INTEGRAL and Swift observations of IGR J19294+1816 in outburst

¹ ISDC data center for astrophysics of the University of Geneva, chemin d’Écogia 16, 1290 Versoix, Switzerland
e-mail: enrico.bozzo@unige.ch
² International Space Science Institute (ISSI), Hallerstrasse 6, 3012 Bern, Switzerland

Received: 15 February 2011
Accepted: 7 May 2011

Abstract

Context. IGR J19294+1816 was discovered by INTEGRAL in 2009 during a bright X-ray outburst and was classified as a possible Be X-ray binary or supergiant fast X-ray transient.

Aims. On 2010 October 28, the source displayed a second X-ray outburst and a two months-long monitoring with Swift was carried out to follow the evolution of the source X-ray flux during the event.

Methods. We report on the INTEGRAL and Swift observations of the second X-ray outburst observed from IGR J19294+1816.

Results. We detected pulsations in the X-ray emission from the source at  ~12.5 s up to 50 keV. The source X-ray flux decreased smoothly during the two months of observation, displaying only marginal spectral changes. Owing to the relatively rapid decay of the source X-ray flux, no significant variations of the source spin period across the event could be measured. This prevented a firm confirmation of the previously suggested orbital period of the source at 117 d. This periodicity was also searched for in archival Swift /BAT data. We detected a marginally significant peak in the periodogram and determined the best period at 116.2  ±  0.6 days (estimated chance probability of a spurious detection 1%).

Conclusions. The smooth decline of the source X-ray flux across the two months of observations after the onset of the second outburst, together with its relatively low value of the spin period and the absence of remarkable changes in the spectral parameters (i.e., the absorption column density), suggests that IGR J19294+1816 is most likely another member of the Be X-ray binaries discovered by INTEGRAL and not a supergiant fast X-ray transient.