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Lin YanMS100-22, Caltech/IPAC, California Institute of Technology, Pasadena, CA 91125, USAR. LunnanDepartment of Astronomy, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USAD. A. PerleyDARKA. Gal‐YamBenoziyo Center for Astrophysics and the Helen Kimmel Center for Planetary Science, Weizmann Institute of Science, 76100 Rehovot, IsraelO. YaronBenoziyo Center for Astrophysics and the Helen Kimmel Center for Planetary Science, Weizmann Institute of Science, 76100 Rehovot, IsraelR. RoyThe Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, SE-10691, Stockholm, SwedenR. M. QuimbyKavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277–8583, JapanJ. SollermanThe Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, SE-10691, Stockholm, SwedenC. FremlingThe Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, SE-10691, Stockholm, SwedenG. LeloudasDARKS. B. CenkoAstrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771, USAP. M. VreeswijkBenoziyo Center for Astrophysics and the Helen Kimmel Center for Planetary Science, Weizmann Institute of Science, 76100 Rehovot, IsraelM. L. GrahamDepartment of Astronomy, University of Washington, Box 351580, U.W., Seattle, WA 98195-1580, USAD. A. HowellLas Cumbres Observatory, 6740 Cortona Drive, Suite 102, Goleta, CA 93117, USAA. DeEuropean Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, GermanyE. O. OfekBenoziyo Center for Astrophysics and the Helen Kimmel Center for Planetary Science, Weizmann Institute of Science, 76100 Rehovot, IsraelP. NugentAstronomy Department, University of California, Berkeley, 501 Campbell Hall, Berkeley, CA 94720, USAS. R. KulkarniCaltech Optical Observatories, California Institute of Technology, Pasadena, CA91125, USAGriffin HosseinzadehDepartment of Physics, University of California, Santa Barbara, Broida Hall, Mail Code 9530, Santa Barbara, CA 93106-9530, USAFrank J. MasciMS100-22, Caltech/IPAC, California Institute of Technology, Pasadena, CA 91125, USACurtis McCullyDepartment of Physics, University of California, Santa Barbara, Broida Hall, Mail Code 9530, Santa Barbara, CA 93106-9530, USAU. D. RebbapragadaJet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USAP. R. WoźniakLos Alamos National Laboratory

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Annotatsiya

We present observations of two new hydrogen-poor superluminous supernovae (SLSN-I), iPTF15esb and iPTF16bad, showing late-time H-alpha emission with line luminosities of (1-3)e+41 erg/s and velocity widths of (4000-6000) km/s. Including the previously published iPTF13ehe, this makes up a total of three such events to date. iPTF13ehe is one of the most luminous and the slowest evolving SLSNe-I, whereas the other two are less luminous and fast decliners. We interpret this as a result of the ejecta running into a neutral H-shell located at a radius of ~ 1.0e+16cm. This implies that violent mass loss must have occurred several decades before the supernova explosion. Such a short time interval suggests that eruptive mass loss could be common shortly prior to the death of a massive star as a SLSN. And more importantly, helium is unlikely to be completely stripped off the progenitor stars and could be present in the ejecta. It is a mystery why helium features are not detected, even though non-thermal energy sources, capable of ionizing He atoms, may exist as suggested by the O II absorption series in the early time spectra. At late times (+240d), our spectra appear to have intrinsically lower [O I]6300A luminosities than that of SN2015bn and SN2007bi, possibly an indication of smaller oxygen masses (<10-30Msun). The blue-shifted H-alpha emission relative to the hosts for all three events may be in tension with the binary star model proposed for iPTF13ehe. Finally, iPTF15esb has a peculiar light curve with three peaks separated from one another by ~ 22 days. The LC undulation is higher in bluer bands. One possible explanation is eject-CSM interaction.

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