INTEGRAL and Swift observations of the supergiant fast X-ray transient AX J1845.0–0433 = IGR J18450–0435

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

Received: 8 August 2006
Accepted: 25 October 2006

Abstract

Context.AX J1845.0-0433 was discovered by ASCA in 1993 during fast outburst activity characterized by several flares on short timescales. Up to now, the source was not detected again by any X-ray mission. Its optical counterpart is suggested to be an O9.5I supergiant star, which is the only remarkable object found inside the ASCA error box.

Aims.To detect and characterize new fast outbursts of AX J1845.0-0433 and confirm its supergiant HMXB nature, using INTEGRAL and archival Swift XRT observations.

Methods.We performed an analysis of INTEGRAL IBIS and JEM–X data with OSA 5.1 as well as an analysis of archive Swift XRT data.

Results.We report on fast flaring activity from the source on timescales of a few tens of minutes, the first to be reported since its discovery in 1993. Two outbursts have been detected by INTEGRAL (Apr. 2005 and Apr. 2006) with similar peak fluxes and peak luminosities of ~80 mCrab and 9.3  10³⁵ erg s^-1 (20–40 keV), respectively. Two other outbursts were detected by Swift XRT on Nov. 2005 and Mar. 2006. The refined Swift XRT position of AX J1845.0-0433 confirms its association with the supergiant star previously proposed as optical counterpart.

Conclusions.Our INTEGRAL and Swift results fully confirm the supergiant HMXB nature of AX J1845.0-0433 which can therefore be classified as a supergiant fast X-ray transient. Moreover they provide for the first time evidence of its recurrent fast transient behaviour.