Little LIEs:Instantaneous measurement of black hole angular Einstein rings with Lens Image Elongations
| Program ID | 19110 |
|---|---|
| Science Category | Stellar Populations |
| Program Type | Analysis |
| Category | Small |
| Principal Investigator | Himanshu Verma |
| PI Institution | Louisiana State University |
| Co-Investigators |
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| Abstract | We propose an archival analysis of Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey (GBTDS) data to perform the first statistical census of isolated stellar-mass black holes (BHs) via a novel technique called Lens Image Elongation (LIE). When two unresolved gravitationally lensed images are blended within a single PSF, the composite PSF image is elongated along the lens-source axis, producing a characteristic dipole or visually ``hamburger'' shape in the residual image when fitted with a single-PSF model. Fitting a two-PSF model to Roman's 8$\times$ oversampled, 8-day stacked F146 band images, near the peak of the light curve, recovers the image separation and hence the angular Einstein angle $\theta_E$ at \textbf{a single epoch} -- eliminating the multi-year astrometric baseline and related calibration required by conventional methods. Our image-level simulation using the STPSF package demonstrate clear LIE signal detection for Einstein angle more than 1.5 mas for the lensed sources brighter than 24 mag in F146 band. Applying this to GULLS synthetic catalogs, we expect about 28 ($\sim$30\% of all BH events per season) BH mass measurements detected per GBTDS season, yielding the first observational constraints on the isolated BH mass function in the Galaxy. All analysis uses archival GBTDS data products; no new observations are required. |