The magnificent five images of Supernova Refsdal: time delay and magnification measurements

Patrick L. Kelly*, Steven Rodney, Tommaso Treu, Simon Birrer, Vivien Bonvin, Luc Dessart, Ryan J. Foley, Alexei V. Filippenko, Daniel Gilman, Saurabh Jha, Jens Hjorth, Kaisey Mandel, Martin Millon, Justin Pierel, Stephen Thorp, Adi Zitrin, Tom Broadhurst, Wenlei Chen, Jose M. Diego, Alan DresslerOr Graur, Mathilde Jauzac, Matthew A. Malkan, Curtis McCully, Masamune Oguri, Marc Postman, Kasper Borello Schmidt, Keren Sharon, Brad E. Tucker, Anja von der Linden, Joachim Wambsganss

*Corresponding author for this work

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In late 2014, four images of Supernova (SN) "Refsdal," the first known example of a strongly lensed SN with multiple resolved images, were detected in the MACS J1149 galaxy-cluster field. Following the images' discovery, the SN was predicted to reappear within hundreds of days at a new position ~8 arcseconds away in the field. The observed reappearance in late 2015 makes it possible to carry out Refsdal's (1964) original proposal to use a multiply imaged SN to measure the Hubble constant H0, since the time delay between appearances should vary inversely with H0. Moreover, the position, brightness, and timing of the reappearance enable a novel test of the blind predictions of galaxy-cluster models, which are typically constrained only by the positions of multiply imaged galaxies. We have developed a new photometry pipeline that uses DOLPHOT to measure the fluxes of the five images of SN Refsdal from difference images. We apply four separate techniques to perform a blind measurement of the relative time delays and magnification ratios (mu_i/mu_1) between the last image SX and the earlier images S1-S4. We measure the relative time delay of SX-S1 to be 376.0+5.6-5.5 days and the relative magnification to be 0.30+0.05-0.03. This corresponds to a 1.5% precision on the time delay and 17% precision for the magnification ratios, and includes uncertainties due to millilensing and microlensing. In an accompanying paper, we place initial and blind constraints on the value of the Hubble constant.
Original languageEnglish
Article number93
Number of pages33
JournalThe Astrophysical Journal
Publication statusPublished - 11 May 2023


  • astro-ph.CO
  • UKRI
  • STFC
  • MRC
  • MR/S017216/1

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