A 0535+26 in the August/September 2005 outburst observed by RXTE and INTEGRAL
Klochkov, D.; Santangelo, A.; Wilms, J.; Segreto, A.; Ferrigno, C.; McBride, V. A.; Pottschmidt, K.; Kretschmar, P.; Staubert, R.; Caballero, I.; Suchy, S.; Kreykenbohm, I.; Rothschild, R. E.; Schönherr, G.; Camero, A.; Wilson, C. A.; Finger, M. H.
Germany, Spain, Italy, United States, Switzerland, United Kingdom
Abstract
Aims: In this Letter we present results from INTEGRAL and RXTE observations of the spectral and timing behavior of the High Mass X-ray Binary A 0535+26 during its August/September 2005 normal (type I) outburst with an average flux F(5-100) keV ∼400 mCrab. The search for cyclotron resonance scattering features (fundamental and harmonic) is one major focus of the paper.
Methods: Our analysis is based on data from INTEGRAL and RXTE Target of Opportunity Observations performed during the outburst. The pulse period is determined. X-ray pulse profiles in different energy ranges are analyzed. The broad band INTEGRAL and RXTE pulse phase averaged X-ray spectra are studied. The evolution of the fundamental cyclotron line at different luminosities is analyzed.
Results: The pulse period P is measured to be 103.39315(5) s at MJD 53614.5137. Two absorption features are detected in the phase averaged spectra at E1∼ 45 keV and E2∼ 100 keV. These can be interpreted as the fundamental cyclotron resonance scattering feature and its first harmonic and therefore the magnetic field can be estimated to be B∼ 4× 1012 G.