Nowak, Michael A.Michael A.NowakPAIZIS, ADAMANTIAADAMANTIAPAIZISJaisawal, Gaurava KumarGaurava KumarJaisawalChenevez, JérômeJérômeChenevezChaty, SylvainSylvainChatyFortin, FrancisFrancisFortinRodriguez, JérômeJérômeRodriguezWilms, JörnJörnWilms2020-12-182020-12-1820190004-637Xhttp://hdl.handle.net/20.500.12386/29013An accreting millisecond X-ray pulsar, IGR J17591-2342 was discovered in 2018 August in scans of the Galactic bulge and center by the International Gamma-Ray Astrophysics Laboratory X-ray and gamma-ray observatory. It exhibited an unusual outburst profile with multiple peaks in the X-ray, as observed by several X-ray satellites over 3 months. Here we present observations of this source performed in the X-ray/gamma-ray and near-infrared domains and focus on a simultaneous observation performed with the Chandra High Energy Transmission Gratings Spectrometer (HETGS) and the Neutron Star Interior Composition Explorer (NICER). The HETGS provides high-resolution spectra of the Si edge region that yield clues as to the source’s distance and reveal evidence (at 99.999% significance) of an outflow with a velocity of 2800 km s<SUP>-1</SUP>. We demonstrate good agreement between the NICER and HETGS continua, provided that one properly accounts for the differing manners in which these instruments view the dust-scattering halo in the source’s foreground. Unusually, we find a possible set of Ca lines in the HETGS spectra (with significances ranging from 97.0% to 99.7%). We hypothesize that IGR J17591-2342 is a neutron star low-mass X-ray binary at the distance of the Galactic bulge or beyond that may have formed from the collapse of a white dwarf system in a rare, calcium-rich Type Ib supernova explosion.STAMPAenArticle10.3847/1538-4357/ab0a712-s2.0-85064439864000462602500002https://iopscience.iop.org/article/10.3847/1538-4357/ab0a712019ApJ...874...69NFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_10 High energy and particle astronomy – X-rays, cosmic rays, gamma rays, neutrinos