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arXiv · 0801.3167

The pre-outburst flare of the A 0535+26 August/September 2005 outburst

I. Caballero·A. Santangelo·P. Kretschmar·R. Staubert·K. Postnov·D. Klochkov·A. Camero-Arranz·M. H. Finger·I. Kreykenbohm·K. Pottschmidt·R. E. Rothschild·S. Suchy·J. Wilms·C. A. Wilson
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Abstract

We study the spectral and temporal behavior of the High Mass X-ray Binary A 0535+26 during a `pre-outburst flare' which took place ~5 d before the peak of a normal (type I) outburst in August/September 2005. We compare the studied behavior with that observed during the outburst. We analyse RXTE observations that monitored A 0535+26 during the outburst. We complete spectral and timing analyses of the data. We study the evolution of the pulse period, present energy-dependent pulse profiles both at the initial pre-outburst flare and close to outburst maximum, and measure how the cyclotron resonance-scattering feature (hereafter CRSF) evolves. We present three main results: a constant period P=103.3960(5)s is measured until periastron passage, followed by a spin-up with a decreasing period derivative of Pdot=(-1.69+/-0.04)x10^(-8)s/s at MJD 53618, and P remains constant again at the end of the main outburst. The spin-up provides evidence for the existence of an accretion disk during the normal outburst. We measure a CRSF energy of Ecyc~50kev during the pre-outburst flare, and Ecyc~46kev during the main outburst. The pulse shape, which varies significantly during both pre-outburst flare and main outburst, evolves strongly with photon energy.

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I. Caballero, A. Santangelo, P. Kretschmar, R. Staubert, K. Postnov, D. Klochkov, A. Camero-Arranz, M. H. Finger, I. Kreykenbohm, K. Pottschmidt, R. E. Rothschild, S. Suchy, J. Wilms, C. A. Wilson. 2008-01-21. The pre-outburst flare of the A 0535+26 August/September 2005 outburst. https://doi.org/10.1051/0004-6361:20079310

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