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Illuminating a dark lens : a Type Ia Supernova magnified by the Frontier Fields galaxy cluster Abell 2744.

Rodney, S. and Patel, B. and Scolnic, D. and Foley, R. J. and Molino, A. and Brammer, G. and Jauzac, M. and Bradac, M. and Broadhurst, T. and Coe, D. and Diego, J. M. and Graur, O. and Hjorth, J. and Hoag, A. and Jha, S. W. and Johnson, T. L. and Kelly, P. and Lam, D. and McCully, C. and Medezinski, E. and Meneghetti, M. and Merten, J. and Richard, J. and Riess, A. and Sharon, K. and Strolger, L.-G. and Treu, T. and Wang, X. and Williams, L. L. R. and Zitrin, A. (2015) 'Illuminating a dark lens : a Type Ia Supernova magnified by the Frontier Fields galaxy cluster Abell 2744.', Astrophysical journal., 811 (1). p. 70.


SN HFF14Tom is a Type Ia SN discovered at $z=1.3457\pm 0.0001$ 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 ${\mu }_{\mathrm{obs}}=2.03\pm 0.29.$ 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 1σ. 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.

Item Type:Article
Keywords:Galaxies: clusters: general, Galaxies: clusters: individual (Abell 2744), Gravitational lensing: strong, Gravitational lensing: weak, Supernovae: general, Supernovae: individual (HFF14Tom).
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Publisher statement:© 2015. The American Astronomical Society. All rights reserved.
Date accepted:14 August 2015
Date deposited:06 November 2015
Date of first online publication:22 September 2015
Date first made open access:No date available

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