Detection of a highly magnified Type Ia Supernova by the intermediate Palomar Transient Factory

ATel #9603; Ariel Goobar (Stockholm University and the Oskar Klein Centre, on behalf of the intermediate Palomar Transient Factory collaboration)
on 7 Oct 2016; 20:26 UT
Credential Certification: Rahman Amanullah (rahman@fysik.su.se)

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The iPTF collaboration reports the detection of iPTF16geu a spectroscopically normal Type Ia supernova at z=0.409. The supernova was first detected on Sep 5, 2016 and was spectroscopically classified on Oct 2 with the SED machine on P60. The transient identification was later verified using P200 on Oct 5 and Oct 6. The P200 spectra show Na ID and Ca II absorption features from which the redshift was measured. Furthermore, multiple absorption and emission features at z=0.216 indicate the presence of gas in the line of sight. These features are likely associated with a galaxy within ~0.5 arcseconds from the SN position for which pre-explosion data from SDSS has been used to derive a photometric redshift z=0.227 +/- 0.045. The supernova brightness, currently R~19.5, is approximately 3.7 magnitudes brighter than what is expected for a normal Type Ia supernova at that redshift, about 10 days past maximum, not accounting for possible extinction in either the host nor the intervening galaxy. Given its otherwise excellent spectral match with a redshfted spectrum (z=0.409) of SN1992A at +9 days on Oct 4 we conclude that the most likely explanation is that the SN is lensed by the galaxy at z=0.216. We are currently working to obtain ground-based AO and HST observations to try to resolve the presumed multiple images of the lensed system. The time delay between the SN images is expected to be small, at most a few days. We seek a maximal spectroscopic and photometric sequence for the event(s) and encourage observers to collaborate on the follow-up campaign led by iPTF. The coordinates of IPTF16geu are (J2000) RA: 21:04:15.86 DEC: -06:20:24.5