Letter to the Editor

INTEGRAL and Swift observations of EXO 2030+375 during a giant outburst^*

¹ Institut für Astronomie und Astrophysik, University of Tübingen, Sand 1, 72076 Tübingen, Germany e-mail: klochkov@astro.uni-tuebingen.de
² INAF IFC-Pa, via U. La Malfa 153, 90146 Palermo, Italy
³ Integral SOC ESA, Madrid, Spain
⁴ INTEGRAL Science Data Centre, Chemin d'Écogia, 16, 1290, Versoix, Switzerland
⁵ INAF IASF-Bo, via Gobetti 101, 40129 Bologna, Italy
⁶ Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138, USA
⁷ Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, CA 92093-0424, USA
⁸ Dr. Karl Remeis-Sternwarte, Astronomisches Institut, Universität Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany

Received: 23 November 2006
Accepted: 26 January 2007

Abstract

Aims.We investigate the X-ray spectral and timing properties of the high mass X-ray binary EXO 2030+375 observed during its June–September 2006 giant (type II) outburst.

Methods.The data analyzed in this work are from partly simultaneous observations with INTEGRAL and Swift. The pulse period P and its temporal derivative are measured. X-ray pulse profiles in different energy ranges and time intervals are constructed. Pulse averaged X-ray spectra for different time intervals are studied.

Results.We report a strong spin-up of the source during the outburst, comparable to that observed in 1985 during the previous giant outburst when the source was discovered. The value of is found to be linearly related to the X-ray luminosity of the source during the outburst. For the first time the hard X-ray (>25 keV) characteristics of the source during a type II outburst are studied. The X-ray pulse profiles apparently change with luminosity. The X-ray spectral continuum in the 3–120 keV energy range is modeled with an absorbed power law with an exponential cutoff around keV. An iron emission line at ~6–7 keV is observed. The spectrum reveals some features between 10 and 20 keV which can be modeled either by a broad emission line at ~13–15 keV (a “bump”) or by two absorption lines at ~10 and ~20 keV.