0 Assigned ID: 573 ----- Attempting Submission 1 (Fri Apr 05 17:44:30 GMT 2019) ----- HST Phase I Proposal 573 (HST_archival_proposal.pdf.apt) successfully submitted. Receipt: # 573-1 ----- Attempting Submission 2 (Fri Apr 05 21:57:09 GMT 2019) ----- The detection of gravitational waves emitted from ~10-100 solar-mass black-hole mergers has revived the search for dark matter formed by primordial black holes (PBHs). If present in foreground galaxy-cluster lenses, PBHs should cause microlensing peaks that extremely magnify well-aligned background stars, allowing the high-redshift stars to be detected with the Hubble Space Telescope (HST). Since the microlensing event rate should be proportional to the density of microlenses times the magnification of the macromodel, searching for lensed stars behind clusters provides one of few avenues to probe stellar-mass PBHs. Only four highly magnified stars have been discovered to date, and all were found behind powerful Hubble Frontier Field (HFF) clusters. The most recently discovered event Warhol in the MACS J0416.1-2403 field was missed when it occurred in 2014, and only recently recovered in systematic searches of archival HFF cluster imaging. This motivates us to propose a comprehensive search for transients in the full set of archival HST imaging data, including that from the large CLASH and RELICS programs. In a preliminary study, we have found >30 bright transient candidates in the HFF fields that include known lensed stars and supernovae. Twenty-four of them, however, have not yet been publicly reported. We propose to extend our search for transients to lower signal-to-noise microlensing event candidates by searching for sources that are present in multiple epochs. We expect this program will improve constraints on the abundance of PBHs in the ~10-100 solar-mass regime. Dr. Patrick Kelly has extensive experience with Hubble Space Telescope (HST) imaging programs, and discovered the "Icarus" blue supergiant at z=1.49 in the MACS J1149 field. Dr. Jose Diego has performed the first ray tracing simulations of the effect of compact objects in a foreground galaxy lens on the light curve of a highly magnified star. Dr. Adi Zitrin is an expert in galaxy-cluster modeling and high-redshift galaxy populations. Dr. Tom Broadhurst is an expert in gravitational lensing. Dr. Wenlei Chen discovered the "Warhol" highly magnified blue supergiant at z=0.94. Cosmology 0 Regular false true false false false SUPPORTED