2012ApJ...757..143N

IGR J18179-1621 is an obscured accreting X-ray pulsar discovered by INTEGRAL on 2012 February 29. We report on our 20 ks Chandra-High Energy Transmission Gratings Spectrometer observation of the source performed on 2012 March 17, on two short contemporaneous Swift observations, and on our two near-infrared (K_s, H_n, and J_n) observations performed on 2012 March 13 and 26. We determine the most accurate X-ray position of IGR J18179-1621, α_J2000= 18^h17^m52.^s18, δ_J2000= -16°21'31".68 (90% uncertainty of 0".6). A strong periodic variability at 11.82 s is clearly detected in the Chandra data, confirming the pulsating nature of the source, with the light-curve softening at the pulse peak. The quasi-simultaneous Chandra-Swift spectra of IGR J18179-1621 can be well fit by a heavily absorbed hard power law (N_H= 2.2±0.3x10²³/cm2 and photon index Γ = 0.4±0.1) with an average absorbed 2-8 keV flux of 1.4x10^–11 erg/cm2/s. At the Chandra-based position, a source is detected in our near-infrared (NIR) maps with K_s= 13.14±0.04 mag, H_n= 16±0.1 mag, and no J_n -band counterpart down to ∼18 mag. The NIR source, compatible with 2MASS J18175218-1621316, shows no variability between 2012 March 13 and 26. Searches of the UKIDSS database show similar NIR flux levels at epochs six months prior to and after a 2007 February 11 archival Chandra observation where the source's X-ray flux was at least 87 times fainter. In many ways IGR J18179-1621 is unusual: its combination of a several week long outburst (without evidence of repeated outbursts in the historical record), high absorption column (a large fraction of which is likely local to the system), and 11.82 s period does not fit neatly into existing X-ray binary categories.