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Published October 10, 2017 | Submitted + Published
Journal Article Open

Hydrogen-poor Superluminous Supernovae with Late-time Hα Emission: Three Events From the Intermediate Palomar Transient Factory

Abstract

We present observations of two new hydrogen-poor superluminous supernovae (SLSN-I), iPTF15esb and iPTF16bad, showing late-time Hα emission with line luminosities of (1-3) x 10^(41) erg s^(−1) and velocity widths of (4000–6000) km s^(−1). 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 ~10^(16) cm. 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 before core collapse, and more importantly helium is unlikely to be completely stripped off the progenitor and could be present in the ejecta. It is a mystery why helium features are not detected, even though nonthermal energy sources, capable of ionizing He, may exist as suggested by the O ii absorption series in the early-time spectra. Our late-time spectra (+240 days) appear to have intrinsically lower [O i] 6300 Å luminosities than that of SN2015bn and SN2007bi, which is possibly an indication of less oxygen (<10 M_⊙). The blueshifted Hα emission relative to the hosts for all three events may be in tension with the binary model proposed for iPTF13ehe. Finally, iPTF15esb has a peculiar light curve (LC) with three peaks separated from one another by ~22 days. The LC undulation is stronger in bluer bands. One possible explanation is ejecta-circumstellar medium interaction.

Additional Information

© 2017 American Astronomical Society. Received 2017 April 16. Accepted 2017 August 29. Published 2017 October 5 . We thank N. Blagorodnova, A. Ho, Y. Cao, H. Vedantham, and V. Ravi at Caltech, Virginia Cunningham at the University of Maryland, Antonino Cucchiara at the Goddard Space Flight Center (GSFC), J. Mauerhan, I. Shivvers, and P. Kelly at the University of Berkeley for taking some of the data for iPTF15esb. This paper benefitted from discussions with Anthony Piro at Carnegie Observatories. The intermediate Palomar Transient Factory project is a scientific collaboration among the California Institute of Technology, Los Alamos National Laboratory, the University of Wisconsin, Milwaukee, the Oskar Klein Center, the Weizmann Institute of Science, the TANGO Program of the University System of Taiwan, and the Kavli Institute for the Physics and Mathematics of the Universe. L.A.N.L.'s participation in iPTF is supported by the US Department of Energy as a part of the Laboratory Directed Research and Development program. A portion of this work was carried out at the Jet Propulsion Laboratory under a Research and Technology Development Grant, under contract with the National Aeronautics and Space Administration. This paper made use of the Lowell Observatory's Discovery Channel Telescope (DCT). Lowell operates the DCT in partnership with Boston University, Northern Arizona University, the University of Maryland, and the University of Toledo. Partial support of the DCT was provided by Discovery Communications. Large Monolithic Imager (LMI) on DCT was built by Lowell Observatory using funds from the National Science Foundation (AST-1005313). DAH, CM, and GH are funding by NSF grant AST-1313484. This paper makes use of data from the Las Cumbres Observatory. This work was partially supported by the GROWTH project funded by the National Science Foundation under Grant No. 1545949. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: Palomar - , Keck - , Discovery Channel Telescope. -

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Published - Yan_2017_ApJ_848_6.pdf

Submitted - 1704.05061.pdf

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Created:
August 19, 2023
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October 17, 2023