Fast Lensing And Sub-minute High-accuracy photometry (FLASH) with JWST: Pipeline and Primordial Black Hole Microlensing Constraints from M31

RESUMO

Minute- and sub-minute microlensing provides a direct probe of compact dark matter at asteroid-mass scales, where primordial black holes with MPBH <~ 10^-10 Msol would produce short-duration, finite-source-suppressed amplifications of stars in extragalactic fields. To enable these measurements, we present FLASH: Fast Lensing And Sub-minute High-accuracy photometry with JWST, a pipeline designed to recover such events from JWST/NIRCam imaging by preserving detector-ramp time information and performing high-precision crowded-field photometry. FLASH begins from Level 1 NIRCam data products, applies microlensing-oriented detector calibration (including improved treatment of non-linearity and position-dependent detector calibration), and extracts forced multi-band light curves in crowded fields. We apply the pipeline to two public JWST/NIRCam datasets targeting the disk of M31 with 21.5 s cadence: GO-4735 and GO-2609. Although these observations are suboptimal as a microlensing survey, they provide a stringent test of JWST time-domain performance in a high-surface-brightness, crowded stellar field. Using these data with our own microlensing simulations, we derive the first JWST-based microlensing constraints toward M31, finding fPBH <~ 100 for MPBH~ 10^-9 Msol. Our results demonstrate that JWST is a competitive platform for high-cadence microlensing and that a dedicated, continuous NIRCam monitoring program could substantially improve constraints on compact dark matter below the current ground-based frontier.