2013A&A...556A..27S

We report on a broad-band X-ray study (0.5-60 keV) of the poorly known candidate supergiant fast X-ray transient (SFXT) IGR J18462-0223, and on optical and near-infrared (NIR) followup observations of field objects. The out-of-outburst X-ray state has been investigated for the first time with archival INTEGRAL/IBIS, ASCA, Chandra, and Swift/XRT observations. This allowed us to place stringent 3σ upper limits on the soft (0.5-10keV) and hard (18-60keV) X-ray emission of 2.9x10^–13erg/cm²/s and 8x10^–12erg/cm²/s, respectively. The source was also detected during an intermediate soft X-ray state with flux equal to 1.6x10^–11erg/cm²/s (0.5-10keV). In addition, we report on the INTEGRAL/IBIS discovery of three fast hard X-ray flares (18-60keV) having a duration in the range 1-12h and the flaring behavior was investigated in soft X-rays (3-10keV) with archival INTEGRAL/JEM-X observations. The duty cycle (1.2%) and the dynamic ranges (>1380 and >190 in the energy bands 0.5-10keV and 18-60keV, respectively) were measured for the first time. Archival UKIDSS JHK NIR data, together with our deep R-band imaging of the field, unveiled a single, very red object inside the intersection of the Swift/XRT and XMM-Newton error circles. This source has optical/NIR photometric properties compatible with a very heavily absorbed blue supergiant located at ∼11kpc, so is a strong candidate for a counterpart to IGR J18462-0223. NIR spectroscopy is advised to confirm the association. Finally, a hint of a possible orbital period was found at ∼2.13-days. If confirmed by further studies, this would make IGR J18462-0223 the SFXT with the shortest orbital period among the currently known systems.