A Double-peaked Outburst of A 0535+26 Observed with INTEGRAL, RXTE, and Suzaku

Creators: Caballero, I.; Pottschmidt, K.; Marcu, D. M.; Barragan, L.; Ferrigno, C.; Klochkov, D.; Zurita Heras, J. A.; Suchy, S.; Wilms, J.; Kretschmar, P.; Santangelo, A.; Kreykenbohm, I.; Fürst, F.; Rothschild, R.; Staubert, R.; Finger, M. H.; Camero-Arranz, A.; Makishima, K.; Enoto, T.; Iwakiri, W.; Terada, Y.

Abstract

The Be/X-ray binary A 0535+26 showed a normal (type I) outburst in 2009 August. It is the fourth in a series of normal outbursts associated with the periastron, but is unusual because it presented a double-peaked light curve. The two peaks reached a flux of ~450 mCrab in the 15-50 keV range. We present results of the timing and spectral analysis of INTEGRAL, RXTE, and Suzaku observations of the outburst. The energy-dependent pulse profiles and their evolution during the outburst are studied. No significant differences with respect to other normal outbursts are observed. The centroid energy of the fundamental cyclotron line shows no significant variation during the outburst. A spectral hardening with increasing luminosity is observed. We conclude that the source is accreting in the sub-critical regime. We discuss possible explanations for the double-peaked outburst.

Additional Information

© 2013 American Astronomical Society. Received 2012 November 23; accepted 2013 January 18; published 2013 February 4. We thank the anonymous referee for useful comments, the RXTE, INTEGRAL, and Suzaku teams for the scheduling of the observations, and ISSI (Bern) for their hospitality during our collaboration meetings. I.C. thanks Philippe Laurent for the help with the INTEGRAL analysis, Yuuki Moritani for useful discussions, and acknowledges financial support from the French Space Agency CNES through CNRS. K.P. and D.M.M. acknowledge support from NASA guest observer grants NNXIOAJ47G for INTEGRAL cycle 6 and NNXIOAJ48G for Suzaku cycle 4. J.W. and I.K. acknowledge partial funding from the Deutsches Zentrum für Luft- und Raumfahrt under contract number 50 OR 1113. A.C.-A. is supported by the grants AYA2009-07391 and SGR2009-811, as well as the Formosa program TW2010005 and iLINK program 2011-0303.

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