We propose a monitoring program of the persistent and soft black hole x-RAY binary LMC x-3. Over a months-long timescale, IT ranges from a few percent eddington to near its eddington limit.…

The Smithsonian Astrophysical Observatory (SAO), operating as a child entity under the Smithsonian Institution, was awarded a $119,973.98 research grant by a civilian federal agency on August 30, 2024, with an ultimate completion date of August 29, 2026. This research grant, with no set-aside designation, supports a scientific monitoring program focused on LMC X-3, a persistent soft black hole X-ray binary system. The project will employ X-ray polarimetric observations across a months-long timescale to assess how the accretion disk geometry changes as the black hole transitions from a few percent of its Eddington limit to near the Eddington limit, providing critical insights into slim-disk effects at high luminosities.

The research leverages X-ray polarimetry to distinguish the role of returning radiation in governing disk geometry and polarization strength, particularly examining how disk scale-height and thickness evolve at luminosities exceeding approximately 30 percent of the Eddington limit. The work will be performed at SAO's Cambridge, Massachusetts location and aligns with the organization's established expertise in astrophysical research and black hole dynamics. This award reflects SAO's competitive positioning in advanced space science research, consistent with the organization's portfolio of federally-funded grants focused on fundamental astrophysics investigations.

We propose a monitoring program of the persistent and soft black hole x-RAY binary LMC x-3. Over a months-long timescale, IT ranges from a few percent eddington to near its eddington limit. Polarimetric data which span this luminosity range allows assessment of "slim-disk" effects on the inner-disk geometry. At low luminosities, the thermal state of black holes in x-RAY binaries is simple and stable, with a fixed inner-disk radius. At high luminosities >~30% of the eddington limit, slim-disk effects onset as the disk scale-height grows. X-RAY polarimetry provides unique insights on the inner-disk geometry across luminosity and will distinguish the role of returning radiation (enhanced for thicker disks), which may be important in governing polarization strength.