Astronomy & Astrophysics

Free access article

A&A 465, L21-L24 (2007)
DOI: 10.1051/0004-6361:20067032

Letter

A 0535+26 in the August/September 2005 outburst observed by RXTE and INTEGRAL

I. Caballero¹, P. Kretschmar², A. Santangelo¹, R. Staubert¹, D. Klochkov¹, A. Camero³, C. Ferrigno⁴, M. H. Finger⁵, I. Kreykenbohm^{1, 6}, V. A. McBride⁷, K. Pottschmidt⁸, R. E. Rothschild⁸, G. Schönherr¹, A. Segreto⁴, S. Suchy⁸, J .Wilms⁹, and C. A. Wilson⁵

¹ Institut für Astronomie und Astrophysik, Sand 1, 72076 Tübingen, Germany
e-mail: isabel@astro.uni-tuebingen.de
² INTEGRAL Science Operations Centre, European Space Astronomy Centre (ESAC), Apartado 50727, 28080 Madrid, Spain
³ GACE, Instituto de Ciencias de los Materiales, Universidad de Valencia, PO Box 20085, 46071 Valencia, Spain
⁴ Instituto di Astrofisica Spaziale e Fisica Cosmica (IASF-INAF), Via La Malfa 153, 90146 Palermo, Italy
⁵ Universities Space Research Association, NASA Marshall Space Flight Center, XD12, Huntsville, AL, USA
⁶ INTEGRAL Science Data Centre, 16 Ch. d'Écogia, 1290 Versoix, Switzerland
⁷ School of Physics and Astronomy, Southampton University, Highfield, S017 1BJ, UK
⁸ CASS, University of California at San Diego, La Jolla, CA 92093-0424, USA
⁹ Dr. Remeis Sternwarte Bamberg, Sternwartstr. 7, 96049 Bamberg, Germany

(Received 27 December 2006 / Accepted 17 February 2007)

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 $F_\,_{\mathrm{keV}} \sim400$ 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 $E_{1}\sim 45$ keV and $E_{2}\sim 100$ 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 $B\sim 4\times 10^$ G.

Key words: X-rays: binaries -- stars:magnetic fields -- stars: individual: A 0535+26

What is OpenURL?