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Register a new userSN Refsdal: Classification as a Luminous and Blue SN 1987A-like Type II Supernova
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We have acquired Hubble Space Telescope (HST) and Very Large Telescope near-infrared spectra and images of supernova (SN) Refsdal after its discovery as an Einstein cross in Fall 2014. The HST light curve of SN Refsdal matches the distinctive, slowly rising light curves of SN 1987A-like supernovae (SNe), and we find strong evidence for a broad H-alpha P-Cygni profile in the HST grism spectrum at the redshift (z = 1.49) of the spiral host galaxy. SNe IIn, powered by circumstellar interaction, could provide a good match to the light curve of SN Refsdal, but the spectrum of a SN IIn would not show broad and strong H-alpha absorption. From the grism spectrum, we measure an H-alpha expansion velocity consistent with those of SN 1987A-like SNe at a similar phase. The luminosity, evolution, and Gaussian profile of the H-alpha emission of the WFC3 and X-shooter spectra, separated by ~2.5 months in the rest frame, provide additional evidence that supports the SN 1987A-like classification. In comparison with other examples of SN 1987A-like SNe, SN Refsdal has a blue B-V color and a high luminosity for the assumed range of potential magnifications. If SN Refsdal can be modeled as a scaled version of SN 1987A, we estimate it would have an ejecta mass of 20+-5 solar masses. The evolution of the light curve at late times will provide additional evidence about the potential existence of any substantial circumstellar material (CSM). Using MOSFIRE and X-shooter spectra, we estimate a subsolar host-galaxy metallicity (8.3+-0.1 dex and <8.4 dex, respectively) near the explosion site.
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We present the local HII region metallicity near the site of the recently discovered multiply lensed supernova (SN; SN Refsdal) at redshift 1.49. SN Refsdal is located at the outer spiral arm ($sim$7 kpc) of the lensed host galaxy, which we have previously reported to exhibit a steep negative galactocentric metallicity gradient. Based on our updated near-infrared integral field spectroscopic data, the gas-phase metallicity averaged in an intrinsic radius of $sim$ 550 pc surrounding an HII region $sim$ 200 pc away from the SN site is 12 + log(O/H)$_{rm PP04N2}$ $le$ 8.67. The metallicity averaged over nine HII regions at similar galactocentric distances ($sim$5-7 kpc) as SN Refsdal is constrained to be 12 + log(O/H)$_{rm PP04N2}$ $le$ 8.11. Given the fortuitous discovery of SN Refsdal in an advantageously lensed face-on spiral, this is the first observational constraint on the local metallicity environment of an SN site at redshift $z>1$.
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