Letter to the Editor

Quasi-periodic flares in EXO 2030+375 observed with INTEGRAL

¹ Institut für Astronomie und Astrophysik, Universität Tübingen (IAAT), Sand 1, 72076 Tübingen, Germany
e-mail: klochkov@astro.uni-tuebingen.de
² ISDC Data Center for Astrophysics of the University of Geneva, chemin d’Écogia 16, 1290 Versoix, Switzerland
³ European Space Astronomy Centre (ESA/ESAC), Science Operations Department, Villanueva de la Canãda ( Madrid), Spain
⁴ CEA Saclay, DSM/IRFU/SAp-UMR AIM (7158) CNRS/CEA/Université Paris Diderot, 91191 Gif-sur-Yvette, France
⁵ Sternberg Astronomical Institute, Universitetski pr. 13, 119991 Moscow, Russia
⁶ NASA Marshall Space Flight Center, Huntsville, AL 35812, USA

Received: 30 September 2011
Accepted: 6 November 2011

Abstract

Context. Episodic flaring activity is a common feature of X-ray pulsars in HMXBs. In some Be/X-ray binaries flares were observed in quiescence or prior to outbursts. EXO 2030+375 is a Be/X-ray binary showing “normal” outbursts almost every  ~46 days, near periastron passage of the orbital revolution. Some of these outbursts were occasionally monitored with the INTEGRAL observatory.

Aims. The INTEGRAL data revealed strong quasi-periodic flaring activity during the rising part of one of the system’s outburst. Such activity has previously been observed in EXO 2030+375 only once, in 1985 with EXOSAT. (Some indications of single flares have also been observed with other satellites.)

Methods. We present the analysis of the flaring behavior of the source based on INTEGRAL data and compare it with the flares observed in EXO 2030+375 in 1985.

Results. Based on the observational properties of the flares, we argue that the instability at the inner edge of the accretion disk is the most probable cause of the flaring activity.