2007ApJ...655L.101G

The supergiant fast X-ray transient IGR J08408-4503 was discovered by INTEGRAL on 2006 May 15 during a bright flare. The source shows sporadic recurrent short bright flares, reaching a peak luminosity of 10³⁶ ergs/s within less than 1 hr. The companion star is HD 74194, an Ob5Ib(f) supergiant star located at 3 kpc in the Vela region. We report the light curves and broadband spectra (0.1-200 keV) of all the three flares of IGR J08408-4503 detected up to now, based on INTEGRAL and Swift data. The flare spectra are well described by a power-law model with a high-energy cutoff at ∼15 keV. The absorption column density during the flares was found to be ∼10²¹/cm2, indicating a very low matter density around the compact object. Using the supergiant donor star parameters, the wind accretion conditions imply an orbital period of the order of 1 yr, a spin period of the order of hours, and a magnetic field of the order of 10¹³ G.