Illuminating a dark lens: a type Ia supernova magnified by the frontier fields galaxy cluster abell 2744

Facility: HST (WFC3).-- Rodney, Steven A. et al.SN HFF14Tom is a Type Ia SN discovered at Z = 1.3457 ± 0.0001 behind the galaxy cluster Abell 2744 (Z = 0.308). In a cosmology-independent analysis, we find that HFF14Tom is 0.77 ± 0.15 mag brighter than unlensed Type Ia SNe at similar redshift, implying a lensing magnification of μ = 2.03 ± 0.29. This observed magnification provides a rare opportunity for a direct empirical test of galaxy cluster lens models. Here we test 17 lens models, 13 of which were generated before the SN magnification was known, qualifying as pure >blind tests. > The models are collectively fairly accurate: 8 of the models deliver median magnifications that are consistent with the measured μ to within 1λ. However, there is a subtle systematic bias: the significant disagreements all involve models overpredicting the magnification. We evaluate possible causes for this mild bias, and find no single physical or methodological explanation to account for it. We do find that model accuracy can be improved to some extent with stringent quality cuts on multiply imaged systems, such as requiring that a large fraction have spectroscopic redshifts. In addition to testing model accuracies as we have done here, Type Ia SN magnifications could also be used as inputs for future lens models of Abell 2744 and other clusters, providing valuable constraints in regions where traditional strong- and weak-lensing information is unavailable.Financial support for this work was provided to S.A.R. by NASA through grants HST-HF-51312 and HST-GO-13386 from STScI, which is operated by Associated Universities for Research in Astronomy, Inc. (AURA), under NASA contract NAS 5-26555. A.M. acknowledge the financial support of the Brazilian funding agency FAPESP (Post-doc fellowship—process number 2014/11806-9). Support for this research at Rutgers University was provided in part by NSF CAREER award AST-0847157 to SWJ. The Dark Cosmology Centre is supported by the Danish National Research Foundation. J.M.D. acknowledges support of the consolider project CSD2010-00064 and AYA2012–39475-C02-01 funded by the Ministerio de Economia y Competitividad. J.M. contributed to this research from the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA and acknowledges support from NASA Grants HST-GO-13343.05-A and HST-GO-13386.13-A. The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/20072013) under REA grant agreement number 627288. A.Z. acknowledges financial support from NASA through grant HST-HF-51334.01-A awarded by STScI and operated by AURA. T.T. acknowledges support by the Packard Foundation in the form of Packard Research Fellowship. GLASS is funded by NASA through HST grant GO-13459. L.L.R.W. acknowledges the support of the Minnesota Supercomputing Institute.N