https://arxiv.org/pdf/1611.00014v1.pdf The discovery of the multiply-imaged lensed Type Ia supernova iPTF16geu Abstract: We report the discovery of a gravitationally lensed Type Ia supernova (SN Ia) by the intermediate Palomar Transient Factory (iPTF). The light originating from SN Ia iPTF16geu, at redshift zSN = 0.409, is magnified by an intervening galaxy at zl = 0.216, acting as a gravitational lens. Using Laser Guide Star Adaptive Optics (LGSAO) OSIRIS and NIRC2 observations at the Keck telescope, as well as measurements with the Hubble Space Telescope, we were able to detect the strong bending of the light path, both for iPTF16geu and its host galaxy. We detect four images of the supernova, approximately 0.3 00 from the center of the lensing galaxy. iPTF16geu is the first SN Ia for which multiple images have been observed. From the fits of the multi-color lightcurve we derive a lensing magnification, ∆m = 4.37 ± 0.15 mag, corresponding to a total amplification of the supernova flux by a factor µ ∼ 56. The discovery of iPTF16geu suggests that lensing by sub-kpc structures may have been greatly underestimated. In that scenario, many discoveries of gravitationally magni- fied objects can be expected in forthcoming surveys of transient phenomena, opening up a new window to precision cosmology with supernovae.
