2013MNRAS.436L..89A

A growing group of low-mass X-ray binaries are found to be accreting at very faint X-ray luminosities of <10³⁶ erg/s (2^SS–10keV). One such system is the new X-ray transient IGR J17494-3030. We present Swift and XMM-Newton observations obtained during its 2012 discovery outburst. The Swift observations trace the peak of the outburst, which reached a luminosity of ∼ 7x10³⁵ (D/8 kpc)2 erg/s (2^–10keV). The XMM-Newton data were obtained when the outburst had decayed to an intensity of ∼ 8x10³⁴ (D/8 kpc)2 erg/s. The spectrum can be described by a power law with an index of Γ ∼ 1.7 and requires an additional soft component with a blackbody temperature of ∼ 0.37keV (contributing ∼ 20 percent to the total unabsorbed flux in the 0.5^–10keV band). Given the similarities with high-quality spectra of very faint neutron-star low-mass X-ray binaries, we suggest that the compact primary in IGR J17494-3030 is a neutron star. Interestingly, the source intensity decreased rapidly during the ∼ 12 h XMM-Newton observation, which was accompanied by a decrease in inferred temperature. We interpret the soft spectral component as arising from the neutron-star surface due to low-level accretion, and propose that the observed decline in intensity was the result of a decrease in the mass-accretion rate on to the neutron star.