4U 0115 + 63 : phase lags and cyclotron resonant scattering
Abstract
Context. High-mass X-ray binaries are among the brightest objects of our Galaxy in the high-energy domain (0.1-100 keV). Despite our relatively good knowledge of their basic emission mechanisms, the complex problem of understanding their time- and energy- dependent X-ray emission has not been completely solved.
Aims: In this paper, we study the energy-dependent pulse profiles of the high-mass X-ray binary pulsar 4U 0115 + 63 to investigate how they are affected by cyclotron resonant scattering.
Methods: We analyzed archival BeppoSAX and RXTE observations performed during the giant outburst of the source that occurred in 1999. We exploited a cross correlation technique to compare the pulse profiles in different energy ranges and developed a relativistic ray-tracing model to interpret our findings. We also studied the phase dependency of the cyclotron absorption features by performing phase-resolved spectroscopy.
Results: The pulse profiles of 4U 0115 + 63 displayed clear "phase-lags" at energies close to those of the cyclotron absorption features that characterize the X-ray emission of the source. We reproduce this phenomenon qualitatively by assuming an energy-dependent beaming of the emission from the column surface and verify that our model is also compatible with the results of phase-resolved spectral analysis.
Conclusions: We show that cyclotron resonant scattering affects the pulse profile formation mechanisms in a complex way, which necessitates both improvements in the modeling and the study of other sources to be better understood.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- August 2011
- DOI:
- 10.1051/0004-6361/201116826
- arXiv:
- arXiv:1106.4930
- Bibcode:
- 2011A&A...532A..76F
- Keywords:
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- X-rays: binaries;
- pulsars: individual: 4U 0115+63;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication of Astronomy &