Search for cyclotron lines in INTEGRAL/SPI spectra of Vela X-1
von Kienlin, A.; Schanne, S.; Kretschmar, P.; Staubert, R.; Attié, D.; Sizun, P.; Kreykenbhom, I.; Chernyakova, M.
France, Germany, Switzerland
Abstract
The wind-accreting X-ray binary pulsar Vela X-1 has been observed during the two INTEGRAL Core Program observations of the Vela region in June July and November December 2003. Preliminary results on time averaged and time resolved spectra of INTEGRAL/SPI for the two observation epochs are presented. Time averages have been used in order to increase the signal to noise ratio, but cyclotron line features expected at ∼20 25 and ∼53 keV are without any doubt detected in the INTEGRAL/SPI spectra. This work shows that the detection of cyclotron feature as given in [Kretschmar, P., Staubert, R., Kreykenbohm, I., et al. In: Proceedings of 5th INTEGRAL Workshop, 2004.] should be taken with caution due to background modelling uncertainties. Further work using a better in-flight energy calibration and background monitoring is planed to improve the analysis.