Research Note

INTEGRAL and Swift/XRT observations of the SFXT IGR J16479–4514: from quiescence to fast flaring activity

¹ IASF/INAF, via Piero Gobetti 101, 40129 Bologna, Italy e-mail: sguera@iasfbo.inaf.it
² IASF/INAF, via Fosso del Cavaliere 100, 00133 Roma, Italy
³ School of Physics and Astronomy, University of Southampton, Highfield SO17 1BJ, UK

Received: 5 December 2007
Accepted: 26 April 2008

Abstract

Context. The fast X-ray transient IGR J16479-4514 is known to display flares typically lasting a few hours. Recently, its counterpart has been identified with a supergiant star, therefore the source can be classified as a member of the newly discovered class of Supergiant Fast X-ray Transients (SFXTs); specifically, it is the one with the highest duty cycle.

Aims. Characterize the quiescent X-ray behaviour of the source and compare its broad band spectrum to those during fast X-ray flares.

Methods. We analysed IBIS and JEM-X data with OSA 5.1, along with archival Swift/XRT data.

Results. We present results from a long-term monitoring of IGR J16479-4514 with detailed spectral and timing information on 19 bright fast X-ray flares, 10 of which are newly discovered. We also report the first results on the quiescent X-ray emission. The typical luminosity value (~10³⁴ erg s^-1) is about 2 orders of magnitude greater than what is typical of SFXTs, while its broad band X-ray spectrum has a shape very similar to the shape during fast X-ray transient activity, i.e. a rather steep power law with .

Conclusions. IGR J16479-4514 is characterised by a quiescent X-ray luminosity higher than what is typical of other known SFXTs but lower than persistent emission from classical SGXBs. We suggest that this source is a kind of transition object between these two systems, supporting the idea that there is a continuum of behaviour between the class of SFXTs and that of classical persistent SGXBs.