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

TL;DR

This paper reports the detection of quasi-periodic flares in the Be/X-ray binary EXO 2030+375 using INTEGRAL data, suggesting disk instability as the likely cause, and compares these with historical observations from 1985.

Contribution

It presents the first detailed analysis of quasi-periodic flares in EXO 2030+375 with INTEGRAL, linking them to accretion disk instabilities and comparing with past flare observations.

Findings

Detection of strong quasi-periodic flaring activity during an outburst.

Flares likely caused by instability at the inner edge of the accretion disk.

Comparison with 1985 observations supports the disk instability hypothesis.

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.