On the cyclotron line in Cep X-4

TL;DR

This study confirms a cyclotron resonance feature in Cep X-4, providing insights into its magnetic field and spectral behavior during an outburst, and suggests a possible orbital period in the system.

Contribution

The paper confirms the cyclotron line at 30.7 keV in Cep X-4 and analyzes its spectral and timing properties during an outburst, enhancing understanding of its magnetic and orbital characteristics.

Findings

Confirmed cyclotron feature at 30.7 keV

Observed spectral and luminosity changes during outburst

Detected a 20.85-day periodicity in the lightcurve

Abstract

Accreting X-ray pulsars provide us with laboratories for the study of extreme gravitational and magnetic fields, hence accurate descriptions of their observational properties contribute to our understanding of this group of objects. We aim to detect a cyclotron resonance scattering feature in the Be/X-ray binary Cep X-4 and to investigate pulse profile and spectral changes through the outburst. Spectral fitting and timing analysis are employed to probe the properties of Cep X-4 during an outburst in 2002 June. A previously announced cyclotron feature at 30.7 keV is confirmed, while the source shows spectral behaviour and luminosity related changes similar to those observed in previous outbursts. The long-term X-ray lightcurve shows a periodicity at 20.85 d, which could be attributed to the orbit in this Be system.