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Lens modelling of the strongly lensed Type Ia supernova iPTF16geu

Mörtsell, E. and Johansson, J. and Dhawan, S. and Goobar, A. and Amanullah, R. and Goldstein, D. A. (2020) Lens modelling of the strongly lensed Type Ia supernova iPTF16geu. Monthly Notices of the Royal Astronomical Society, 496 (3). pp. 3270-3280. ISSN 0035-8711.

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In 2016, the first strongly lensed Type Ia supernova (SN Ia), iPTF16geu, at redshift z = 0.409 with four resolved images arranged symmetrically around the lens galaxy at z = 0.2163, was discovered. Here, refined observations of iPTF16geu, including the time delay between images, are used to decrease uncertainties in the lens model, including the the slope of the projected surface density of the lens galaxy, Σ ∝ r^(1 − η), and to constrain the universal expansion rate H₀. Imaging with Hubble Space Telescope provides an upper limit on the slope η, in slight tension with the steeper density profiles indicated by imaging with Keck after iPTF16geu had faded, potentially due to dust extinction not corrected for in host galaxy imaging. Since smaller η implies larger magnifications, we take advantage of the standard candle nature of SNe Ia constraining the image magnifications, to obtain an independent constraint of the slope. We find that a smooth lens density fails to explain the iPTF16geu fluxes, regardless of the slope, and additional substructure lensing is needed. The total probability for the smooth halo model combined with star microlensing to explain the iPTF16geu image fluxes is maximized at 12 per cent for η ∼ 1.8, in excellent agreement with Keck high-spatial-resolution data, and flatter than an isothermal halo. It also agrees perfectly with independent constraints on the slope from lens velocity dispersion measurements. Combining with the observed time delays between the images, we infer a lower bound on the Hubble constant, H₀ ≳ 40 km s⁻¹ Mpc⁻¹⁠, at 68.3 per cent confidence level.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Johansson, J.0000-0001-5975-290X
Dhawan, S.0000-0002-2376-6979
Goobar, A.0000-0002-4163-4996
Amanullah, R.0000-0002-5559-9351
Goldstein, D. A.0000-0003-3461-8661
Additional Information:© The Author(s) 2020. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Accepted 2020 June 2. Received 2020 May 8; in original form 2019 July 15. We thank the anonymous referee for many insightful comments helping to improve the quality of this paper. Also, thanks to Simon Birrer, Rahul Gupta, and Mattia Bulla for help in running LENSTRONOMY. AG acknowledges support from the Swedish National Space Agency and the Swedish Research Council.
Funding AgencyGrant Number
Swedish National Space AgencyUNSPECIFIED
Swedish Research CouncilUNSPECIFIED
Subject Keywords:gravitational lensing: strong, gravitational lensing: micro, supernovae: individual, distance scale
Issue or Number:3
Record Number:CaltechAUTHORS:20201022-161608680
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Official Citation:E Mörtsell, J Johansson, S Dhawan, A Goobar, R Amanullah, D A Goldstein, Lens modelling of the strongly lensed Type Ia supernova iPTF16geu, Monthly Notices of the Royal Astronomical Society, Volume 496, Issue 3, August 2020, Pages 3270–3280,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106237
Deposited By: George Porter
Deposited On:23 Oct 2020 15:18
Last Modified:23 Oct 2020 15:18

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