الوصف غير متاح. |