Probing the nature of the X-ray source IGR J16327-4940 with Chandra
Sidoli, L.; Sguera, V.; Postnov, K.; Esposito, P.; Oskinova, L.
We report on the results of a Chandra observation of the source IGRJ16327-4940, suggested to be a high mass X-ray binary hosting a luminous blue variable star (LBV). The source field was imaged by ACIS-I in 2023 to search for X-ray emission from the LBV star and eventually confirm this association. No X-ray emission is detected from the LBV star, with an upper limit on the X-ray luminosity of L(0.5-10keV) < 2.9 (+1.6,-1.1) 1032 erg/s (at the LBV distance d=12.7 (+3.2,-2.7) kpc). We detected 21 faint X-ray sources, 8 of which inside the INTEGRAL error circle. The brightest one is the best candidate soft X-ray counterpart of IGRJ16327-4940, showing a hard power law spectrum and a flux corrected for the absorption UF(0.5-10keV) = 2.5 1013 erg/cm2/s, implying a luminosity of 3.0 1033 (d/10kpc)2 erg/s. No optical/near-infrared counterparts have been found. Previous X--ray observations of the source field with Swift/XRT and ART-XC did not detect any source consistent with the INTEGRAL position. These findings exclude the proposed LBV star as the optical association, and pinpoint the most likely soft X-ray counterpart. In this case, the source properties suggest a low mass X-ray binary, possibly a new member of the very faint X-ray transient class.