Probing the nature of IGR J16493−4348: spectral and temporal analysis of the 1-100 keV emission

Abstract

IGR J16493?4348 was one of the first new sources to be detected by the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) ?-ray telescope in the 18-100 keV energy band. Based on spatial coincidence, the source was originally associated with the free radio pulsar PSR J1649?4349. Presented here are the results of 2.8 Ms of observations made by the INTEGRAL mission and a 5.6-ks observation with the Swift/X-ray Telescope (XRT). Spectral analysis indicates that the source is best modelled by an absorbed power law with a high energy cut-off at Ecut? 15 keV and a hydrogen absorbing column of NH= 5.4+1.3?1× 1022?cm?2 . Analysis of the light curves indicates that the source is a weak, persistent ?-ray emitter showing indications of variability in the 2-9 and 22-100 keV bands. The average source flux is ?1.1 × 10?10?erg?cm?2?s?1 in the 1-100 keV energy band. No coherent timing signal is identified at any time-scale in the INTEGRAL or Swift data. The refined source location and positional uncertainty of IGR J16493?4348 places PSR J1649?4349 outside the 90 per cent error circle. We conclude that IGR J16493?4348 is not associated with PSR J1649?4349. Combining the INTEGRAL observations with Swift/XRT data and information gathered by RXTE and Chandra, we suggest that IGR J16493?4348 is an X-ray binary, and that the source characteristics favour a high-mass X-ray binary although a low-mass X-ray binary nature cannot be ruled out.